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Sahu G, Turner RW. The Molecular Basis for the Calcium-Dependent Slow Afterhyperpolarization in CA1 Hippocampal Pyramidal Neurons. Front Physiol 2022; 12:759707. [PMID: 35002757 PMCID: PMC8730529 DOI: 10.3389/fphys.2021.759707] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2021] [Accepted: 11/01/2021] [Indexed: 12/02/2022] Open
Abstract
Neuronal signal transmission depends on the frequency, pattern, and timing of spike output, each of which are shaped by spike afterhyperpolarizations (AHPs). There are classically three post-spike AHPs of increasing duration categorized as fast, medium and slow AHPs that hyperpolarize a cell over a range of 10 ms to 30 s. Intensive early work on CA1 hippocampal pyramidal cells revealed that all three AHPs incorporate activation of calcium-gated potassium channels. The ionic basis for a fAHP was rapidly attributed to the actions of big conductance (BK) and the mAHP to small conductance (SK) or Kv7 potassium channels. In stark contrast, the ionic basis for a prominent slow AHP of up to 30 s duration remained an enigma for over 30 years. Recent advances in pharmacological, molecular, and imaging tools have uncovered the expression of a calcium-gated intermediate conductance potassium channel (IK, KCa3.1) in central neurons that proves to contribute to the slow AHP in CA1 hippocampal pyramidal cells. Together the data show that the sAHP arises in part from a core tripartite complex between Cav1.3 (L-type) calcium channels, ryanodine receptors, and IK channels at endoplasmic reticulum-plasma membrane junctions. Work on the sAHP in CA1 pyramidal neurons has again quickened pace, with identified contributions by both IK channels and the Na-K pump providing answers to several mysteries in the pharmacological properties of the sAHP.
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Affiliation(s)
- Giriraj Sahu
- National Institute of Pharmaceutical Education and Research Ahmedabad, Ahmedabad, India
| | - Ray W Turner
- Department Cell Biology & Anatomy, Cumming School of Medicine, Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada
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Koussoulas K, Gwynne RM, Foong JPP, Bornstein JC. Cholera Toxin Induces Sustained Hyperexcitability in Myenteric, but Not Submucosal, AH Neurons in Guinea Pig Jejunum. Front Physiol 2017; 8:254. [PMID: 28496413 PMCID: PMC5406514 DOI: 10.3389/fphys.2017.00254] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2017] [Accepted: 04/10/2017] [Indexed: 01/04/2023] Open
Abstract
Background and Aims: Cholera toxin (CT)-induced hypersecretion requires activation of secretomotor pathways in the enteric nervous system (ENS). AH neurons, which have been identified as a population of intrinsic sensory neurons (ISNs), are a source of excitatory input to the secretomotor pathways. We therefore examined effects of CT in the intestinal lumen on myenteric and submucosal AH neurons. Methods: Isolated segments of guinea pig jejunum were incubated for 90 min with saline plus CT (12.5 μg/ml) or CT + neurotransmitter antagonist, or CT + tetrodotoxin (TTX) in their lumen. After washing CT away, submucosal or myenteric plexus preparations were dissected keeping circumferentially adjacent mucosa intact. Submucosal AH neurons were impaled adjacent to intact mucosa and myenteric AH neurons were impaled adjacent to, more than 5 mm from, and in the absence of intact mucosa. Neuronal excitability was monitored by injecting 500 ms current pulses through the recording electrode. Results: After CT pre-treatment, excitability of myenteric AH neurons adjacent to intact mucosa (n = 29) was greater than that of control neurons (n = 24), but submucosal AH neurons (n = 33, control n = 27) were unaffected. CT also induced excitability increases in myenteric AH neurons impaled distant from the mucosa (n = 6) or in its absence (n = 5). Coincubation with tetrodotoxin or SR142801 (NK3 receptor antagonist), but not SR140333 (NK1 antagonist) or granisetron (5-HT3 receptor antagonist) prevented the increased excitability induced by CT. Increased excitability was associated with a reduction in the characteristic AHP and an increase in the ADP of these neurons, but not a change in the hyperpolarization-activated inward current, Ih. Conclusions: CT increases excitability of myenteric, but not submucosal, AH neurons. This is neurally mediated and depends on NK3, but not 5-HT3 receptors. Therefore, CT may act to amplify the secretomotor response to CT via an increase in the activity of the afferent limb of the enteric reflex circuitry.
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Affiliation(s)
- Katerina Koussoulas
- Enteric Neuroscience Laboratory, Department of Physiology, University of MelbourneParkville, VIC, Australia
| | - Rachel M Gwynne
- Enteric Neuroscience Laboratory, Department of Physiology, University of MelbourneParkville, VIC, Australia
| | - Jaime P P Foong
- Enteric Neuroscience Laboratory, Department of Physiology, University of MelbourneParkville, VIC, Australia
| | - Joel C Bornstein
- Enteric Neuroscience Laboratory, Department of Physiology, University of MelbourneParkville, VIC, Australia
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Turner RW, Asmara H, Engbers JDT, Miclat J, Rizwan AP, Sahu G, Zamponi GW. Assessing the role of IKCa channels in generating the sAHP of CA1 hippocampal pyramidal cells. Channels (Austin) 2016; 10:313-9. [PMID: 26950800 PMCID: PMC4954577 DOI: 10.1080/19336950.2016.1161988] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Our previous work reported that KCa3.1 (IKCa) channels are expressed in CA1 hippocampal pyramidal cells and contribute to the slow afterhyperpolarization that regulates spike accommodation in these cells. The current report presents data from single cell RT-PCR that further reveals mRNA in CA1 cells that corresponds to the sequence of an IKCa channel from transmembrane segments 5 through 6 including the pore region, revealing the established binding sites for 4 different IKCa channel blockers. A comparison of methods to internally apply the IKCa channel blocker TRAM-34 shows that including the drug in an electrode from the onset of an experiment is unviable given the speed of drug action upon gaining access for whole-cell recordings. Together the data firmly establish IKCa channel expression in CA1 neurons and clarify methodological requirements to obtain a block of IKCa channel activity through internal application of TRAM-34.
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Affiliation(s)
- Ray W Turner
- a Hotchkiss Brain Institute, University of Calgary , Calgary , AB , Canada
| | - Hadhimulya Asmara
- a Hotchkiss Brain Institute, University of Calgary , Calgary , AB , Canada
| | - Jordan D T Engbers
- a Hotchkiss Brain Institute, University of Calgary , Calgary , AB , Canada
| | - Jason Miclat
- a Hotchkiss Brain Institute, University of Calgary , Calgary , AB , Canada
| | - Arsalan P Rizwan
- a Hotchkiss Brain Institute, University of Calgary , Calgary , AB , Canada
| | - Giriraj Sahu
- a Hotchkiss Brain Institute, University of Calgary , Calgary , AB , Canada
| | - Gerald W Zamponi
- a Hotchkiss Brain Institute, University of Calgary , Calgary , AB , Canada
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4
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King B, Rizwan AP, Asmara H, Heath NC, Engbers JDT, Dykstra S, Bartoletti TM, Hameed S, Zamponi GW, Turner RW. IKCa channels are a critical determinant of the slow AHP in CA1 pyramidal neurons. Cell Rep 2016; 11:175-82. [PMID: 25865881 DOI: 10.1016/j.celrep.2015.03.026] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2014] [Revised: 01/30/2015] [Accepted: 03/10/2015] [Indexed: 12/23/2022] Open
Abstract
Control over the frequency and pattern of neuronal spike discharge depends on Ca2+-gated K+ channels that reduce cell excitability by hyperpolarizing the membrane potential. The Ca2+-dependent slow afterhyperpolarization (sAHP) is one of the most prominent inhibitory responses in the brain, with sAHP amplitude linked to a host of circuit and behavioral functions, yet the channel that underlies the sAHP has defied identification for decades. Here, we show that intermediate-conductance Ca2+-dependent K+ (IKCa) channels underlie the sAHP generated by trains of synaptic input or postsynaptic stimuli in CA1 hippocampal pyramidal cells. These findings are significant in providing a molecular identity for the sAHP of central neurons that will identify pharmacological tools capable of potentially modifying the several behavioral or disease states associated with the sAHP.
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Chambers JD, Bornstein JC, Gwynne RM, Koussoulas K, Thomas EA. A detailed, conductance-based computer model of intrinsic sensory neurons of the gastrointestinal tract. Am J Physiol Gastrointest Liver Physiol 2014; 307:G517-32. [PMID: 25012843 DOI: 10.1152/ajpgi.00228.2013] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Intrinsic sensory neurons (ISNs) of the enteric nervous system respond to stimuli such as muscle tension, muscle length, distortion of the mucosa, and the chemical content in the lumen. ISNs form recurrent networks that probably drive many intestinal motor patterns and reflexes. ISNs express a large number of voltage- and calcium-gated ion channels, some of which are modified by inflammation or repeated physiological stimuli, but how interactions between different ionic currents in ISNs produce both normal and pathological behaviors in the intestine remains unclear. We constructed a model of ISNs including voltage-gated sodium and potassium channels, N-type calcium channels, big conductance calcium-dependent potassium (BK) channels, calcium-dependent nonspecific cation channels (NSCa), intermediate conductance calcium-dependent potassium (IK) channels, hyperpolarization-activated cation (Ih) channels, and internal calcium dynamics. The model was based on data from the literature and our electrophysiological studies. The model reproduced responses to short or long depolarizing current pulses and responses to long hyperpolarizing current pulses. Sensitivity analysis showed that Ih, IK, NSCa, and BK have the largest influence on the number of action potentials observed during prolonged depolarizations. The model also predicts that changes to the voltage of activation for Ih have a large influence on excitability, but changes to the time constant of activation for Ih have a minor effect. Our model identifies how interactions between different iconic currents influence the excitability of ISNs and highlights an important role for Ih in enteric neuroplasticity resulting from disease.
