1
|
Aldossary HS, Alzahrani AA, Nathanael D, Alhuthail EA, Ray CJ, Batis N, Kumar P, Coney AM, Holmes AP. G-Protein-Coupled Receptor (GPCR) Signaling in the Carotid Body: Roles in Hypoxia and Cardiovascular and Respiratory Disease. Int J Mol Sci 2020; 21:ijms21176012. [PMID: 32825527 PMCID: PMC7503665 DOI: 10.3390/ijms21176012] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2020] [Revised: 08/13/2020] [Accepted: 08/16/2020] [Indexed: 12/17/2022] Open
Abstract
The carotid body (CB) is an important organ located at the carotid bifurcation that constantly monitors the blood supplying the brain. During hypoxia, the CB immediately triggers an alarm in the form of nerve impulses sent to the brain. This activates protective reflexes including hyperventilation, tachycardia and vasoconstriction, to ensure blood and oxygen delivery to the brain and vital organs. However, in certain conditions, including obstructive sleep apnea, heart failure and essential/spontaneous hypertension, the CB becomes hyperactive, promoting neurogenic hypertension and arrhythmia. G-protein-coupled receptors (GPCRs) are very highly expressed in the CB and have key roles in mediating baseline CB activity and hypoxic sensitivity. Here, we provide a brief overview of the numerous GPCRs that are expressed in the CB, their mechanism of action and downstream effects. Furthermore, we will address how these GPCRs and signaling pathways may contribute to CB hyperactivity and cardiovascular and respiratory disease. GPCRs are a major target for drug discovery development. This information highlights specific GPCRs that could be targeted by novel or existing drugs to enable more personalized treatment of CB-mediated cardiovascular and respiratory disease.
Collapse
Affiliation(s)
- Hayyaf S. Aldossary
- Institute of Clinical Sciences, University of Birmingham, Birmingham B15 2TT, UK; (H.S.A.); (A.A.A.); (D.N.); (E.A.A.); (C.J.R.); (P.K.); (A.M.C.)
- College of Medicine, Basic Medical Sciences, King Saud bin Abdulaziz University for Health Sciences, Riyadh 11481, Saudi Arabia
| | - Abdulaziz A. Alzahrani
- Institute of Clinical Sciences, University of Birmingham, Birmingham B15 2TT, UK; (H.S.A.); (A.A.A.); (D.N.); (E.A.A.); (C.J.R.); (P.K.); (A.M.C.)
- Respiratory Care Department, Faculty of Applied Medical Sciences, Umm Al-Qura University, Makkah 24381, Saudi Arabia
| | - Demitris Nathanael
- Institute of Clinical Sciences, University of Birmingham, Birmingham B15 2TT, UK; (H.S.A.); (A.A.A.); (D.N.); (E.A.A.); (C.J.R.); (P.K.); (A.M.C.)
| | - Eyas A. Alhuthail
- Institute of Clinical Sciences, University of Birmingham, Birmingham B15 2TT, UK; (H.S.A.); (A.A.A.); (D.N.); (E.A.A.); (C.J.R.); (P.K.); (A.M.C.)
- Collage of Sciences and Health Professions, Basic Sciences Department, King Saud bin Abdulaziz University for Health Sciences, Riyadh 11481, Saudi Arabia
| | - Clare J. Ray
- Institute of Clinical Sciences, University of Birmingham, Birmingham B15 2TT, UK; (H.S.A.); (A.A.A.); (D.N.); (E.A.A.); (C.J.R.); (P.K.); (A.M.C.)
| | - Nikolaos Batis
- Institute of Cancer and Genomic Sciences, University of Birmingham, Birmingham B15 2TT, UK;
| | - Prem Kumar
- Institute of Clinical Sciences, University of Birmingham, Birmingham B15 2TT, UK; (H.S.A.); (A.A.A.); (D.N.); (E.A.A.); (C.J.R.); (P.K.); (A.M.C.)
| | - Andrew M. Coney
- Institute of Clinical Sciences, University of Birmingham, Birmingham B15 2TT, UK; (H.S.A.); (A.A.A.); (D.N.); (E.A.A.); (C.J.R.); (P.K.); (A.M.C.)
| | - Andrew P. Holmes
- Institute of Clinical Sciences, University of Birmingham, Birmingham B15 2TT, UK; (H.S.A.); (A.A.A.); (D.N.); (E.A.A.); (C.J.R.); (P.K.); (A.M.C.)
- Institute of Cardiovascular Sciences, University of Birmingham, Birmingham B15 2TT, UK
- Correspondence: ; Tel.: +44-121-415-8161
| |
Collapse
|
2
|
O'Donohoe PB, Turner PJ, Huskens N, Buckler KJ, Pandit JJ. Influence of propofol on isolated neonatal rat carotid body glomus cell response to hypoxia and hypercapnia. Respir Physiol Neurobiol 2018; 260:17-27. [PMID: 30389452 PMCID: PMC6336315 DOI: 10.1016/j.resp.2018.10.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Revised: 10/14/2018] [Accepted: 10/29/2018] [Indexed: 11/06/2022]
Abstract
The intravenous anaesthetic propofol acts directly on carotid body glomus cells to inhibit their response to hypoxia. Propofol acts via novel mechanisms, as we excluded action via its known target receptors (nicotinic, GABA-ergic, or K+ channel). Inhibition of the hypoxic response is clinically relevant in anaesthesia.
In humans the intravenous anaesthetic propofol depresses ventilatory responses to hypoxia and CO2. Animal studies suggest that this may in part be due to inhibition of synaptic transmission between chemoreceptor glomus cells of the carotid body and the afferent carotid sinus nerve. It is however unknown if propofol can also act directly on the glomus cell. Here we report that propofol can indeed inhibit intracellular Ca2+ responses to hypoxia and hypercapnia in isolated rat glomus cells. Neither this propofol effect, nor the glomus cell response to hypoxia in the absence of propofol, were influenced by GABA receptor activation (using GABA, muscimol and baclofen) or inhibition (using bicuculline and 5-aminovaleric acid). Suggesting that these effects of propofol are not mediated through GABA receptors. Propofol inhibited calcium responses to nicotine in glomus cells but the nicotinic antagonists vecuronium and methyllycaconitine did not inhibit calcium responses to hypoxia. TASK channel activity was not altered by propofol. The glomus cell Ca2+ response to depolarisation with 30 mM K+ was however modestly inhibited by propofol. In summary we conclude that propofol does have a direct effect upon hypoxia signalling in isolated type-1 cells and that this may be partially due to its ability to inhibit voltage gated Ca2+v channels. We also note that propofol has the capacity to supress glomus cell excitation via nicotinic receptors and may therefore also interfere with paracrine/autocrine cholinergic signalling in the intact organ. The effects of propofol on chemoreceptor function are however clearly complex and require further investigation.
Collapse
Affiliation(s)
- Peadar B O'Donohoe
- Department of Physiology, Anatomy & Genetics, Parks Road, University of Oxford, Oxford, OX1 3PT, UK; Nuffield Department of Anaesthetics, Oxford University Hospitals NHS Trust, Oxford, OX3 9DU, UK
| | - Philip J Turner
- Department of Physiology, Anatomy & Genetics, Parks Road, University of Oxford, Oxford, OX1 3PT, UK
| | - Nicky Huskens
- Department of Physiology, Anatomy & Genetics, Parks Road, University of Oxford, Oxford, OX1 3PT, UK
| | - Keith J Buckler
- Department of Physiology, Anatomy & Genetics, Parks Road, University of Oxford, Oxford, OX1 3PT, UK
| | - Jaideep J Pandit
- Nuffield Department of Anaesthetics, Oxford University Hospitals NHS Trust, Oxford, OX3 9DU, UK.
| |
Collapse
|
3
|
Holmes AP, Ray CJ, Pearson SA, Coney AM, Kumar P. Ecto-5'-nucleotidase (CD73) regulates peripheral chemoreceptor activity and cardiorespiratory responses to hypoxia. J Physiol 2018; 596:3137-3148. [PMID: 28560821 PMCID: PMC6068227 DOI: 10.1113/jp274498] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2017] [Accepted: 05/25/2017] [Indexed: 12/17/2022] Open
Abstract
KEY POINTS Carotid body dysfunction is recognized as a cause of hypertension in a number of cardiorespiratory diseases states and has therefore been identified as a potential therapeutic target. Purinergic transmission is an important element of the carotid body chemotransduction pathway. We show that inhibition of ecto-5'-nucleotidase (CD73) in vitro reduces carotid body basal discharge and responses to hypoxia and mitochondrial inhibition. Additionally, inhibition of CD73 in vivo decreased the hypoxic ventilatory response, reduced the hypoxia-induced heart rate elevation and exaggerated the blood pressure decrease in response to hypoxia. Our data show CD73 to be a novel regulator of carotid body sensory function and therefore suggest that this enzyme may offer a new target for reducing carotid body activity in selected cardiovascular diseases. ABSTRACT Augmented sensory neuronal activity from the carotid body (CB) has emerged as a principal cause of hypertension in a number of cardiovascular related pathologies, including obstructive sleep apnoea, heart failure and diabetes. Development of new targets and pharmacological treatment strategies aiming to reduce CB sensory activity may thus improve outcomes in these key patient cohorts. The present study investigated whether ecto-5'-nucleotidase (CD73), an enzyme that generates adenosine, is functionally important in modifying CB sensory activity and cardiovascular respiratory responses to hypoxia. Inhibition of CD73 by α,β-methylene ADP (AOPCP) in the whole CB preparation in vitro reduced basal discharge frequency by 76 ± 5% and reduced sensory activity throughout graded hypoxia. AOPCP also significantly attenuated elevations in sensory activity evoked by mitochondrial inhibition. These effects were mimicked by antagonism of adenosine receptors with 8-(p-sulfophenyl) theophylline. Infusion of AOPCP in vivo significantly decreased the hypoxic ventilatory response (Δ V ̇ E control 74 ± 6%, Δ V ̇ E AOPCP 64 ± 5%, P < 0.05). AOPCP also modified cardiovascular responses to hypoxia, as indicated by reduced elevations in heart rate and exaggerated changes in femoral vascular conductance and mean arterial blood pressure. Thus we identify CD73 as a novel regulator of CB sensory activity. Future investigations are warranted to clarify whether inhibition of CD73 can effectively reduce CB activity in CB-mediated cardiovascular pathology.
