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Sanders KM, Drumm BT, Cobine CA, Baker SA. Ca 2+ dynamics in interstitial cells: foundational mechanisms for the motor patterns in the gastrointestinal tract. Physiol Rev 2024; 104:329-398. [PMID: 37561138 PMCID: PMC11281822 DOI: 10.1152/physrev.00036.2022] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2022] [Revised: 06/29/2023] [Accepted: 08/06/2023] [Indexed: 08/11/2023] Open
Abstract
The gastrointestinal (GI) tract displays multiple motor patterns that move nutrients and wastes through the body. Smooth muscle cells (SMCs) provide the forces necessary for GI motility, but interstitial cells, electrically coupled to SMCs, tune SMC excitability, transduce inputs from enteric motor neurons, and generate pacemaker activity that underlies major motor patterns, such as peristalsis and segmentation. The interstitial cells regulating SMCs are interstitial cells of Cajal (ICC) and PDGF receptor (PDGFR)α+ cells. Together these cells form the SIP syncytium. ICC and PDGFRα+ cells express signature Ca2+-dependent conductances: ICC express Ca2+-activated Cl- channels, encoded by Ano1, that generate inward current, and PDGFRα+ cells express Ca2+-activated K+ channels, encoded by Kcnn3, that generate outward current. The open probabilities of interstitial cell conductances are controlled by Ca2+ release from the endoplasmic reticulum. The resulting Ca2+ transients occur spontaneously in a stochastic manner. Ca2+ transients in ICC induce spontaneous transient inward currents and spontaneous transient depolarizations (STDs). Neurotransmission increases or decreases Ca2+ transients, and the resulting depolarizing or hyperpolarizing responses conduct to other cells in the SIP syncytium. In pacemaker ICC, STDs activate voltage-dependent Ca2+ influx, which initiates a cluster of Ca2+ transients and sustains activation of ANO1 channels and depolarization during slow waves. Regulation of GI motility has traditionally been described as neurogenic and myogenic. Recent advances in understanding Ca2+ handling mechanisms in interstitial cells and how these mechanisms influence motor patterns of the GI tract suggest that the term "myogenic" should be replaced by the term "SIPgenic," as this review discusses.
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Affiliation(s)
- Kenton M Sanders
- Department of Physiology and Cell Biology, School of Medicine, University of Nevada-Reno, Reno, Nevada, United States
| | - Bernard T Drumm
- Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Ireland
| | - Caroline A Cobine
- Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Ireland
| | - Salah A Baker
- Department of Physiology and Cell Biology, School of Medicine, University of Nevada-Reno, Reno, Nevada, United States
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Sanders KM, Santana LF, Baker SA. Interstitial cells of Cajal - pacemakers of the gastrointestinal tract. J Physiol 2023. [PMID: 37997170 DOI: 10.1113/jp284745] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2023] [Accepted: 11/06/2023] [Indexed: 11/25/2023] Open
Abstract
Gastrointestinal (GI) organs display spontaneous, non-neurogenic electrical, and mechanical rhythmicity that underlies fundamental motility patterns, such as peristalsis and segmentation. Electrical rhythmicity (aka slow waves) results from pacemaker activity generated by interstitial cells of Cajal (ICC). ICC express a unique set of ionic conductances and Ca2+ handling mechanisms that generate and actively propagate slow waves. GI smooth muscle cells lack these conductances. Slow waves propagate actively within ICC networks and conduct electrotonically to smooth muscle cells via gap junctions. Slow waves depolarize smooth muscle cells and activate voltage-dependent Ca2+ channels (predominantly CaV1.2), causing Ca2+ influx and excitation-contraction coupling. The main conductances responsible for pacemaker activity in ICC are ANO1, a Ca2+ -activated Cl- conductance, and CaV3.2. The pacemaker cycle, as currently understood, begins with spontaneous, localized Ca2+ release events in ICC that activate spontaneous transient inward currents due to activation of ANO1 channels. Depolarization activates CaV 3.2 channels, causing the upstroke depolarization phase of slow waves. The upstroke is transient and followed by a long-duration plateau phase that can last for several seconds. The plateau phase results from Ca2+ -induced Ca2+ release and a temporal cluster of localized Ca2+ transients in ICC that sustains activation of ANO1 channels and clamps membrane potential near the equilibrium potential for Cl- ions. The plateau phase ends, and repolarization occurs, when Ca2+ stores are depleted, Ca2+ release ceases and ANO1 channels deactivate. This review summarizes key mechanisms responsible for electrical rhythmicity in gastrointestinal organs.