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Affiliation(s)
- Jordan D Chambers
- Department of Physiology, University of Melbourne, Parkville, Victoria, Australia; and
| | - Joel C Bornstein
- Department of Physiology, University of Melbourne, Parkville, Victoria, Australia; and
| | - Rachel M Gwynne
- Department of Physiology, University of Melbourne, Parkville, Victoria, Australia; and
| | - Katerina Koussoulas
- Department of Physiology, University of Melbourne, Parkville, Victoria, Australia; and
| | - Evan A Thomas
- Florey Neuroscience Institutes, Parkville, Victoria, Australia
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6
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Neuronal expression of the intermediate conductance calcium-activated potassium channel KCa3.1 in the mammalian central nervous system. Pflugers Arch 2014; 467:311-28. [PMID: 24797146 DOI: 10.1007/s00424-014-1523-1] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2013] [Revised: 04/14/2014] [Accepted: 04/15/2014] [Indexed: 01/09/2023]
Abstract
The expression pattern and functional roles for calcium-activated potassium channels of the KCa2.x family and KCa1.1 have been extensively examined in central neurons. Recent work indicates that intermediate conductance calcium-activated potassium channels (KCa3.1) are also expressed in central neurons of the cerebellum and spinal cord. The current study used immunocytochemistry and GFP linked to KCNN4 promoter activity in a transgenic mouse to determine the expression pattern of KCa3.1 channels in rat or mouse neocortex, hippocampus, thalamus, and cerebellum. KCa3.1 immunolabel and GFP expression were closely matched and detected in both excitatory and inhibitory cells of all regions examined. KCa3.1 immunolabel was localized primarily to the somatic region of excitatory cells in cortical structures but at the soma and over longer segments of dendrites of cells in deep cerebellar nuclei. More extensive labeling was apparent for inhibitory cells at the somatic and dendritic level with no detectable label associated with axon tracts or regions of intense synaptic innervation. The data indicate that KCa3.1 channels are expressed in the CNS with a differential pattern of distribution between cells, suggesting important functional roles for these calcium-activated potassium channels in regulating the excitability of central neurons.
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Abstract
The electrical output of neurons relies critically on voltage- and calcium-gated ion channels. The traditional view of ion channels is that they operate independently of each other in the plasma membrane in a manner that could be predicted according to biophysical characteristics of the isolated current. However, there is increasing evidence that channels interact with each other not just functionally but also physically. This is exemplified in the case of Cav3 T-type calcium channels, where new work indicates the ability to form signaling complexes with different types of calcium-gated and even voltage-gated potassium channels. The formation of a Cav3-K complex provides the calcium source required to activate KCa1.1 or KCa3.1 channels and, furthermore, to bestow a calcium-dependent regulation of Kv4 channels via associated KChIP proteins. Here, we review these interactions and discuss their significance in the context of neuronal firing properties.
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8
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Kulkarni S, Zou B, Hanson J, Micci MA, Tiwari G, Becker L, Kaiser M, Xie X(S, Pasricha PJ. Gut-derived factors promote neurogenesis of CNS-neural stem cells and nudge their differentiation to an enteric-like neuronal phenotype. Am J Physiol Gastrointest Liver Physiol 2011; 301:G644-55. [PMID: 21817062 PMCID: PMC3191554 DOI: 10.1152/ajpgi.00123.2011] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Recent studies have explored the potential of central nervous system-derived neural stem cells (CNS-NSC) to repopulate the enteric nervous system. However, the exact phenotypic fate of gut-transplanted CNS-NSC has not been characterized. The aim of this study was to investigate the effect of the gut microenvironment on phenotypic fate of CNS-NSC in vitro. With the use of Transwell culture, differentiation of mouse embryonic CNS-NSC was studied when cocultured without direct contact with mouse intestinal longitudinal muscle-myenteric plexus preparations (LM-MP) compared with control noncocultured cells, in a differentiating medium. Differentiated cells were analyzed by immunocytochemistry and quantitative RT-PCR to assess the expression of specific markers and by whole cell patch-clamp studies for functional characterization of their phenotype. We found that LM-MP cocultured cells had a significant increase in the numbers of cells that were immune reactive against the panneuronal marker β-tubulin, neurotransmitters neuronal nitric oxide synthase (nNOS), choline acetyltransferase (ChAT), and neuropeptide vasoactive intestinal peptide (VIP) and showed an increase in expression of these genes, compared with control cells. Whole cell patch-clamp analysis showed that coculture with LM-MP decreases cell excitability and reduces voltage-gated Na(+) currents but significantly enhances A-current and late afterhyperpolarization (AHP) and increases the expression of the four AHP-generating Ca(2+)-dependent K(+) channel genes (KCNN), compared with control cells. In a separate experiment, differentiation of LM-MP cocultured CNS-NSC produced a significant increase in the numbers of cells that were immune reactive against the neurotransmitters nNOS, ChAT, and the neuropeptide VIP compared with CNS-NSC differentiated similarly in the presence of neonatal brain tissue. Our results show that the gut microenvironment induces CNS-NSC to produce neurons that share some of the characteristics of classical enteric neurons, further supporting the therapeutic use of these cells for gastrointestinal disorders.
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Affiliation(s)
- Subhash Kulkarni
- 1Division of Gastroenterology and Hepatology, Stanford University School of Medicine, Stanford, California;
| | - Bende Zou
- 1Division of Gastroenterology and Hepatology, Stanford University School of Medicine, Stanford, California; ,2AfaSci Research Laboratory, Redwood City, California;
| | - Jesse Hanson
- 2AfaSci Research Laboratory, Redwood City, California; ,5Genentech, Inc., South San Francisco, California
| | - Maria-Adelaide Micci
- 3Department of Anesthesiology, University of Texas Medical Branch, Galveston, Texas;
| | - Gunjan Tiwari
- 1Division of Gastroenterology and Hepatology, Stanford University School of Medicine, Stanford, California;
| | - Laren Becker
- 1Division of Gastroenterology and Hepatology, Stanford University School of Medicine, Stanford, California;
| | - Martin Kaiser
- 4Department of Computer Science and Microsystems Technology, UAS, Kaiserlautern, Germany; and
| | - Xinmin (Simon) Xie
- 1Division of Gastroenterology and Hepatology, Stanford University School of Medicine, Stanford, California; ,2AfaSci Research Laboratory, Redwood City, California;
| | - Pankaj Jay Pasricha
- 1Division of Gastroenterology and Hepatology, Stanford University School of Medicine, Stanford, California;
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9
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Fahanik-babaei J, Eliassi A, Jafari A, Sauve R, Salari S, Saghiri R. Electro-pharmacological profile of a mitochondrial inner membrane big-potassium channel from rat brain. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1808:454-60. [DOI: 10.1016/j.bbamem.2010.10.005] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2010] [Revised: 09/25/2010] [Accepted: 10/12/2010] [Indexed: 11/16/2022]
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10
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Nurgali K, Qu Z, Hunne B, Thacker M, Pontell L, Furness JB. Morphological and functional changes in guinea-pig neurons projecting to the ileal mucosa at early stages after inflammatory damage. J Physiol 2010; 589:325-39. [PMID: 21098001 DOI: 10.1113/jphysiol.2010.197707] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
In the present study the relationship between tissue damage and changed electro-physiological properties of Dogiel type II myenteric neurons within the first 24 hours after induction of inflammation with trinitrobenzene sulfonate (TNBS) in the guinea-pig ileum was investigated. Treatment with TNBS causes damage to the mucosa, inflammatory responses in the mucosa and enteric ganglia and changes in myenteric neuron properties. Thus we hypothesise that the physiological changes in the myenteric neurons could be due to damage to their mucosal processes or inflammation in the vicinity of cell bodies or the processes. We found an association between hyperexcitability of myenteric Dogiel type II neurons and damage to the mucosa and its innervation at 3 and 24 h, times when there was also an inflammatory reaction. The lack of hyperexcitability in neurons from control tissues in which axons projecting to the mucosa were severed suggests that inflammation may be an important contributing factor to the neuronal hyperexcitability at the acute stage of inflammation. Despite mucosal repair and re-innervation of the mucosa before 7 days after induction of inflammation, neuronal hyperexcitability persists. Although the mechanisms underlying neuronal hyperexcitability at the acute stage of inflammation might be different from those underlying long-term changes in the absence of active inflammation in the ganglia, the persistent changes in neuronal excitability may contribute to post-inflammatory gut dysfunctions.
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Affiliation(s)
- Kulmira Nurgali
- School of Biomedical and Health Sciences, Victoria University, Melbourne, Victoria, Australia.
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11
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Wang B, Mao YK, Diorio C, Wang L, Huizinga JD, Bienenstock J, Kunze W. Lactobacillus reuteri ingestion and IK(Ca) channel blockade have similar effects on rat colon motility and myenteric neurones. Neurogastroenterol Motil 2010; 22:98-107, e33. [PMID: 19788711 DOI: 10.1111/j.1365-2982.2009.01384.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
BACKGROUND We have previously shown that ingestion of Lactobacillus reuteri may modulate colonic enteric neuron activity but with unknown effects on colon motility. The aim of the present report was to elucidate the neuronal mechanisms of action of the probiotic by comparing the effects on motility of L. reuteri ingestion with blockade of a specific ionic current in enteric neurons. METHODS We have used intraluminal pressure recordings from ex vivo rat colon segments and whole cell patch clamp recordings from neurons of rat longitudinal muscle myenteric plexus preparations to investigate the effects of L. reuteri and TRAM-34 on colon motility and neurophysiology. The effects of daily feeding of 10(9) L. reuteri bacteria or acute application of TRAM-34 on threshold fluid filling pressure or pulse pressure was measured. KEY RESULTS Lactobacillus reuteri increased intraluminal fluid filling pressure thresholds for evoking pressure pulses by 51% from 0.47 +/- 0.17 hPa; the probiotic also decreased the pulse pressure amplitudes, but not frequency, by 18% from 3.91 +/- 0.52 hPa. The intermediate conductance calcium-dependent potassium (IK(Ca)) channel blocker TRAM-34 (3 micromol L(-1)) increased filling threshold pressure by 43% from 0.52 +/- 0.22 hPa and reduced pulse pressure amplitude by 40% from 2.63 +/- 1.11 hPa; contraction frequency was unaltered. TRAM-34 (3 micromol L(-1)) reduced membrane polarization, leak conductance and the slow afterhyperpolarization current in 16/16 myenteric rat colon AH cells but 19/19 S cells were unaffected. CONCLUSIONS & INFERENCES The present results are consistent with L. reuteri enhancing tonic inhibition of colon contractile activity by acting via the IK(Ca) channel current in AH cells.