Collapse
Affiliation(s)
| | - Clare J. Ray
- Institute of Clinical SciencesUniversity of BirminghamEdgbastonBirminghamUK
| | - Selina A. Pearson
- Mouse Pipelines, Wellcome Trust Sanger InstituteWellcome Genome CampusHinxtonCambridgeUK
| | - Andrew M. Coney
- Institute of Clinical SciencesUniversity of BirminghamEdgbastonBirminghamUK
| | - Prem Kumar
- Institute of Clinical SciencesUniversity of BirminghamEdgbastonBirminghamUK
| |
Collapse
|
4
|
Conde SV, Monteiro EC, Sacramento JF. Purines and Carotid Body: New Roles in Pathological Conditions. Front Pharmacol 2017; 8:913. [PMID: 29311923 PMCID: PMC5733106 DOI: 10.3389/fphar.2017.00913] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2017] [Accepted: 11/29/2017] [Indexed: 01/28/2023] Open
Abstract
It is known that adenosine and adenosine-5′-triphosphate (ATP) are excitatory mediators involved in carotid body (CB) hypoxic signaling. The CBs are peripheral chemoreceptors classically defined by O2, CO2, and pH sensors. When hypoxia activates the CB, it induces the release of neurotransmitters from chemoreceptor cells leading to an increase in the action potentials frequency at the carotid sinus nerve (CSN). This increase in the firing frequency of the CSN is integrated in the brainstem to induce cardiorespiratory compensatory responses. In the last decade several pathologies, as, hypertension, diabetes, obstructive sleep apnea and heart failure have been associated with CB overactivation. In the first section of the present manuscript we review in a concise manner fundamental aspects of purine metabolism. The second section is devoted to the role of purines on the hypoxic response of the CB, providing the state-of-the art for the presence of adenosine and ATP receptors in the CB; for the role of purines at presynaptic level in CB chemoreceptor cells, as well as, its metabolism and regulation; at postsynaptic level in the CSN activity; and on the ventilatory responses to hypoxia. Recently, we have showed that adenosine is involved in CB hypersensitization during chronic intermittent hypoxia (CIH), which mimics obstructive sleep apnea, since caffeine, a non-selective adenosine receptor antagonist that inhibits A2A and A2B adenosine receptors, decreased CSN chemosensory activity in animals subjected to CIH. Apart from this involvement of adenosine in CB sensitization in sleep apnea, it was recently found that P2X3 ATP receptor in the CB contributes to increased chemoreflex hypersensitivity and hypertension in spontaneously hypertension rats. Therefore the last section of this manuscript is devoted to review the recent findings on the role of purines in CB-mediated pathologies as hypertension, diabetes and sleep apnea emphasizing the potential clinical importance of modulating purines levels and action to treat pathologies associated with CB dysfunction.
Collapse
Affiliation(s)
- Silvia V Conde
- Centro de Estudos de Doenças Crónicas, NOVA Medical School - Faculdade de Ciências Médicas, Universidade NOVA de Lisboa, Lisboa, Portugal
| | - Emilia C Monteiro
- Centro de Estudos de Doenças Crónicas, NOVA Medical School - Faculdade de Ciências Médicas, Universidade NOVA de Lisboa, Lisboa, Portugal
| | - Joana F Sacramento
- Centro de Estudos de Doenças Crónicas, NOVA Medical School - Faculdade de Ciências Médicas, Universidade NOVA de Lisboa, Lisboa, Portugal
| |
Collapse
|
5
|
Zhang M, Vollmer C, Nurse CA. Adenosine and dopamine oppositely modulate a hyperpolarization-activated current I h in chemosensory neurons of the rat carotid body in co-culture. J Physiol 2017; 596:3101-3117. [PMID: 28801916 DOI: 10.1113/jp274743] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2017] [Accepted: 08/08/2017] [Indexed: 12/24/2022] Open
Abstract
KEY POINTS Adenosine and dopamine (DA) are neuromodulators in the carotid body (CB) chemoafferent pathway, but their mechanisms of action are incompletely understood. Using functional co-cultures of rat CB chemoreceptor (type I) cells and sensory petrosal neurons (PNs), we show that adenosine enhanced a hyperpolarization-activated cation current Ih in chemosensory PNs via A2a receptors, whereas DA had the opposite effect via D2 receptors. Adenosine caused a depolarizing shift in the Ih activation curve and increased firing frequency, whereas DA caused a hyperpolarizing shift in the curve and decreased firing frequency. Acute hypoxia and isohydric hypercapnia depolarized type I cells concomitant with increased excitation of adjacent PNs; the A2a receptor blocker SCH58261 inhibited both type I and PN responses during hypoxia, but only the PN response during isohydric hypercapnia. We propose that adenosine and DA control firing frequency in chemosensory PNs via their opposing actions on Ih . ABSTRACT Adenosine and dopamine (DA) act as neurotransmitters or neuromodulators at the carotid body (CB) chemosensory synapse, but their mechanisms of action are not fully understood. Using a functional co-culture model of rat CB chemoreceptor (type I) cell clusters and juxtaposed afferent petrosal neurons (PNs), we tested the hypothesis that adenosine and DA act postsynaptically to modulate a hyperpolarization-activated, cyclic nucleotide-gated (HCN) cation current (Ih ). In whole-cell recordings from hypoxia-responsive PNs, cAMP mimetics enhanced Ih whereas the HCN blocker ZD7288 (2 μm) reversibly inhibited Ih . Adenosine caused a potentiation of Ih (EC50 ∼ 35 nm) that was sensitive to the A2a blocker SCH58261 (5 nm), and an ∼16 mV depolarizing shift in V½ for voltage dependence of Ih activation. By contrast, DA (10 μm) caused an inhibition of Ih that was sensitive to the D2 blocker sulpiride (1-10 μm), and an ∼11 mV hyperpolarizing shift in V½ . Sulpiride potentiated Ih in neurons adjacent to, but not distant from, type I cell clusters. DA also decreased PN action potential frequency whereas adenosine had the opposite effect. During simultaneous paired recordings, SCH58261 inhibited both the presynaptic hypoxia-induced receptor potential in type I cells and the postsynaptic PN response. By contrast, SCH58261 inhibited only the postsynaptic PN response induced by isohydric hypercapnia. Confocal immunofluorescence confirmed the localization of HCN4 subunits in tyrosine hydroxylase-positive chemoafferent neurons in tissue sections of rat petrosal ganglia. These data suggest that adenosine and DA, acting through A2a and D2 receptors respectively, regulate PN excitability via their opposing actions on Ih .
Collapse
Affiliation(s)
- Min Zhang
- Department of Biology, McMaster University, 1280 Main St. West, Hamilton, Ontario, L8S 4K1, Canada
| | - Cathy Vollmer
- Department of Biology, McMaster University, 1280 Main St. West, Hamilton, Ontario, L8S 4K1, Canada
| | - Colin A Nurse
- Department of Biology, McMaster University, 1280 Main St. West, Hamilton, Ontario, L8S 4K1, Canada
| |
Collapse
|
6
|
Wang J, Hogan JO, Kim D. Voltage- and receptor-mediated activation of a non-selective cation channel in rat carotid body glomus cells. Respir Physiol Neurobiol 2016; 237:13-21. [PMID: 28013061 DOI: 10.1016/j.resp.2016.12.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2016] [Revised: 11/16/2016] [Accepted: 12/08/2016] [Indexed: 10/20/2022]
Abstract
A recent study showed that hypoxia activates a Ca2+-sensitive, Na+-permeable non-selective cation channel (NSC) in carotid body glomus cells. We studied the effects of mitochondrial inhibitors that increase Ca2+ influx via Ca2+ channel (Cav), and receptor agonists that release Ca2+ from endoplasmic reticulum (ER) on NSC. Mitochondrial inhibitors (NaCN, FCCP, H2S, NO) elevated [Ca2+]i and activated NSC. Angiotensin II and acetylcholine that elevate [Ca2+]i via the Gq-IP3 pathway activated NSC. However, endothelin-1 (Gq) and 5-HT (Gq) showed little or no effect on [Ca2+]i and did not activate NSC. Adenosine (Gs) caused a weak rise in [Ca2+]i but did not activate NSC. Dopamine (Gs) and γ-aminobytyric acid (Gi) were ineffective in raising [Ca2+]i and failed to activate NSC. Store-operated Ca2+ entry (SOCE) produced by depletion of Ca2+ stores with cyclopiazonic acid activated NSC. Our results show that Ca2+ entry via Cav, ER Ca2+ release and SOCE can activate NSC. Thus, NSC contributes to both voltage- and receptor-mediated excitation of glomus cells.