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Affiliation(s)
- Kenton M Sanders
- Department of Physiology and Cell Biology, School of Medicine, University of Nevada, Reno, NV, USA
| | - L Fernando Santana
- Department of Physiology and Membrane Biology, University of California, Davis, CA, USA
| | - Salah A Baker
- Department of Physiology and Cell Biology, School of Medicine, University of Nevada, Reno, NV, USA
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Filho FC, Silva JDP, Petri C, Almendra JSL, de Sousa ÍA, Cavalcanti SMG, Silva BA, Formiga Melo MF, Cavalcanti PMDS. Pharmacological evidence that GABA-induced relaxation of rat proximal duodenum longitudinal muscle depends on NKCC cotransporter activity and Ca 2+ influx. Can J Physiol Pharmacol 2022; 100:728-740. [PMID: 35880679 DOI: 10.1139/cjpp-2021-0639] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
γ-Aminobutyric acid (GABA) is the main inhibitory neurotransmitter in adult central nervous system (CNS) synapses, but it excites immature CNS neurons as well as neurons in the myenteric plexus. The present work aimed to determine whether GABA-induced nonadrenergic, noncholinergic (NANC) neuronal-mediated relaxation of the rat duodenum is dependent on the activity of Na+ K+ Cl- cotransporters (NKCC) and requires calcium influx. In the presence of guanethidine (3 µmol/L), atropine (3 µmol/L), and indomethacin (1 µmol/L), relaxations induced by GABA (100 µmol/L), KCl (5-10 mmol/L) and electrical field stimulation (1-8 Hz, 2 ms, 60 V), but not those induced by bradykinin (10-100 nmol/L) were abolished by lidocaine (300 µmol/L). However, only GABA-induced relaxations were reduced in a concentration-dependent manner by the NKCC1/2 inhibitors bumetanide (0.1-1 µmol/L) and furosemide (1-10 µmol/L). GABA-induced NANC neuronal relaxation was abolished by bicuculline (30 µmol/L) and inhibited by N-nitroarginine methyl ester (l-NAME, 300 µmol/L). The ω-conotoxin GVIA (1 µmol/L), which acts exclusively on neuronal CaV2 channels, but not on smooth muscle voltage-gated Ca2+ CaV1 channels, and nonselective blockers of these channels (verapamil 100 nmol/L and ruthenium red 10 µmol/L), reduced GABA-induced relaxations. These results showed that the activation of GABAA receptors induces NANC nitrergic neuronal relaxations in the rat duodenum, which depend on NKCC activity and CaV2 channel activation, suggesting that this phenomenon results from neuronal depolarization promoted by Cl- efflux through GABAA receptors, with subsequent Ca2+ influx and nitric oxide release.
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Affiliation(s)
- Francisco Chagas Filho
- Biophysics and Physiology Department, 64049-550, Health Sciences Center, Federal University of Piauí, Teresina, Piauí, Brazil
| | - Janyerson Dannys Pereira Silva
- Biophysics and Physiology Department, 64049-550, Health Sciences Center, Federal University of Piauí, Teresina, Piauí, Brazil
| | - Caio Petri
- Biophysics and Physiology Department, 64049-550, Health Sciences Center, Federal University of Piauí, Teresina, Piauí, Brazil
| | - João Santos Lima Almendra
- Biophysics and Physiology Department, 64049-550, Health Sciences Center, Federal University of Piauí, Teresina, Piauí, Brazil
| | - Ícaro Araújo de Sousa
- Biophysics and Physiology Department, 64049-550, Health Sciences Center, Federal University of Piauí, Teresina, Piauí, Brazil
| | | | - Bagnólia A Silva
- Pharmacological Sciences Department, 58051-900, Health Sciences Center, Federal University of Paraíba, João Pessoa, Paraíba, Brazil
| | - Margareth Fátima Formiga Melo
- Pharmacological Sciences Department, 58051-900, Health Sciences Center, Federal University of Paraíba, João Pessoa, Paraíba, Brazil
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Sanders KM, Baker SA, Drumm BT, Kurahashi M. Ca 2+ Signaling Is the Basis for Pacemaker Activity and Neurotransduction in Interstitial Cells of the GI Tract. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2022; 1383:229-241. [PMID: 36587162 DOI: 10.1007/978-3-031-05843-1_22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Years ago gastrointestinal motility was thought to be due to interactions between enteric nerves and smooth muscle cells (SMCs) in the tunica muscularis. Thus, regulatory mechanisms controlling motility were either myogenic or neurogenic. Now we know that populations of interstitial cells, c-Kit+ (interstitial cells of Cajal or ICC), and PDGFRα+ cells (formerly "fibroblast-like" cells) are electrically coupled to SMCs, forming the SIP syncytium. Pacemaker and neurotransduction functions are provided by interstitial cells through Ca2+ release from the endoplasmic reticulum (ER) and activation of Ca2+-activated ion channels in the plasma membrane (PM). ICC express Ca2+-activated Cl- channels encoded by Ano1. When activated, Ano1 channels produce inward current and, therefore, depolarizing or excitatory effects in the SIP syncytium. PDGFRα+ cells express Ca2+-activated K+ channels encoded by Kcnn3. These channels generate outward current when activated and hyperpolarizing or membrane-stabilizing effects in the SIP syncytium. Inputs from enteric and sympathetic neurons regulate Ca2+ transients in ICC and PDGFRα+ cells, and currents activated in these cells conduct to SMCs and regulate contractile behaviors. ICC also serve as pacemakers, generating slow waves that are the electrophysiological basis for gastric peristalsis and intestinal segmentation. Pacemaker types of ICC express voltage-dependent Ca2+ conductances that organize Ca2+ transients, and therefore Ano1 channel openings, into clusters that define the amplitude and duration of slow waves. Ca2+ handling mechanisms are at the heart of interstitial cell function, yet little is known about what happens to Ca2+ dynamics in these cells in GI motility disorders.