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Affiliation(s)
- B Wang
- Department of Medicine, McMaster University, Hamilton, ON, Canada
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12
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Kunze WA, Mao YK, Wang B, Huizinga JD, Ma X, Forsythe P, Bienenstock J. Lactobacillus reuteri enhances excitability of colonic AH neurons by inhibiting calcium-dependent potassium channel opening. J Cell Mol Med 2009; 13:2261-2270. [PMID: 19210574 DOI: 10.1111/j.1582-4934.2009.00686.x] [Citation(s) in RCA: 242] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Probiotics are live non-pathogenic commensal organisms that exert therapeutic effects in travellers' diarrhea, irritable bowel syndrome and inflammatory bowel disease. Little is known about mechanisms of action of commensal bacteria on intestinal motility and motility-induced pain. It has been proposed that probiotics affect intestinal nerve function, but direct evidence for this has thus far been lacking. We hypothesized that probiotic effects might be mediated by actions on colonic intrinsic sensory neurons. We first determined whether sensory neurons were present in rat colon by their responses to chemical mucosal stimulation and identified them in terms of physiological phenotype and soma morphotype. Enteric neuron excitability and ion channel activity were measured using patch clamp recordings. We fed 10(9)Lactobacillus reuteri (LR) or vehicle control to rats for 9 days. LR ingestion increased excitability (threshold for evoking action potentials) and number of action potentials per depolarizing pulse, decreased calcium-dependent potassium channel (IK(Ca)) opening and decreased the slow afterhyperpolarization (sAHP) in sensory AH neurons, similar to the IK(Ca) antagonists Tram-34 and clotrimazole. LR did not affect threshold for action potential generation in S neurons. Our results demonstrate that LR targets an ion channel in enteric sensory nerves through which LR may affect gut motility and pain perception.
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Affiliation(s)
- Wolfgang A Kunze
- The Brain-Body Institute, St. Joseph's Healthcare, Hamilton, ON, Canada.,Department of Psychiatry and Behavioral Neurosciences, McMaster University, Hamilton, ON, Canada
| | - Yu-Kang Mao
- The Brain-Body Institute, St. Joseph's Healthcare, Hamilton, ON, Canada
| | - Bingxian Wang
- Department of Medicine, McMaster University, Hamilton, ON, Canada
| | - Jan D Huizinga
- Department of Medicine, McMaster University, Hamilton, ON, Canada
| | - Xuelian Ma
- The Brain-Body Institute, St. Joseph's Healthcare, Hamilton, ON, Canada
| | - Paul Forsythe
- The Brain-Body Institute, St. Joseph's Healthcare, Hamilton, ON, Canada.,Department of Medicine, McMaster University, Hamilton, ON, Canada
| | - John Bienenstock
- The Brain-Body Institute, St. Joseph's Healthcare, Hamilton, ON, Canada.,Department of Pathology and Molecular Medicine, McMaster University, Hamilton, ON, Canada
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Vatanparast J, Janahmadi M. Contribution of apamin-sensitive SK channels to the firing precision but not to the slow afterhyperpolarization and spike frequency adaptation in snail neurons. Brain Res 2008; 1255:57-66. [PMID: 19100724 DOI: 10.1016/j.brainres.2008.12.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2008] [Revised: 12/01/2008] [Accepted: 12/02/2008] [Indexed: 10/21/2022]
Abstract
Apamin-sensitive small conductance Ca(2+)-dependent K(+)(SK) channels are generally accepted as responsible for the medium afterhyperpolarization (mAHP) after single or train of action potentials. Here, we examined the functional involvement of these channels in the firing precision, post train AHP and spike frequency adaptation (SFA) in neurons of snail Caucasotachea atrolabiata. Apamin, a selective SK channel antagonist, reduced the duration of single-spike AHP and disrupted the spontaneous rhythmic activity. High frequency trains of evoked action potentials showed a time-dependent decrease in the action potential discharge rate (spike frequency adaptation) and followed by a prominent post stimulus inhibitory period (PSIP) as a marker of slow AHP (sAHP). Neither sAHP nor SFA was attenuated by apamin, suggesting that apamin-sensitive SK channels can strongly affect the rhythmicity, but are probably not involved in the SFA and sAHP. Nifedipine, antagonist of L-type Ca(2+) channels, decreased the firing frequency and neuronal rhythmicity. When PSIP was normalized to the background interspike interval, a suppressing effect of nifedipine on PSIP was also observed. Intracellular iontophoretic injection of BAPTA, a potent Ca(2+) chelator, dramatically suppressed PSIP that confirms the intracellular Ca(2+) dependence of the sAHP, but had no discernable effect on the SFA. During train-evoked activity a reduction in the action potential overshoot and maximum depolarization rate was also observed, along with a decrease in the firing frequency, while the action potential threshold increased, which indicated that Na(+) channels, rather than Ca(2+)-dependent K(+) channels, are involved in the SFA.
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Affiliation(s)
- Jafar Vatanparast
- Department of Biology, College of Sciences, Shiraz University, Adabiat Intersection, Shiraz 71454, Iran.
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14
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Krauter EM, Strong DS, Brooks EM, Linden DR, Sharkey KA, Mawe GM. Changes in colonic motility and the electrophysiological properties of myenteric neurons persist following recovery from trinitrobenzene sulfonic acid colitis in the guinea pig. Neurogastroenterol Motil 2007; 19:990-1000. [PMID: 17973636 DOI: 10.1111/j.1365-2982.2007.00986.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Persistent changes in gastrointestinal motility frequently accompany the resolution of colitis, through mechanisms that remain to be determined. Trinitrobenzene sulfonic acid (TNBS) colitis in the guinea pig decreases the rate of propulsive motility, causes hyperexcitability of AH neurons, and induces synaptic facilitation. The changes in motility and AH neurons are sensitive to cyclooxygenase-2 (COX-2) inhibition. The aim of this investigation was to determine if the motility and neurophysiological changes persist following recovery from colitis. Evaluations of inflammation, colonic motility and intracellular electrophysiology of myenteric neurons 8 weeks after TNBS administration were performed and compared to matched control conditions. Myeloperoxidase levels in the colons were comparable to control levels 56 days after TNBS treatment. At this time point, the rate of colonic motility was decreased relative to controls following treatment with TNBS alone or TNBS plus a COX-2 inhibitor. Furthermore, the electrical properties of AH neurons and fast synaptic potentials in S neurons were significantly different from controls and comparable to those detected during active inflammation. Collectively, these data suggest that altered myenteric neurophysiology initiated during active colitis persists long term, and provide a potential mechanism underlying altered gut function in individuals during remission from inflammatory bowel disease.
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Affiliation(s)
- E M Krauter
- Department of Anatomy and Neurobiology, The University of Vermont College of Medicine, Burlington, VT 05405, USA
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15
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Ren J, Galligan JJ. A novel calcium-sensitive potassium conductance is coupled to P2X3 subunit containing receptors in myenteric neurons of guinea pig ileum. Neurogastroenterol Motil 2007; 19:912-22. [PMID: 17973642 PMCID: PMC2668217 DOI: 10.1111/j.1365-2982.2007.00952.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
This study characterized P2X receptors in guinea pig ileum myenteric S neurons (n = 124) in vitro using electrophysiological methods. ATP or alpha,beta-methylene ATP (alpha,beta-mATP), an agonist at P2X(1) and P2X(3) subunit containing receptors, depolarized 103 neurons (85%). Pyridoxal-phosphate-6-azophenyl-2',4' disulfonic acid (10 micromol L(-1)) blocked ATP- and alpha,beta-mATP-induced depolarizations. ATP-induced depolarizations and fast excitatory postsynaptic potentials (fEPSPs) were reduced by trinitrophenyl-ATP (10 micromol L(-1)), an antagonist that can block P2X(3) receptors. Ivermectin (10 micromol L(-1)), a modulator of P2X(4) and P2X(4/6) receptors, had no effect on alpha,beta-mATP-induced depolarizations. In 58% of neurons, the alpha,beta-mATP induced-depolarization was followed by an afterhyperpolarization (AHP) (P2X-AHP). Under voltage clamp, alpha,beta-mATP induced an inward current followed by an outward current which reversed polarity at 0 and -80 mV respectively. The P2X-AHP was reduced in low extracellular Ca(2+) solutions. Blockers of large, intermediate and small conductance Ca(2+)-activated K(+) channels or voltage-gated K(+) channels did not inhibit the P2X-AHP. Half of the neurons exhibiting the P2X-AHP contained nitric oxide synthase (NOS)-immunoreactivity (ir). In summary, NOS-ir S neurons express P2X(3) subunit containing P2X receptors. P2X receptors couple to activation of a Ca(2+)-activated K(+) conductance that mediates an AHP. As P2X receptors contribute to fEPSPs, the P2X-AHP may modulate S neuron excitability during purinergic synaptic transmission.
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Affiliation(s)
- J Ren
- The Neuroscience Program, Department of Pharmacology & Toxicology, Michigan State University, East Lansing, MI 48824, USA
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Nurgali K, Nguyen TV, Matsuyama H, Thacker M, Robbins HL, Furness JB. Phenotypic changes of morphologically identified guinea-pig myenteric neurons following intestinal inflammation. J Physiol 2007; 583:593-609. [PMID: 17615102 PMCID: PMC2277021 DOI: 10.1113/jphysiol.2007.135947] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
We investigated the responses of morphologically identified myenteric neurons of the guinea-pig ileum to inflammation that was induced by the intraluminal injection of trinitrobenzene sulphonate, 6 or 7 days previously. Electrophysiological properties were examined with intracellular microelectrodes using in vitro preparations from the inflamed or control ileum. The neurons were injected with marker dyes during recording and later they were recovered for morphological examination. A proportion of neurons with Dogiel type I morphology, 45% (32/71), from the inflamed ileum had a changed phenotype. These neurons exhibited an action potential with a tetrodotoxin-resistant component, and a prolonged after-hyperpolarizing potential followed the action potential. Of the other 39 Dogiel type I neurons, no changes were observed in 36 and 3 had increased excitability. The afterhyperpolarizing potential (AHP) in Dogiel type I neurons was blocked by the intermediate conductance, Ca(2+)-dependent K(+) channel blocker TRAM-34. Neurons which showed these phenotypic changes had anally directed axonal projections. Neither a tetrodotoxin-resistant action potential nor an AHP was seen in Dogiel type I neurons from control preparations. Dogiel type II neurons retained their distinguishing AH phenotype, including an inflection on the falling phase of the action potential, an AHP and, in over 90% of neurons, an absence of fast excitatory transmission. However, they became hyperexcitable and exhibited anodal break action potentials, which, unlike control Dogiel type II neurons, were not all blocked by the h current (I(h)) antagonist Cs(+). It is concluded that inflammation selectively affects different classes of myenteric neurons and causes specific changes in their electrophysiological properties.