Collapse
Affiliation(s)
- Jiaju Wang
- Department of Physiology and Biophysics, Chicago Medical School, Rosalind Franklin University of Medicine and Science, 3333 Green Bay Road, North Chicago, IL 60064, USA
| | - James O Hogan
- Department of Physiology and Biophysics, Chicago Medical School, Rosalind Franklin University of Medicine and Science, 3333 Green Bay Road, North Chicago, IL 60064, USA
| | - Donghee Kim
- Department of Physiology and Biophysics, Chicago Medical School, Rosalind Franklin University of Medicine and Science, 3333 Green Bay Road, North Chicago, IL 60064, USA.
| |
Collapse
|
7
|
TASK channels in arterial chemoreceptors and their role in oxygen and acid sensing. Pflugers Arch 2015; 467:1013-25. [PMID: 25623783 PMCID: PMC4428840 DOI: 10.1007/s00424-015-1689-1] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2014] [Revised: 01/06/2015] [Accepted: 01/07/2015] [Indexed: 01/05/2023]
Abstract
Arterial chemoreceptors play a vital role in cardiorespiratory control by providing the brain with information regarding blood oxygen, carbon dioxide, and pH. The main chemoreceptor, the carotid body, is composed of sensory (type 1) cells which respond to hypoxia or acidosis with a depolarising receptor potential which in turn activates voltage-gated calcium entry, neurosecretion and excitation of adjacent afferent nerves. The receptor potential is generated by inhibition of Twik-related acid-sensitive K(+) channel 1 and 3 (TASK1/TASK3) heterodimeric channels which normally maintain the cells' resting membrane potential. These channels are thought to be directly inhibited by acidosis. Oxygen sensitivity, however, probably derives from a metabolic signalling pathway. The carotid body, isolated type 1 cells, and all forms of TASK channel found in the type 1 cell, are highly sensitive to inhibitors of mitochondrial metabolism. Moreover, type1 cell TASK channels are activated by millimolar levels of MgATP. In addition to their role in the transduction of chemostimuli, type 1 cell TASK channels have also been implicated in the modulation of chemoreceptor function by a number of neurocrine/paracrine signalling molecules including adenosine, GABA, and serotonin. They may also be instrumental in mediating the depression of the acute hypoxic ventilatory response that occurs with some general anaesthetics. Modulation of TASK channel activity is therefore a key mechanism by which the excitability of chemoreceptors can be controlled. This is not only of physiological importance but may also offer a therapeutic strategy for the treatment of cardiorespiratory disorders that are associated with chemoreceptor dysfunction.
Collapse
|
8
|
Abstract
The main functions of the respiratory neural network are to produce a coordinated, efficient, rhythmic motor behavior and maintain homeostatic control over blood oxygen and CO2/pH levels. Purinergic (ATP) signaling features prominently in these homeostatic reflexes. The signaling actions of ATP are produced through its binding to a diversity of ionotropic P2X and metabotropic P2Y receptors. However, its net effect on neuronal and network excitability is determined by the interaction between the three limbs of a complex system comprising the signaling actions of ATP at P2Rs, the distribution of multiple ectonucleotidases that differentially metabolize ATP into ADP, AMP, and adenosine (ADO), and the signaling actions of ATP metabolites, especially ADP at P2YRs and ADO at P1Rs. Understanding the significance of purinergic signaling is further complicated by the fact that neurons, glia, and the vasculature differentially express P2 and P1Rs, and that both neurons and glia release ATP. This article reviews at cellular, synaptic, and network levels, current understanding and emerging concepts about the diverse roles played by this three-part signaling system in: mediating the chemosensitivity of respiratory networks to hypoxia and CO2/pH; modulating the activity of rhythm generating networks and inspiratory motoneurons, and; controlling blood flow through the cerebral vasculature.
Collapse
Affiliation(s)
- Gregory D Funk
- Department of Physiology, Centre for Neuroscience, Women & Children's Health Research Institute (WCHRI), Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada.
| |
Collapse
|
9
|
Livermore S, Nurse CA. Enhanced adenosine A2breceptor signaling facilitates stimulus-induced catecholamine secretion in chronically hypoxic carotid body type I cells. Am J Physiol Cell Physiol 2013; 305:C739-50. [DOI: 10.1152/ajpcell.00137.2013] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Chronic hypoxia (CHox) augments chemoafferent activity in sensory fibers innervating carotid body (CB) chemoreceptor type I cells; however, the underlying mechanisms are poorly understood. We tested the hypothesis that enhanced paracrine signaling via adenosine (Ado) A2breceptors is involved. Dissociated rat CB cultures were exposed for 24 h to normoxia (Nox, 21% O2) or CHox (2% O2) or treated with the hypoxia mimetic deferoxamine mesylate (DFX), and catecholamine secretion from type I cells was monitored by amperometry. Catecholamine secretion was more robust in CHox and DFX type I cells than Nox controls after acute exposure to acid hypercapnia (10% CO2, pH 7.1) and high K+(75 mM). Exogenous Ado increased catecholamine secretion in a dose-dependent manner, and the EC50was shifted to the right from ∼21 μM Ado in Nox cells to ∼78 μM in CHox cells. Ado-evoked secretion in Nox and CHox cells was markedly inhibited by MRS-1754, an A2breceptor blocker, but was unaffected by SCH-58261, an A2areceptor blocker. Similarly, MRS-1754, but not SCH-58261, partially inhibited high-K+-evoked catecholamine secretion, suggesting a contribution from paracrine activation of A2breceptors by endogenous Ado. CB chemostimuli, acid hypercapnia, and hypoxia elicited a MRS-1754-sensitive rise in intracellular Ca2+that was more robust in CHox and DFX than Nox cells. Taken together, these data suggest that paracrine Ado A2breceptor signaling contributes to stimulus-evoked catecholamine secretion in Nox and CHox CB chemoreceptors; however, the effects of Ado are more robust after CHox.
Collapse
Affiliation(s)
- Simon Livermore
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Colin A. Nurse
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| |
Collapse
|
10
|
Roy A, Derakhshan F, Wilson RJA. Stress peptide PACAP engages multiple signaling pathways within the carotid body to initiate excitatory responses in respiratory and sympathetic chemosensory afferents. Am J Physiol Regul Integr Comp Physiol 2013; 304:R1070-84. [PMID: 23594614 DOI: 10.1152/ajpregu.00465.2012] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Consistent with a critical role in respiratory and autonomic stress responses, the carotid bodies are strongly excited by pituitary adenylate cyclase-activating polypeptide (PACAP), a neuropeptide implicated in stress responses throughout the sympathetic nervous system. PACAP excites isolated carotid body glomus cells via activation of PAC1 receptors, with one study suggesting PAC1-induced excitation is due entirely to protein kinase A (PKA)-mediated inhibition of TASK channels. However, in other systems, PAC1 is known to be coupled to multiple intracellular signaling pathways, including PKA, phospholipase C (PLC), phospholipase D (PLD), and protein kinase C (PKC), that trigger multiple downstream effectors including increased Ca²⁺ mobilization, inhibition of various K⁺ channels, and activation of nonselective cation channels. This study tests if non-PKA/TASK channel signaling helps mediate the stimulatory effects of PACAP on the carotid body. Using an ex vivo arterially perfused rat carotid body preparation, we show that PACAP-38 stimulates carotid sinus nerve activity in a biphasic manner (peak response, falling to plateau). PKA blocker H-89 only reduced the plateau response (~41%), whereas the TASK-1-like K⁺ channel blocker/transient receptor potential vanilloid 1 channel agonist anandamide only inhibited the peak response (~48%), suggesting involvement of additional pathways. The PLD blocker CAY10594 significantly inhibited both peak and plateau responses. The PLC blocker U73122 decimated both peak and plateau responses. Brefeldin A, a blocker of Epac (cAMP-activated guanine exchange factor, reported to link Gs-coupled receptors with PLC/PLD), also reduced both phases of the response, as did blocking signaling downstream of PLC/PLD with the PKC inhibitors chelerythrine chloride and GF109203X. Suggesting the involvement of non-TASK ion channels in the effects of PACAP, the A-type K⁺ channel blocker 4-aminopyridine, and the putative transient receptor potential channel (TRPC)/T-type calcium channel blocker SKF96365 each significantly inhibited the peak and steady-state responses. These data suggest the stimulatory effect of PACAP-38 on carotid body sensory activity is mediated through multiple signaling pathways: the PLC-PKC pathways predominates, with TRPC and/or T-type channel activation and Kv channel inactivation; only partial involvement is attributable to PKA and PLD activation.
Collapse
Affiliation(s)
- Arijit Roy
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada
| | | | | |
Collapse
|
11
|
Tse A, Yan L, Lee AK, Tse FW. Autocrine and paracrine actions of ATP in rat carotid body. Can J Physiol Pharmacol 2012; 90:705-11. [PMID: 22509744 DOI: 10.1139/y2012-054] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Carotid bodies are peripheral chemoreceptors that detect lowering of arterial blood O(2) level. The carotid body comprises clusters of glomus (type I) cells surrounded by glial-like sustentacular (type II) cells. Hypoxia triggers depolarization and cytosolic [Ca(2+)] ([Ca(2+)](i)) elevation in glomus cells, resulting in the release of multiple transmitters, including ATP. While ATP has been shown to be an important excitatory transmitter in the stimulation of carotid sinus nerve, there is considerable evidence that ATP exerts autocrine and paracrine actions in carotid body. ATP acting via P2Y(1) receptors, causes hyperpolarization in glomus cells and inhibits the hypoxia-mediated [Ca(2+)](i) rise. In contrast, adenosine (an ATP metabolite) triggers depolarization and [Ca(2+)](i) rise in glomus cells via A(2A) receptors. We suggest that during prolonged hypoxia, the negative and positive feedback actions of ATP and adenosine may result in an oscillatory Ca(2+) signal in glomus cells. Such mechanisms may allow cyclic release of transmitters from glomus cells during prolonged hypoxia without causing cellular damage from a persistent [Ca(2+)](i) rise. ATP also stimulates intracellular Ca(2+) release in sustentacular cells via P2Y(2) receptors. The autocine and paracrine actions of ATP suggest that ATP has important roles in coordinating chemosensory transmission in the carotid body.
