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Remba-Shapiro I, Nachtigall LB. Treatment of acromegaly with oral octreotide. Best Pract Res Clin Endocrinol Metab 2024; 38:101888. [PMID: 38443224 DOI: 10.1016/j.beem.2024.101888] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 03/07/2024]
Abstract
Acromegaly is a rare disease caused by a growth hormone excess, usually due to a secreting pituitary adenoma. Somatostatin receptor ligands (SRL) are the mainstay of medical therapy for patients with acromegaly who fail to achieve biochemical control post-operatively or are not eligible for surgical treatment. SRLs are typically administered as monthly injections and have shown to be effective in maintaining biochemical and radiological control of acromegaly. However, these injections may cause local adverse events and are associated with increased psychological burden in some patients. Oral octreotide provides a new alternative for patients responding to injectable SRLs. This new formulation has shown to have similar safety and efficacy profiles compared to injectable SRLs and may be a preferable option for some patients with acromegaly. The aim of this review is to provide an overview of the role of oral octreotide in the management of acromegaly.
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Affiliation(s)
- Ilan Remba-Shapiro
- Neuroendocrine Unit, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
| | - Lisa B Nachtigall
- Neuroendocrine Unit, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
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2
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Qiu J, Voliotis M, Bosch MA, Li XF, Zweifel LS, Tsaneva-Atanasova K, O’Byrne KT, Rønnekleiv OK, Kelly MJ. Estradiol elicits distinct firing patterns in arcuate nucleus kisspeptin neurons of females through altering ion channel conductances. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.02.20.581121. [PMID: 38915596 PMCID: PMC11195100 DOI: 10.1101/2024.02.20.581121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/26/2024]
Abstract
Hypothalamic kisspeptin (Kiss1) neurons are vital for pubertal development and reproduction. Arcuate nucleus Kiss1 (Kiss1ARH) neurons are responsible for the pulsatile release of Gonadotropin-releasing Hormone (GnRH). In females, the behavior of Kiss1ARH neurons, expressing Kiss1, Neurokinin B (NKB), and Dynorphin (Dyn), varies throughout the ovarian cycle. Studies indicate that 17β-estradiol (E2) reduces peptide expression but increases Vglut2 mRNA and glutamate neurotransmission in these neurons, suggesting a shift from peptidergic to glutamatergic signaling. To investigate this shift, we combined transcriptomics, electrophysiology, and mathematical modeling. Our results demonstrate that E2 treatment upregulates the mRNA expression of voltage-activated calcium channels, elevating the whole-cell calcium current and that contribute to high-frequency burst firing. Additionally, E2 treatment decreased the mRNA levels of Canonical Transient Receptor Potential (TPRC) 5 and G protein-coupled K+ (GIRK) channels. When TRPC5 channels in Kiss1ARH neurons were deleted using CRISPR, the slow excitatory postsynaptic potential (sEPSP) was eliminated. Our data enabled us to formulate a biophysically realistic mathematical model of the Kiss1ARH neuron, suggesting that E2 modifies ionic conductances in Kiss1ARH neurons, enabling the transition from high frequency synchronous firing through NKB-driven activation of TRPC5 channels to a short bursting mode facilitating glutamate release. In a low E2 milieu, synchronous firing of Kiss1ARH neurons drives pulsatile release of GnRH, while the transition to burst firing with high, preovulatory levels of E2 would facilitate the GnRH surge through its glutamatergic synaptic connection to preoptic Kiss1 neurons.
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Affiliation(s)
- Jian Qiu
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Portland, OR 97239, USA
| | - Margaritis Voliotis
- Department of Mathematics and Statistics, University of Exeter, Stocker Rd, Exeter, EX4 4PY, UK
- Living Systems Institute, University of Exeter, Stocker Rd, Exeter, EX4 4PY, UK
| | - Martha A. Bosch
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Portland, OR 97239, USA
| | - Xiao Feng Li
- Department of Women and Children’s Health, School of Life Course and Population Sciences, King’s College London, Guy’s Campus, London SE1 1UL, UK
| | - Larry S. Zweifel
- Department of Psychiatry and Behavioral Sciences, University of Washington, Seattle, WA 98195, USA
- Depatment of Pharmacology, University of Washington, Seattle, WA 98195, USA
| | - Krasimira Tsaneva-Atanasova
- Department of Mathematics and Statistics, University of Exeter, Stocker Rd, Exeter, EX4 4PY, UK
- Living Systems Institute, University of Exeter, Stocker Rd, Exeter, EX4 4PY, UK
| | - Kevin T. O’Byrne
- Department of Women and Children’s Health, School of Life Course and Population Sciences, King’s College London, Guy’s Campus, London SE1 1UL, UK
| | - Oline K. Rønnekleiv
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Portland, OR 97239, USA
- Division of Neuroscience, Oregon National Primate Research Center, Beaverton, OR 97006, USA
| | - Martin J. Kelly
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, Portland, OR 97239, USA
- Division of Neuroscience, Oregon National Primate Research Center, Beaverton, OR 97006, USA
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3
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Churilov AN, Milton JG. Modeling pulsativity in the hypothalamic-pituitary-adrenal hormonal axis. Sci Rep 2022; 12:8480. [PMID: 35589935 PMCID: PMC9120490 DOI: 10.1038/s41598-022-12513-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Accepted: 05/04/2022] [Indexed: 11/18/2022] Open
Abstract
A new mathematical model for biological rhythms in the hypothalamic–pituitary–adrenal (HPA) axis is proposed. This model takes the form of a system of impulsive time-delay differential equations which include pulsatile release of adrenocorticotropin (ACTH) by the pituitary gland and a time delay for the release of glucocorticoid hormones by the adrenal gland. Numerical simulations demonstrate that the model’s response to periodic and circadian inputs from the hypothalamus are consistent with those generated by recent models which do not include a pulsatile pituitary. In contrast the oscillatory phenomena generated by the impulsive delay equation mode occur even if the time delay is zero. The observation that the time delay merely introduces a small phase shift suggesting that the effects of the adrenal gland are “downstream” to the origin of pulsativity. In addition, the model accounts for the occurrence of ultradian oscillations in an isolated pituitary gland. These observations suggest that principles of pulse modulated control, familiar to control engineers, may have an increasing role to play in understanding the HPA axis.
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Affiliation(s)
- Alexander N Churilov
- Faculty of Mathematics and Mechanics, Saint Petersburg State University, Saint Petersburg, Russia
| | - John G Milton
- W. M. Keck Science Center, The Claremont Colleges, Claremont, CA, USA.
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4
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Sodium background currents in endocrine/neuroendocrine cells: Towards unraveling channel identity and contribution in hormone secretion. Front Neuroendocrinol 2021; 63:100947. [PMID: 34592201 DOI: 10.1016/j.yfrne.2021.100947] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/16/2021] [Revised: 09/03/2021] [Accepted: 09/23/2021] [Indexed: 02/04/2023]
Abstract
In endocrine/neuroendocrine tissues, excitability of secretory cells is patterned by the repertoire of ion channels and there is clear evidence that extracellular sodium (Na+) ions contribute to hormone secretion. While voltage-gated channels involved in action potential generation are well-described, the background 'leak' channels operating near the resting membrane potential are much less known, and in particular the channels supporting a background entry of Na+ ions. These background Na+ currents (called here 'INab') have the ability to modulate the resting membrane potential and subsequently affect action potential firing. Here we compile and analyze the data collected from three endocrine/neuroendocrine tissues: the anterior pituitary gland, the adrenal medulla and the endocrine pancreas. We also model how INab can be functionally involved in cellular excitability. Finally, towards deciphering the physiological role of INab in endocrine/neuroendocrine cells, its implication in hormone release is also discussed.
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5
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Fazli M, Vo T, Bertram R. Fast-slow analysis of a stochastic mechanism for electrical bursting. CHAOS (WOODBURY, N.Y.) 2021; 31:103128. [PMID: 34717336 DOI: 10.1063/5.0059338] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2021] [Accepted: 09/03/2021] [Indexed: 06/13/2023]
Abstract
Electrical bursting oscillations in neurons and endocrine cells are activity patterns that facilitate the secretion of neurotransmitters and hormones and have been the focus of study for several decades. Mathematical modeling has been an extremely useful tool in this effort, and the use of fast-slow analysis has made it possible to understand bursting from a dynamic perspective and to make testable predictions about changes in system parameters or the cellular environment. It is typically the case that the electrical impulses that occur during the active phase of a burst are due to stable limit cycles in the fast subsystem of equations or, in the case of so-called "pseudo-plateau bursting," canards that are induced by a folded node singularity. In this article, we show an entirely different mechanism for bursting that relies on stochastic opening and closing of a key ion channel. We demonstrate, using fast-slow analysis, how the short-lived stochastic channel openings can yield a much longer response in which single action potentials are converted into bursts of action potentials. Without this stochastic element, the system is incapable of bursting. This mechanism can describe stochastic bursting in pituitary corticotrophs, which are small cells that exhibit a great deal of noise as well as other pituitary cells, such as lactotrophs and somatotrophs that exhibit noisy bursts of electrical activity.
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Affiliation(s)
- Mehran Fazli
- Department of Mathematics, Florida State University, Tallahassee, Florida 32306, USA
| | - Theodore Vo
- School of Mathematics, Monash University, Clayton, Victoria 3800, Australia
| | - Richard Bertram
- Department of Mathematics, Florida State University, Tallahassee, Florida 32306, USA
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6
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Impheng H, Lemmers C, Bouasse M, Legros C, Pakaprot N, Guérineau NC, Lory P, Monteil A. The sodium leak channel NALCN regulates cell excitability of pituitary endocrine cells. FASEB J 2021; 35:e21400. [PMID: 33793981 DOI: 10.1096/fj.202000841rr] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2020] [Revised: 01/11/2021] [Accepted: 01/13/2021] [Indexed: 11/11/2022]
Abstract
Anterior pituitary endocrine cells that release hormones such as growth hormone and prolactin are excitable and fire action potentials. In these cells, several studies previously showed that extracellular sodium (Na+ ) removal resulted in a negative shift of the resting membrane potential (RMP) and a subsequent inhibition of the spontaneous firing of action potentials, suggesting the contribution of a Na+ background conductance. Here, we show that the Na+ leak channel NALCN conducts a Ca2+ - Gd3+ -sensitive and TTX-resistant Na+ background conductance in the GH3 cell line, a cell model of pituitary endocrine cells. NALCN knockdown hyperpolarized the RMP, altered GH3 cell electrical properties and inhibited prolactin secretion. Conversely, the overexpression of NALCN depolarized the RMP, also reshaping the electrical properties of GH3 cells. Overall, our results indicate that NALCN is functional in GH3 cells and involved in endocrine cell excitability as well as in hormone secretion. Indeed, the GH3 cell line suitably models native pituitary cells that display a similar Na+ background conductance and appears as a proper cellular model to study the role of NALCN in cellular excitability.