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Affiliation(s)
- Kulmira Nurgali
- Department of Anatomy and Cell Bioology, University of Melbourne, Parkville, Victoria 3010, Australia.
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17
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Strong DS, Krauter EM, Mawe GM. From molecules to motion: altering neuronal ion channel function can lead to changes in intestinal motility. Neurogastroenterol Motil 2007; 19:329-32. [PMID: 17509014 DOI: 10.1111/j.1365-2982.2007.00932.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- D S Strong
- Department of Anatomy and Neurobiology, The University of Vermont College of Medicine, Burlington, VT 05405, USA
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18
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Ferens D, Baell J, Lessene G, Smith JE, Furness JB. Effects of modulators of Ca(2+)-activated, intermediate-conductance potassium channels on motility of the rat small intestine, in vivo. Neurogastroenterol Motil 2007; 19:383-9. [PMID: 17509020 DOI: 10.1111/j.1365-2982.2007.00898.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The movements of the intestine shift between different motor patterns, including between propulsion and mixing, but there is little information concerning mechanisms that may lead to changes in the patterns of motility. We have investigated the influence on intestinal motility of drugs that affect the after-hyperpolarization potential (AHP) of intrinsic primary afferent neurons (IPANs). The current of the AHP is carried by the intermediate conductance, calcium-activated, potassium (IK) channel. In anaesthetized rats, the IK channel blocker, 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (0.05-1 mg kg(-1), i.v.) disrupted the regular propulsive pressure waves that occur in the small intestine and reduced propulsion of the contents (after 1 mg kg(-1), the fluid propelled was <25% of control). If the propulsion in the intestine was regular, the IK channel opener, 5,6-dichloro-1-ethyl-2-benzimidazolinone (DC-EBIO, 0.1 mg kg(-1) h(-1)) had no effect. DC-EBIO (0.1 mg kg(-1) h(-1)) restored propulsive activity after the nitric oxide synthase inhibitor, Nomega-nitro-l-arginine had changed motility to a mixing pattern. We suggest that the AHP determines the synchrony of action potential firing in synaptically coupled IPANs, and that this synchrony influences the patterns of firing of muscle motor neurons, and hence the pattern of contraction of the muscle and whether the pattern is predominantly propulsive or predominantly mixing.
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Affiliation(s)
- D Ferens
- Department of Anatomy and Cell Biology and Centre for Neuroscience, University of Melbourne, Parkville, Victoria, Australia
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19
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Nguyen TV, Matsuyama H, Baell J, Hunne B, Fowler CJ, Smith JE, Nurgali K, Furness JB. Effects of Compounds That Influence IK (KCNN4) Channels on Afterhyperpolarizing Potentials, and Determination of IK Channel Sequence, in Guinea Pig Enteric Neurons. J Neurophysiol 2007; 97:2024-31. [PMID: 17229825 DOI: 10.1152/jn.00935.2006] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The late afterhyperpolarizing potential (AHP) that follows the action potential in intrinsic primary afferent neurons of the gastrointestinal tract has a profound influence on their firing patterns. There has been uncertainty about the identity of the channels that carry the late AHP current, especially in guinea pigs, where the majority of the physiological studies have been made. In the present work, the late AHP was recorded with intracellular microelectrodes from myenteric neurons in the guinea pig small intestine. mRNA was extracted from the ganglia to determine the identity of the guinea pig intermediate conductance potassium ( IK) channel gene transcript. The late AHP was inhibited by two blockers of IK channels, TRAM34 (0.1–1 μM) and clotrimazole (10 μM), and was enhanced by the potentiator of the opening of these channels, DC-EBIO (100 nM). Action potential characteristics were unchanged by TRAM34 or DC-EBIO. The full sequence of the gene transcript and the deduced amino acid sequence were determined from extracts including myenteric ganglia and from bladder urothelium, which is a rich source of IK channel mRNA. This showed that the guinea pig sequence has a high degree of homology with other mammalian sequences but that the guinea pig channel lacks a phosphorylation site that was thought to be critical for channel regulation. It is concluded that the channels that carry the current of the late afterhyperpolarizing potential in guinea pig enteric neurons are IK channels.
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Affiliation(s)
- Trung V Nguyen
- Department of Anatomy and Cell Biology, University of Melbourne, Parkville, VIC 3010, Australia
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20
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Mao Y, Wang B, Kunze W. Characterization of Myenteric Sensory Neurons in the Mouse Small Intestine. J Neurophysiol 2006; 96:998-1010. [PMID: 16899648 DOI: 10.1152/jn.00204.2006] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
We recorded from myenteric AH/Dogiel type II cells, demonstrated mechanosensitive responses, and characterized their basic properties. Recordings were obtained using the mouse longitudinal muscle myenteric plexus preparation with patch-clamp and sharp intracellular electrodes. The neurons had an action potential hump and a slow afterhyperpolarization (AHP) current. The slow AHP was carried by intermediate conductance Ca2+-dependent K+-channel currents sensitive to charybdotoxin and clotrimazole. All possessed a hyperpolarization-activated current that was blocked by extracellular cesium. They also expressed a TTX-resistant Na+ current with an onset near the resting potential. Pressing on the ganglion containing the patched neuron evoked depolarizing potentials in 17/18 cells. The potentials persisted after synaptic transmission was blocked. Volleys of presynaptic electrical stimuli evoked slow excitatory postsynaptic potentials (EPSPs) in 9/11 sensory neurons, but 0/29 cells received fast EPSP input. The slow EPSP was generated by removal of a voltage-insensitive K+ current. Patch-clamp recording with a KMeSO4-containing, but not a conventional KCl-rich, intracellular solution reproduced the single-spike slow AHPs and low input resistances seen with sharp intracellular recording. Cell-attached recording of intermediate conductance potassium channels supported the conclusion that the single-spike slow AHP is an intrinsic property of intestinal AH/sensory neurons. Unitary current recordings also suggested that the slow AHP current probably does not contribute significantly to the high resting background conductance seen in these cells. The characterization of mouse myenteric sensory neurons opens the way for the study of their roles in normal and pathological physiology.
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Affiliation(s)
- Yukang Mao
- Brain-Brody Institute, McMaster University, Hamilton, Ontario, Canada
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21
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Neylon CB, Fowler CJ, Furness JB. Regulation of the slow afterhyperpolarization in enteric neurons by protein kinase A. Auton Neurosci 2006; 126-127:258-63. [PMID: 16647306 DOI: 10.1016/j.autneu.2006.02.028] [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] [Received: 01/18/2006] [Accepted: 02/27/2006] [Indexed: 10/24/2022]
Abstract
The slow after-hyperpolarization (sAHP) following the action potential is an important determinant of the firing patterns of enteric neurons. The channel responsible for the sAHP thus serves as a critical control point at which neurotransmitters and inflammatory mediators modulate gut motility. Many of these receptor-evoked pathways are known to inhibit the sAHP and, thus, excite enteric neurons. They act through protein kinase A (PKA) which is a strong inhibitor of the sAHP current while protein phosphatases enhance the current. Increasing evidence suggests that the sAHP is mediated by the opening of intermediate-conductance Ca-activated potassium (IK) channels. This neuronal IK channel, previously known to be expressed in a variety of non-excitable cells, is strongly influenced by protein kinases. Investigation of the molecular basis for the modulation of IK channels by protein phosphorylation indicates that there are multiple mechanisms of channel control. Inhibition of channel activity by PKA involves phosphorylation sites located within the calmodulin-binding domain of the channel. The localization of these sites within the region involved in Ca2+ activation suggests that PKA-mediated phosphorylation of the channel opposes the conformational changes caused by binding of Ca/calmodulin, which would otherwise lead to opening of the channel. We suggest that the channel exists as a macromolecular complex involving calmodulin, protein kinases, protein phosphatase and possibly other proteins. The regulation of the channel through kinases and phophatases results in exquisite control of neuronal firing and subsequent modulation of enteric reflexes.
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Affiliation(s)
- Craig B Neylon
- Department of Anatomy and Cell Biology, University of Melbourne, Parkville 3010, Australia.
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22
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Davies PJ, Thomas EA, Bornstein JC. Different types of potassium channels underlie the long afterhyperpolarization in guinea-pig sympathetic and enteric neurons. Auton Neurosci 2006; 124:26-30. [PMID: 16325477 DOI: 10.1016/j.autneu.2005.10.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2005] [Revised: 10/06/2005] [Accepted: 10/27/2005] [Indexed: 11/15/2022]
Abstract
Ca(2+)-activated K(+) channels play an important role in the control of neuronal excitability via the generation of the afterhyperpolarization. While both small and large conductance Ca(2+)-activated K(+) channels underlie afterhyperpolarizations in different neuron types, the role of intermediate conductance Ca(2+)-activated K(+) channels (IK(Ca)) in the generation of afterhyperpolarizations remains unclear. The effects of blockade of IK(Ca) on guinea pig coeliac and ileal myenteric neurons were studied using single microelectrode current and voltage clamp. In coeliac neurons, TRAM-39, a selective blocker of IK(Ca), depressed the amplitude of the prolonged conductance underlying the slow afterhyperpolarization, (gKCa2) by 57%. In contrast, the conductance underlying the prolonged afterhyperpolarization in AH-type myenteric neurons was unaffected by TRAM-39, although it has been suggested that this AHP is mediated by IK(Ca). In both types of neurons, TRAM-39 did not alter the resting cell properties or the properties of the action potential. TRAM-39 had no effect on the amplitude of the fast component of the afterhyperpolarization present in sympathetic LAH neurons. The results of this study suggest that in sympathetic LAH neurons, activation of IK(Ca) underlies at least part of the prolonged afterhyperpolarization while the nature of the channel underlying the AHP in enteric neurons remains unclear.
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Affiliation(s)
- P J Davies
- Department of Physiology, The University of Melbourne, Parkville, VIC 3010, Australia.