Collapse
Affiliation(s)
- Amy Tse
- Department of Pharmacology and Center for Neuroscience, 9-70 Medical Science Building, University of Alberta, Edmonton, AB T6G 2H7, Canada.
| | | | | | | |
Collapse
|
12
|
Conde SV, Monteiro EC, Rigual R, Obeso A, Gonzalez C. Hypoxic intensity: a determinant for the contribution of ATP and adenosine to the genesis of carotid body chemosensory activity. J Appl Physiol (1985) 2012; 112:2002-10. [PMID: 22500005 DOI: 10.1152/japplphysiol.01617.2011] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Excitatory effects of adenosine and ATP on carotid body (CB) chemoreception have been previously described. Our hypothesis is that both ATP and adenosine are the key neurotransmitters responsible for the hypoxic chemotransmission in the CB sensory synapse, their relative contribution depending on the intensity of hypoxic challenge. To test this hypothesis we measured carotid sinus nerve (CSN) activity in response to moderate and intense hypoxic stimuli (7 and 0% O(2)) in the absence and in the presence of adenosine and ATP receptor antagonists. Additionally, we quantified the release of adenosine and ATP in normoxia (21% O(2)) and in response to hypoxias of different intensities (10, 5, and 2% O(2)) to study the release pathways. We found that ZM241385, an A(2) antagonist, decreased the CSN discharges evoked by 0 and 7% O(2) by 30.8 and 72.5%, respectively. Suramin, a P(2)X antagonist, decreased the CSN discharges evoked by 0 and 7% O(2) by 64.3 and 17.1%, respectively. Simultaneous application of both antagonists strongly inhibited CSN discharges elicited by both hypoxic intensities. ATP release by CB increased in parallel to hypoxia intensity while adenosine release increased preferably in response to mild hypoxia. We have also found that the lower the O(2) levels are, the higher is the percentage of adenosine produced from extracellular catabolism of ATP. Our results demonstrate that ATP and adenosine are key neurotransmitters involved in hypoxic CB chemotransduction, with a more relevant contribution of adenosine during mild hypoxia, while vesicular ATP release constitutes the preferential origin of extracellular adenosine in high-intensity hypoxia.
Collapse
Affiliation(s)
- S V Conde
- CEDOC, Departamento de Farmacologia, Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Lisbon, Portugal.
| | | | | | | | | |
Collapse
|
13
|
Abstract
The discovery of the sensory nature of the carotid body dates back to the beginning of the 20th century. Following these seminal discoveries, research into carotid body mechanisms moved forward progressively through the 20th century, with many descriptions of the ultrastructure of the organ and stimulus-response measurements at the level of the whole organ. The later part of 20th century witnessed the first descriptions of the cellular responses and electrophysiology of isolated and cultured type I and type II cells, and there now exist a number of testable hypotheses of chemotransduction. The goal of this article is to provide a comprehensive review of current concepts on sensory transduction and transmission of the hypoxic stimulus at the carotid body with an emphasis on integrating cellular mechanisms with the whole organ responses and highlighting the gaps or discrepancies in our knowledge. It is increasingly evident that in addition to hypoxia, the carotid body responds to a wide variety of blood-borne stimuli, including reduced glucose and immune-related cytokines and we therefore also consider the evidence for a polymodal function of the carotid body and its implications. It is clear that the sensory function of the carotid body exhibits considerable plasticity in response to the chronic perturbations in environmental O2 that is associated with many physiological and pathological conditions. The mechanisms and consequences of carotid body plasticity in health and disease are discussed in the final sections of this article.
Collapse
Affiliation(s)
- Prem Kumar
- School of Clinical and Experimental Medicine, College of Medical and Dental Sciences, The University of Birmingham, Birmingham, United Kingdom.
| | | |
Collapse
|
14
|
Koos BJ. Adenosine A₂a receptors and O₂ sensing in development. Am J Physiol Regul Integr Comp Physiol 2011; 301:R601-22. [PMID: 21677265 DOI: 10.1152/ajpregu.00664.2010] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Reduced mitochondrial oxidative phosphorylation, via activation of adenylate kinase and the resulting exponential rise in the cellular AMP/ATP ratio, appears to be a critical factor underlying O₂ sensing in many chemoreceptive tissues in mammals. The elevated AMP/ATP ratio, in turn, activates key enzymes that are involved in physiologic adjustments that tend to balance ATP supply and demand. An example is the conversion of AMP to adenosine via 5'-nucleotidase and the resulting activation of adenosine A(₂A) receptors, which are involved in acute oxygen sensing by both carotid bodies and the brain. In fetal sheep, A(₂A) receptors associated with carotid bodies trigger hypoxic cardiovascular chemoreflexes, while central A(₂A) receptors mediate hypoxic inhibition of breathing and rapid eye movements. A(₂A) receptors are also involved in hypoxic regulation of fetal endocrine systems, metabolism, and vascular tone. In developing lambs, A(₂A) receptors play virtually no role in O₂ sensing by the carotid bodies, but brain A(₂A) receptors remain critically involved in the roll-off ventilatory response to hypoxia. In adult mammals, A(₂A) receptors have been implicated in O₂ sensing by carotid glomus cells, while central A(₂A) receptors likely blunt hypoxic hyperventilation. In conclusion, A(₂A) receptors are crucially involved in the transduction mechanisms of O₂ sensing in fetal carotid bodies and brains. Postnatally, central A(₂A) receptors remain key mediators of hypoxic respiratory depression, but they are less critical for O₂ sensing in carotid chemoreceptors, particularly in developing lambs.
Collapse
Affiliation(s)
- Brian J Koos
- Department of Obstetrics and Gynecology; Brain Research Institute, David Geffen School of Medicine at University of California Los Angeles, Los Angeles, California, USA.
| |
Collapse
|
15
|
Nurse CA. Neurotransmitter and neuromodulatory mechanisms at peripheral arterial chemoreceptors. Exp Physiol 2010; 95:657-67. [PMID: 20360424 DOI: 10.1113/expphysiol.2009.049312] [Citation(s) in RCA: 139] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The control of breathing depends critically on sensory inputs to the central pattern generator of the brainstem, arising from peripheral arterial chemoreceptors located principally in the carotid bodies (CBs). The CB receptors, i.e. glomus or type I cells, are excited by chemical stimuli in arterial blood, particularly hypoxia, hypercapnia, acidosis and low glucose, which initiate corrective reflex cardiorespiratory and cardiovascular adjustments. Type I cells occur in clusters and are innervated by petrosal afferent fibres. Synaptic specializations (both chemical and electrical) occur between type I cells and petrosal terminals, and between neighbouring type I cells. This, together with the presence of a wide array of neurotransmitters and neuromodulators linked to both ionotropic and metabotropic receptors, allows for a complex modulation of CB sensory output. Studies in several laboratories over the last 20 years have provided much insight into the transduction mechanisms. More recent studies, aided by the development of a co-culture model of the rat CB, have shed light on the role of neurotransmitters and neuromodulators in shaping the afferent response. This review highlights some of these developments, which have contributed to our current understanding of information processing at CB chemoreceptors.
Collapse
Affiliation(s)
- Colin A Nurse
- Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4K1.
| |
Collapse
|
16
|
The impact of adenosine and an A2A adenosine receptor agonist on the ACh-induced increase in intracellular calcium of the glomus cells of the cat carotid body. Brain Res 2009; 1301:20-33. [PMID: 19761761 DOI: 10.1016/j.brainres.2009.08.100] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2007] [Revised: 08/25/2009] [Accepted: 08/26/2009] [Indexed: 11/20/2022]
Abstract
The carotid body (CB) is a polymodal chemosensor of arterial blood located next to the internal carotid artery. The basic chemosensing unit is composed of the neurotransmitter (NT)-containing glomus cells (GCs) and the sensory afferent fibers synapsing onto the GCs. Nicotinic and muscarinic receptors have been found on both the sensory afferent fibers and on the GCs. Neural output from the CB (CBNO) increases when arterial blood perfusing it is hypoxic, hypoglycemic, hypercapnic, or acidic. The increased CBNO due to GC release of excitatory NTs must be preceded by an entrance of calcium into the GCs. With repeated release of ACh from the GCs, cholinergic receptors could become desensitized, particularly nicotinic receptors which function as calcium channels. The purpose of the present study was to see if adenosine (ADO), known to alter receptor sensitivities, could attenuate or eliminate any desensitization of the nicotinic receptors occurring during the repeated application of ACh. Cat CBs were harvested with techniques approved by the University's Animal Care/Use Committee. The GCs were cultured and prepared for detecting [Ca(++)](i) with standard techniques. Repeated application of ACh produced a progressively decreasing increase in [Ca(++)](i). With the use of ADO or an A2(A) ADO receptor agonist the decrease was avoided. Though ADO also increased GC [Ca(++)](i), the sum of ADO increase and ACh increase, when superfused separately, was less than the increase when they were both included in the same superfusion. This suggested the possible involvement of a new path in the action. Potential mechanisms to explain the phenomena are discussed.
Collapse
|
17
|
Conde SV, Monteiro EC, Obeso A, Gonzalez C. Adenosine in peripheral chemoreception: new insights into a historically overlooked molecule--invited article. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2009; 648:145-59. [PMID: 19536476 DOI: 10.1007/978-90-481-2259-2_17] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
In the present article we review in a concise manner the literature on the general biology of adenosine signalling. In the first section we describe briefly the historical aspects of adenosine research. In the second section is presented the biochemical characteristics of this nucleoside, namely its metabolism and regulation, and its physiological actions. In the third section we have succinctly described the role of adenosine and its metabolism in hypoxia. The final section is devoted to the role of adenosine in chemoreception in the carotid body, providing a review of the literature on the presence of adenosine receptors in the carotid body; on the effects of adenosine at presynaptic level in carotid body chemoreceptor cells, as well as, its metabolism and regulation; and at postsynaptic level in carotid sinus nerve activity. Additionally, a review on the effects of adenosine in ventilation was done. This review discusses evidence for a key role of adenosine in the hypoxic response of carotid body and emphasizes new research likely to be important in the future.