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Affiliation(s)
- Kenton M Sanders
- Department of Physiology and Cell Biology, University of Nevada, Reno, School of Medicine, Reno, NV, USA.
| | - Salah A Baker
- Department of Physiology and Cell Biology, University of Nevada, Reno, School of Medicine, Reno, NV, USA
| | - Bernard T Drumm
- Department of Physiology and Cell Biology, University of Nevada, Reno, School of Medicine, Reno, NV, USA
| | - Masaaki Kurahashi
- Department of Physiology and Cell Biology, University of Nevada, Reno, School of Medicine, Reno, NV, USA.,Department of Internal Medicine, Division of Gastroenterology and Hepatology, University of Iowa, Iowa, Iowa City, USA
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Baker SA, Hwang SJ, Blair PJ, Sireika C, Wei L, Ro S, Ward SM, Sanders KM. Ca 2+ transients in ICC-MY define the basis for the dominance of the corpus in gastric pacemaking. Cell Calcium 2021; 99:102472. [PMID: 34537580 PMCID: PMC8592010 DOI: 10.1016/j.ceca.2021.102472] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2021] [Revised: 09/03/2021] [Accepted: 09/05/2021] [Indexed: 12/13/2022]
Abstract
Myenteric interstitial cells of Cajal (ICC-MY) generate and actively propagate electrical slow waves in the stomach. Slow wave generation and propagation are altered in gastric motor disorders, such as gastroparesis, and the mechanism for the gradient in slow wave frequency that facilitates proximal to distal propagation of slow waves and normal gastric peristalsis is poorly understood. Slow waves depend upon Ca2+-activated Cl- channels (encoded by Ano1). We characterized Ca2+ signaling in ICC-MY in situ using mice engineered to have cell-specific expression of GCaMP6f in ICC. Ca2+ signaling differed in ICC-MY in corpus and antrum. Localized Ca2+ transients were generated from multiple firing sites and were organized into Ca2+ transient clusters (CTCs). Ca2+ transient refractory periods occurred upon cessation of CTCs, but a relatively higher frequency of Ca2+ transients persisted during the inter-CTC interval in corpus than in antrum ICC-MY. The onset of Ca2+ transients after the refractory period was associated with initiation of the next CTC. Thus, CTCs were initiated at higher frequencies in corpus than in antrum ICC-MY. Initiation and propagation of CTCs (and electrical slow waves) depends upon T-type Ca2+ channels, and durations of CTCs relied upon L-type Ca2+ channels. The durations of CTCs mirrored the durations of slow waves. CTCs and Ca2+ transients between CTCs resulted from release of Ca2+ from intracellular stores and were maintained, in part, by store-operated Ca2+ entry. Our data suggest that Ca2+ release and activation of Ano1 channels both initiate and contribute to the plateau phase of slow waves.
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Affiliation(s)
- Salah A Baker
- Department of Physiology and Cell Biology, University of Nevada, Reno, School of Medicine, Reno, Nevada 89557, USA.
| | - Sung Jin Hwang
- Department of Physiology and Cell Biology, University of Nevada, Reno, School of Medicine, Reno, Nevada 89557, USA
| | - Peter J Blair
- Department of Physiology and Cell Biology, University of Nevada, Reno, School of Medicine, Reno, Nevada 89557, USA
| | - Carlee Sireika
- Department of Physiology and Cell Biology, University of Nevada, Reno, School of Medicine, Reno, Nevada 89557, USA
| | - Lai Wei
- Department of Physiology and Cell Biology, University of Nevada, Reno, School of Medicine, Reno, Nevada 89557, USA
| | - Seungil Ro
- Department of Physiology and Cell Biology, University of Nevada, Reno, School of Medicine, Reno, Nevada 89557, USA
| | - Sean M Ward
- Department of Physiology and Cell Biology, University of Nevada, Reno, School of Medicine, Reno, Nevada 89557, USA
| | - Kenton M Sanders
- Department of Physiology and Cell Biology, University of Nevada, Reno, School of Medicine, Reno, Nevada 89557, USA.
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Garneau AP, Slimani S, Fiola MJ, Tremblay LE, Isenring P. Multiple Facets and Roles of Na+-K+-Cl−Cotransport: Mechanisms and Therapeutic Implications. Physiology (Bethesda) 2020; 35:415-429. [DOI: 10.1152/physiol.00012.2020] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The Na+-K+-Cl−cotransporters play key physiological and pathophysiological roles by regulating the membrane potential of many cell types and the movement of fluid across a variety of epithelial or endothelial structures. As such, they should soon become invaluable targets for the treatment of various disorders including pain, epilepsy, brain edema, and hypertension. This review highlights the nature of these roles, the mechanisms at play, and the unresolved issues in the field.
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Affiliation(s)
- A. P. Garneau
- Department of Medicine, Nephrology Research Group, Laval University, Québec, Canada; and
- Cardiometabolic Axis, School of Kinesiology and Physical Activity Sciences, University of Montréal, Montréal, Canada
| | - S. Slimani
- Department of Medicine, Nephrology Research Group, Laval University, Québec, Canada; and
| | - M. J. Fiola
- Department of Medicine, Nephrology Research Group, Laval University, Québec, Canada; and
| | - L. E. Tremblay
- Department of Medicine, Nephrology Research Group, Laval University, Québec, Canada; and
| | - P. Isenring
- Department of Medicine, Nephrology Research Group, Laval University, Québec, Canada; and
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Mitsui R, Hashitani H. Synchrony of spontaneous Ca 2+ activity in microvascular mural cells. J Smooth Muscle Res 2020; 56:1-18. [PMID: 32249242 PMCID: PMC7132055 DOI: 10.1540/jsmr.56.1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Spontaneous rhythmic constrictions known as vasomotion are developed in several microvascular beds in vivo. Vasomotion in arterioles is considered to facilitate blood flow, while venular vasomotion would facilitate tissue metabolite drainage. Mechanisms underlying vasomotion periodically generate synchronous Ca2+ transients in vascular smooth muscle cells (VSMCs). In visceral organs, mural cells (pericytes and VSMCs) in arterioles, capillaries and venules exhibit synchronous spontaneous Ca2+ transients. Since sympathetic regulation is rather limited in the intra-organ microvessels, spontaneous activity of mural cells may play an essential role in maintaining tissue perfusion. Synchronous spontaneous Ca2+ transients in precapillary arterioles (PCAs)/capillaries appear to propagate to upstream arterioles to drive their vasomotion, while venules develop their own synchronous Ca2+ transients and associated vasomotion. Spontaneous Ca2+ transients of mural cells primarily arise from IP3 and/or ryanodine receptor-mediated Ca2+ release from sarcoendoplasmic reticulum (SR/ER) Ca2+ stores. The resultant opening of Ca2+-activated Cl- channels (CaCCs) causes a membrane depolarisation that triggers Ca2+ influx via T-type and/or L-type voltage-dependent Ca2+ channels (VDCCs). Mural cells are electrically coupled with each other via gap junctions, and thus allow the sequential spread of CaCC or VDCC-dependent depolarisations to develop the synchrony of Ca2+ transients within their network. Importantly, the synchrony of spontaneous Ca2+ transients also requires a certain range of the resting membrane potential that is maintained by the opening of Kv7 voltage-dependent K+ (Kv7) and inward rectifier K+ (Kir) channels. Thus, a depolarised membrane would evoke asynchronous, 'premature' spontaneous Ca2+ transients, while a hyperpolarised membrane prevents any spontaneous activity.