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Affiliation(s)
- Hathaichanok Impheng
- IGF, Université de Montpellier, CNRS, INSERM, Montpellier, France.,LabEx 'Ion Channel Science and Therapeutics', Montpellier, France
| | - Céline Lemmers
- IGF, Université de Montpellier, CNRS, INSERM, Montpellier, France.,PVM, BCM, Université de Montpellier, CNRS, INSERM, Montpellier, France
| | - Malik Bouasse
- IGF, Université de Montpellier, CNRS, INSERM, Montpellier, France.,LabEx 'Ion Channel Science and Therapeutics', Montpellier, France
| | - Christian Legros
- MITOVASC Institute, UMR CNRS 6015 - UMR INSERM U1083, Université d'Angers, Angers, France
| | - Narawut Pakaprot
- Department of Physiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
| | - Nathalie C Guérineau
- IGF, Université de Montpellier, CNRS, INSERM, Montpellier, France.,LabEx 'Ion Channel Science and Therapeutics', Montpellier, France
| | - Philippe Lory
- IGF, Université de Montpellier, CNRS, INSERM, Montpellier, France.,LabEx 'Ion Channel Science and Therapeutics', Montpellier, France
| | - Arnaud Monteil
- IGF, Université de Montpellier, CNRS, INSERM, Montpellier, France.,LabEx 'Ion Channel Science and Therapeutics', Montpellier, France.,PVM, BCM, Université de Montpellier, CNRS, INSERM, Montpellier, France
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7
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Involvement of NMDA and GABA(A) receptors in modulation of spontaneous activity in hippocampal culture: Interrelations between burst firing and intracellular calcium signal. Biochem Biophys Res Commun 2021; 553:99-106. [PMID: 33765560 DOI: 10.1016/j.bbrc.2021.02.149] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2021] [Accepted: 02/09/2021] [Indexed: 12/28/2022]
Abstract
Spontaneous burst firing is a hallmark attributed to the neuronal network activity. It is known to be accompanied by intracellular calcium [Са2+]i oscillations within the bursting neurons. Studying mechanisms underlying regulation of burst firing is highly relevant, since impairment in neuronal bursting accompanies different neurological disorders. In the present study, the contribution of NMDA and GABA(A) receptors to the shape formation of spontaneous burst -was studied in cultured hippocampal neurons. A combination of inhibitory analysis with simultaneous registration of neuronal bursting by whole-cell patch clamp and calcium imaging was used to assess spontaneous burst firing and [Са2+]i level. Using bicuculline and D-AP5 we showed that GABA(A) and NMDA receptors effectively modulate burst plateau phase and [Са2+]i transient spike which can further affect action potential (AP) amplitudes and firing frequency within a burst. Bicuculline significantly elevated the amplitude and reduced the duration of both burst plateau phase and [Са2+]i spike resulting in an increase of AP firing frequency and shortening of AP amplitudes within a burst. D-AP5 significantly decreases the amplitude of both plateau phase and [Са2+]i spike along with a burst duration that correlated with an increase in AP amplitudes and reduced firing frequency within a burst. The effect of bicuculline was occluded by co-addition of D-AP5 revealing modulatory role of GABA(A) receptors to the NMDA receptor-mediated formation of the burst. Our results provide new evidence on importance of NMDA and GABA(A) receptors in shaping burst firing and Ca2+transient spikes in cultured hippocampal neurons.
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8
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Milman A, Ventéo S, Bossu JL, Fontanaud P, Monteil A, Lory P, Guérineau NC. A sodium background conductance controls the spiking pattern of mouse adrenal chromaffin cells in situ. J Physiol 2021; 599:1855-1883. [PMID: 33450050 PMCID: PMC7986707 DOI: 10.1113/jp281044] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Accepted: 01/04/2021] [Indexed: 12/11/2022] Open
Abstract
KEY POINTS Mouse chromaffin cells in acute adrenal slices exhibit two distinct spiking patterns, a repetitive mode and a bursting mode. A sodium background conductance operates at rest as demonstrated by the membrane hyperpolarization evoked by a low Na+ -containing extracellular saline. This sodium background current is insensitive to TTX, is not blocked by Cs+ ions and displays a linear I-V relationship at potentials close to chromaffin cell resting potential. Its properties are reminiscent of those of the sodium leak channel NALCN. In the adrenal gland, Nalcn mRNA is selectively expressed in chromaffin cells. The study fosters our understanding of how the spiking pattern of chromaffin cells is regulated and adds a sodium background conductance to the list of players involved in the stimulus-secretion coupling of the adrenomedullary tissue. ABSTRACT Chromaffin cells (CCs) are the master neuroendocrine units for the secretory function of the adrenal medulla and a finely-tuned regulation of their electrical activity is required for appropriate catecholamine secretion in response to the organismal demand. Here, we aim at deciphering how the spiking pattern of mouse CCs is regulated by the ion conductances operating near the resting membrane potential (RMP). At RMP, mouse CCs display a composite firing pattern, alternating between active periods composed of action potentials spiking with a regular or a bursting mode, and silent periods. RMP is sensitive to changes in extracellular sodium concentration, and a low Na+ -containing saline hyperpolarizes the membrane, regardless of the discharge pattern. This RMP drive reflects the contribution of a depolarizing conductance, which is (i) not blocked by tetrodotoxin or caesium, (ii) displays a linear I-V relationship between -110 and -40 mV, and (iii) is carried by cations with a conductance sequence gNa > gK > gCs . These biophysical attributes, together with the expression of the sodium-leak channel Nalcn transcript in CCs, state credible the contribution of NALCN. This inaugural report opens new research routes in the field of CC stimulus-secretion coupling, and extends the inventory of tissues in which NALCN is expressed to neuroendocrine glands.
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Affiliation(s)
- Alexandre Milman
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, INSERM, Montpellier, France.,LabEx "Ion Channel Science and Therapeutics", Montpellier, France
| | | | - Jean-Louis Bossu
- Institut des Neurosciences Cellulaires et Intégratives, CNRS UPR 3212, Strasbourg, France
| | - Pierre Fontanaud
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, INSERM, Montpellier, France
| | - Arnaud Monteil
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, INSERM, Montpellier, France.,LabEx "Ion Channel Science and Therapeutics", Montpellier, France
| | - Philippe Lory
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, INSERM, Montpellier, France.,LabEx "Ion Channel Science and Therapeutics", Montpellier, France
| | - Nathalie C Guérineau
- Institut de Génomique Fonctionnelle, Université de Montpellier, CNRS, INSERM, Montpellier, France.,LabEx "Ion Channel Science and Therapeutics", Montpellier, France
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9
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Fukuoka H, Shichi H, Yamamoto M, Takahashi Y. The Mechanisms Underlying Autonomous Adrenocorticotropic Hormone Secretion in Cushing's Disease. Int J Mol Sci 2020; 21:ijms21239132. [PMID: 33266265 PMCID: PMC7730156 DOI: 10.3390/ijms21239132] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Revised: 11/21/2020] [Accepted: 11/29/2020] [Indexed: 12/16/2022] Open
Abstract
Cushing’s disease caused due to adrenocorticotropic hormone (ACTH)-secreting pituitary adenomas (ACTHomas) leads to hypercortisolemia, resulting in increased morbidity and mortality. Autonomous ACTH secretion is attributed to the impaired glucocorticoid negative feedback (glucocorticoid resistance) response. Interestingly, other conditions, such as ectopic ACTH syndrome (EAS) and non-neoplastic hypercortisolemia (NNH, also known as pseudo-Cushing’s syndrome) also exhibit glucocorticoid resistance. Therefore, to differentiate between these conditions, several dynamic tests, including those with desmopressin (DDAVP), corticotrophin-releasing hormone (CRH), and Dex/CRH have been developed. In normal pituitary corticotrophs, ACTH synthesis and secretion are regulated mainly by CRH and glucocorticoids, which are the ACTH secretion-stimulating and -suppressing factors, respectively. These factors regulate ACTH synthesis and secretion through genomic and non-genomic mechanisms. Conversely, glucocorticoid negative feedback is impaired in ACTHomas, which could be due to the overexpression of 11β-HSD2, HSP90, or TR4, or loss of expression of CABLES1 or nuclear BRG1 proteins. Genetic analysis has indicated the involvement of several genes in the etiology of ACTHomas, including USP8, USP48, BRAF, and TP53. However, the association between glucocorticoid resistance and these genes remains unclear. Here, we review the clinical aspects and molecular mechanisms of ACTHomas and compare them to those of other related conditions.
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Affiliation(s)
- Hidenori Fukuoka
- Division of Diabetes and Endocrinology, Kobe University Hospital, 7-5-2, Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan;
- Correspondence: ; Tel.: +81-78-382-5861; Fax: +81-78-382-2080
| | - Hiroki Shichi
- Division of Diabetes and Endocrinology, Kobe University Graduate School of Medicine, 7-5-2, Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan; (H.S.); (Y.T.)
| | - Masaaki Yamamoto
- Division of Diabetes and Endocrinology, Kobe University Hospital, 7-5-2, Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan;
| | - Yutaka Takahashi
- Division of Diabetes and Endocrinology, Kobe University Graduate School of Medicine, 7-5-2, Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan; (H.S.); (Y.T.)
- Department of Diabetes and Endocrinology, Nara Medical University, 840 Shijo-cho, Kashihara, Nara 634-8522, Japan
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10
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Richards DM, Walker JJ, Tabak J. Ion channel noise shapes the electrical activity of endocrine cells. PLoS Comput Biol 2020; 16:e1007769. [PMID: 32251433 PMCID: PMC7162531 DOI: 10.1371/journal.pcbi.1007769] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2019] [Revised: 04/16/2020] [Accepted: 03/03/2020] [Indexed: 11/24/2022] Open
Abstract
Endocrine cells in the pituitary gland typically display either spiking or bursting electrical activity, which is related to the level of hormone secretion. Recent work, which combines mathematical modelling with dynamic clamp experiments, suggests the difference is due to the presence or absence of a few large-conductance potassium channels. Since endocrine cells only contain a handful of these channels, it is likely that stochastic effects play an important role in the pattern of electrical activity. Here, for the first time, we explicitly determine the effect of such noise by studying a mathematical model that includes the realistic noisy opening and closing of ion channels. This allows us to investigate how noise affects the electrical activity, examine the origin of spiking and bursting, and determine which channel types are responsible for the greatest noise. Further, for the first time, we address the role of cell size in endocrine cell electrical activity, finding that larger cells typically display more bursting, while the smallest cells almost always only exhibit spiking behaviour.
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Affiliation(s)
- David M. Richards
- Living Systems Institute, University of Exeter, Exeter, United Kingdom
| | - Jamie J. Walker
- College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, United Kingdom
- Bristol Medical School, Translational Health Sciences, University of Bristol, Bristol, United Kingdom
| | - Joel Tabak
- University of Exeter Medical School, University of Exeter, Exeter, United Kingdom
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11
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Wang Y, Rubin JE. Complex bursting dynamics in an embryonic respiratory neuron model. CHAOS (WOODBURY, N.Y.) 2020; 30:043127. [PMID: 32357647 DOI: 10.1063/1.5138993] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2019] [Accepted: 03/23/2020] [Indexed: 06/11/2023]
Abstract
Pre-Bötzinger complex (pre-BötC) network activity within the mammalian brainstem controls the inspiratory phase of the respiratory rhythm. While bursting in pre-BötC neurons during the postnatal period has been extensively studied, less is known regarding inspiratory pacemaker neuron behavior at embryonic stages. Recent data in mouse embryo brainstem slices have revealed the existence of a variety of bursting activity patterns depending on distinct combinations of burst-generating INaP and ICAN conductances. In this work, we consider a model of an isolated embryonic pre-BötC neuron featuring two distinct bursting mechanisms. We use methods of dynamical systems theory, such as phase plane analysis, fast-slow decomposition, and bifurcation analysis, to uncover mechanisms underlying several different types of intrinsic bursting dynamics observed experimentally including several forms of plateau bursts, bursts involving depolarization block, and various combinations of these patterns. Our analysis also yields predictions about how changes in the balance of the two bursting mechanisms contribute to alterations in an inspiratory pacemaker neuron activity during prenatal development.