Collapse
Affiliation(s)
- S V Conde
- Department of Pharmacology, Faculty of Medical Sciences, New University of Lisbon, Campo Mártires da Pátria 130, 1169-056 Lisboa, Portugal.
| | | | | | | |
Collapse
|
18
|
Abstract
Acute intermittent hypoxia elicits a form of spinal, brain-derived neurotrophic factor (BDNF)-dependent respiratory plasticity known as phrenic long-term facilitation. Ligands that activate G(s)-protein-coupled receptors, such as the adenosine 2a receptor, mimic the effects of neurotrophins in vitro by transactivating their high-affinity receptor tyrosine kinases, the Trk receptors. Thus, we hypothesized that A2a receptor agonists would elicit phrenic long-term facilitation by mimicking the effects of BDNF on TrkB receptors. Here we demonstrate that spinal A2a receptor agonists transactivate TrkB receptors in the rat cervical spinal cord near phrenic motoneurons, thus inducing long-lasting (hours) phrenic motor facilitation. A2a receptor activation increased phosphorylation and new synthesis of an immature TrkB protein, induced TrkB signaling through Akt, and strengthened synaptic pathways to phrenic motoneurons. RNA interference targeting TrkB mRNA demonstrated that new TrkB protein synthesis is necessary for A2a-induced phrenic motor facilitation. A2a receptor activation also increased breathing in unanesthetized rats, and improved breathing in rats with cervical spinal injuries. Thus, small, highly permeable drugs (such as adenosine receptor agonists) that transactivate TrkB receptors may provide an effective therapeutic strategy in the treatment of patients with ventilatory control disorders, such as obstructive sleep apnea, or respiratory insufficiency after spinal injury or during neurodegenerative diseases.
Collapse
|
19
|
Stimulatory Actions of Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) in Rat Carotid Glomus Cells. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2008; 605:69-74. [DOI: 10.1007/978-0-387-73693-8_12] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/17/2023]
|
20
|
Lautt WW. Regulatory processes interacting to maintain hepatic blood flow constancy: Vascular compliance, hepatic arterial buffer response, hepatorenal reflex, liver regeneration, escape from vasoconstriction. Hepatol Res 2007; 37:891-903. [PMID: 17854463 PMCID: PMC2981600 DOI: 10.1111/j.1872-034x.2007.00148.x] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Constancy of hepatic blood flow (HBF) is crucial for several homeostatic roles. The present conceptual review focuses on interrelated mechanisms that act to maintain a constant HBF per liver mass. The liver cannot directly control portal blood flow (PF); therefore, these mechanisms largely operate to compensate for PF changes. A reduction in PF leads to reduced intrahepatic distending pressure, resulting in the highly compliant hepatic vasculature passively expelling up to 50% of its blood volume, thus adding to venous return, cardiac output and HBF. Also activated immediately upon reduction of PF are the hepatic arterial buffer response and an HBF-dependent hepatorenal reflex. Adenosine is secreted at a constant rate into the small fluid space of Mall which surrounds the terminal branches of the hepatic arterioles, portal venules and sensory nerves. The concentration of adenosine is regulated by washout into the portal venules. Reduced PFreduces the washout and the accumulated adenosine causes dilation of the hepatic artery, thus buffering the PF change. Adenosine also activates hepatic sensory nerves to cause reflex renal fluid retention, thus increasing circulating blood volume and maintaining cardiac output and PF. If these mechanisms are not able to maintain total HBF, the hemodynamic imbalance results in hepatocyte proliferation, or apoptosis, by a shear stress/nitric oxide-dependent mechanism, to adjust total liver mass to match the blood supply. These mechanisms are specific to this unique vascular bed and provide an excellent example of multiple integrative regulation of a major homeostatic organ.
Collapse
Affiliation(s)
- W Wayne Lautt
- Department of Pharmacology and Therapeutics, Faculty of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada
| |
Collapse
|
21
|
Abstract
The carotid body is a peripheral sensory organ that can transduce modest falls in the arterial PO2 (partial pressure of oxygen) into a neural signal that provides the afferent limb of a set of stereotypic cardiorespiratory reflexes that are graded according to the intensity of the stimulus. The stimulus sensed is tissue PO2 and this can be estimated to be around 50 mmHg during arterial normoxia, falling to between 10–40 mmHg during hypoxia. The chemoafferent hypoxia stimulus-response curve is exponential, rising in discharge frequency with falling PO2, and with no absolute threshold apparent in hyperoxia. Although the oxygen sensor has not been definitely identified, it is believed to reside within type I cells of the carotid body, and presently two major hypotheses have been put forward to account for the sensing mechanism. The first relies upon alterations in the cell energy status that is sensed by the cytosolic enzyme AMPK (AMP-activated protein kinase) subsequent to hypoxia-induced increases in the cellular AMP/ATP ratio during hypoxia. AMPK is localized close to the plasma membrane and its activation can inhibit both large conductance, calcium-activated potassium (BK) and background, TASK-like potassium channels, inducing membrane depolarization, voltage-gated calcium entry and neurosecretion of a range of transmitter and modulator substances, including catecholamines, ATP and acetylcholine. The alternative hypothesis considers a role for haemoxygenase-2, which uses oxygen as a substrate and may act to gate an associated BK channel through the action of its products, carbon monoxide and possibly haem. It is likely however, that these and other hypotheses of oxygen transduction are not mutually exclusive and that each plays a role, via its own particular sensitivity, in shaping the full response of this organ between hyperoxia and anoxia.
Collapse
Affiliation(s)
- Prem Kumar
- Department of Physiology, The Medical School, University of Birmingham, Birmingham B15 2TT, U.K.
| |
Collapse
|
22
|
Xu F, Tse FW, Tse A. Pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates the oxygen sensing type I (glomus) cells of rat carotid bodies via reduction of a background TASK-like K+current. J Neurochem 2007; 101:1284-93. [PMID: 17498241 DOI: 10.1111/j.1471-4159.2007.04468.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Pituitary adenylate cyclase-activating polypeptide (PACAP)-deficient mice are prone to sudden neonatal death and have reduced respiratory response to hypoxia. Here we found that PACAP-38 elevated cytosolic [Ca(2+)] ([Ca(2+)](i)) in the oxygen sensing type I cells but not the glial-like type II (sustentacular) cells of the rat carotid body. This action of PACAP could not be mimicked by vasoactive intestinal peptide but was abolished by PACAP 6-38, implicating the involvement of PAC(1) receptors. H89, a protein kinase A (PKA) inhibitor attenuated the PACAP response. Simultaneous measurement of membrane potential and [Ca(2+)](i) showed that the PACAP-mediated [Ca(2+)](i) rise was accompanied by depolarization and action potential firing. Ni(2+), a blocker of voltage-gated Ca(2+) channels (VGCC) or the removal of extracellular Ca(2+) reversibly inhibited the PACAP-mediated [Ca(2+)](i) rise. In the presence of tetraethylammonium (TEA) and 4-aminopyridine (4-AP), PACAP reduced a background K(+) current. Anandamide, a blocker of TWIK-related acid-sensitive K(+) (TASK)-like K(+) channel, occluded the inhibitory action of PACAP on K(+) current. We conclude that PACAP, acting via the PAC(1) receptors coupled PKA pathway inhibits a TASK-like K(+) current and causes depolarization and VGCC activation. This stimulatory action of PACAP in carotid type I cells can partly account for the role of PACAP in respiratory disorders.
Collapse
Affiliation(s)
- Fenglian Xu
- Department of Pharmacology and Center for Neurosciences, 9-70 Medical Science Building, University of Alberta, Edmonton, Alberta, Canada
| | | | | |
Collapse
|
23
|
Ming Z, Lautt WW. Intrahepatic adenosine-mediated activation of hepatorenal reflex is via A1 receptors in rats. Can J Physiol Pharmacol 2007; 84:1177-84. [PMID: 17218982 DOI: 10.1139/y06-063] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Previous studies have shown that intrahepatic adenosine is involved in activation of the hepatorenal reflex that regulates renal sodium and water excretion. The present study aims to determine which subtype of adenosine receptors is implicated in the process. Mean arterial pressure, portal venous pressure and flow, and renal arterial flow were monitored in pentobarbital anesthetized rats. Urine was collected from the bladder. Intraportal administration of 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), a selective adenosine A1 receptor antagonist, increased urine flow by 24%, 89%, and 143% at the dose of 0.01, 0.03, and 0.1 mg x kg(-1), respectively; in contrast, DPCPX, when administered intravenously at the same doses, only increased urine flow by 0%, 18%, and 36%. The increases in urine flow induced by intraportal administration of DPCPX were abolished in rats with liver denervation. Intrahepatic infusion of adenosine significantly decreased urine flow and this response was abolished by intraportal administration of DPCPX. Neither intraportal nor intravenous administration of 3,7-dimethyl-1-propargylxanthine, a selective adenosine A2 receptor antagonist, showed significant influence on urine flow. Systemic arterial pressure, renal blood flow and glomerular filtration rate were unaltered by the administration of any of the drugs. In conclusion, intrahepatic adenosine A1 receptors are responsible for the adenosine-mediated hepatorenal reflex that regulates renal water and sodium excretion.