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23
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Mongan LC, Hill MJ, Chen MX, Tate SN, Collins SD, Buckby L, Grubb BD. The distribution of small and intermediate conductance calcium-activated potassium channels in the rat sensory nervous system. Neuroscience 2005; 131:161-75. [PMID: 15680700 DOI: 10.1016/j.neuroscience.2004.09.062] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/04/2004] [Indexed: 10/26/2022]
Abstract
Small (SK) and intermediate (IK) conductance calcium-activated potassium channels are candidate ion channels for the regulation of excitability in nociceptive neurones. We have used unique peptide-directed antisera to describe the immunocytochemical distribution of the known isoforms of these ion channels in dorsal root ganglia (DRG) and spinal cord of the rat. These investigations sought to characterize further the phenotype and hence possible functions of nociceptive neurone subpopulations in the rat. In addition, using Western blotting, we sought to determine the level of protein expression of SK and IK channels in sensory nervous tissues following induction of inflammation (Freund's Complete Adjuvant (FCA) arthritis model) or nerve injury (chronic constriction injury model). We show that SK1, SK2, SK3 and IK1 are all expressed in DRG and spinal cord. Morphometric analysis revealed that SK1, SK2 and IK1 were preferentially localized to neurones having cell bodies <1000 microm2 (putative nociceptors) in DRG. Dual labeling immunocytochemistry showed that these ion channels co-localize with both CGRP and IB4, known markers of nociceptor sub-populations. SK2 was localized almost exclusively in the superficial laminae of the spinal cord dorsal horn, the region in which many sensory afferents terminate; the distribution of SK1 and IK1 was more widespread in spinal cord, although some preferential labeling within the dorsal horn was observed in the case of IK1. Here we show evidence for a distinctive pattern of expression for certain members of the calcium-activated potassium channel family in the rat DRG.
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Affiliation(s)
- L C Mongan
- Department of Cell Physiology and Pharmacology, University of Leicester, PO Box 138, Leicester LE1 9HN, UK.
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24
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Lomax AE, Mawe GM, Sharkey KA. Synaptic facilitation and enhanced neuronal excitability in the submucosal plexus during experimental colitis in guinea-pig. J Physiol 2005; 564:863-75. [PMID: 15774518 PMCID: PMC1464458 DOI: 10.1113/jphysiol.2005.084285] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Intestinal secretion is regulated by submucosal neurones of the enteric nervous system. Inflammation of the intestines leads to aberrant secretory activity; therefore we hypothesized that the synaptic and electrical behaviours of submucosal neurones are altered during colitis. To test this hypothesis, we used intracellular microelectrode recording to compare the excitability and synaptic properties of submucosal neurones from normal and trinitrobenzene sulphonic acid (TNBS)-inflamed guinea-pig colons. Inflammation differentially affected the electrophysiological characteristics of the two functional classes of submucosal neurones. AH neurones from inflamed colons were more excitable, had shorter action potential durations and reduced afterhyperpolarizations. Stimulus-evoked fast and slow excitatory postsynaptic potentials (EPSPs) in S neurones were larger during colitis, and the incidence of spontaneous fast EPSPs was increased. In control preparations, fast EPSPs were almost completely blocked by the nicotinic receptor antagonist hexamethonium, whereas fast EPSPs in inflamed S neurones were only partially inhibited by hexamethonium. In inflamed tissues, components of the fast EPSP in S neurones were sensitive to blockade of P2(X) and 5-HT(3) receptors while these antagonists had little effect in control preparations. Control and inflamed S neurones were equally sensitive to brief application of acetylcholine, ATP and 5-HT, suggesting that synaptic facilitation was due to a presynaptic mechanism. Immunoreactivity for 5-HT in the submucosal plexus was unchanged by inflammation; this indicates that altered synaptic transmission was not due to anatomical remodelling of submucosal nerve terminals. This is the first demonstration of alterations in synaptic pharmacology in the enteric nervous system during inflammation.
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Affiliation(s)
- Alan E Lomax
- Department of Physiology and Biophysics, University of Calgary, 3330 Hospital Dr. NW, Calgary, Alberta T2N 4N1, Canada
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25
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Nguyen TV, Poole DP, Harvey JR, Stebbing MJ, Furness JB. Investigation of PKC isoform-specific translocation and targeting of the current of the late afterhyperpolarizing potential of myenteric AH neurons. Eur J Neurosci 2005; 21:905-13. [PMID: 15787697 DOI: 10.1111/j.1460-9568.2005.03931.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
AH neurons in the enteric nervous system play an essential role in initiating intestinal reflexes and factors that control AH neuron excitability therefore influence the state of the digestive system. Prominent afterhyperpolarizations that follow action potentials in these neurons strongly affect their excitability. In the present work, we have investigated the regulation of the afterhyperpolarizing current (I(AHP)) by protein kinase C (PKC). Electrophysiological responses and protein translocation were investigated in AH neurons of freshly dissected preparations of myenteric ganglia from the guinea-pig ileum. The activator of conventional and novel PKCs, phorbol dibutyrate, but not the activator of novel PKCs, ingenol, blocked the I(AHP). Phorbol dibutyrate had no effect on the hyperpolarization-activated current (I(h)) or on the A current (I(A)). Stimulation of synaptic inputs to the neurons also reduced the I(AHP), and had no effect on I(h) or I(A). Phorbol dibutyrate also reduced a background outward current that was present after the I(AHP) current had been blocked by clotrimazole. Both phorbol dibutyrate and ingenol caused translocation of the novel PKC, PKCepsilon, in these neurons. Only phorbol dibutyrate caused translocation of PKCgamma, a conventional PKC. The studies thus indicate that the activation of PKC by phorbol esters and by nerve stimulation affects AH neurons in a similar way, and that PKC activation targets both the I(AHP) and another background K(+) current. The I(AHP) is targeted by a conventional PKC, suggested to be PKCgamma, as this is the only conventional PKC that is prominent in AH neurons.
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Affiliation(s)
- Trung V Nguyen
- Department of Anatomy & Cell Biology and Centre for Neuroscience, University of Melbourne, Parkville, Victoria 3010, Australia
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26
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Nguyen TV, Stebbing MJ, Clerc N, Kawai M, Harvey JR, Furness JB. Evidence for protein kinase involvement in long-term postsynaptic excitation of intrinsic primary afferent neurons in the intestine. Auton Neurosci 2005; 115:1-6. [PMID: 15507400 DOI: 10.1016/j.autneu.2004.06.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2004] [Revised: 03/11/2004] [Accepted: 06/21/2004] [Indexed: 11/26/2022]
Abstract
We have investigated the effects of protein kinase inhibitors on the sustained slow postsynaptic excitation (SSPE) that is evoked by prolonged stimulation of synaptic inputs to intrinsic primary afferent neurons (IPANs) in the small intestines of guinea pigs. Stimulation of synaptic inputs to the IPANs caused depolarisation, increased input resistance, and increased excitation that continued after the cessation of stimulation. The excitation was substantially reduced by the broad-spectrum kinase inhibitor staurosporine (1 microM), PKC inhibitors Ro 31-8220 (3.3 microM) and calphostin C (1 microM), but not by the PKA inhibitor H89 (1 microM). At a higher concentration, 10 microM Ro 31-8220 reduced the excitability of axons to electrical stimulation. Phorbol dibutyrate (1 microM) caused excitability increases, membrane depolarisation, and increased input resistance that mimicked the SSPE. We conclude that the generation of the SSPE requires a phosphorylation step that is mediated by protein kinase C.
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Affiliation(s)
- T V Nguyen
- Department of Anatomy and Cell Biology and Centre for Neuroscience, University of Melbourne, Parkville, Victoria 3010, Australia
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27
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Bertrand PP, Thomas EA. MULTIPLE LEVELS OF SENSORY INTEGRATION IN THE INTRINSIC SENSORY NEURONS OF THE ENTERIC NERVOUS SYSTEM. Clin Exp Pharmacol Physiol 2004; 31:745-55. [PMID: 15566388 DOI: 10.1111/j.1440-1681.2004.04092.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
1. The enteric nervous system (ENS) is present in the wall of the gastrointestinal tract and contains all the functional classes of neuron required for complete reflex arcs. One of the most important and intriguing classes of neuron is that responsive to sensory stimuli: sensory neurons with cell bodies intrinsic to the ENS. 2. These neurons have three outstanding and interrelated features: (i) reciprocal connections with each other; (ii) a slow excitatory post-synaptic potential (EPSP) resulting from high-speed firing in other sensory neurons; and (iii) a large after-hyperpolarizing potential (AHP) at the soma. Slow EPSP depolarize the cell body, generate action potentials (APs) and reduce the AHP. Conversely, the AHP limits the firing rate and, hence, reduces transmission of slow EPSP. 3. Processing of sensory information starts at the input terminals as different patterns of APs depending on the sensory modality and recent sensory history. At the soma, the ability to fire APs and, hence, drive outputs is also strongly determined by the recent firing history of the neuron (through the AHP) and network activity (through the slow EPSP). Positive feedback within the population of intrinsic sensory neurons means that the network is able to drive outputs well beyond the duration of the stimuli that triggered them. 4. Thus, sensory input and subsequent reflex generation are integrated over several hierarchical levels within the network on intrinsic sensory neurons.
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Affiliation(s)
- Paul P Bertrand
- Department of Physiology, University of Melbourne, Parkville, Victoria, Australia.
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28
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Stocker M, Hirzel K, D'hoedt D, Pedarzani P. Matching molecules to function: neuronal Ca2+-activated K+ channels and afterhyperpolarizations. Toxicon 2004; 43:933-49. [PMID: 15208027 DOI: 10.1016/j.toxicon.2003.12.009] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2003] [Accepted: 12/06/2003] [Indexed: 11/21/2022]
Abstract
Potassium channels regulate the membrane excitability of neurons, play a major role in shaping action potentials, determining firing patterns and regulating neurotransmitter release, and thus significantly contribute to neuronal signal encoding and integration. This review focuses on the molecular and cellular basis for the specific function of small-conductance calcium-activated potassium channels (SK channels) in the nervous system. SK channels are activated by an intracellular increase of free calcium during action potentials. They mediate currents that modulate the firing frequency of neurons. Three SK channel subunits have been cloned and form channels, which are voltage-insensitive, activated by submicromolar intracellular calcium concentrations, and are blocked, with different affinities, by a number of toxins and organic compounds. Different neurons in the central and peripheral nervous system express distinct subsets of SK channel subunits. Recent progress has been made in relating cloned SK channels to their native counterparts. These findings argue in favour of regulatory mechanisms conferring to native SK channels with specific subunit compositions distinct and specific functional profiles in different neurons.