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Affiliation(s)
- Retsu Mitsui
- Department of Cell Physiology, Nagoya City University Graduate School of Medical Sciences, Nagoya 467-8601, Japan
| | - Hikaru Hashitani
- Department of Cell Physiology, Nagoya City University Graduate School of Medical Sciences, Nagoya 467-8601, Japan
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Li H, Xu W, Liu X, Ye J, Li P, Shang F, Yu X. Curcumin Alleviates the Side Effects of Cisplatin on Gastric Emptying of Mice by Inhibiting the Signal Changes of Acetylcholine and Interstitial Cells of Cajal. J Med Food 2020; 23:920-927. [PMID: 32833554 DOI: 10.1089/jmf.2019.4599] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Cisplatin is a widely used anticancer drug that has adverse effects on gastrointestinal function. Curcumin is a natural polyphenol extracted from the rhizome of turmeric that has a wide range of biological activities. The present study investigated the effects of cisplatin on gastric emptying in mice and examined whether these can be inhibited by curcumin. We found that pretreatment with curcumin (200 mg/kg/day) for 10-30 days partly inhibited the decreases in gastric emptying rate and body weight induced by cisplatin. Furthermore, cisplatin reduced acetylcholine (ACh) concentration and the messenger RNA (mRNA) level of ACh receptor (AChR) as well as acetylcholinesterase activity in the stomach of mice; caused ultrastructural damage to interstitial cells of Cajal (ICC); and altered the expression of c-kit/stem cell factor and the gap junction protein connexin 43 in ICC. Curcumin pretreatment inhibited the effects of cisplatin on ACh indicators and ICC. These results demonstrate that curcumin can protect against cisplatin-induced gastric emptying disorder and thus has therapeutic potential for alleviating this condition in cancer patients receiving cisplatin chemotherapy.
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Affiliation(s)
- Hui Li
- Department of Physiology and Pathophysiology, Qingdao University Medical College, Qingdao, P.R. China
| | - Wenhua Xu
- Department of Laboratory Biochemistry, Qingdao University Medical College, Qingdao, P.R. China
| | - Xuying Liu
- Student of "5 + 3" Integration of Clinical Medicine, Grade 2015, Qingdao University Medical College, Qingdao, P.R. China
| | - Junli Ye
- Department of Physiology and Pathophysiology, Qingdao University Medical College, Qingdao, P.R. China
| | - Peijie Li
- Department of Pathology, The First Affiliated Hospital of Zhejiang University, Hangzhou, P.R. China
| | - Fangfang Shang
- Department of Pathology, Navy 971 Hospital of PLA, Qingdao, P.R. China
| | - Xiaoling Yu
- Department of Physiology and Pathophysiology, Qingdao University Medical College, Qingdao, P.R. China
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Hannigan KI, Bossey AP, Foulkes HJL, Drumm BT, Baker SA, Ward SM, Sanders KM, Keef KD, Cobine CA. A novel intramuscular Interstitial Cell of Cajal is a candidate for generating pacemaker activity in the mouse internal anal sphincter. Sci Rep 2020; 10:10378. [PMID: 32587396 PMCID: PMC7316801 DOI: 10.1038/s41598-020-67142-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2019] [Accepted: 06/03/2020] [Indexed: 12/14/2022] Open
Abstract
The internal anal sphincter (IAS) generates phasic contractions and tone. Slow waves (SWs) produced by interstitial cells of Cajal (ICC) underlie phasic contractions in other gastrointestinal regions. SWs are also present in the IAS where only intramuscular ICC (ICC-IM) are found, however the evidence linking ICC-IM to SWs is limited. This study examined the possible relationship between ICC-IM and SWs by recording Ca2+ transients in mice expressing a genetically-encoded Ca2+-indicator in ICC (Kit-Cre-GCaMP6f). A role for L-type Ca2+ channels (CavL) and anoctamin 1 (ANO1) was tested since each is essential for SW and tone generation. Two distinct ICC-IM populations were identified. Type I cells (36% of total) displayed localised asynchronous Ca2+ transients not dependent on CavL or ANO1; properties typical of ICC-IM mediating neural responses in other gastrointestinal regions. A second novel sub-type, i.e., Type II cells (64% of total) generated rhythmic, global Ca2+ transients at the SW frequency that were synchronised with neighbouring Type II cells and were abolished following blockade of either CavL or ANO1. Thus, the spatiotemporal characteristics of Type II cells and their dependence upon CavL and ANO1 all suggest that these cells are viable candidates for the generation of SWs and tone in the IAS.