Collapse
Affiliation(s)
- Zhi Ming
- Department of Pharmacology and Therapeutics, Faculty of Medicine, University of Manitoba, 753 McDermot Avenue, Winnipeg, MB R3E 0T6, Canada
| | | |
Collapse
|
24
|
Lahiri S, Mitchell CH, Reigada D, Roy A, Cherniack NS. Purines, the carotid body and respiration. Respir Physiol Neurobiol 2007; 157:123-9. [PMID: 17383945 PMCID: PMC1975770 DOI: 10.1016/j.resp.2007.02.015] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2006] [Revised: 02/19/2007] [Accepted: 02/21/2007] [Indexed: 10/23/2022]
Abstract
The carotid body is essential to detecting levels of oxygen in the blood and initiating the compensatory response. Increasing evidence suggests that the purines ATP and adenosine make a key contribution to this signaling by the carotid body. The glomus cells release ATP in response to hypoxia. This released ATP can stimulate P2X receptors on the carotid body to elevate intracellular Ca(2+) and to produce an excitatory response. This released ATP can be dephosphorylated to adenosine by a series of extracellular enzymes, which in turn can stimulate A(1), A(2A) and A(2B) adenosine receptors. Levels of extracellular adenosine can also be altered by membrane transporters. Endogenous adenosine stimulates these receptors to increase the ventilation rate and may modulate the catecholamine release from the carotid sinus nerve. Prolonged hypoxic challenge can alter the expression of purinergic receptors, suggesting a role in the adaptation. This review discusses evidence for a key role of ATP and adenosine in the hypoxic response of the carotid body, and emphasizes areas of new contributions likely to be important in the future.
Collapse
Affiliation(s)
- S. Lahiri
- Department of Physiology; University of Pennsylvania School of Medicine, Philadelphia, PA
| | - C. H. Mitchell
- Department of Physiology; University of Pennsylvania School of Medicine, Philadelphia, PA
| | - D. Reigada
- Department of Physiology; University of Pennsylvania School of Medicine, Philadelphia, PA
| | - A. Roy
- Department of Physiology; University of Pennsylvania School of Medicine, Philadelphia, PA
| | - N. S. Cherniack
- Departments of Medicine and Physiology, Case Western Reserve School of Medicine, Cleveland, OH
- Department of Medicine University of Medicine and Dentistry of New Jersey, Newark, NJ
| |
Collapse
|
25
|
Kumar P, Bin-Jaliah I. Adequate stimuli of the carotid body: more than an oxygen sensor? Respir Physiol Neurobiol 2007; 157:12-21. [PMID: 17291838 DOI: 10.1016/j.resp.2007.01.007] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2006] [Revised: 01/12/2007] [Accepted: 01/15/2007] [Indexed: 11/15/2022]
Abstract
The past 10-20 years has seen a significant increase in the number of studies aimed at elucidating the mechanism of action of the carotid body and this has led to an increased knowledge of how this sensory organ transduces hypoxaemia into afferent chemodischarge. Whilst hypoxia is often considered as the most significant, peripheral chemostimulus, the carotid body is able to transduce many other physico-chemical stimuli, including not only arterial P(CO2) and pH but also blood potassium concentration, temperature and osmolarity as well as, potentially, blood glucose levels and all with appropriate physiological sensitivity. Although it is difficult to be definitive, these other stimuli appear to be sensed independently of the hypoxia transduction process, albeit converging at the point of type I cell membrane depolarisation or Ca(2+) -dependent neurosecretion. We suggest, therefore, that the carotid body might better be viewed as a polymodal receptor with its multiple adequate stimuli interacting to provide additive or greater than additive effects upon chemoafferent discharge for the purpose of cardiorespiratory homeostasis during periods of stress.
Collapse
Affiliation(s)
- Prem Kumar
- Department of Physiology, The Medical School, University of Birmingham, Birmingham, UK.
| | | |
Collapse
|
26
|
Wyatt CN, Mustard KJ, Pearson SA, Dallas ML, Atkinson L, Kumar P, Peers C, Hardie DG, Evans AM. AMP-activated protein kinase mediates carotid body excitation by hypoxia. J Biol Chem 2006; 282:8092-8. [PMID: 17179156 PMCID: PMC1832262 DOI: 10.1074/jbc.m608742200] [Citation(s) in RCA: 120] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Early detection of an O2 deficit in the bloodstream is essential to initiate corrective changes in the breathing pattern of mammals. Carotid bodies serve an essential role in this respect; their type I cells depolarize when O2 levels fall, causing voltage-gated Ca2+ entry. Subsequent neurosecretion elicits increased afferent chemosensory fiber discharge to induce appropriate changes in respiratory function (1). Although depolarization of type I cells by hypoxia is known to arise from K+ channel inhibition, the identity of the signaling pathway has been contested, and the coupling mechanism is unknown (2). We tested the hypothesis that AMP-activated protein kinase (AMPK) is the effector of hypoxic chemotransduction. AMPK is co-localized at the plasma membrane of type I cells with O2-sensitive K+ channels. In isolated type I cells, activation of AMPK using 5-aminoimidazole-4-carboxamide riboside (AICAR) inhibited O2-sensitive K+ currents (carried by large conductance Ca2+-activated (BKCa) channels and TASK (tandem pore, acid-sensing potassium channel)-like channels, leading to plasma membrane depolarization, Ca2+ influx, and increased chemosensory fiber discharge. Conversely, the AMPK antagonist compound C reversed the effects of hypoxia and AICAR on type I cell and carotid body activation. These results suggest that AMPK activation is both sufficient and necessary for the effects of hypoxia. Furthermore, AMPK activation inhibited currents carried by recombinant BKCa channels, whereas purified AMPK phosphorylated thealpha subunit of the channel in immunoprecipitates, an effect that was stimulated by AMP and inhibited by compound C. Our findings demonstrate a central role for AMPK in stimulus-response coupling by hypoxia and identify for the first time a link between metabolic stress and ion channel regulation in an O2-sensing system.
Collapse
Affiliation(s)
- Christopher N. Wyatt
- From the Department of Biomedical Sciences, School of Biology, Bute Building, University of St Andrews, St. Andrews, Fife. KY16 9TS, UK
| | - Kirsty J.W. Mustard
- Division of Molecular Physiology, College of Life Sciences, Sir James Black Centre, University of Dundee, Dow Street,DD1 5EH, UK
| | - Selina A. Pearson
- Department of Physiology, The Medical School, University of Birmingham, Birmingham B15 2TT, UK
| | - Mark L Dallas
- School of Medicine, University of Leeds, Leeds LS2 9JT, UK
| | - Lucy Atkinson
- School of Medicine, University of Leeds, Leeds LS2 9JT, UK
| | - Prem Kumar
- Department of Physiology, The Medical School, University of Birmingham, Birmingham B15 2TT, UK
| | - Chris Peers
- School of Medicine, University of Leeds, Leeds LS2 9JT, UK
| | - D. Grahame Hardie
- Division of Molecular Physiology, College of Life Sciences, Sir James Black Centre, University of Dundee, Dow Street,DD1 5EH, UK
| | - A. Mark Evans
- From the Department of Biomedical Sciences, School of Biology, Bute Building, University of St Andrews, St. Andrews, Fife. KY16 9TS, UK
| |
Collapse
|
27
|
Ming Z, Fan YJ, Yang X, Lautt WW. Contribution of hepatic adenosine A1 receptors to renal dysfunction associated with acute liver injury in rats. Hepatology 2006; 44:813-22. [PMID: 17006917 DOI: 10.1002/hep.21336] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Acute liver injury is associated with renal insufficiency, whose mechanism may be related to activation of the hepatorenal reflex. We previously showed that intrahepatic adenosine is involved in activation of the hepatorenal reflex to restrict urine production in both healthy rats and in rats with cirrhosis. The aim of the present study was to test the hypothesis that activation of intrahepatic adenosine receptors is involved in the pathogenesis of the renal insufficiency seen in acute liver injury. Acute liver injury was induced by intraperitoneal injection of thioacetamide (TAA, 500 mg/kg) in rats. The animals were instrumented 24 hours later to monitor systemic, hepatic, and renal circulation and urine production. Severe liver injury developed following TAA insult, which was associated with renal insufficiency, as demonstrated by decreased (approximately 25%) renal arterial blood flow, a lower (approximately 30%) glomerular filtration rate, and decreased urine production. Further, the increase in urine production following volume expansion challenge was inhibited. Intraportal, but not intravenous, administration of a nonselective adenosine receptor antagonist, 8-phenyltheophylline, improved urine production. To specify receptor subtype, the effects of 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, an adenosine A(1) receptor antagonist) and 3,7-dimethyl-1-propargylxanthine (DMPX, an adenosine A(2) receptor antagonist) were compared. Intraportal but not intravenous administration of DPCPX greatly improved impaired renal function induced by acute liver injury, and this beneficial effect was blunted in rats with liver denervation. In contrast, neither intraportal nor intravenous administration of DMPX showed significant improvement in renal function. In conclusion, an activated hepatorenal reflex, triggered by intrahepatic adenosine A(1) receptors, contributed to the pathogenesis of the water and sodium retention associated with acute liver injury.