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Affiliation(s)
- Yangyang Wang
- Department of Mathematics, The University of Iowa, Iowa City, Iowa 52242, USA
| | - Jonathan E Rubin
- Department of Mathematics, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
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12
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Vélez EJ, Unniappan S. A Comparative Update on the Neuroendocrine Regulation of Growth Hormone in Vertebrates. Front Endocrinol (Lausanne) 2020; 11:614981. [PMID: 33708174 PMCID: PMC7940767 DOI: 10.3389/fendo.2020.614981] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Accepted: 12/31/2020] [Indexed: 12/22/2022] Open
Abstract
Growth hormone (GH), mainly produced from the pituitary somatotrophs is a key endocrine regulator of somatic growth. GH, a pleiotropic hormone, is also involved in regulating vital processes, including nutrition, reproduction, physical activity, neuroprotection, immunity, and osmotic pressure in vertebrates. The dysregulation of the pituitary GH and hepatic insulin-like growth factors (IGFs) affects many cellular processes associated with growth promotion, including protein synthesis, cell proliferation and metabolism, leading to growth disorders. The metabolic and growth effects of GH have interesting applications in different fields, including the livestock industry and aquaculture. The latest discoveries on new regulators of pituitary GH synthesis and secretion deserve our attention. These novel regulators include the stimulators adropin, klotho, and the fibroblast growth factors, as well as the inhibitors, nucleobindin-encoded peptides (nesfatin-1 and nesfatin-1-like peptide) and irisin. This review aims for a comparative analysis of our current understanding of the endocrine regulation of GH from the pituitary of vertebrates. In addition, we will consider useful pharmacological molecules (i.e. stimulators and inhibitors of the GH signaling pathways) that are important in studying GH and somatotroph biology. The main goal of this review is to provide an overview and update on GH regulators in 2020. While an extensive review of each of the GH regulators and an in-depth analysis of specifics are beyond its scope, we have compiled information on the main endogenous and pharmacological regulators to facilitate an easy access. Overall, this review aims to serve as a resource on GH endocrinology for a beginner to intermediate level knowledge seeker on this topic.
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13
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A computational model for gonadotropin releasing cells in the teleost fish medaka. PLoS Comput Biol 2019; 15:e1006662. [PMID: 31437161 PMCID: PMC6726249 DOI: 10.1371/journal.pcbi.1006662] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2018] [Revised: 09/04/2019] [Accepted: 08/01/2019] [Indexed: 01/16/2023] Open
Abstract
Pituitary endocrine cells fire action potentials (APs) to regulate their cytosolic Ca2+ concentration and hormone secretion rate. Depending on animal species, cell type, and biological conditions, pituitary APs are generated either by TTX-sensitive Na+ currents (INa), high-voltage activated Ca2+ currents (ICa), or by a combination of the two. Previous computational models of pituitary cells have mainly been based on data from rats, where INa is largely inactivated at the resting potential, and spontaneous APs are predominantly mediated by ICa. Unlike in rats, spontaneous INa-mediated APs are consistently seen in pituitary cells of several other animal species, including several species of fish. In the current work we develop a computational model of gonadotropin releasing cells in the teleost fish medaka (Oryzias latipes). The model stands out from previous modeling efforts by being (1) the first model of a pituitary cell in teleosts, (2) the first pituitary cell model that fires sponateous APs that are predominantly mediated by INa, and (3) the first pituitary cell model where the kinetics of the depolarizing currents, INa and ICa, are directly fitted to voltage-clamp data. We explore the firing properties of the model, and compare it to the properties of previous models that fire ICa-based APs. We put a particular focus on how the big conductance K+ current (IBK) modulates the AP shape. Interestingly, we find that IBK can prolong AP duration in models that fire ICa-based APs, while it consistently shortens the duration of the predominantly INa-mediated APs in the medaka gonadotroph model. Although the model is constrained to experimental data from gonadotroph cells in medaka, it may likely provide insights also into other pituitary cell types that fire INa-mediated APs. Excitable cells elicit electrical pulses called action potentials (APs), which are generated and shaped by a combination of ion channels in the cell membrane. Since one type of ion channels is permeable to Ca2+ ions, there is typically an influx of Ca2+ during an AP. Pituitary cells therefore use AP firing to regulate their cytosolic Ca2+ concentration, which in turn controls their hormone secretion rate. The amount of Ca2+ that enters during an AP depends strongly on how long it lasts, and it is therefore important to understand the mechanisms that control this. Pituitary APs are generally mediated by a combination of Ca2+ channels and Na+ channels, and the relative contributions of from the two vary between cell types, animal species and biological conditions. Previous computer models have predominantly been adapted to data from pituitary cells which tend to fire Ca2+-based APs. Here we develop a new model, adapted to data from pituitary cells in the fish medaka, which APs that are predominantly Na+-based, and compare its dynamical properties to the previous models that fire Ca2+-based APs.
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Esposito S, Leonardi A, Lanciotti L, Cofini M, Muzi G, Penta L. Vitamin D and growth hormone in children: a review of the current scientific knowledge. J Transl Med 2019; 17:87. [PMID: 30885216 PMCID: PMC6421660 DOI: 10.1186/s12967-019-1840-4] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2018] [Accepted: 03/09/2019] [Indexed: 12/23/2022] Open
Abstract
Background Human growth is a complex mechanism that depends on genetic, environmental, nutritional and hormonal factors. The main hormone involved in growth at each stage of development is growth hormone (GH) and its mediator, insulin-like growth factor 1 (IGF-1). In contrast, vitamin D is involved in the processes of bone growth and mineralization through the regulation of calcium and phosphorus metabolism. Nevertheless, no scientific study has yet elucidated how they interact with one another, especially as a dysfunction in which one influences the other, even if numerous biochemical and clinical studies confirm the presence of a close relationship. Main body We reviewed and analyzed the clinical studies that have considered the relationship between vitamin D and the GH/IGF-1 axis in pediatric populations. We found two main areas of interest: the vitamin D deficiency status in patients affected by GH deficit (GHD) and the relationship between serum vitamin D metabolites and IGF-1. Although limited by some bias, from the analysis of the studies presented in the scientific literature, it is possible to hypothesize a greater frequency of hypovitaminosis D in the subjects affected by GHD, a reduced possibility of its correction with only substitution treatment with recombinant growth hormone (rGH) and an improvement of IGF-1 levels after supplementation treatment with vitamin D. Conclusions These results could be followed by preventive interventions aimed at reducing the vitamin D deficit in pediatric age. In addition, further research is needed to fully understand how vitamin D and growth are intertwined.
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Affiliation(s)
- Susanna Esposito
- Pediatric Clinic, Department of Surgical and Biomedical Sciences, Università degli Studi di Perugia, Piazza Menghini 1, 06129, Perugia, Italy.
| | - Alberto Leonardi
- Pediatric Clinic, Department of Surgical and Biomedical Sciences, Università degli Studi di Perugia, Piazza Menghini 1, 06129, Perugia, Italy
| | - Lucia Lanciotti
- Pediatric Clinic, Department of Surgical and Biomedical Sciences, Università degli Studi di Perugia, Piazza Menghini 1, 06129, Perugia, Italy
| | - Marta Cofini
- Pediatric Clinic, Department of Surgical and Biomedical Sciences, Università degli Studi di Perugia, Piazza Menghini 1, 06129, Perugia, Italy
| | - Giulia Muzi
- Pediatric Clinic, Department of Surgical and Biomedical Sciences, Università degli Studi di Perugia, Piazza Menghini 1, 06129, Perugia, Italy
| | - Laura Penta
- Pediatric Clinic, Department of Surgical and Biomedical Sciences, Università degli Studi di Perugia, Piazza Menghini 1, 06129, Perugia, Italy
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15
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Leng G, MacGregor DJ. Models in neuroendocrinology. Math Biosci 2018; 305:29-41. [DOI: 10.1016/j.mbs.2018.07.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Revised: 07/20/2018] [Accepted: 07/24/2018] [Indexed: 12/18/2022]
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16
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Yamamoto M, Ben-Shlomo A, Kameda H, Fukuoka H, Deng N, Ding Y, Melmed S. Somatostatin receptor subtype 5 modifies hypothalamic-pituitary-adrenal axis stress function. JCI Insight 2018; 3:122932. [PMID: 30282821 PMCID: PMC6237446 DOI: 10.1172/jci.insight.122932] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2018] [Accepted: 08/29/2018] [Indexed: 11/17/2022] Open
Abstract
Pituitary corticotroph somatostatin receptor subtype 5 (SSTR5) signals to inhibit adrenocorticotrophin (ACTH) secretion. As ACTH deficiency results in attenuated adrenal cortisol production and an impaired stress response, we sought to clarify the role of SSTR5 in modifying the hypothalamic/pituitary/adrenal (HPA) axis. We generated Tg HP5 mice overexpressing SSTR5 in pituitary corticotrophs that produce the ACTH precursor proopiomelanocortin (POMC). Basal ACTH and corticosterone were similar in HP5 and WT mice, while HP5 mice showed attenuated ACTH and corticosterone responses to corticotrophin releasing hormone (CRH). HP5 mice exhibited attenuated corticosterone responses upon a restraint stress test and inflammatory stress following LPS injection, as well as increased anxiety-like and depressive-like behavior on open field and forced swim tests. Pituitary corticotroph CRH receptor subtype 1 (CRHR1) mRNA expression and ACTH responses to CRH were also attenuated in HP5 mice. In AtT20 cells stably overexpressing SSTR5, CRHR1 expression and cAMP response to CRH were reduced, whereas both were increased after SSTR5 KO. In elucidating mechanisms for these observations, we show that SSTR5-induced miR-449c suppresses both CRHR1 expression and function. We conclude that corticotroph SSTR5 attenuates HPA axis responses via CRHR1 downregulation, suggesting a role for SSTR5 in the pathogenesis of secondary adrenal insufficiency.
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Affiliation(s)
| | | | | | | | - Nan Deng
- Biostatistics and Bioinformatics Research Center, Samuel Oschin Comprehensive Cancer Institute, Cedars-Sinai Medical Center, Los Angeles, California, USA
| | - Yan Ding
- Pituitary Center, Department of Medicine, and
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Abstract
The hypothalamic-pituitary-adrenal (HPA) axis is the major neuroendocrine axis regulating homeostasis in mammals. Glucocorticoid hormones are rapidly synthesized and secreted from the adrenal gland in response to stress. In addition, under basal conditions glucocorticoids are released rhythmically with both a circadian and an ultradian (pulsatile) pattern. These rhythms are important not only for normal function of glucocorticoid target organs, but also for the HPA axis responses to stress. Several studies have shown that disruption of glucocorticoid rhythms is associated with disease both in humans and in rodents. In this review, we will discuss our knowledge of the negative feedback mechanisms that regulate basal ultradian synthesis and secretion of glucocorticoids, including the role of glucocorticoid and mineralocorticoid receptors and their chaperone protein FKBP51. Moreover, in light of recent findings, we will also discuss the importance of intra-adrenal glucocorticoid receptor signaling in regulating glucocorticoid synthesis.
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Affiliation(s)
- Julia K Gjerstad
- Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK
| | - Stafford L Lightman
- Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK
| | - Francesca Spiga
- Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK
- CONTACT Francesca SpigaUniversity of Bristol, Translational Health Sciences, Bristol Medical School, Dorothy Hodgkin Building, Whitson Street, BristolBS1 3NY, UK
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Fletcher PA, Sherman A, Stojilkovic SS. Common and diverse elements of ion channels and receptors underlying electrical activity in endocrine pituitary cells. Mol Cell Endocrinol 2018; 463:23-36. [PMID: 28652171 PMCID: PMC5742314 DOI: 10.1016/j.mce.2017.06.022] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/24/2017] [Revised: 06/20/2017] [Accepted: 06/22/2017] [Indexed: 12/30/2022]
Abstract
The pituitary gland contains six types of endocrine cells defined by hormones they secrete: corticotrophs, melanotrophs, gonadotrophs, thyrotrophs, somatotrophs, and lactotrophs. All these cell types are electrically excitable, and voltage-gated calcium influx is the major trigger for their hormone secretion. Along with hormone intracellular content, G-protein-coupled receptor and ion channel expression can also be considered as defining cell type identity. While many aspects of the developmental and activity dependent regulation of hormone and G-protein-coupled receptor expression have been elucidated, much less is known about the regulation of the ion channels needed for excitation-secretion coupling in these cells. We compare the spontaneous and receptor-controlled patterns of electrical signaling among endocrine pituitary cell types, including insights gained from mathematical modeling. We argue that a common set of ionic currents unites these cells, while differential expression of another subset of ionic currents could underlie cell type-specific patterns. We demonstrate these ideas using a generic mathematical model, showing that it reproduces many observed features of pituitary electrical signaling. Mapping these observations to the developmental lineage suggests possible modes of regulation that may give rise to mature pituitary cell types.