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Affiliation(s)
- Karen I Hannigan
- Department of Physiology and Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV, 89557, USA
| | - Aaron P Bossey
- Department of Physiology and Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV, 89557, USA
| | - Holly J L Foulkes
- Department of Physiology and Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV, 89557, USA
| | - Bernard T Drumm
- Department of Physiology and Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV, 89557, USA
| | - Salah A Baker
- Department of Physiology and Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV, 89557, USA
| | - Sean M Ward
- Department of Physiology and Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV, 89557, USA
| | - Kenton M Sanders
- Department of Physiology and Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV, 89557, USA
| | - Kathleen D Keef
- Department of Physiology and Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV, 89557, USA
| | - Caroline A Cobine
- Department of Physiology and Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV, 89557, USA.
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Cobine CA, Hannigan KI, McMahon M, Bhraonain EPN, Baker SA, Keef KD. Rhythmic calcium transients in smooth muscle cells of the mouse internal anal sphincter. Neurogastroenterol Motil 2020; 32:e13746. [PMID: 31625250 PMCID: PMC7047590 DOI: 10.1111/nmo.13746] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Revised: 09/22/2019] [Accepted: 09/26/2019] [Indexed: 12/12/2022]
Abstract
BACKGROUND The internal anal sphincter (IAS) exhibits slow waves (SWs) and tone that are dependent upon L-type Ca2+ channels (CavL ) suggesting that phasic events (ie, SWs) play a fundamental role in tone generation. The present study further examined phasic activity in the IAS by measuring the spatiotemporal properties of Ca2+ transients (CTs) in IAS smooth muscle cells (SMCs). METHODS Ca2+ transients were recorded with spinning disk confocal microscopy from the IAS of SM-GCaMP mice. Muscles were pinned submucosal surface up at two different lengths. Drugs were applied by inclusion in the superfusate. KEY RESULTS Ca2+ transients displayed ongoing rhythmic firings at both lengths and were abolished by nifedipine and the KATP channel activator pinacidil indicating their dependence upon CavL . Like SWs, CTs were greatest in frequency (average 70.6 cpm) and amplitude at the distal extremity and conducted proximally. Removal of the distal IAS reduced but did not abolish CTs. The time constant for clearing cytoplasmic Ca2+ averaged 0.46 seconds and basal Ca2+ levels were significantly elevated. CONCLUSIONS & INFERENCES The similarities in spatiotemporal and pharmacological properties of CTs and SWs suggest that SW gives rise to CTs while muscle stretch is not required. Elevated relative basal Ca2+ in the IAS is likely due to the inability of cells to clear or sequester Ca2+ between rapid frequency voltage-dependent Ca2+ entry events, that is, conditions that will lead to tone development. The conduction of CTs from distal to proximal IAS will lead to orally directed contractions and likely contribute to the maintenance of fecal continence.
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Affiliation(s)
- Caroline A Cobine
- Corresponding Author: Caroline Cobine, Ph.D., Department of Physiology and Cell Biology, University of Nevada, Reno School of Medicine, 1664 N. Virginia St., MS 352, Reno, NV 89557, USA, Phone: 1-775-682-8840, Fax: 1-775-784-6903,
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Role of Pericytes in the Initiation and Propagation of Spontaneous Activity in the Microvasculature. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1124:329-356. [PMID: 31183834 DOI: 10.1007/978-981-13-5895-1_14] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The microvasculature is composed of arterioles, capillaries and venules. Spontaneous arteriolar constrictions reduce effective vascular resistance to enhance tissue perfusion, while spontaneous venular constrictions facilitate the drainage of tissue metabolites by pumping blood. In the venules of visceral organs, mural cells, i.e. smooth muscle cells (SMCs) or pericytes, periodically generate spontaneous phasic constrictions, Ca2+ transients and transient depolarisations. These events arise from spontaneous Ca2+ release from the sarco-endoplasmic reticulum (SR/ER) and the subsequent opening of Ca2+-activated chloride channels (CaCCs). CaCC-dependent depolarisation further activates L-type voltage-dependent Ca2+ channels (LVDCCs) that play a critical role in maintaining the synchrony amongst mural cells. Mural cells in arterioles or capillaries are also capable of developing spontaneous activity. Non-contractile capillary pericytes generate spontaneous Ca2+ transients primarily relying on SR/ER Ca2+ release. Synchrony amongst capillary pericytes depends on gap junction-mediated spread of depolarisations resulting from the opening of either CaCCs or T-type VDCCs (TVDCCs) in a microvascular bed-dependent manner. The propagation of capillary Ca2+ transients into arterioles requires the opening of either L- or TVDCCs again depending on the microvascular bed. Since the blockade of gap junctions or CaCCs prevents spontaneous Ca2+ transients in arterioles and venules but not capillaries, capillary pericytes appear to play a primary role in generating spontaneous activity of the microvasculature unit. Pericytes in capillaries where the interchange of substances between tissues and the circulation takes place may provide the fundamental drive for upstream arterioles and downstream venules so that the microvasculature network functions as an integrated unit.