Collapse
Affiliation(s)
- Zhi Ming
- Department of Pharmacology & Therapeutics, University of Manitoba, Winnipeg, Manitoba, Canada
| | | | | | | |
Collapse
|
28
|
Jacono FJ, Peng YJ, Nethery D, Faress JA, Lee Z, Kern JA, Prabhakar NR. Acute lung injury augments hypoxic ventilatory response in the absence of systemic hypoxemia. J Appl Physiol (1985) 2006; 101:1795-802. [PMID: 16888052 DOI: 10.1152/japplphysiol.00100.2006] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The objective of the present study was to examine the impact of early stages of lung injury on ventilatory control by hypoxia and hypercapnia. Lung injury was induced with intratracheal instillation of bleomycin (BM; 1 unit) in adult, male Sprague-Dawley rats. Control animals underwent sham surgery with saline instillation. Five days after the injections, lung injury was present in BM-treated animals as evidenced by increased neutrophils and protein levels in bronchoalveolar lavage fluid, as well as by changes in lung histology and computed tomography images. There was no evidence of pulmonary fibrosis, as indicated by lung collagen content. Basal core body temperature, arterial Po(2), and arterial Pco(2) were comparable between both groups of animals. Ventilatory responses to hypoxia (12% O(2)) and hypercapnia (7% CO(2)) were measured by whole body plethysmography in unanesthetized animals. Baseline respiratory rate and the hypoxic ventilatory response were significantly higher in BM-injected compared with control animals (P = 0.003), whereas hypercapnic ventilatory response was not statistically different. In anesthetized, spontaneously breathing animals, response to brief hyperoxia (Dejours' test, an index of peripheral chemoreceptor sensitivity) and neural hypoxic ventilatory response were augmented in BM-exposed relative to control animals, as measured by diaphragmatic electromyelograms. The enhanced hypoxic sensitivity persisted following bilateral vagotomy, but was abolished by bilateral carotid sinus nerve transection. These data demonstrate that afferent sensory input from the carotid body contributes to a selective enhancement of hypoxic ventilatory drive in early lung injury in the absence of pulmonary fibrosis and arterial hypoxemia.
Collapse
Affiliation(s)
- F J Jacono
- Department of Medicine, Division of Pulmonary & Critical Care, Case Western Reserve University, Cleveland, Ohio, USA.
| | | | | | | | | | | | | |
Collapse
|
29
|
Xu F, Xu J, Tse FW, Tse A. Adenosine stimulates depolarization and rise in cytoplasmic [Ca2+] in type I cells of rat carotid bodies. Am J Physiol Cell Physiol 2006; 290:C1592-8. [PMID: 16436472 DOI: 10.1152/ajpcell.00546.2005] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
During hypoxia, the level of adenosine in the carotid bodies increases as a result of ATP catabolism and adenosine efflux via adenosine transporters. Using Ca2+imaging, we found that adenosine, acting via A2Areceptors, triggered a rise in cytoplasmic [Ca2+] ([Ca2+]i) in type I (glomus) cells of rat carotid bodies. The adenosine response could be mimicked by forskolin (but not its inactive analog), and could be abolished by the PKA inhibitor H89. Simultaneous measurements of membrane potential (perforated patch recording) and [Ca2+]ishowed that the adenosine-mediated [Ca2+]irise was accompanied by depolarization. Ni2+, a voltage-gated Ca2+channel (VGCC) blocker, abolished the adenosine-mediated [Ca2+]irise. Although adenosine was reported to inhibit a 4-aminopyridine (4-AP)-sensitive K+current, 4-AP failed to trigger any [Ca2+]irise, or to attenuate the adenosine response. In contrast, anandamide, an inhibitor of the TWIK-related acid-sensitive K+-1 (TASK-1) channels, triggered depolarization and [Ca2+]irise. The adenosine response was attenuated by anandamide but not by tetraethylammonium. Our results suggest that adenosine, acting via the adenylate cyclase and PKA pathways, inhibits the TASK-1 K+channels. This leads to depolarization and activation of Ca2+entry via VGCC. This excitatory action of adenosine on type I cells may contribute to the chemosensitivity of the carotid body during hypoxia.
Collapse
Affiliation(s)
- Fenglian Xu
- Dept. of Pharmacology and Center for Neurosciences, Univ. of Alberta, Edmonton, Alberta, Canada T6G 2H7
| | | | | | | |
Collapse
|
30
|
Buck LT, Pamenter ME. Adaptive responses of vertebrate neurons to anoxia--matching supply to demand. Respir Physiol Neurobiol 2006; 154:226-40. [PMID: 16621734 DOI: 10.1016/j.resp.2006.03.004] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2005] [Revised: 03/08/2006] [Accepted: 03/10/2006] [Indexed: 01/13/2023]
Abstract
Oxygen depleted environments are relatively common on earth and represent both a challenge and an opportunity to organisms that survive there. A commonly observed survival strategy to this kind of stress is a lowering of metabolic rate or metabolic depression. Whether metabolic rate is at a normal or a depressed level the supply of ATP (glycolysis and oxidative phosphorylation) must match the cellular demand for ATP (protein synthesis and ion pumping), a condition that must of course be met for long-term survival in hypoxic and anoxic environments. Underlying a decrease in metabolic rate is a corresponding decrease in both ATP supply and ATP demand pathways setting a new lower level for ATP turnover. Both sides of this equation can be actively regulated by second messenger pathways but it is less clear if they are regulated differentially or even sequentially with the onset of anoxia. The vertebrate brain is extremely sensitive to low oxygen levels yet some species can survive in oxygen depleted environments for extended periods and offer a working model of brain survival without oxygen. Hypoxia tolerant vertebrate brain will be the primary focus of this review; however, we will draw upon research involving hypoxia/ischemia tolerance mechanisms in liver and heart to offer clues to how brain can tolerate anoxia. The issue of regulating ATP supply or demand pathways will also be addressed with a focus on ion channel arrest being a significant mechanism to reduce ATP demand and therefore metabolic rate. Furthermore, mitochondria are ideally situated to serve as cellular oxygen sensors and mediator of protective mechanisms such as ion channel arrest. Therefore, we will also describe a mitochondria based mechanism of ion channel arrest involving ATP-sensitive mitochondrial K(+) channels, cytosolic calcium and reaction oxygen species concentrations.
Collapse
Affiliation(s)
- L T Buck
- University of Toronto, Department of Zoology, Toronto, Ont., Canada
| | | |
Collapse
|
31
|
Carroll JL, Kim I. Postnatal development of carotid body glomus cell O2 sensitivity. Respir Physiol Neurobiol 2005; 149:201-15. [PMID: 15886071 DOI: 10.1016/j.resp.2005.04.009] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2005] [Revised: 04/07/2005] [Accepted: 04/07/2005] [Indexed: 01/17/2023]
Abstract
In mammals, the main sensors of arterial oxygen level are the carotid chemoreceptors, which exhibit low sensitivity to hypoxia at birth and become more sensitive over the first few days or weeks of life. This postnatal increase in hypoxia sensitivity of the arterial chemoreceptors, termed "resetting", remains poorly understood. In the carotid body, hypoxia is transduced by glomus cells, which are secretory sensory neurons that respond to hypoxia at higher P(O2) levels than non-chemoreceptor cell types. Maturation or resetting of carotid body O2 sensitivity potentially involves numerous aspects of the O2 transduction cascade at the glomus cell level, including glomus cell neurotransmitter secretion, neuromodulator function, neurotransmitter receptor expression, glomus cell depolarization in response to hypoxia, [Ca2+]i responses to hypoxia, K+ and Ca2+ channel O2 sensitivity and K+ channel expression. However, although progress has been made in the understanding of carotid body development, the precise mechanisms underlying postnatal maturation of these numerous aspects of chemotransduction remain obscure.
Collapse
Affiliation(s)
- John L Carroll
- University of Arkansas for Medical Sciences College of Medicine, Department of Pediatrics, Pediatric Respiratory Medicine Section, Arkansas Children's Hospital, Little Rock, AR 72202, USA.
| | | |
Collapse
|
32
|
Nurse CA. Neurotransmission and neuromodulation in the chemosensory carotid body. Auton Neurosci 2005; 120:1-9. [PMID: 15955746 DOI: 10.1016/j.autneu.2005.04.008] [Citation(s) in RCA: 137] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2005] [Revised: 04/12/2005] [Accepted: 04/14/2005] [Indexed: 11/20/2022]
Abstract
The mammalian carotid body is a small chemosensory organ that helps maintain the chemical composition of arterial blood via reflex control of ventilation. Thus, in response to decreased PO2 (hypoxia), increased PCO2 (hypercapnia), or decreased pH (acidity), chemoreceptor glomus or type I cells become stimulated and release neuroactive agents that excite apposed sensory terminals of the carotid sinus nerve. The resulting increase in afferent discharge ultimately leads to corrective changes in ventilation so as to maintain blood gas and pH homeostasis. Recent evidence that the organ can also sense low glucose further emphasizes its role as a polymodal sensor of blood-borne stimuli. The chemoreceptors occur in organized cell clusters that receive sensory innervation from petrosal afferents and are intimately associated with the blood supply. Additionally, synaptic specializations between neighboring receptor cells allow for autocrine and paracrine regulation of the sensory output. Though not without controversy, significant progress has been made in elucidating the various chemotransductive pathways, as well as the neurotransmitter and neuromodulatory mechanisms that translate the receptor potential into an afferent sensory discharge. Progress in the latter has been hampered by the presence of a wide variety of endogenous ligands, and an even broader spectrum of receptor subtypes, that apparently help shape the chemoreceptor output and afferent discharge. This review will highlight recent advances in understanding the role of these neuroactive ligands in carotid body function.