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Affiliation(s)
- Patrick A Fletcher
- Laboratory of Biological Modeling, National Institute of Diabetes, Digestive and Kidney Diseases, NIH, Bethesda, MD, USA.
| | - Arthur Sherman
- Laboratory of Biological Modeling, National Institute of Diabetes, Digestive and Kidney Diseases, NIH, Bethesda, MD, USA
| | - Stanko S Stojilkovic
- Section on Cellular Signaling, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD, USA
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Shipston MJ. Control of anterior pituitary cell excitability by calcium-activated potassium channels. Mol Cell Endocrinol 2018; 463:37-48. [PMID: 28596131 DOI: 10.1016/j.mce.2017.06.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/14/2017] [Revised: 06/02/2017] [Accepted: 06/02/2017] [Indexed: 01/01/2023]
Abstract
In anterior pituitary endocrine cells, large (BK), small (SK) and intermediate (IK) conductance calcium activated potassium channels are key determinants in shaping cellular excitability in a cell type- and context-specific manner. Indeed, these channels are targeted by multiple signaling pathways that stimulate or inhibit cellular excitability. BK channels can, paradoxically, both promote electrical bursting as well as terminate bursting and spiking dependent upon intrinsic BK channel properties and proximity to voltage gated calcium channels in somatotrophs, lactotrophs and corticotrophs. In contrast, SK channels are predominantly activated by calcium released from intracellular IP3-sensitive calcium stores and mediate membrane hyperpolarization in cells including gonadotrophs and corticotrophs. IK channels are predominantly expressed in corticotrophs where they limit membrane excitability. A major challenge for the future is to determine the cell-type specific molecular composition of calcium-activated potassium channels and how they control anterior pituitary hormone secretion as well as other calcium-dependent processes.
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Affiliation(s)
- Michael J Shipston
- Centre for Integrative Physiology, Edinburgh Medical School: Biomedical Sciences, University of Edinburgh, Edinburgh, EH89XD, UK.
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Fletcher PA, Zemkova H, Stojilkovic SS, Sherman A. Modeling the diversity of spontaneous and agonist-induced electrical activity in anterior pituitary corticotrophs. J Neurophysiol 2017; 117:2298-2311. [PMID: 28228586 DOI: 10.1152/jn.00948.2016] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2016] [Revised: 02/08/2017] [Accepted: 02/21/2017] [Indexed: 01/10/2023] Open
Abstract
Pituitary corticotrophs fire action potentials spontaneously and in response to stimulation with corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP), and such electrical activity is critical for calcium signaling and calcium-dependent adrenocorticotropic hormone secretion. These cells typically fire tall, sharp action potentials when spontaneously active, but a variety of other spontaneous patterns have also been reported, including various modes of bursting. There is variability in reports of the fraction of corticotrophs that are electrically active, as well as their patterns of activity, and the sources of this variation are not well understood. The ionic mechanisms responsible for CRH- and AVP-triggered electrical activity in corticotrophs are also poorly characterized. We use electrophysiological measurements and mathematical modeling to investigate possible sources of variability in patterns of spontaneous and agonist-induced corticotroph electrical activity. In the model, variation in as few as two parameters can give rise to many of the types of patterns observed in electrophysiological recordings of corticotrophs. We compare the known mechanisms for CRH, AVP, and glucocorticoid actions and find that different ionic mechanisms can contribute in different but complementary ways to generate the complex time courses of CRH and AVP responses. In summary, our modeling suggests that corticotrophs have several mechanisms at their disposal to achieve their primary function of pacemaking depolarization and increased electrical activity in response to CRH and AVP.NEW & NOTEWORTHY We and others recently demonstrated that the electrical activity and calcium dynamics of corticotrophs are strikingly diverse, both spontaneously and in response to the agonists CRH and AVP. Here we demonstrate this diversity with electrophysiological measurements and use mathematical modeling to investigate its possible sources. We compare the known mechanisms of agonist-induced activity in the model, showing how the context of ionic conductances dictates the effects of agonists even when their target is fixed.
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Affiliation(s)
- Patrick A Fletcher
- Laboratory of Biological Modeling, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland;
| | - Hana Zemkova
- Department of Cellular and Molecular Neuroendocrinology, Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic; and.,Section on Cellular Signaling, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland
| | - Stanko S Stojilkovic
- Section on Cellular Signaling, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland
| | - Arthur Sherman
- Laboratory of Biological Modeling, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland
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Stojilkovic SS, Bjelobaba I, Zemkova H. Ion Channels of Pituitary Gonadotrophs and Their Roles in Signaling and Secretion. Front Endocrinol (Lausanne) 2017; 8:126. [PMID: 28649232 PMCID: PMC5465261 DOI: 10.3389/fendo.2017.00126] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Gonadotrophs are basophilic cells of the anterior pituitary gland specialized to secrete gonadotropins in response to elevation in intracellular calcium concentration. These cells fire action potentials (APs) spontaneously, coupled with voltage-gated calcium influx of insufficient amplitude to trigger gonadotropin release. The spontaneous excitability of gonadotrophs reflects the expression of voltage-gated sodium, calcium, potassium, non-selective cation-conducting, and chloride channels at their plasma membrane (PM). These cells also express the hyperpolarization-activated and cyclic nucleotide-gated cation channels at the PM, as well as GABAA, nicotinic, and purinergic P2X channels gated by γ-aminobutyric acid (GABA), acetylcholine (ACh), and ATP, respectively. Activation of these channels leads to initiation or amplification of the pacemaking activity, facilitation of calcium influx, and activation of the exocytic pathway. Gonadotrophs also express calcium-conducting channels at the endoplasmic reticulum membranes gated by inositol trisphosphate and intracellular calcium. These channels are activated potently by hypothalamic gonadotropin-releasing hormone (GnRH) and less potently by several paracrine calcium-mobilizing agonists, including pituitary adenylate cyclase-activating peptides, endothelins, ACh, vasopressin, and oxytocin. Activation of these channels causes oscillatory calcium release and a rapid gonadotropin release, accompanied with a shift from tonic firing of single APs to periodic bursting type of electrical activity, which accounts for a sustained calcium signaling and gonadotropin secretion. This review summarizes our current understanding of ion channels as signaling molecules in gonadotrophs, the role of GnRH and paracrine agonists in their gating, and the cross talk among channels.
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Affiliation(s)
- Stanko S. Stojilkovic
- Section on Cellular Signaling, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, United States
- *Correspondence: Stanko S. Stojilkovic,
| | - Ivana Bjelobaba
- Institute for Biological Research “Siniša Stanković”, University of Belgrade, Belgrade, Serbia
| | - Hana Zemkova
- Department of Cellular and Molecular Neuroendocrinology, Institute of Physiology Academy of Sciences of the Czech Republic, Prague, Czechia
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Duncan PJ, Tabak J, Ruth P, Bertram R, Shipston MJ. Glucocorticoids Inhibit CRH/AVP-Evoked Bursting Activity of Male Murine Anterior Pituitary Corticotrophs. Endocrinology 2016; 157:3108-21. [PMID: 27254001 PMCID: PMC4967125 DOI: 10.1210/en.2016-1115] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Corticotroph cells from the anterior pituitary are an integral component of the hypothalamic-pituitary-adrenal (HPA) axis, which governs the neuroendocrine response to stress. Corticotrophs are electrically excitable and fire spontaneous single-spike action potentials and also display secretagogue-induced bursting behavior. The HPA axis function is dependent on effective negative feedback in which elevated plasma glucocorticoids result in inhibition at the level of both the pituitary and the hypothalamus. In this study, we have used an electrophysiological approach coupled with mathematical modeling to investigate the regulation of spontaneous and CRH/arginine vasopressin-induced activity of corticotrophs by glucocorticoids. We reveal that pretreatment of corticotrophs with 100 nM corticosterone (CORT; 90 and 150 min) reduces spontaneous activity and prevents a transition from spiking to bursting after CRH/arginine vasopressin stimulation. In addition, previous studies have identified a role for large-conductance calcium- and voltage-activated potassium (BK) channels in the generation of secretagogue-induced bursting in corticotrophs. Using the dynamic clamp technique, we demonstrated that CRH-induced bursting can be switched to spiking by subtracting a fast BK current, whereas the addition of a fast BK current can induce bursting in CORT-treated cells. In addition, recordings from BK knockout mice (BK(-/-)) revealed that CORT can also inhibit excitability through BK-independent mechanisms to control spike frequency. Thus, we have established that glucocorticoids can modulate multiple properties of corticotroph electrical excitability through both BK-dependent and BK-independent mechanisms.
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Affiliation(s)
- Peter J Duncan
- Centre for Integrative Physiology (P.J.D., M.J.S.), College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom; Biomedical Neuroscience Research Group (J.T.), University of Exeter Medical School, Exeter EX4 4PL, United Kingdom; Division of Pharmacology, Toxicology, and Clinical Pharmacy (P.R.), Institute for Pharmacy, University of Tübingen, D-72076 Tübingen, Germany; and Department of Mathematics and Programs in Neuroscience and Molecular Biophysics (R.B.), Florida State University, Tallahassee, Florida 32306
| | - Joël Tabak
- Centre for Integrative Physiology (P.J.D., M.J.S.), College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom; Biomedical Neuroscience Research Group (J.T.), University of Exeter Medical School, Exeter EX4 4PL, United Kingdom; Division of Pharmacology, Toxicology, and Clinical Pharmacy (P.R.), Institute for Pharmacy, University of Tübingen, D-72076 Tübingen, Germany; and Department of Mathematics and Programs in Neuroscience and Molecular Biophysics (R.B.), Florida State University, Tallahassee, Florida 32306
| | - Peter Ruth
- Centre for Integrative Physiology (P.J.D., M.J.S.), College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom; Biomedical Neuroscience Research Group (J.T.), University of Exeter Medical School, Exeter EX4 4PL, United Kingdom; Division of Pharmacology, Toxicology, and Clinical Pharmacy (P.R.), Institute for Pharmacy, University of Tübingen, D-72076 Tübingen, Germany; and Department of Mathematics and Programs in Neuroscience and Molecular Biophysics (R.B.), Florida State University, Tallahassee, Florida 32306
| | - Richard Bertram
- Centre for Integrative Physiology (P.J.D., M.J.S.), College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom; Biomedical Neuroscience Research Group (J.T.), University of Exeter Medical School, Exeter EX4 4PL, United Kingdom; Division of Pharmacology, Toxicology, and Clinical Pharmacy (P.R.), Institute for Pharmacy, University of Tübingen, D-72076 Tübingen, Germany; and Department of Mathematics and Programs in Neuroscience and Molecular Biophysics (R.B.), Florida State University, Tallahassee, Florida 32306
| | - Michael J Shipston
- Centre for Integrative Physiology (P.J.D., M.J.S.), College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom; Biomedical Neuroscience Research Group (J.T.), University of Exeter Medical School, Exeter EX4 4PL, United Kingdom; Division of Pharmacology, Toxicology, and Clinical Pharmacy (P.R.), Institute for Pharmacy, University of Tübingen, D-72076 Tübingen, Germany; and Department of Mathematics and Programs in Neuroscience and Molecular Biophysics (R.B.), Florida State University, Tallahassee, Florida 32306
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Atherton LA, Prince LY, Tsaneva-Atanasova K. Bifurcation analysis of a two-compartment hippocampal pyramidal cell model. J Comput Neurosci 2016; 41:91-106. [PMID: 27221619 PMCID: PMC4927618 DOI: 10.1007/s10827-016-0606-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2015] [Revised: 04/19/2016] [Accepted: 04/25/2016] [Indexed: 01/27/2023]
Abstract
The Pinsky-Rinzel model is a non-smooth 2-compartmental CA3 pyramidal cell model that has been used widely within the field of neuroscience. Here we propose a modified (smooth) system that captures the qualitative behaviour of the original model, while allowing the use of available, numerical continuation methods to perform full-system bifurcation and fast-slow analysis. We study the bifurcation structure of the full system as a function of the applied current and the maximal calcium conductance. We identify the bifurcations that shape the transitions between resting, bursting and spiking behaviours, and which lead to the disappearance of bursting when the calcium conductance is reduced. Insights gained from this analysis, are then used to firstly illustrate how the irregular spiking activity found between bursting and stable spiking states, can be influenced by phase differences in the calcium and dendritic voltage, which lead to corresponding changes in the calcium-sensitive potassium current. Furthermore, we use fast-slow analysis to investigate the mechanisms of bursting and show that bursting in the model is dependent on the intermediately slow variable, calcium, while the other slow variable, the activation gate of the afterhyperpolarisation current, does not contribute to setting the intraburst dynamics but participates in setting the interburst interval. Finally, we discuss how some of the described bifurcations affect spiking behaviour, during sharp-wave ripples, in a larger network of Pinsky-Rinzel cells.