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Generation of Spontaneous Tone by Gastrointestinal Sphincters. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019. [PMID: 31183822 DOI: 10.1007/978-981-13-5895-1_2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/05/2023]
Abstract
An important feature of the gastrointestinal (GI) muscularis externa is its ability to generate phasic contractile activity. However, in some GI regions, a more sustained contraction, referred to as "tone," also occurs. Sphincters are muscles oriented in an annular manner that raise intraluminal pressure, thereby reducing or blocking the movement of luminal contents from one compartment to another. Spontaneous tone generation is often a feature of these muscles. Four distinct smooth muscle sphincters are present in the GI tract: the lower esophageal sphincter (LES), the pyloric sphincter (PS), the ileocecal sphincter (ICS), and the internal anal sphincter (IAS). This chapter examines how tone generation contributes to the functional behavior of these sphincters. Historically, tone was attributed to contractile activity arising directly from the properties of the smooth muscle cells. However, there is increasing evidence that interstitial cells of Cajal (ICC) play a significant role in tone generation in GI muscles. Indeed, ICC are present in each of the sphincters listed above. In this chapter, we explore various mechanisms that may contribute to tone generation in sphincters including: (1) summation of asynchronous phasic activity, (2) partial tetanus, (3) window current, and (4) myofilament sensitization. Importantly, the first two mechanisms involve tone generation through summation of phasic events. Thus, the historical distinction between "phasic" versus "tonic" smooth muscles in the GI tract requires revision. As described in this chapter, it is clear that the unique functional role of each sphincter in the GI tract is accompanied by a unique combination of contractile mechanisms.
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Keef KD, Cobine CA. Control of Motility in the Internal Anal Sphincter. J Neurogastroenterol Motil 2019; 25:189-204. [PMID: 30827084 PMCID: PMC6474703 DOI: 10.5056/jnm18172] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Revised: 11/28/2018] [Accepted: 12/09/2018] [Indexed: 12/14/2022] Open
Abstract
The internal anal sphincter (IAS) plays an important role in the maintenance of fecal continence since it generates tone and is responsible for > 70% of resting anal pressure. During normal defecation the IAS relaxes. Historically, tone generation in gastrointestinal muscles was attributed to mechanisms arising directly from smooth muscle cells, ie, myogenic activity. However, slow waves are now known to play a fundamental role in regulating gastrointestinal motility and these electrical events are generated by the interstitial cells of Cajal. Recently, interstitial cells of Cajal, as well as slow waves, have also been identified in the IAS making them viable candidates for tone generation. In this review we discuss four different mechanisms that likely contribute to tone generation in the IAS. Three of these involve membrane potential, L-type Ca2+ channels and electromechanical coupling (ie, summation of asynchronous phasic activity, partial tetanus, and window current), whereas the fourth involves the regulation of myofilament Ca2+ sensitivity. Contractile activity in the IAS is also modulated by sympathetic motor neurons that significantly increase tone and anal pressure, as well as inhibitory motor neurons (particularly nitrergic and vasoactive intestinal peptidergic) that abolish contraction and assist with normal defecation. Alterations in IAS motility are associated with disorders such as fecal incontinence and anal fissures that significantly decrease the quality of life. Understanding in greater detail how tone is regulated in the IAS is important for developing more effective treatment strategies for these debilitating defecation disorders.
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Affiliation(s)
- Kathleen D Keef
- Department of Physiology and Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV, USA
| | - Caroline A Cobine
- Department of Physiology and Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV, USA
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Sanders KM. Spontaneous Electrical Activity and Rhythmicity in Gastrointestinal Smooth Muscles. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1124:3-46. [PMID: 31183821 PMCID: PMC7035145 DOI: 10.1007/978-981-13-5895-1_1] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The gastrointestinal (GI) tract has multifold tasks of ingesting, processing, and assimilating nutrients and disposing of wastes at appropriate times. These tasks are facilitated by several stereotypical motor patterns that build upon the intrinsic rhythmicity of the smooth muscles that generate phasic contractions in many regions of the gut. Phasic contractions result from a cyclical depolarization/repolarization cycle, known as electrical slow waves, which result from intrinsic pacemaker activity. Interstitial cells of Cajal (ICC) are electrically coupled to smooth muscle cells (SMCs) and generate and propagate pacemaker activity and slow waves. The mechanism of slow waves is dependent upon specialized conductances expressed by pacemaker ICC. The primary conductances responsible for slow waves in mice are Ano1, Ca2+-activated Cl- channels (CaCCs), and CaV3.2, T-type, voltage-dependent Ca2+ channels. Release of Ca2+ from intracellular stores in ICC appears to be the initiator of pacemaker depolarizations, activation of T-type current provides voltage-dependent Ca2+ entry into ICC, as slow waves propagate through ICC networks, and Ca2+-induced Ca2+ release and activation of Ano1 in ICC amplifies slow wave depolarizations. Slow waves conduct to coupled SMCs, and depolarization elicited by these events enhances the open-probability of L-type voltage-dependent Ca2+ channels, promotes Ca2+ entry, and initiates contraction. Phasic contractions timed by the occurrence of slow waves provide the basis for motility patterns such as gastric peristalsis and segmentation. This chapter discusses the properties of ICC and proposed mechanism of electrical rhythmicity in GI muscles.
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Affiliation(s)
- Kenton M Sanders
- Department of Physiology and Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV, USA.