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Affiliation(s)
- Martin Stocker
- Wellcome Laboratory for Molecular Pharmacology, Department of Pharmacology, University College London, Gower Street, London WC1E 6BT, UK.
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29
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Neylon CB, D'Souza T, Reinhart PH. Protein kinase A inhibits intermediate conductance Ca2+-activated K+ channels expressed in Xenopus oocytes. Pflugers Arch 2004; 448:613-20. [PMID: 15243742 DOI: 10.1007/s00424-004-1302-5] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2004] [Accepted: 05/25/2004] [Indexed: 10/26/2022]
Abstract
Intermediate-conductance (IK) Ca(2+)-activated K(+) channels are expressed in many different cell types where they perform a variety of functions including cell volume regulation, transepithelial secretion, lymphocyte activation and cell cycle progression. IK channels are thought to be regulated by phosphorylation; however, whether kinases act directly on the channel is unclear. Using IK channels heterologously expressed in Xenopus oocytes, we demonstrate that IK channels are potently inhibited (60%) by the catalytic subunit of protein kinase A (PKA). Inhibition of IK channel current by PKA is abolished by mutation of four phosphorylation residues (S312, T327, S332, and T348) in the putative calmodulin-binding region of the channel. Evidence for direct modulation of the IK channel by PKA was further demonstrated using GST fusion proteins. The major site of phosphorylation was found to be serine 332; however, other residues were also phosphorylated. We conclude that IK channels can be directly regulated by the cAMP second-messenger system. The mechanism appears to involve direct phosphorylation by PKA of a modulatory locus in the cytoplasmic region of the channel, the site at which calmodulin is thought to interact. Modulation of IK channels by protein kinases may be an important mechanism regulating cell function.
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Affiliation(s)
- Craig B Neylon
- Department of Neurobiology, Duke University Medical Center, P.O. Box 3209, Durham, NC, USA
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30
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Furness JB, Jones C, Nurgali K, Clerc N. Intrinsic primary afferent neurons and nerve circuits within the intestine. Prog Neurobiol 2004; 72:143-64. [PMID: 15063530 DOI: 10.1016/j.pneurobio.2003.12.004] [Citation(s) in RCA: 268] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2003] [Accepted: 12/03/2003] [Indexed: 02/08/2023]
Abstract
Intrinsic primary afferent neurons (IPANs) of the enteric nervous system are quite different from all other peripheral neurons. The IPANs are transducers of physiological stimuli, including movement of the villi or distortion of the mucosa, contraction of intestinal muscle and changes in the chemistry of the contents of the gut lumen. They are the first neurons in intrinsic reflexes that influence the patterns of motility, secretion of fluid across the mucosal epithelium and local blood flow in the small and large intestines. In the guinea pig small intestine, where they have been characterized in detail, IPANs have Dogiel type II morphology, that is they are large round or oval neurons with multiple processes, some of which end close to the luminal surface of the intestine, and some of which form synapses with enteric interneurons, motor neurons and with other IPANs. The IPANs have well-defined ionic currents through which their excitability, and their functions in enteric nerve circuits, is determined. These include voltage-gated Na(+) and Ca(2+) currents, a long lasting calcium-activated K(+) current, and a hyperpolarization-activated cationic current. The IPANs exhibit long-term changes in their states of excitation that can be induced by extended periods of low frequency activity in synaptic inputs and by inflammatory mediators, either applied directly or released during an inflammatory challenge. The IPANs may be involved in pathological changes in enteric function following inflammation.
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Affiliation(s)
- John B Furness
- Department of Anatomy & Cell Biology and Centre for Neuroscience, University of Melbourne, Parkville, Vic. 3010, Australia.
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Furness JB, Kearney K, Robbins HL, Hunne B, Selmer IS, Neylon CB, Chen MX, Tjandra JJ. Intermediate conductance potassium (IK) channels occur in human enteric neurons. Auton Neurosci 2004; 112:93-7. [PMID: 15233935 DOI: 10.1016/j.autneu.2004.02.003] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2004] [Accepted: 02/11/2004] [Indexed: 11/28/2022]
Abstract
IK channels, which had been previously found in hemopoetically derived cells (including erythrocytes and lymphocytes) and epithelial cells, where they regulate proliferation, cell volume regulation and secretion, have only recently been discovered in neurons, where they had previously been claimed not to occur. Based on immunohistochemical detection of IK channel-like immunoreactivity, it has been reported that IK channel expression in enteric neurons is suppressed in Crohn's disease. In the present work we have investigated whether authentic IK channels are expressed by enteric neurons. Human and mouse tissue was investigated by immunohistochemistry, Western blot and RT-PCR. Immunohistochemical studies revealed IK channel-like immunoreactivity in large myenteric neurons, but not in other cell types in the external muscle layers. Many of these nerve cells had calbindin immunoreactivity. Western blots from the external muscle revealed an immunoreactive band at the molecular weight of the IK channel. Using RT-PCR, we detected a transcript corresponding to the IK channel gene in extracts from the ganglion containing layer. The sequence obtained from the RT-PCR product was identical to that previously published for the IK channel. We conclude that IK channels are expressed by human enteric neurons, including large smooth surfaced neurons that are possibly the human equivalent of the Dogiel type II neurons that express these channels in small mammals.
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Affiliation(s)
- John B Furness
- Department of Anatomy and Cell Biology and Centre for Neuroscience, University of Melbourne, Parkville, Victoria 3010, Australia.
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Vogalis F, Harvey JR, Furness JB. Suppression of a slow post-spike afterhyperpolarization by calcineurin inhibitors. Eur J Neurosci 2004; 19:2650-8. [PMID: 15147299 DOI: 10.1111/j.0953-816x.2004.03369.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
A subset of myenteric neurons in the intestine (AH neurons) generate prolonged (>5 s) post-spike afterhyperpolarizations (slow AHPs) that are insensitive to apamin and tetraethylammonium. Generation of slow AHPs depends critically on Ca(2+) entry and intracellular release of Ca(2+) from stores, which then leads to the activation of a K(+) conductance that underlies the slow AHP (g(sAHP)). Slow AHPs are inhibited by stimulation of the cAMP/protein kinase A (PKA) pathway, suggesting that phosphorylation of the K(+)-channels that mediate the g(sAHP) (K(sAHP)-channels) is responsible for suppression of slow AHPs and possibly for the repolarization phase of slow AHPs. In the present study, we investigated the possibility that the rising phase of the slow AHP is mediated by dephosphorylation of K(sAHP)-channels by calcineurin (CaN), a Ca(2+)-calmodulin-dependent protein phosphatase, leading to an increase in g(sAHP) and activation of the associated current I(sAHP). Slow AHPs and I(sAHP) were recorded using conventional recording techniques, and we tested the actions of two inhibitors of CaN, FK506 and cyclosporin A, and also the effect of the CaN autoinhibitory peptide applied intracellularly, on these events. We report here that all three treatments inhibited the slow AHP and I(sAHP) (>70%) without significantly affecting the ability of neurons to fire action potentials. In addition, the slow AHP and I(sAHP) were suppressed by okadaic acid, an inhibitor of protein phosphatases 1 and 2A. Our results indicate that activation of the g(sAHP) that underlies the post-depolarization slow AHPs in AH neurons is mediated by the actions CaN and non-Ca(2+)-dependent phosphatases.
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Affiliation(s)
- F Vogalis
- Department of Anatomy & Cell Biology, University of Melbourne, Parkville, VIC 3010, Australia.
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Abstract
Calcium-activated potassium channels are a large family of potassium channels that are found throughout the central nervous system and in many other cell types. These channels are activated by rises in cytosolic calcium largely in response to calcium influx via voltage-gated calcium channels that open during action potentials. Activation of these potassium channels is involved in the control of a number of physiological processes from the firing properties of neurons to the control of transmitter release. These channels form the target for modulation for a range of neurotransmitters and have been implicated in the pathogenesis of neurological and psychiatric disorders. Here the authors summarize the varieties of calcium-activated potassium channels present in central neurons and their defining molecular and biophysical properties.
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Affiliation(s)
- E S Louise Faber
- Division of Neuroscience, John Curtin School of Medical Research, Australian National University, Canberra, Australia
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Abstract
Intrinsic primary afferent neurones of the intestine are specialized neurones that encode information about the state of the intestine by transducing mechanical and chemical stimuli that reflect tension in the gut wall and the chemical nature of its contents. They connect with interneurones and motor neurones in the gut to form the circuits of intrinsic muscle motor, secretomotor and vasomotor reflexes. A large range of ionic currents occur in these neurones. The neurones have voltage-activated inward sodium currents (both tetrodotoxin-sensitive and tetrodotoxin-insensitive) and inward calcium currents. Calcium entering during the action potential activates a slow after hyperpolarizing potassium current that has a profound influence on subsequent action potential firing. They also exhibit a prominent hyperpolarization-activated nonspecific cation current. The excitability of these neurones and sensory transduction are altered when the gut is inflamed. Changed excitability can persist after the inflammatory state has subsided. Intrinsic primary afferent neurones are thus important, both to the normal physiology and to pathophysiology of the small and large intestines.
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Affiliation(s)
- N Clerc
- Laboratory ITIS, UMR CNRS-University Méditerranée, Marseille, France.