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Affiliation(s)
- Laura A Atherton
- Engineering Mathematics, and Physiology, Pharmacology & Neuroscience, University of Bristol, Bristol, England, UK
| | - Luke Y Prince
- Physiology, Pharmacology & Neuroscience, University of Bristol, Bristol, England, UK
| | - Krasimira Tsaneva-Atanasova
- Department of Mathematics, College of Engineering, Mathematics and Physical Sciences, & EPSRC Centre for Predictive Modelling in Healthcare, University of Exeter, Exeter, Devon, EX4 4QF, UK.
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Zemkova H, Tomić M, Kucka M, Aguilera G, Stojilkovic SS. Spontaneous and CRH-Induced Excitability and Calcium Signaling in Mice Corticotrophs Involves Sodium, Calcium, and Cation-Conducting Channels. Endocrinology 2016; 157:1576-89. [PMID: 26901094 PMCID: PMC4816721 DOI: 10.1210/en.2015-1899] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Transgenic mice expressing the tdimer2(12) form of Discosoma red fluorescent protein under control of the proopiomelanocortin gene's regulatory elements are a useful model for studying corticotrophs. Using these mice, we studied the ion channels and mechanisms controlling corticotroph excitability. Corticotrophs were either quiescent or electrically active, with a 22-mV difference in the resting membrane potential (RMP) between the 2 groups. In quiescent cells, CRH depolarized the membrane, leading to initial single spiking and sustained bursting; in active cells, CRH further facilitated or inhibited electrical activity and calcium spiking, depending on the initial activity pattern and CRH concentration. The stimulatory but not inhibitory action of CRH on electrical activity was mimicked by cAMP independently of the presence or absence of arachidonic acid. Removal of bath sodium silenced spiking and hyperpolarized the majority of cells; in contrast, the removal of bath calcium did not affect RMP but reduced CRH-induced depolarization, which abolished bursting electrical activity and decreased the spiking frequency but not the amplitude of single spikes. Corticotrophs with inhibited voltage-gated sodium channels fired calcium-dependent action potentials, whereas cells with inhibited L-type calcium channels fired sodium-dependent spikes; blockade of both channels abolished spiking without affecting the RMP. These results indicate that the background voltage-insensitive sodium conductance influences RMP, the CRH-depolarization current is driven by a cationic conductance, and the interplay between voltage-gated sodium and calcium channels plays a critical role in determining the status and pattern of electrical activity and calcium signaling.
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Affiliation(s)
- Hana Zemkova
- Department of Cellular and Molecular Neuroendocrinology, Institute of Physiology Academy of Sciences of the Czech Republic, 142 20 Prague 4, Czech Republic (H.Z.); and Sections on Cellular Signaling (H.Z., M.T., M.K., S.S.S.) and Endocrine Physiology (G.A.), Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-4510
| | - Melanija Tomić
- Department of Cellular and Molecular Neuroendocrinology, Institute of Physiology Academy of Sciences of the Czech Republic, 142 20 Prague 4, Czech Republic (H.Z.); and Sections on Cellular Signaling (H.Z., M.T., M.K., S.S.S.) and Endocrine Physiology (G.A.), Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-4510
| | - Marek Kucka
- Department of Cellular and Molecular Neuroendocrinology, Institute of Physiology Academy of Sciences of the Czech Republic, 142 20 Prague 4, Czech Republic (H.Z.); and Sections on Cellular Signaling (H.Z., M.T., M.K., S.S.S.) and Endocrine Physiology (G.A.), Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-4510
| | - Greti Aguilera
- Department of Cellular and Molecular Neuroendocrinology, Institute of Physiology Academy of Sciences of the Czech Republic, 142 20 Prague 4, Czech Republic (H.Z.); and Sections on Cellular Signaling (H.Z., M.T., M.K., S.S.S.) and Endocrine Physiology (G.A.), Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-4510
| | - Stanko S Stojilkovic
- Department of Cellular and Molecular Neuroendocrinology, Institute of Physiology Academy of Sciences of the Czech Republic, 142 20 Prague 4, Czech Republic (H.Z.); and Sections on Cellular Signaling (H.Z., M.T., M.K., S.S.S.) and Endocrine Physiology (G.A.), Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-4510
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Duncan PJ, Shipston MJ. BK Channels and the Control of the Pituitary. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2016; 128:343-68. [PMID: 27238268 DOI: 10.1016/bs.irn.2016.03.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/21/2023]
Abstract
The pituitary gland provides the important link between the nervous system and the endocrine system and regulates a diverse range of physiological functions. The pituitary is connected to the hypothalamus by the pituitary stalk and is comprised primarily of two lobes. The anterior lobe consists of five hormone-secreting cell types which are electrically excitable and display single-spike action potentials as well as complex bursting patterns. Bursting is of particular interest as it raises intracellular calcium to a greater extent than spiking and is believed to underlie secretagogue-induced hormone secretion. BK channels have been identified as a key regulator of bursting in anterior pituitary cells. Experimental data and mathematical modeling have demonstrated that BK activation during the upstroke of an action potential results in a prolonged depolarization and an increase in intracellular calcium. In contrast, the posterior lobe is primarily composed of axonal projections of magnocellular neurosecretory cells which extend from the supraoptic and paraventricular nuclei of the hypothalamus. In these neuroendocrine cells, BK channel activation results in a decrease in excitability and hormone secretion. The opposite effect of BK channels in the anterior and posterior pituitary highlights the diverse role of BK channels in regulating the activity of excitable cells. Further studies of pituitary cell excitability and the specific role of BK channels would lead to a greater understanding of how pituitary cell excitability is regulated by both hypothalamic secretagogues and negative feedback loops, and could ultimately lead to novel treatments to pituitary-related disorders.
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Affiliation(s)
- P J Duncan
- Centre for Integrative Physiology, College of Medicine & Veterinary Medicine, University of Edinburgh, Edinburgh, United Kingdom.
| | - M J Shipston
- Centre for Integrative Physiology, College of Medicine & Veterinary Medicine, University of Edinburgh, Edinburgh, United Kingdom
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Fridlyand LE, Tamarina NA, Schally AV, Philipson LH. Growth Hormone-Releasing Hormone in Diabetes. Front Endocrinol (Lausanne) 2016; 7:129. [PMID: 27777568 PMCID: PMC5056186 DOI: 10.3389/fendo.2016.00129] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/17/2016] [Accepted: 09/06/2016] [Indexed: 12/13/2022] Open
Abstract
Growth hormone-releasing hormone (GHRH) is produced by the hypothalamus and stimulates growth hormone synthesis and release in the anterior pituitary gland. In addition, GHRH is an important regulator of cellular functions in many cells and organs. Expression of GHRH G-Protein Coupled Receptor (GHRHR) has been demonstrated in different peripheral tissues and cell types, including pancreatic islets. Among the peripheral activities, recent studies demonstrate a novel ability of GHRH analogs to increase and preserve insulin secretion by beta-cells in isolated pancreatic islets, which makes them potentially useful for diabetes treatment. This review considers the role of GHRHR in the beta-cell and addresses the unique engineered GHRH agonists and antagonists for treatment of type 2 diabetes mellitus. We discuss the similarity of signaling pathways activated by GHRHR in pituitary somatotrophs and in pancreatic beta-cells and possible ways as to how the GHRHR pathway can interact with glucose and other secretagogues to stimulate insulin secretion. We also consider the hypothesis that novel GHRHR agonists can improve glucose metabolism in Type 2 diabetes by preserving the function and survival of pancreatic beta-cells. Wound healing and cardioprotective action with new GHRH agonists suggest that they may prove useful in ameliorating certain diabetic complications. These findings highlight the future potential therapeutic effectiveness of modulators of GHRHR activity for the development of new therapeutic approaches in diabetes and its complications.
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Affiliation(s)
- Leonid E. Fridlyand
- Department of Medicine, Kovler Diabetes Center, The University of Chicago, Chicago, IL, USA
- *Correspondence: Leonid E. Fridlyand,
| | - Natalia A. Tamarina
- Department of Medicine, Kovler Diabetes Center, The University of Chicago, Chicago, IL, USA
| | - Andrew V. Schally
- VA Medical Center, Miami, FL, USA
- Department of Pathology and Medicine, Division of Endocrinology and Hematology-Oncology, Sylvester Comprehensive Cancer Center, University of Miami Miller School of Medicine, Miami, FL, USA
| | - Louis H. Philipson
- Department of Medicine, Kovler Diabetes Center, The University of Chicago, Chicago, IL, USA
- Department of Pediatrics, The University of Chicago, Chicago, IL, USA
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Fan X, Mao Z, He D, Liao C, Jiang X, Lei N, Hu B, Wang X, Li Z, Lin Y, Gou X, Zhu Y, Wang H. Expression of somatostatin receptor subtype 2 in growth hormone-secreting pituitary adenoma and the regulation of miR-185. J Endocrinol Invest 2015; 38:1117-28. [PMID: 26036598 DOI: 10.1007/s40618-015-0306-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/09/2014] [Accepted: 04/30/2015] [Indexed: 12/12/2022]
Abstract
INTRODUCTION Long-acting somatostatin analogs (SSAs) are most widely used to treat growth hormone (GH)-secreting pituitary adenoma. However, approximately 30 % of treated patients show resistance to SSAs, which may be associated with the reduction of somatostatin receptor subtype 2 (SSTR2) mRNA and protein expression. MATERIALS AND METHODS The present study used immunohistochemistry to detect the expression of SSTR2 and SSTR5 in twenty human GH-secreting adenoma samples treated with SSAs and seven normal pituitary samples. RESULTS The staining intensities of SSTR2 and SSTR5 were stronger in most adenoma samples than in normal pituitary. The expression of SSTR2 tended to be lower in the SSA non-responder group than in responders. A search of the Bioinformatics data bank and the miRCURY™ LNA array confirmed miR-185 as the putative mircoRNA (miRNA) regulating the expression of SSTR2. An in vitro study using Dual Luciferase reporter assay demonstrated that miR-185 likely targets the 3'-UTR of SSTR2 mRNA in the rat pituitary adenoma GH3 cell line. MiR-185 also downregulated or upregulated the expression of SSTR2 mRNA and SSTR2 protein, following transfection with miR-185 mimics or inhibitors, respectively. CONCLUSION MiR-185 enhanced the cell proliferation and inhibited the apoptosis of GH3 cells.