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Drumm BT, Sung TS, Zheng H, Baker SA, Koh SD, Sanders KM. The effects of mitochondrial inhibitors on Ca 2+ signalling and electrical conductances required for pacemaking in interstitial cells of Cajal in the mouse small intestine. Cell Calcium 2018; 72:1-17. [PMID: 29748128 DOI: 10.1016/j.ceca.2018.01.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2017] [Revised: 01/26/2018] [Accepted: 01/27/2018] [Indexed: 01/16/2023]
Abstract
Interstitial cells of Cajal (ICC-MY) are pacemakers that generate and propagate electrical slow waves in gastrointestinal (GI) muscles. Slow waves appear to be generated by the release of Ca2+ from intracellular stores and activation of Ca2+-activated Cl- channels (Ano1). Conduction of slow waves to smooth muscle cells coordinates rhythmic contractions. Mitochondrial Ca2+ handling is currently thought to be critical for ICC pacemaking. Protonophores, inhibitors of the electron transport chain (FCCP, CCCP or antimycin) or mitochondrial Na+/Ca2+ exchange blockers inhibited slow waves in several GI muscles. Here we utilized Ca2+ imaging of ICC in small intestinal muscles in situ to determine the effects of mitochondrial drugs on Ca2+ transients in ICC. Muscles were obtained from mice expressing a genetically encoded Ca2+ indicator (GCaMP3) in ICC. FCCP, CCCP, antimycin, a uniporter blocker, Ru360, and a mitochondrial Na+/Ca2+ exchange inhibitor, CGP-37157 inhibited Ca2+ transients in ICC-MY. Effects were not due to depletion of ATP, as oligomycin did not affect Ca2+ transients. Patch-clamp experiments were performed to test the effects of the mitochondrial drugs on key pacemaker conductances, Ano1 and T-type Ca2+ (CaV3.2), in HEK293 cells. Antimycin blocked Ano1 and reduced CaV3.2 currents. CCCP blocked CaV3.2 current but did not affect Ano1 current. Ano1 and Cav3.2 currents were inhibited by CGP-37157. Inhibitory effects of mitochondrial drugs on slow waves and Ca2+ signalling in ICC can be explained by direct antagonism of key pacemaker conductances in ICC that generate and propagate slow waves. A direct obligatory role for mitochondria in pacemaker activity is therefore questionable.
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Affiliation(s)
- Bernard T Drumm
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV 89557, USA
| | - Tae S Sung
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV 89557, USA
| | - Haifeng Zheng
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV 89557, USA
| | - Salah A Baker
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV 89557, USA
| | - Sang D Koh
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV 89557, USA
| | - Kenton M Sanders
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV 89557, USA.
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Drumm BT, Hennig GW, Battersby MJ, Cunningham EK, Sung TS, Ward SM, Sanders KM, Baker SA. Clustering of Ca 2+ transients in interstitial cells of Cajal defines slow wave duration. J Gen Physiol 2017; 149:703-725. [PMID: 28592421 PMCID: PMC5496507 DOI: 10.1085/jgp.201711771] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2016] [Accepted: 05/02/2017] [Indexed: 12/13/2022] Open
Abstract
Electrical slow waves in the small intestine are generated by pacemaker cells called interstitial cells of Cajal. Drumm et al. record clusters of Ca2+ transients in these cells that are entrained by voltage-dependent Ca2+ entry and which define the duration of the electrical slow waves. Interstitial cells of Cajal (ICC) in the myenteric plexus region (ICC-MY) of the small intestine are pacemakers that generate rhythmic depolarizations known as slow waves. Slow waves depend on activation of Ca2+-activated Cl− channels (ANO1) in ICC, propagate actively within networks of ICC-MY, and conduct to smooth muscle cells where they generate action potentials and phasic contractions. Thus, mechanisms of Ca2+ regulation in ICC are fundamental to the motor patterns of the bowel. Here, we characterize the nature of Ca2+ transients in ICC-MY within intact muscles, using mice expressing a genetically encoded Ca2+ sensor, GCaMP3, in ICC. Ca2+ transients in ICC-MY display a complex firing pattern caused by localized Ca2+ release events arising from multiple sites in cell somata and processes. Ca2+ transients are clustered within the time course of slow waves but fire asynchronously during these clusters. The durations of Ca2+ transient clusters (CTCs) correspond to slow wave durations (plateau phase). Simultaneous imaging and intracellular electrical recordings revealed that the upstroke depolarization of slow waves precedes clusters of Ca2+ transients. Summation of CTCs results in relatively uniform Ca2+ responses from one slow wave to another. These Ca2+ transients are caused by Ca2+ release from intracellular stores and depend on ryanodine receptors as well as amplification from IP3 receptors. Reduced extracellular Ca2+ concentrations and T-type Ca2+ channel blockers decreased the number of firing sites and firing probability of Ca2+ transients. In summary, the fundamental electrical events of small intestinal muscles generated by ICC-MY depend on asynchronous firing of Ca2+ transients from multiple intracellular release sites. These events are organized into clusters by Ca2+ influx through T-type Ca2+ channels to sustain activation of ANO1 channels and generate the plateau phase of slow waves.