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Galligan JJ. Enteric P2X receptors as potential targets for drug treatment of the irritable bowel syndrome. Br J Pharmacol 2004; 141:1294-302. [PMID: 15051631 PMCID: PMC1574905 DOI: 10.1038/sj.bjp.0705761] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The irritable bowel syndrome (IBS) is a gastrointestinal motility disorder affecting millions of patients. IBS symptoms include diarrhea, constipation and pain. The etiology of IBS is due partly to changes in the function of nerves supplying the gastrointestinal tract, immune system activation and to psychological factors. P2X receptors are multimeric ATP-gated cation channels expressed by neuronal and non-neuronal cells. Sensory nerve endings in the gastrointestinal tract express P2X receptors. ATP released from gastrointestinal cells activates P2X receptors on sensory nerve endings to stimulate motor reflexes and to transmit nociceptive signals. Antagonists acting at P2X receptors on sensory nerves could attenuate abdominal pain in IBS patients. Primary afferent neurons intrinsic to the gut, and enteric motor- and interneurons express P2X receptors. These neurons participate in motor reflexes. Agonists acting at enteric P2X receptors may enhance gastrointestinal propulsion and secretion, and these drugs could be useful for treating constipation-predominant IBS. Antagonists acting at enteric P2X receptors would decrease propulsion and secretion and they might be useful for treating diarrhea-predominant IBS. Current knowledge of P2X receptor distribution and function in the gut of laboratory animals provides a rational basis for further exploration of the therapeutic potential for drugs acting at P2X receptors in IBS patients. However, more information about P2X receptor distribution and function in the human gastrointestinal tract is needed. Data on the distribution and function of P2X receptors on gastrointestinal immune cells would also provide insights into the therapeutic potential of P2X receptor agents in IBS.
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Affiliation(s)
- James J Galligan
- Department of Pharmacology and Toxicology, Neuroscience Program, Life Science B440, Michigan State University, East Lansing, MI 48824, U.S.A.
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Wittekindt OH, Visan V, Tomita H, Imtiaz F, Gargus JJ, Lehmann-Horn F, Grissmer S, Morris-Rosendahl DJ. An Apamin- and Scyllatoxin-Insensitive Isoform of the Human SK3 Channel. Mol Pharmacol 2004; 65:788-801. [PMID: 14978258 DOI: 10.1124/mol.65.3.788] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
We have isolated an hSK3 isoform from a human embryonic cDNA library that we have named hSK3_ex4. This isoform contains a 15 amino acid insertion within the S5 to P-loop segment. Transcripts encoding hSK3_ex4 are coexpressed at lower levels with hSK3 in neuronal as well as in non-neuronal tissues. To investigate the pharmacokinetic properties of hSK3_ex4, we expressed the isoforms hSK3 and hSK3_ex4 in tsA cells. Both isoforms were similarly activated by cytosolic Ca2+ (hSK3, EC50=0.91 +/- 0.4 microM; hSK3_ex4, EC50=0.78 +/- 0.2 microM) and by 1-ethyl-2-benzimidazolinone (hSK3, EC50=0.17 mM; hSK3_ex4, 0.19 mM). They were both blocked by tetraethylammonium (hSK3, Kd=2.2 mM; hSK3_ex4, 2.6 mM) and showed similar permeabilities relative to K+ for Cs+ (hSK3, 0.17 +/- 0.04, n=3; hSK3_ex4, 0.17 +/- 0.05, n=3) and Rb+ (hSK3, 0.79 +/- 0.04, n=3; hSK3_ex4, 0.8 +/- 0.07, n=3). Ba2+ blocked both isoforms, and in both cases, the block was strongest at hyperpolarizing membrane potentials. However, the voltage-dependence of hSK3 was stronger than that of hSK3_ex4. The most obvious distinguishing feature of this new isoform was that whereas hSK3 was blocked by apamin (Kd=0.8 nM), scyllatoxin (Kd=2.1 nM), and d-tubocurarine (Kd=33.4 microM), hSK3_ex4 was not affected by apamin up to 100 nM, scyllatoxin up to 500 nM, and d-tubocurarine up to 500 microM. So far, isoform hSK3_ex4 forms the only small-conductance calcium-activated potassium (SK) channels, which are insensitive to the classic SK blockers.
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Vogalis F, Storm JF, Lancaster B. SK channels and the varieties of slow after-hyperpolarizations in neurons. Eur J Neurosci 2003; 18:3155-66. [PMID: 14686890 DOI: 10.1111/j.1460-9568.2003.03040.x] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Action potentials and associated Ca2+ influx can be followed by slow after-hyperpolarizations (sAHPs) caused by a voltage-insensitive, Ca2+-dependent K+ current. Slow AHPs are a widespread phenomenon in mammalian (including human) neurons and are present in both peripheral and central nervous systems. Although, the molecular identity of ion channels responsible for common membrane potential mechanisms has been largely determined, the nature of the channels that underlie the sAHPs in neurons, both in the brain and in the periphery, remains unresolved. This short review discusses why there is no clear molecular candidate for sAHPs.
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Affiliation(s)
- Fivos Vogalis
- Department of Anatomy & Cell Biology, University of Melbourne, Parkville, Victoria, Australia
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38
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Abstract
ATP is a neurotransmitter in the central and peripheral nervous systems and is also involved in peripheral inflammation and transmission of the sensation of pain. Recently, the regulated release of ATP from non-neuronal sources has been shown to play a role in the activation of sensory nerve terminals. Within the enteric nervous system, which is present in the wall of the gastrointestinal tract, ATP plays three major roles. ATP acts as an inhibitory transmitter from the enteric motor neurons to the smooth muscle via P2Y receptors. ATP is released as an excitatory neurotransmitter between enteric interneurons and from the interneurons to the motor neurons via P2Y and P2X receptors. Finally, ATP may act as a sensory mediator, from epithelial sources to the intrinsic sensory nerve terminals. Thus, ATP participates in the transduction of sensory stimuli from the gut lumen and in the subsequent initiation and propagation of enteric reflexes.
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Affiliation(s)
- Paul P Bertrand
- Department of Physiology, University of Melbourne Parkville, Victoria, Australia.
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Poole DP, Hunne B, Robbins HL, Furness JB. Protein kinase C isoforms in the enteric nervous system. Histochem Cell Biol 2003; 120:51-61. [PMID: 12811573 DOI: 10.1007/s00418-003-0541-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/14/2003] [Indexed: 10/26/2022]
Abstract
C kinases (PKCs) are a family of enzymes essential for the transduction of signals in a diverse range of cell types, including neurons. The different isoforms vary in their activation requirements. Therefore, cell-specific expression of different isoforms has implications for PKC-mediated control of organ function. This study has investigated the types and distributions of PKC isoforms in the small intestine of the guinea-pig, with particular emphasis on their localisation in myenteric neurons, using immunohistochemistry and western blotting techniques. Three PKC isoforms, gamma, eta and theta, were detected in the calbindin-immunoreactive subset of intrinsic primary afferent neurons, but not in other myenteric neurons. Both gamma and theta immunoreactivities were also located in interstitial cells of Cajal. In contrast to these isoforms, immunoreactivity for PKCs lambda and epsilon was present in all myenteric neurons of the ileum. PKCalpha immunoreactivity was detected primarily in the glial network, as shown through double labelling with antibodies to the glial filament protein, S100b. Myenteric neurons were also weakly immunoreactive for this isoform. PKCdelta immunoreactivity was very highly expressed in smooth muscle, but was largely absent from neurons. Immunoreactivity for RACK1, a binding protein for PKCbeta, was detected in both calbindin-immunoreactive neurons and in smooth muscle cells. This study indicates a selective distribution of PKC isoforms to specific cell types. Isoform-specific activity of these enzymes could provide a means through which targeted modulation of intestinal function is achieved.
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Affiliation(s)
- Daniel P Poole
- Department of Anatomy and Cell Biology and Centre for Neuroscience, University of Melbourne, Parkville, VIC 3010, Australia
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40
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Vogalis F, Harvey JR, Furness JB. PKA-mediated inhibition of a novel K+ channel underlies the slow after-hyperpolarization in enteric AH neurons. J Physiol 2003; 548:801-14. [PMID: 12640013 PMCID: PMC2342885 DOI: 10.1113/jphysiol.2002.037325] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Postspike after-hyperpolarizations (AHPs) control the excitability of neurons and are important in shaping firing patterns. The duration of some of these events extends to tens of seconds and they can render neurons inexcitable for much of their time course. While consensus is strong that the medium duration (< 1 s AHPs are mediated by the opening of small conductance Ca2+-activated K+ channels, the K+ channels mediating slow AHPs (> 5 s in a subset of enteric (AH) neurons) have an intermediate unit conductance (IKCa). Using whole-cell and excised-patch recording, we have demonstrated that the cAMP-protein kinase A (PKA) pathway regulates the activity of these channels. In whole-cell mode, forskolin (0.003-1 microM) inhibited the current underlying the slow AHP (IsAHP) by 90 %, and this was partially sensitive to inhibition of PKA with internal Rp-cAMPS (500 microM). Rp-cAMPS alone increased the current following break-in and caused a 20 mV hyperpolarization, suggesting that PKA maintains slow AHP channels in the closed state. Internal perfusion of the inhibitory peptide PKI5-24 slightly increased the IsAHP and opposed the inhibitory action of forskolin. Internal perfusion of the catalytic subunit of PKA (PKAcat) suppressed the IsAHP by 50 % without affecting membrane potential or action potential configuration. In inside-out patches containing IKCa-like channels, PKAcat decreased the open probability of IKCa-like channels while alkaline phosphatase activated them. These results suggest that the IKCa-like channels that underlie the slow AHP in myenteric AH neurons are subject to inhibition by PKA-dependent phosphorylation and that PKA plays an integral role in their gating.
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Affiliation(s)
- Fivos Vogalis
- Department of Anatomy and Cell Biology, University of Melbourne, Parkville, Victoria, Australia.
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41
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Kang SH, Vanden Berghe P, Smith TK. Ca2+-activated Cl- current in cultured myenteric neurons from murine proximal colon. Am J Physiol Cell Physiol 2003; 284:C839-47. [PMID: 12456397 DOI: 10.1152/ajpcell.00437.2002] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Whole cell patch-clamp recordings were made from cultured myenteric neurons taken from murine proximal colon. The micropipette contained Cs(+) to remove K(+) currents. Depolarization elicited a slowly activating time-dependent outward current (I(tdo)), whereas repolarization was followed by a slowly deactivating tail current (I(tail)). I(tdo) and I(tail) were present in approximately 70% of neurons. We identified these currents as Cl(-) currents (I(Cl)), because changing the transmembrane Cl(-) gradient altered the measured reversal potential (E(rev)) of both I(tdo) and I(tail) with that for I(tail) shifted close to the calculated Cl(-) equilibrium potential (E(Cl)). I(Cl) are Ca(2+)-activated Cl(-) current [I(Cl(Ca))] because they were Ca(2+) dependent. E(Cl), which was measured from the E(rev) of I(Cl(Ca)) using a gramicidin perforated patch, was -33 mV. This value is more positive than the resting membrane potential (-56.3 +/- 2.7 mV), suggesting myenteric neurons accumulate intracellular Cl(-). omega-Conotoxin GIVA [0.3 microM; N-type Ca(2+) channel blocker] and niflumic acid [10 microM; known I(Cl(Ca)) blocker], decreased the I(Cl(Ca)). In conclusion, these neurons have I(Cl(Ca)) that are activated by Ca(2+) entry through N-type Ca(2+) channels. These currents likely regulate postspike frequency adaptation.