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Affiliation(s)
- X Fan
- Department of Neurosurgery and Pituitary Tumor Center, Zhongshan School of Medicine, The First Affiliated Hospital of Sun Yat-sen University, 52# Zhongshan Er Road, Guangzhou, 510080, China
- Department of Neurosurgery, The Fifth Affiliated Hospital of Sun Yat-sen University, Zhuhai, 519000, China
| | - Z Mao
- Department of Neurosurgery and Pituitary Tumor Center, Zhongshan School of Medicine, The First Affiliated Hospital of Sun Yat-sen University, 52# Zhongshan Er Road, Guangzhou, 510080, China
| | - D He
- Department of Neurosurgery and Pituitary Tumor Center, Zhongshan School of Medicine, The First Affiliated Hospital of Sun Yat-sen University, 52# Zhongshan Er Road, Guangzhou, 510080, China
| | - C Liao
- Department of Neurosurgery and Pituitary Tumor Center, Zhongshan School of Medicine, The First Affiliated Hospital of Sun Yat-sen University, 52# Zhongshan Er Road, Guangzhou, 510080, China
| | - X Jiang
- Department of Neurosurgery and Pituitary Tumor Center, Zhongshan School of Medicine, The First Affiliated Hospital of Sun Yat-sen University, 52# Zhongshan Er Road, Guangzhou, 510080, China
| | - N Lei
- Department of Histology and Embryology, Medical school of Sun Yat-sen University, 74# Zhongshan Er Road, Guangzhou, 510080, China
| | - B Hu
- Department of Neurosurgery and Pituitary Tumor Center, Zhongshan School of Medicine, The First Affiliated Hospital of Sun Yat-sen University, 52# Zhongshan Er Road, Guangzhou, 510080, China
| | - X Wang
- Department of Histology and Embryology, Medical school of Sun Yat-sen University, 74# Zhongshan Er Road, Guangzhou, 510080, China
| | - Z Li
- Department of Pathology, The First Affiliated hospital of Sun Yat-sen University, Guangzhou, 510080, China
| | - Y Lin
- Department of Pathology, The Fifth Affiliated Hospital of Sun Yat-sen University, Zhuhai, 519000, China
| | - X Gou
- Department of Pathology, The Fifth Affiliated Hospital of Sun Yat-sen University, Zhuhai, 519000, China
| | - Y Zhu
- Department of Histology and Embryology, Medical school of Sun Yat-sen University, 74# Zhongshan Er Road, Guangzhou, 510080, China.
| | - H Wang
- Department of Neurosurgery and Pituitary Tumor Center, Zhongshan School of Medicine, The First Affiliated Hospital of Sun Yat-sen University, 52# Zhongshan Er Road, Guangzhou, 510080, China.
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Tomić M, Bargi-Souza P, Leiva-Salcedo E, Nunes MT, Stojilkovic SS. Calcium signaling properties of a thyrotroph cell line, mouse TαT1 cells. Cell Calcium 2015; 58:598-605. [PMID: 26453278 DOI: 10.1016/j.ceca.2015.09.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2015] [Revised: 09/14/2015] [Accepted: 09/20/2015] [Indexed: 01/14/2023]
Abstract
TαT1 cells are mouse thyrotroph cell line frequently used for studies on thyroid-stimulating hormone beta subunit gene expression and other cellular functions. Here we have characterized calcium-signaling pathways in TαT1 cells, an issue not previously addressed in these cells and incompletely described in native thyrotrophs. TαT1 cells are excitable and fire action potentials spontaneously and in response to application of thyrotropin-releasing hormone (TRH), the native hypothalamic agonist for thyrotrophs. Spontaneous electrical activity is coupled to small amplitude fluctuations in intracellular calcium, whereas TRH stimulates both calcium mobilization from intracellular pools and calcium influx. Non-receptor-mediated depletion of intracellular pool also leads to a prominent facilitation of calcium influx. Both receptor and non-receptor stimulated calcium influx is substantially attenuated but not completely abolished by inhibition of voltage-gated calcium channels, suggesting that depletion of intracellular calcium pool in these cells provides a signal for both voltage-independent and -dependent calcium influx, the latter by facilitating the pacemaking activity. These cells also express purinergic P2Y1 receptors and their activation by extracellular ATP mimics TRH action on calcium mobilization and influx. The thyroid hormone triiodothyronine prolongs duration of TRH-induced calcium spikes during 30-min exposure. These data indicate that TαT1 cells are capable of responding to natively feed-forward TRH signaling and intrapituitary ATP signaling with acute calcium mobilization and sustained calcium influx. Amplification of TRH-induced calcium signaling by triiodothyronine further suggests the existence of a pathway for positive feedback effects of thyroid hormones probably in a non-genomic manner.
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Affiliation(s)
- Melanija Tomić
- Section on Cellular Signaling, The Eunice Kennedy Shiver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-4510, United States
| | - Paula Bargi-Souza
- Section on Cellular Signaling, The Eunice Kennedy Shiver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-4510, United States; Department of Physiology and Biophysics of the Institute of Biomedical Sciences, University of São Paulo, SP, Brazil
| | - Elias Leiva-Salcedo
- Section on Cellular Signaling, The Eunice Kennedy Shiver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-4510, United States
| | - Maria Tereza Nunes
- Department of Physiology and Biophysics of the Institute of Biomedical Sciences, University of São Paulo, SP, Brazil
| | - Stanko S Stojilkovic
- Section on Cellular Signaling, The Eunice Kennedy Shiver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-4510, United States.
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Proudan N, Peroski M, Grignol G, Merchenthaler I, Dudas B. Juxtapositions between the somatostatinergic and growth hormone-releasing hormone (GHRH) neurons in the human hypothalamus. Neuroscience 2015; 297:205-10. [DOI: 10.1016/j.neuroscience.2015.03.054] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2015] [Revised: 03/06/2015] [Accepted: 03/24/2015] [Indexed: 11/29/2022]
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Magdaleno-Méndez A, Domínguez B, Rodríguez-Andrade A, Barrientos-Morales M, Cervantes-Acosta P, Hernández-Beltrán A, González-Ramírez R, Felix R. Ghrelin increases growth hormone production and functional expression of NaV1.1 and Na V1.2 channels in pituitary somatotropes. Endocrine 2015; 48:929-36. [PMID: 25151402 DOI: 10.1007/s12020-014-0392-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/28/2014] [Accepted: 08/11/2014] [Indexed: 12/19/2022]
Abstract
A variety of ion channels are expressed in the plasma membrane of somatotropes within the anterior pituitary gland. Modification of these channels is linked to intracellular Ca2+ levels and therefore to hormone secretion. Previous investigations have shown that the gut-derived orexigenic peptide hormone ghrelin and synthetic GH-releasing peptides (GHRPs) stimulate release of growth hormone (GH) and increase the number of functional voltage-gated Ca2+ and Na+ channels in the membrane of clonal GC somatotropes. Here, we reveal that chronic treatment with ghrelin and its synthetic analog GHRP-6 also increases GH release from bovine pituitary somatotropes in culture, and that this action is associated with a significant increase in Na+ macroscopic current. Consistent with this, Na+ current blockade with tetrodotoxin (TTX) abolished the ghrelin- and GHRP-6-induced increase in GH release. Furthermore, semi-quantitative and real-time RT-PCR analysis revealed an upregulation in the transcript levels of GH, as well as of NaV1.1 and NaV1.2, two isoforms of TTX-sensitive Na+ channels expressed in somatotropes, after treatment with ghrelin or GHRP-6. These findings improve our knowledge on (i) the cellular mechanisms involved in the control of GH secretion, (ii) the molecular diversity of Na+ channels in pituitary somatotropes, and (iii) the regulation of GH and Na+ channel gene expression by ghrelin and GHRPs.
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Affiliation(s)
- Adasue Magdaleno-Méndez
- Laboratory of Cell Biology, School of Veterinary Medicine and Animal Science, University of Veracruz, Circunvalación esquina Yáñez s/n, C.P. 91710, Veracruz, Mexico
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Duncan PJ, Şengül S, Tabak J, Ruth P, Bertram R, Shipston MJ. Large conductance Ca²⁺-activated K⁺ (BK) channels promote secretagogue-induced transition from spiking to bursting in murine anterior pituitary corticotrophs. J Physiol 2015; 593:1197-211. [PMID: 25615909 PMCID: PMC4358680 DOI: 10.1113/jphysiol.2015.284471] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2014] [Accepted: 12/16/2014] [Indexed: 12/14/2022] Open
Abstract
Anterior pituitary corticotroph cells are a central component of the hypothalamic-pituitary-adrenal (HPA) axis essential for the neuroendocrine response to stress. Corticotrophs are excitable cells that receive input from two hypothalamic secretagogues, corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP) to control the release of adrenocorticotrophic hormone (ACTH). Although corticotrophs are spontaneously active and increase in excitability in response to CRH and AVP the patterns of electrical excitability and underlying ionic conductances are poorly understood. In this study, we have used electrophysiological, pharmacological and genetic approaches coupled with mathematical modelling to investigate whether CRH and AVP promote distinct patterns of electrical excitability and to interrogate the role of large conductance calcium- and voltage-activated potassium (BK) channels in spontaneous and secretagogue-induced activity. We reveal that BK channels do not play a significant role in the generation of spontaneous activity but are critical for the transition to bursting in response to CRH. In contrast, AVP promotes an increase in single spike frequency, a mechanism independent of BK channels but dependent on background non-selective conductances. Co-stimulation with CRH and AVP results in complex patterns of excitability including increases in both single spike frequency and bursting. The ability of corticotroph excitability to be differentially regulated by hypothalamic secretagogues provides a mechanism for differential control of corticotroph excitability in response to different stressors.
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Affiliation(s)
- Peter J Duncan
- Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh, EH8 9XD, UK
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Abstract
The somatostatin (SRIF) system, which includes the SRIF ligand and receptors, regulates anterior pituitary gland function, mainly inhibiting hormone secretion and to some extent pituitary tumor cell growth. SRIF-14 via its cognate G-protein-coupled receptors (subtypes 1-5) activates multiple cellular signaling pathways including adenylate cyclase/cAMP, MAPK, ion channel-dependent pathways, and others. In addition, recent data have suggested SRIF-independent constitutive SRIF receptor activity responsible for GH and ACTH inhibition in vitro. This review summarizes current knowledge on ligand-dependent and independent SRIF receptor molecular and functional effects on hormone-secreting cells in the anterior pituitary gland.
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Affiliation(s)
- Tamar Eigler
- Division of EndocrinologyDiabetes and Metabolism, Department of Medicine, Pituitary Center, Cedars Sinai Medical Center, Davis Building, Room 3066, 8700 Beverly Boulevard, Los Angeles, California 90048, USA
| | - Anat Ben-Shlomo
- Division of EndocrinologyDiabetes and Metabolism, Department of Medicine, Pituitary Center, Cedars Sinai Medical Center, Davis Building, Room 3066, 8700 Beverly Boulevard, Los Angeles, California 90048, USA
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Upregulation of voltage-gated calcium channel cav1.3 in bovine somatotropes treated with ghrelin. JOURNAL OF SIGNAL TRANSDUCTION 2014; 2013:527253. [PMID: 24455243 PMCID: PMC3880704 DOI: 10.1155/2013/527253] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/13/2013] [Accepted: 10/06/2013] [Indexed: 11/25/2022]
Abstract
Activation of the growth hormone (GH) secretagogue receptor (GHS-R) by synthetic GH releasing peptides (GHRP) or its endogenous ligand (Ghrelin) stimulates GH release. Though much is known about the signal transduction underlying short-term regulation, there is far less information on the mechanisms that produce long-term effects. In the current report, using an enzyme-linked immunosorbent assay for GH detection and whole-cell patch-clamp recordings, we assessed the long-term actions of such regulatory factors on voltage-activated Ca2+ currents in bovine somatotropes (BS) separated on a Percoll gradient and detected by immunohistochemistry. After 24 h of treatment with Ghrelin (10 nM) or GHRP-6 (100 nM) enhanced BS secretory activity; GH secretion stimulated by GHS through the activation of GHS-R because treatment with the antagonist of GHS-R (D-Lys3-GHRP-6, 10 μM) blocked the GH secretion, and the effect was dose and time dependent (24, 48, and 72 h). GH secretion stimulated by GHRP-6 was abolished by nifedipine (0.5 μM), a blocker of L-type HVA Ca2+ channels, and KN-62 (10 μM), an inhibitor of Ca2+/CaM-KII. After 72 h in culture, all recorded BS exhibited two main Ca2+ currents: a low voltage-activated (LVA; T-type) and a high voltage-activated (HVA; mostly dihydropyridine-sensitive L-type) current. Interestingly, HVA and LVA channels were differentially upregulated by Ghrelin. Chronic treatment with the GHS induced a significant selective increase on the Ba2+ current through HVA Ca2+ channels, and caused only a small increase of currents through LVA channels. The stimulatory effect on HVA current density was accompanied by an augment in maximal conductance with no apparent changes in the kinetics and the voltage dependence of the Ca2+ currents, suggesting an increase in the number of functional channels in the cell membrane. Lastly, in consistency with the functional data, quantitative real-time RT-PCR revealed transcripts encoding for the Cav1.2 and Cav1.3 pore-forming subunits of L-type channels. The treatment with Ghrelin significantly increased the Cav1.3 subunit expression, suggeting that the chronic stimulation of the GHS receptor with Ghrelin or GHRP-6 increases the number of voltage-gated Ca2+ channels at the cell surface of BS.