Collapse
Affiliation(s)
- Colin A Nurse
- Department of Biology, McMaster University, 1280 Main St. West, Hamilton, Ontario, Canada L8S 4K1.
| |
Collapse
|
33
|
Bin-Jaliah I, Maskell PD, Kumar P. Carbon dioxide sensitivity during hypoglycaemia-induced, elevated metabolism in the anaesthetized rat. J Physiol 2005; 563:883-93. [PMID: 15661819 PMCID: PMC1665607 DOI: 10.1113/jphysiol.2004.080085] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
We have utilized an anaesthetized rat model of insulin-induced hypoglycaemia to test the hypothesis that peripheral chemoreceptor gain is augmented during hypermetabolism. Insulin infusion at 0.4 U kg (-1)min(-1) decreased blood glucose concentration significantly to 3.37 +/- 0.12 mmol l(-1). Whole-body metabolism and basal ventilation were elevated without increase in P(a,CO(2)) (altered non-significantly from the control level, to 37.3 +/- 2.6 mmHg). Chemoreceptor gain, measured either as spontaneous ventilatory airflow sensitivity to P(a,CO(2)) during rebreathing, or by phrenic minute activity responses to altered P(a,CO(2)) induced by varying the level of artificial ventilation, was doubled during the period of hypermetabolism. This stimulatory effect was primarily upon the mean inspiratory flow rate, or phrenic ramp component of breathing and was reduced by 75% following bilateral carotid sinus nerve section. In vitro recordings of single carotid body chemoafferents showed that reducing superfusate glucose concentration from 10 mM to 2 mM reduced CO(2) chemosensitivity significantly from 0.007 +/- 0.002 Hz mmHg(-1) to 0.001 +/- 0.002 Hz mmHg(-1). Taken together, these data suggest that the hyperpnoea observed during hypermetabolism might be mediated by an increase in the CO(2) sensitivity of the carotid body, and this effect is not due to the insulin-induced fall in blood glucose concentration.
Collapse
Affiliation(s)
- I Bin-Jaliah
- Department of Physiology, Division of Medical Sciences, The Medical School, University of Birmingham, Birmingham B15 2TT, UK
| | | | | |
Collapse
|
34
|
Abstract
The peripheral arterial chemoreceptors of the carotid body participate in the ventilatory responses to hypoxia and hypercapnia, the arousal responses to asphyxial apnea, and the acclimatization to high altitude. In response to an excitatory stimuli, glomus cells in the carotid body depolarize, their intracellular calcium levels rise, and neurotransmitters are released from them. Neurotransmitters then bind to autoreceptors on glomus cells and postsynaptic receptors on chemoafferents of the carotid sinus nerve. Binding to inhibitory or excitatory receptors on chemoafferents control the electrical activity of the carotid sinus nerve, which provides the input to respiratory-related brainstem nuclei. We and others have used gene expression in the carotid body as a tool to determine what neurotransmitters mediate the response of peripheral arterial chemoreceptors to excitatory stimuli, specifically hypoxia. Data from physiological studies support the involvement of numerous putative neurotransmitters in hypoxic chemosensitivity. This article reviews how in situ hybridization histochemistry and other cellular localization techniques confirm, refute, or expand what is known about the role of dopamine, norepinephrine, substance P, acetylcholine, adenosine, and ATP in chemotransmission. In spite of some species differences, review of the available data support that 1). dopamine and norepinephrine are synthesized and released from glomus cells in all species and play an inhibitory role in hypoxic chemosensitivity; 2). substance P and acetylcholine are not synthesized in glomus cells of most species but may be made and released from nerve fibers innervating the carotid body in essentially all species; 3). adenosine and ATP are ubiquitous molecules that most likely play an excitatory role in hypoxic chemosensitivity.
Collapse
Affiliation(s)
- Estelle B Gauda
- Department of Pediatrics, Division of Neonatology, Johns Hopkins Institutions, Baltimore, Maryland 21287-3200, USA.
| |
Collapse
|
35
|
Ming Z, Smyth DD, Lautt WW. Decreases in portal flow trigger a hepatorenal reflex to inhibit renal sodium and water excretion in rats: role of adenosine. Hepatology 2002; 35:167-75. [PMID: 11786973 DOI: 10.1053/jhep.2002.30425] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The regulation of renal sodium and water excretion through a hepatorenal reflex activated by the changes in hemodynamics of the portal circulation has been suggested. We hypothesize that the changes in intrahepatic blood flow and flow-related intrahepatic adenosine are involved in the control of renal water and sodium excretion by triggering a hepatorenal reflex. Anesthetized rats were instrumented to monitor the systemic, hepatic, and renal circulation. A vascular shunt connecting the portal vein and central vena cava was established to allow for control of the portal venous blood flow (PVBF). Urine was collected from the bladder. The effects of decreased PVBF on renal water and sodium excretion were compared in normal and hepatic denervated rats. Decreasing intrahepatic PVBF by half for 30 minutes decreased urine flow by 38% (12.1 +/- 1.1 vs. 7.5 +/- 0.7 microL. min(-1)) and urine sodium excretion by 44% (1.11 +/- 0.30 vs. 0.62 +/- 0.17 micromol. min(-1)). Renal arterial blood flow (RABF) and creatinine clearance were also reduced by the decreases in intrahepatic PVBF. Hepatic denervation, or intrahepatic administration of an adenosine receptor antagonist, 8-phenyltheophylline (8-PT), abolished the effects of decreasing PVBF on urine flow and sodium excretion. The data suggest that the decrease in intrahepatic PVBF triggers a hepatorenal reflex through the activation of adenosine receptors within the liver, thereby inhibiting renal water and sodium excretion. The water and sodium retention commonly seen in the hepatorenal syndrome may be related to intrahepatic adenosine accumulation resulting from the associated decrease in intrahepatic portal flow.
Collapse
Affiliation(s)
- Zhi Ming
- Department of Pharmacology & Therapeutics, Faculty of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada
| | | | | |
Collapse
|
36
|
Ming Z, Smyth DD, Lautt WW. Intrahepatic adenosine triggers a hepatorenal reflex to regulate renal sodium and water excretion. Auton Neurosci 2001; 93:1-7. [PMID: 11695700 DOI: 10.1016/s1566-0702(01)00315-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The mechanism for water and sodium retention in liver cirrhosis is related to the disturbance in hepatic portal circulation. We hypothesize that the increases in intraportal adenosine, which occur when the portal blood flow decreases, may trigger the hepatorenal reflex to inhibit renal water and sodium excretion. In anesthetized rats, intravenous vs. intraportal adenosine-induced effect on renal water and sodium excretion was compared in normal animals and animals with hepatic or renal denervation, and in the presence of an adenosine receptor antagonist. Compared to saline infusion, intraportal adenosine (0.02 mg kg(-1) min(-1) for 1 h) infusion decreased urine flow by 51.3% (11.7 +/- 2.3 vs. 5.7 +/- 0.5 microl min(-1)) for the first 30 min and by 49% (22.8 +/- 5.4 vs. 11.6 +/- 1.5 microl min(-1)) for the second 30-min duration. Urinary sodium excretion was also decreased. Intraportal administration of an adenosine receptor antagonist (8-phenyltheophylline (8-PT), 3 mg kg(-1) bolus injection followed by 0.05 mg kg(-1) min(-1) continuous infusion), as well as liver or kidney denervation, abolished adenosine-induced inhibition. In contrast, intravenous adenosine infusion had no influence on either urine flow or sodium excretion. The data indicated that selectively increased intraportal adenosine inhibited renal water and sodium excretion. The water and sodium retention commonly seen in the hepatorenal syndrome may be related to intraportal adenosine accumulation due to the decrease in intraportal portal flow.
Collapse
Affiliation(s)
- Z Ming
- Department of Pharmacology and Therapeutics, Faculty of Medicine, University of Manitoba, Winnipeg, Canada
| | | | | |
Collapse
|
37
|
Kumar P, Conway AF, Vandier C, Marshall NJ, Bruynseels J, Matthews GM. Effect of adenosine on CO2 chemosensitivity. Functional, cellular, and molecular studies. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2000; 475:405-10. [PMID: 10849680 DOI: 10.1007/0-306-46825-5_38] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
Affiliation(s)
- P Kumar
- Department of Physiology, Medical School, University of Birmingham, UK
| | | | | | | | | | | |
Collapse
|
38
|
Kobayashi S, Conforti L, Millhorn DE. Gene expression and function of adenosine A(2A) receptor in the rat carotid body. Am J Physiol Lung Cell Mol Physiol 2000; 279:L273-82. [PMID: 10926550 DOI: 10.1152/ajplung.2000.279.2.l273] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The present study was undertaken to determine whether rat carotid bodies express adenosine (Ado) A(2A) receptors and whether this receptor is involved in the cellular response to hypoxia. Our results demonstrate that rat carotid bodies express the A(2A) and A(2B) Ado receptor mRNAs but not the A(1) or A(3) receptor mRNAs as determined by reverse transcriptase-polymerase chain reaction. In situ hybridization confirmed the expression of the A(2A) receptor mRNA. Immunohistochemical studies further showed that the A(2A) receptor is expressed in the carotid body and that it is colocalized with tyrosine hydroxylase in type I cells. Whole cell voltage-clamp studies using isolated type I cells showed that Ado inhibited the voltage-dependent Ca(2+) currents and that this inhibition was abolished by the selective A(2A) receptor antagonist ZM-241385. Ca(2+) imaging studies using fura 2 revealed that exposure to severe hypoxia induced elevation of intracellular Ca(2+) concentration ([Ca(2+)](i)) in type I cells and that extracellularly applied Ado significantly attenuated the hypoxia-induced elevation of [Ca(2+)](i). Taken together, our findings indicate that A(2A) receptors are present in type I cells and that activation of A(2A) receptors modulates Ca(2+) accumulation during hypoxia. This mechanism may play a role in regulating intracellular Ca(2+) homeostasis and cellular excitability during hypoxia.
Collapse
Affiliation(s)
- S Kobayashi
- Department of Molecular and Cellular Physiology, Department of Internal Medicine, University of Cincinnati, Cincinnati, Ohio 45267-0576, USA
| | | | | |
Collapse
|