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Affiliation(s)
- Sok Han Kang
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada 89557, USA
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42
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Linden DR, Sharkey KA, Mawe GM. Enhanced excitability of myenteric AH neurones in the inflamed guinea-pig distal colon. J Physiol 2003; 547:589-601. [PMID: 12562910 PMCID: PMC2342639 DOI: 10.1113/jphysiol.2002.035147] [Citation(s) in RCA: 152] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The electrical and synaptic properties of myenteric neurones in normal and inflamed guinea-pig distal colons were evaluated by intracellular microelectrode recording. Chronic inflammation was established 6 days following administration of trinitrobenzene sulfonic acid (TNBS). In S neurones, inflammation only altered synaptic inputs as the amplitude of fast excitatory postsynaptic potentials were significantly larger (31 +/- 2 mV compared to 20 +/- 1 mV) and they were more likely to receive slow excitatory synaptic input (85% compared to 55%). AH neurones displayed altered electrical properties in colitis compared to control tissues: they generated more action potentials during a maximal depolarising current pulse (7 +/- 1 compared to 1.6 +/- 0.2); they had a smaller after hyperpolarisation (9 +/- 2 mV s compared to 20 +/- 2 mV s); and they were more likely to receive fast excitatory synaptic input (74% compared to 17%), possess spontaneous activity (46% compared to 3%), and generate anodal break action potentials (58% compared to 19%). Although the resting membrane potential, input resistance and action potential characteristics were unaltered in AH neurones from inflamed tissues, they exhibited an enhanced Cs+-sensitive rectification of the current-voltage relationship. This suggests that the increase in excitability of AH neurones may involve a colitis-induced augmentation of the hyperpolarisation-activated cation current (Ih) in these cells. An increased excitability, selectively in AH neurones, suggests that the afferent limb of intrinsic motor reflexes is disrupted in the inflamed colon and this may contribute to dysmotility associated with inflammatory diseases.
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Affiliation(s)
- David R Linden
- Department of Anatomy and Neurobiology, The University of Vermont College of Medicine, Burlington, VT 05405, USA
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43
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Arnold SJ, Facer P, Yiangou Y, Chen MX, Plumpton C, Tate SN, Bountra C, Chan CLH, Williams NS, Anand P. Decreased potassium channel IK1 and its regulator neurotrophin-3 (NT-3) in inflamed human bowel. Neuroreport 2003; 14:191-5. [PMID: 12598727 DOI: 10.1097/00001756-200302100-00006] [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: 11/26/2022]
Abstract
Calcium-activated potassium currents of intermediate conductance (IK1) have been described in the rodent enteric nervous system, where they may regulate afterhyperpolarisation of intrinsic primary afferent neurons. Using specific antibodies for immuno-cytochemistry, we now report IK1-like immunoreactivity for the first time in enteric neurons of human colon, and a significant decrease of IK1-positive cells in myenteric plexus in inflamed colon from patients with Crohn's disease and ulcerative colitis (p = 0.031). Neurotrophin-3 (NT-3), which regulates IK1 expression, was also observed in fewer neurons of the myenteric ganglia in Crohn's bowel (p = 0.048), and in inflamed colonic extracts by Western blotting (p = 0.004); the numbers of neurons expressing the NT-3 high affinity receptor trk C were unchanged. Our findings may explain the diarrhoea and colicky abdominal pain produced by inflammatory bowel disease, and by IK1-blocking pyridine drugs prescribed for neuromuscular disorders.
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Affiliation(s)
- Steven J Arnold
- Imperial College of Sciences, Technology and Medicine, Hammersmith Hospital, London, UK
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44
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Vogalis F, Harvey JR, Lohman RJ, Furness JB. Action potential afterdepolarization mediated by a Ca2+-activated cation conductance in myenteric AH neurons. Neuroscience 2003; 115:375-93. [PMID: 12421604 DOI: 10.1016/s0306-4522(02)00410-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We investigated the nature of afterdepolarizing potentials in AH neurons from the guinea-pig duodenum using whole-cell patch-clamp recordings in intact myenteric ganglia. Afterdepolarizing potentials were minimally activated following action-potential firing under normal conditions, but after application of charybdotoxin (40 nM) or tetraethyl ammonium (TEA; 10-20 mM) to the bathing solution, prominent afterdepolarizing potentials followed action potentials. The whole-cell current underlying afterdepolarizing potentials (I(ADP)) in the presence of TEA (10-20 mM) reversed at -38 mV and was not voltage-dependent. Reduction of NaCl in the bathing (Krebs) solution to 58 mM shifted the reversal potential of the I(ADP) to -58 mV, suggesting that the current underlying the afterdepolarizing potential was carried by a mixture of cations. The relative contributions of Na(+) and K(+) to this current were estimated to be about 1:5. Substitution of external Na(+) with N-methyl D-glucamine blocked the current while replacement of internal Cl(-) with gluconate did not block the I(ADP). The I(ADP) was also inhibited when CsCl-filled patch pipettes were used. The I(ADP) was blocked or substantially decreased in amplitude in the presence of N-type Ca(2+) channel antagonists, omega-conotoxin GVIA and omega-conotoxin MVIIC, respectively, and was eliminated by external Cd(2+), indicating that it was dependent on Ca(2+) entry. The I(ADP) was also inhibited by ryanodine (10-20 microM), indicating that Ca(2+)-induced Ca(2+) release was involved in its activation. Niflumic acid consistently inhibited the I(ADP) with an IC(50) of 63 microM. Using antibodies against the pore-forming subunits of L-, N- and P/Q-type voltage-gated Ca(2+) channels, we have demonstrated that myenteric AH neurons express N- and P/Q, but not L-type voltage-gated Ca(2+) channels. We conclude that the ADP in myenteric AH neurons, in the presence of an L-type Ca(2+)-channel blocker, is generated by the opening of Ca(2+)-activated non-selective cation channels following action potential-mediated Ca(2+) entry mainly through N-type Ca(2+) channels. Ca(2+) release from ryanodine-sensitive stores triggered by Ca(2+) entry contributes significantly to the activation of this current.
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Affiliation(s)
- F Vogalis
- Department of Anatomy and Cell Biology, University of Melbourne, Parkville, Vic. 3010, Australia.
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Vogalis F, Harvey JR, Neylon CB, Furness JB. Regulation of K+ channels underlying the slow afterhyperpolarization in enteric afterhyperpolarization-generating myenteric neurons: role of calcium and phosphorylation. Clin Exp Pharmacol Physiol 2002; 29:935-43. [PMID: 12207575 DOI: 10.1046/j.1440-1681.2002.03755.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
1. Myenteric afterhyperpolarization-generating myenteric (AH) neurons serve as intrinsic primary afferent neurons of the enteric nervous system and generate prolonged or slow afterhyperpolarizing potentials (slow AHP). The slow AHP is generated by an increase in a Ca2+-activated K+ conductance (gK-Ca) and is inhibited by enteric neurotransmitters leading to increased excitability. 2. Using cell-attached patch-clamp recordings from AH neurons, we have shown that K+ channels with an intermediate unitary conductance (IK channels) open following action potential firing. 3. In excised patches from AH neurons, we have identified an IK-like channel that can be activated by submicromolar levels of cytoplasmic Ca2+ and is not voltage dependent. 4. Application of the catalytic subunit of cAMP-dependent protein kinase to the cytoplasmic surface of inside-out patches inhibits the opening of IK-like channels previously activated by Ca2+. 5. The IK-like channels are resistant to external tetraethylammonium (5 mmol/L) and apamin (0.3-1 micro mol/L), but are inhibited by clotrimazole (10 micro mol/L). 6. Our present data support the idea that an increase in the open probability of IK-like channels in AH neurons following an increase in cytoplasmic [Ca2+] is responsible for the slow AHP and their opening is modulated by kinases.
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Affiliation(s)
- Fivos Vogalis
- Department of Anatomy and Cell Biology, University of Melbourne, Parkville, Victoria, Australia.
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46
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Abstract
We investigated the role of mitochondria in the regulation of intracellular Ca2+ ([Ca2+]i) and excitability of myenteric neurons in guinea pig ileum, using microelectrodes and fura-2 [Ca2+]i measurements. In AH/Type-II neurons, action potentials evoke ryanodine-sensitive increases in [Ca2+]i that activate Ca2+-dependent K+ channels and slow afterhyperpolarizations (AH) lasting approximately 15 sec. Exposure to the protonophore carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone (FCCP; 1 microm) had no significant effect on the membrane potential or resting [Ca2+]i. However, action potentials elicited in the presence of FCCP triggered a sustained (>5 min) increase in [Ca2+]i and a compound hyperpolarization (13.4 +/- 1.5 mV). The respiratory chain blockers antimycin A and rotenone (10 microm) had similar effects that developed more slowly. Depletion of the intracellular Ca2+ stores with thapsigargin (2 microm) or ryanodine (10 microm) greatly attenuated the hyperpolarization caused by FCCP. S/Type-I neurons that do not have AH were hyperpolarized by mitochondrial inhibition independently of action potentials. Blockade of the F0F1 ATPase by oligomycin (10 microm) had variable effects on myenteric neurons. The majority of AH/Type-II neurons were hyperpolarized by oligomycin, most likely by activating ATP-dependent K+ channels. This hyperpolarization was not triggered by action potential firing and not accompanied by an increase in [Ca2+]i. MitoTracker staining revealed a dense mitochondrial network particularly in myenteric AH/Type-II neurons, supporting the importance of mitochondrial Ca2+ buffering in this subset of neurons. The data indicate that mitochondrial uptake of Ca2+ released from the endoplasmic reticulum sets [Ca2+]i and the activity of Ca2+-dependent conductances, thus regulating the excitability of myenteric neurons.
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