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Osinga HM, Tsaneva-Atanasova KT. Geometric analysis of transient bursts. CHAOS (WOODBURY, N.Y.) 2013; 23:046107. [PMID: 24387586 DOI: 10.1063/1.4826655] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We consider the effect of a brief stimulation from the rest state of a minimal neuronal model with multiple time scales. Such transient dynamics brings out the intrinsic bursting capabilities of the system. Our main goal is to show that a minimum of three dimensions is enough to generate spike-adding phenomena in transient responses, and that the onset of a new spike can be tracked using existing continuation packages. We take a geometric approach to illustrate how the underlying fast subsystem organises the spike adding in much the same way as for spike adding in periodic bursts, but the bifurcation analysis for spike onset is entirely different. By using a generic model, we further strengthen claims made in our earlier work that our numerical method for spike onset can be used for a broad class of systems.
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Affiliation(s)
- Hinke M Osinga
- Department of Mathematics, the University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
| | - Krasimira T Tsaneva-Atanasova
- College of Engineering, Mathematics and Physical Sciences, University of Exeter, North Park Road, Exeter EX4 4QF, United Kingdom
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36
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A geometric understanding of how fast activating potassium channels promote bursting in pituitary cells. J Comput Neurosci 2013; 36:259-78. [DOI: 10.1007/s10827-013-0470-8] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2013] [Revised: 04/25/2013] [Accepted: 05/29/2013] [Indexed: 12/13/2022]
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Tomaiuolo M, Bertram R, Leng G, Tabak J. Models of electrical activity: calibration and prediction testing on the same cell. Biophys J 2013. [PMID: 23199930 DOI: 10.1016/j.bpj.2012.09.034] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
Abstract
Mathematical models are increasingly important in biology, and testability is becoming a critical issue. One limitation is that one model simulation tests a parameter set representing one instance of the biological counterpart, whereas biological systems are heterogeneous in their properties and behavior, and a model often is fitted to represent an ideal average. This is also true for models of a cell's electrical activity; even within a narrowly defined population there can be considerable variation in electrophysiological phenotype. Here, we describe a computational experimental approach for parameterizing a model of the electrical activity of a cell in real time. We combine the inexpensive parallel computational power of a programmable graphics processing unit with the flexibility of the dynamic clamp method. The approach involves 1), recording a cell's electrical activity, 2), parameterizing a model to the recording, 3), generating predictions, and 4), testing the predictions on the same cell used for the calibration. We demonstrate the experimental feasibility of our approach using a cell line (GH4C1). These cells are electrically active, and they display tonic spiking or bursting. We use our approach to predict parameter changes that can convert one pattern to the other.
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Affiliation(s)
- Maurizio Tomaiuolo
- Department of Biological Science and Program in Neuroscience, Florida State University, Tallahassee, Florida, USA
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Gadelha MR, Kasuki L, Korbonits M. Novel pathway for somatostatin analogs in patients with acromegaly. Trends Endocrinol Metab 2013; 24:238-46. [PMID: 23270713 DOI: 10.1016/j.tem.2012.11.007] [Citation(s) in RCA: 105] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/14/2012] [Revised: 11/21/2012] [Accepted: 11/24/2012] [Indexed: 01/11/2023]
Abstract
Acromegaly is a chronic disease with increased morbidity and mortality, where usually multiple treatment modalities are used. The somatostatin analogs (SSAs) are the mainstay of medical therapy but, in many patients, including those with a germline mutation in the aryl hydrocarbon receptor-interacting protein (AIP) gene, disease activity cannot be controlled with these drugs. Previous data have suggested the involvement of the tumor-suppressor gene ZAC1 in the mechanism of action of SSAs, and more recent findings suggested that SSAs could regulate AIP, which in turn can stimulate ZAC1, therefore suggesting the existence of a SSA-AIP-ZAC1-somatostatin effect pathway. The current review discusses these novel observations, highlighting their significance in the treatment of sporadic and familial somatotroph adenomas.
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Affiliation(s)
- Mônica R Gadelha
- Division of Endocrinology, Clementino Fraga Filho University Hospital, Federal University of Rio de Janeiro, Professor Rodolpho Paulo Rocco street 255, Rio de Janeiro, Brazil
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MURRAY PHILIPG, CLAYTON PETERE. Endocrine Control of Growth. AMERICAN JOURNAL OF MEDICAL GENETICS PART C-SEMINARS IN MEDICAL GENETICS 2013; 163C:76-85. [DOI: 10.1002/ajmg.c.31357] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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Nowacki J, Osinga HM, Tsaneva-Atanasova KT. Continuation-Based Numerical Detection of After-Depolarization and Spike-Adding Thresholds. Neural Comput 2013; 25:877-900. [DOI: 10.1162/neco_a_00425] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
The changes in neuronal firing pattern are signatures of brain function, and it is of interest to understand how such changes evolve as a function of neuronal biophysical properties. We address this important problem by the analysis and numerical investigation of a class of mechanistic mathematical models. We focus on a hippocampal pyramidal neuron model and study the occurrence of bursting related to the after-depolarization (ADP) that follows a brief current injection. This type of burst is a transient phenomenon that is not amenable to the classical bifurcation analysis done, for example, for periodic bursting oscillators. In this letter, we show how to formulate such transient behavior as a two-point boundary value problem (2PBVP), which can be solved using well-known continuation methods. The 2PBVP is formulated such that the transient response is represented by a finite orbit segment for which onsets of ADP and additional spikes in a burst can be detected as bifurcations during a one-parameter continuation. This in turn provides us with a direct method to approximate the boundaries of regions in a two-parameter plane where certain model behavior of interest occurs. More precisely, we use two-parameter continuation of the detected onset points to identify the boundaries between regions with and without ADP and bursts with different numbers of spikes. Our 2PBVP formulation is a novel approach to parameter sensitivity analysis that can be applied to a wide range of problems.
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Affiliation(s)
| | - Hinke M. Osinga
- Department of Mathematics, University of Auckland, Auckland 1142, New Zealand
| | - Krasimira T. Tsaneva-Atanasova
- Bristol Centre for Applied Nonlinear Mathematics, Department of Engineering Mathematics, University of Bristol, Bristol BS8 1TR, U.K
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Teka W, Tabak J, Bertram R. The relationship between two fast/slow analysis techniques for bursting oscillations. CHAOS (WOODBURY, N.Y.) 2012; 22:043117. [PMID: 23278052 PMCID: PMC3523400 DOI: 10.1063/1.4766943] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Accepted: 10/04/2012] [Indexed: 06/01/2023]
Abstract
Bursting oscillations in excitable systems reflect multi-timescale dynamics. These oscillations have often been studied in mathematical models by splitting the equations into fast and slow subsystems. Typically, one treats the slow variables as parameters of the fast subsystem and studies the bifurcation structure of this subsystem. This has key features such as a z-curve (stationary branch) and a Hopf bifurcation that gives rise to a branch of periodic spiking solutions. In models of bursting in pituitary cells, we have recently used a different approach that focuses on the dynamics of the slow subsystem. Characteristic features of this approach are folded node singularities and a critical manifold. In this article, we investigate the relationships between the key structures of the two analysis techniques. We find that the z-curve and Hopf bifurcation of the two-fast/one-slow decomposition are closely related to the voltage nullcline and folded node singularity of the one-fast/two-slow decomposition, respectively. They become identical in the double singular limit in which voltage is infinitely fast and calcium is infinitely slow.
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Affiliation(s)
- Wondimu Teka
- Department of Mathematics, Florida State University, Tallahassee, Florida 32306, USA
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Stojilkovic SS, Kretschmannova K, Tomić M, Stratakis CA. Dependence of the excitability of pituitary cells on cyclic nucleotides. J Neuroendocrinol 2012; 24:1183-200. [PMID: 22564128 PMCID: PMC3421050 DOI: 10.1111/j.1365-2826.2012.02335.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Cyclic 3',5'-adenosine monophosphate and cyclic 3',5'-guanosine monophosphate are intracellular (second) messengers that are produced from the nucleotide triphosphates by a family of enzymes consisting of adenylyl and guanylyl cyclases. These enzymes are involved in a broad array of signal transduction pathways mediated by the cyclic nucleotide monophosphates and their kinases, which control multiple aspects of cell function through the phosphorylation of protein substrates. We review the findings and working hypotheses on the role of the cyclic nucleotides and their kinases in the control of electrical activity of the endocrine pituitary cells and the plasma membrane channels involved in this process.
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Affiliation(s)
- S S Stojilkovic
- Sections on Cellular Signalling and Endocrinology and Genetics, The Eunice Kennedy Shiver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
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Kucka M, Kretschmannova K, Stojilkovic SS, Zemkova H, Tomić M. Dependence of spontaneous electrical activity and basal prolactin release on nonselective cation channels in pituitary lactotrophs. Physiol Res 2012; 61:267-75. [PMID: 22480423 PMCID: PMC3674129 DOI: 10.33549/physiolres.932301] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
All secretory anterior pituitary cells fire action potentials spontaneously and exhibit a high resting cation conductance, but the channels involved in the background permeability have not been identified. In cultured lactotrophs and immortalized GH(3) cells, replacement of extracellular Na(+) with large organic cations, but not blockade of voltage-gated Na(+) influx, led to an instantaneous hyperpolarization of cell membranes that was associated with a cessation of spontaneous firing. When cells were clamped at -50 mV, which was close to the resting membrane potential in these cells, replacement of bath Na(+) with organic cations resulted in an outward-like current, reflecting an inhibition of the inward holding membrane current and indicating loss of a background-depolarizing conductance. Quantitative RT-PCR analysis revealed the high expression of mRNA transcripts for TRPC1 and much lower expression of TRPC6 in both lactotrophs and GH(3) cells. Very low expression of TRPC3, TRPC4, and TRPC5 mRNA transcripts were also present in pituitary but not GH(3) cells. 2-APB and SKF-96365, relatively selective blockers of TRPC channels, inhibited electrical activity, Ca(2+) influx and prolactin release in a concentration-dependent manner. Gd(3+), a common Ca(2+) channel blocker, and flufenamic acid, an inhibitor of non-selective cation channels, also inhibited electrical activity, Ca(2+) influx and prolactin release. These results indicate that nonselective cation channels, presumably belonging to the TRPC family, contribute to the background depolarizing conductance and firing of action potentials with consequent contribution to Ca(2+) influx and hormone release in lactotrophs and GH(3) cells.
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Affiliation(s)
- Marek Kucka
- Section on Cellular Signaling, PDN, NICHD, National Institutes of Health, Bethesda, MD 20892-4510
| | - Karla Kretschmannova
- Section on Cellular Signaling, PDN, NICHD, National Institutes of Health, Bethesda, MD 20892-4510
| | - Stanko S. Stojilkovic
- Section on Cellular Signaling, PDN, NICHD, National Institutes of Health, Bethesda, MD 20892-4510
| | - Hana Zemkova
- Section on Cellular Signaling, PDN, NICHD, National Institutes of Health, Bethesda, MD 20892-4510
- Department of Cellular and Molecular Neuroendocrinology, Institute of Physiology of the Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Melanija Tomić
- Section on Cellular Signaling, PDN, NICHD, National Institutes of Health, Bethesda, MD 20892-4510
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Fast-activating voltage- and calcium-dependent potassium (BK) conductance promotes bursting in pituitary cells: a dynamic clamp study. J Neurosci 2012; 31:16855-63. [PMID: 22090511 DOI: 10.1523/jneurosci.3235-11.2011] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The electrical activity pattern of endocrine pituitary cells regulates their basal secretion level. Rat somatotrophs and lactotrophs exhibit spontaneous bursting and have high basal levels of hormone secretion, while gonadotrophs exhibit spontaneous spiking and have low basal hormone secretion. It has been proposed that the difference in electrical activity between bursting somatotrophs and spiking gonadotrophs is due to the presence of large conductance potassium (BK) channels on somatotrophs but not on gonadotrophs. This is one example where the role of an ion channel type may be clearly established. We demonstrate here that BK channels indeed promote bursting activity in pituitary cells. Blocking BK channels in bursting lacto-somatotroph GH4C1 cells changes their firing activity to spiking, while further adding an artificial BK conductance via dynamic clamp restores bursting. Importantly, this burst-promoting effect requires a relatively fast BK activation/deactivation, as predicted by computational models. We also show that adding a fast-activating BK conductance to spiking gonadotrophs converts the activity of these cells to bursting. Together, our results suggest that differences in BK channel expression may underlie the differences in electrical activity and basal hormone secretion levels among pituitary cell types and that the rapid rate of BK channel activation is key to its role in burst promotion.
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Vo T, Bertram R, Wechselberger M. Bifurcations of canard-induced mixed mode oscillations in a pituitary Lactotroph model. ACTA ACUST UNITED AC 2012. [DOI: 10.3934/dcds.2012.32.2879] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Osinga HM, Sherman A, Tsaneva-Atanasova K. CROSS-CURRENTS BETWEEN BIOLOGY AND MATHEMATICS: THE CODIMENSION OF PSEUDO-PLATEAU BURSTING. ACTA ACUST UNITED AC 2012; 32:2853-2877. [PMID: 22984340 DOI: 10.3934/dcds.2012.32.2853] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
A great deal of work has gone into classifying bursting oscillations, periodic alternations of spiking and quiescence modeled by fast-slow systems. In such systems, one or more slow variables carry the fast variables through a sequence of bifurcations that mediate transitions between oscillations and steady states. A rigorous classification approach is to characterize the bifurcations found in the neighborhood of a singularity; a measure of the complexity of the bursting oscillation is then given by the smallest codimension of the singularities near which it occurs. Fold/homoclinic bursting, along with most other burst types of interest, has been shown to occur near a singularity of codimension three by examining bifurcations of a cubic Liénard system; hence, these types of bursting have at most codimension three. Modeling and biological considerations suggest that fold/homoclinic bursting should be found near fold/subHopf bursting, a more recently identified burst type whose codimension has not been determined yet. One would expect that fold/subHopf bursting has the same codimension as fold/homoclinic bursting, because models of these two burst types have very similar underlying bifurcation diagrams. However, no codimension-three singularity is known that supports fold/subHopf bursting, which indicates that it may have codimension four. We identify a three-dimensional slice in a partial unfolding of a doubly-degenerate Bodganov-Takens point, and show that this codimension-four singularity gives rise to almost all known types of bursting.
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Affiliation(s)
- Hinke M Osinga
- Bristol Centre for Applied Nonlinear Mathematics Department of Engineering Mathematics University of Bristol, Queen's Building, University Walk Bristol BS8 1TR, UK
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Liang Z, Chen L, McClafferty H, Lukowski R, MacGregor D, King JT, Rizzi S, Sausbier M, McCobb DP, Knaus HG, Ruth P, Shipston MJ. Control of hypothalamic-pituitary-adrenal stress axis activity by the intermediate conductance calcium-activated potassium channel, SK4. J Physiol 2011; 589:5965-86. [PMID: 22041182 PMCID: PMC3286679 DOI: 10.1113/jphysiol.2011.219378] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2011] [Accepted: 10/28/2011] [Indexed: 11/26/2022] Open
Abstract
The anterior pituitary corticotroph is a major control point for the regulation of the hypothalamic-pituitary-adrenal (HPA) axis and the neuroendocrine response to stress. Although corticotrophs are known to be electrically excitable, ion channels controlling the electrical properties of corticotrophs are poorly understood. Here, we exploited a lentiviral transduction system to allow the unequivocal identification of live murine corticotrophs in culture. We demonstrate that corticotrophs display highly heterogeneous spontaneous action-potential firing patterns and their resting membrane potential is modulated by a background sodium conductance. Physiological concentrations of corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP) cause a depolarization of corticotrophs, leading to a sustained increase in action potential firing. A major component of the outward potassium conductance was mediated via intermediate conductance calcium-activated (SK4) potassium channels. Inhibition of SK4 channels with TRAM-34 resulted in an increase in corticotroph excitability and exaggerated CRH/AVP-stimulated ACTH secretion in vitro. In accordance with a physiological role for SK4 channels in vivo, restraint stress-induced plasma ACTH and corticosterone concentrations were significantly enhanced in gene-targeted mice lacking SK4 channels (Kcnn4(-/-)). In addition, Kcnn4(-/-) mutant mice displayed enhanced hypothalamic c-fos and nur77 mRNA expression following restraint, suggesting increased neuronal activation. Thus, stress hyperresponsiveness observed in Kcnn4(-/-) mice results from enhanced secretagogue-induced ACTH output from anterior pituitary corticotrophs and may also involve increased hypothalamic drive, thereby suggesting an important role for SK4 channels in HPA axis function.
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Affiliation(s)
- Zhi Liang
- Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh EH89XD, Scotland, UK
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Molecular mechanisms of pituitary endocrine cell calcium handling. Cell Calcium 2011; 51:212-21. [PMID: 22138111 DOI: 10.1016/j.ceca.2011.11.003] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2011] [Revised: 10/30/2011] [Accepted: 11/07/2011] [Indexed: 11/23/2022]
Abstract
Endocrine pituitary cells express numerous voltage-gated Na(+), Ca(2+), K(+), and Cl(-) channels and several ligand-gated channels, and they fire action potentials spontaneously. Depending on the cell type, this electrical activity can generate localized or global Ca(2+) signals, the latter reaching the threshold for stimulus-secretion coupling. These cells also express numerous G-protein-coupled receptors, which can stimulate or silence electrical activity and Ca(2+) influx through voltage-gated Ca(2+) channels and hormone release. Receptors positively coupled to the adenylyl cyclase signaling pathway stimulate electrical activity with cAMP, which activates hyperpolarization-activated cyclic nucleotide-regulated channels directly, or by cAMP-dependent kinase-mediated phosphorylation of K(+), Na(+), Ca(2+), and/or non-selective cation-conducting channels. Receptors that are negatively coupled to adenylyl cyclase signaling pathways inhibit spontaneous electrical activity and accompanied Ca(2+) transients predominantly through the activation of inwardly rectifying K(+) channels and the inhibition of voltage-gated Ca(2+) channels. The Ca(2+)-mobilizing receptors activate inositol trisphosphate-gated Ca(2+) channels in the endoplasmic reticulum, leading to Ca(2+) release in an oscillatory or non-oscillatory manner, depending on the cell type. This Ca(2+) release causes a cell type-specific modulation of electrical activity and intracellular Ca(2+) handling.
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Chang JP, Habibi HR, Yu Y, Moussavi M, Grey CL, Pemberton JG. Calcium and other signalling pathways in neuroendocrine regulation of somatotroph functions. Cell Calcium 2011; 51:240-52. [PMID: 22137240 DOI: 10.1016/j.ceca.2011.11.001] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2011] [Revised: 11/01/2011] [Accepted: 11/07/2011] [Indexed: 12/22/2022]
Abstract
Relative to mammals, the neuroendocrine control of pituitary growth hormone (GH) secretion and synthesis in teleost fish involves numerous stimulatory and inhibitory regulators, many of which are delivered to the somatotrophs via direct innervation. Among teleosts, how multifactorial regulation of somatotroph functions are mediated at the level of post-receptor signalling is best characterized in goldfish. Supplemented with recent findings, this review focuses on the known intracellular signal transduction mechanisms mediating the ligand- and function-specific actions in multifactorial control of GH release and synthesis, as well as basal GH secretion, in goldfish somatotrophs. These include membrane voltage-sensitive ion channels, Na(+)/H(+) antiport, Ca(2+) signalling, multiple pharmacologically distinct intracellular Ca(2+) stores, cAMP/PKA, PKC, nitric oxide, cGMP, MEK/ERK and PI3K. Signalling pathways mediating the major neuroendocrine regulators of mammalian somatotrophs, as well as those in other major teleost study model systems are also briefly highlighted. Interestingly, unlike mammals, spontaneous action potential firings are not observed in goldfish somatotrophs in culture. Furthermore, three goldfish brain somatostatin forms directly affect pituitary GH secretion via ligand-specific actions on membrane ion channels and intracellular Ca(2+) levels, as well as exert isoform-specific action on basal and stimulated GH mRNA expression, suggesting the importance of somatostatins other than somatostatin-14.
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Affiliation(s)
- John P Chang
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.
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50
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Kretschmannova K, Kucka M, Gonzalez-Iglesias AE, Stojilkovic SS. The expression and role of hyperpolarization-activated and cyclic nucleotide-gated channels in endocrine anterior pituitary cells. Mol Endocrinol 2011; 26:153-64. [PMID: 22135067 DOI: 10.1210/me.2011-1207] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Pituitary cells fire action potentials independently of external stimuli, and such spontaneous electrical activity is modulated by a large variety of hypothalamic and intrapituitary agonists. Here, we focused on the potential role of hyperpolarization-activated and cyclic nucleotide-gated (HCN) channels in electrical activity of cultured rat anterior pituitary cells. Quantitative RT-PCR analysis showed higher level of expression of mRNA transcripts for HCN2 and HCN3 subunits and lower expression of HCN1 and HCN4 subunits in these cells. Western immunoblot analysis of lysates from normal and GH(3) immortalized pituitary cells showed bands with appropriate molecular weights for HCN2, HCN3, and HCN4. Electrophysiological experiments showed the presence of a slowly developing hyperpolarization-activated inward current, which was blocked by Cs(+) and ZD7288, in gonadotrophs, thyrotrophs, somatotrophs, and a fraction of lactotrophs, as well as in other unidentified pituitary cell types. Stimulation of adenylyl cyclase and addition of 8-Br-cAMP enhanced this current and depolarized the cell membrane, whereas 8-Br-cGMP did not alter the current and hyperpolarized the cell membrane. Both inhibition of basal adenylyl cyclase activity and stimulation of phospholipase C signaling pathway inhibited this current. Inhibition of HCN channels affected the frequency of firing but did not abolish spontaneous electrical activity. These experiments indicate that cAMP and cGMP have opposite effects on the excitability of endocrine pituitary cells, that basal cAMP production in cultured cells is sufficient to integrate the majority of HCN channels in electrical activity, and that depletion of phosphatidylinositol 4,5-bisphosphate caused by activation of phospholipase C silences them.
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Affiliation(s)
- Karla Kretschmannova
- Section on Cellular Signaling, Program in Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-4510, USA
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