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Affiliation(s)
- Bernard T Drumm
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV
| | - Grant W Hennig
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV
| | - Matthew J Battersby
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV
| | - Erin K Cunningham
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV
| | - Tae Sik Sung
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV
| | - Sean M Ward
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV
| | - Kenton M Sanders
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV
| | - Salah A Baker
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV
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Mitsui R, Hashitani H. Properties of synchronous spontaneous Ca 2+ transients in the mural cells of rat rectal arterioles. Pflugers Arch 2017; 469:1189-1202. [PMID: 28429070 DOI: 10.1007/s00424-017-1978-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2017] [Revised: 03/20/2017] [Accepted: 04/05/2017] [Indexed: 10/19/2022]
Abstract
Synchrony of spontaneous Ca2+ transients among venular mural cells (smooth muscle cells and pericytes) in visceral organs relies on the intercellular spread of L-type voltage-dependent Ca2+ channel (LVDCC)-dependent depolarisations. However, the mechanisms underlying the synchrony of spontaneous Ca2+ transients between arteriolar mural cells are less understood. The spontaneous intracellular Ca2+ dynamics of arteriolar mural cells in the rat rectal submucosa were visualised by Cal-520 Ca2+ imaging to analyse their synchrony. The mural cells in fine arterioles that had a rounded cell body with several extended processes developed spontaneous 'synchronous' Ca2+ transients arising from Ca2+ released from sarcoendoplasmic reticulum Ca2+ stores. Gap junction blockers (3 μM carbenoxolone, 10 μM 18β-glycyrrhetinic acid), a Ca2+-activated Cl- channel (CaCC) blocker (100 μM 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid) or lowering extracellular Cl- concentration (from 134.4 to 12.4 mM) disrupted the synchrony of Ca2+ transients between arteriolar mural cells. Blockers of T-type voltage-dependent Ca2+ channels (TVDCCs, 1 μM mibefradil or ML218) or LVDCCs (1 μM nifedipine) reduced the Ca2+ transient frequency or their area under curve (AUC), respectively. However, neither TVDCC nor LVDCC blockers disrupted the synchrony of Ca2+ transients among arteriolar mural cells. This is in contrast with rectal venules in which nifedipine disrupted the synchrony of spontaneous Ca2+ transients. Thus, spontaneous transient depolarisations arising from the opening of CaCCs may effectively spread to neighbouring arteriolar mural cells via gap junctions to maintain the Ca2+ transient synchrony. Activation of TVDCCs appears to accelerate spontaneous Ca2+ transients, while LVDCCs predominantly contribute to the duration of Ca2+ transients.
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Affiliation(s)
- Retsu Mitsui
- Department of Cell Physiology, Nagoya City University Graduate School of Medical Sciences, 1, Kawasumi, Mizuho-cho, Mizuho-Ku, Nagoya, 467-8601, Japan.
| | - Hikaru Hashitani
- Department of Cell Physiology, Nagoya City University Graduate School of Medical Sciences, 1, Kawasumi, Mizuho-cho, Mizuho-Ku, Nagoya, 467-8601, Japan
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Sanders KM, Kito Y, Hwang SJ, Ward SM. Regulation of Gastrointestinal Smooth Muscle Function by Interstitial Cells. Physiology (Bethesda) 2017; 31:316-26. [PMID: 27488743 DOI: 10.1152/physiol.00006.2016] [Citation(s) in RCA: 72] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Interstitial cells of mesenchymal origin form gap junctions with smooth muscle cells in visceral smooth muscles and provide important regulatory functions. In gastrointestinal (GI) muscles, there are two distinct classes of interstitial cells, c-Kit(+) interstitial cells of Cajal and PDGFRα(+) cells, that regulate motility patterns. Loss of these cells may contribute to symptoms in GI motility disorders.
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Affiliation(s)
- Kenton M Sanders
- Department of Physiology and Cell Biology, University of Nevada Reno School of Medicine, Reno, Nevada; and
| | - Yoshihiko Kito
- Department of Pharmacology, Faculty of Medicine, Saga University, Nabeshima, Japan
| | - Sung Jin Hwang
- Department of Physiology and Cell Biology, University of Nevada Reno School of Medicine, Reno, Nevada; and
| | - Sean M Ward
- Department of Physiology and Cell Biology, University of Nevada Reno School of Medicine, Reno, Nevada; and
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Zhu MH, Sung TS, Kurahashi M, O'Kane LE, O'Driscoll K, Koh SD, Sanders KM. Na+-K+-Cl- cotransporter (NKCC) maintains the chloride gradient to sustain pacemaker activity in interstitial cells of Cajal. Am J Physiol Gastrointest Liver Physiol 2016; 311:G1037-G1046. [PMID: 27742704 PMCID: PMC5206290 DOI: 10.1152/ajpgi.00277.2016] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/02/2016] [Accepted: 10/11/2016] [Indexed: 01/31/2023]
Abstract
Interstitial cells of Cajal (ICC) generate electrical slow waves by coordinated openings of ANO1 channels, a Ca2+-activated Cl- (CaCC) conductance. Efflux of Cl- during slow waves must be significant, as there is high current density during slow-wave currents and slow waves are of sufficient magnitude to depolarize the syncytium of smooth muscle cells and PDGFRα+ cells to which they are electrically coupled. We investigated how the driving force for Cl- current is maintained in ICC. We found robust expression of Slc12a2 (which encodes an Na+-K+-Cl- cotransporter, NKCC1) and immunohistochemical confirmation that NKCC1 is expressed in ICC. With the use of the gramicidin permeabilized-patch technique, which is reported to not disturb [Cl-]i, the reversal potential for spontaneous transient inward currents (ESTICs) was -10.5 mV. This value corresponds to the peak of slow waves when they are recorded directly from ICC in situ. Inhibition of NKCC1 with bumetanide shifted ESTICs to more negative potentials within a few minutes and reduced pacemaker activity. Bumetanide had no direct effects on ANO1 or CaV3.2 channels expressed in HEK293 cells or L-type Ca2+ currents. Reducing extracellular Cl- to 10 mM shifted ESTICs to positive potentials as predicted by the Nernst equation. The relatively rapid shift in ESTICs when NKCC1 was blocked suggests that significant changes in the transmembrane Cl- gradient occur during the slow-wave cycle, possibly within microdomains formed between endoplasmic reticulum and the plasma membrane in ICC. Recovery of Cl- via NKCC1 might have additional consequences on shaping the waveforms of slow waves via Na+ entry into microdomains.
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Affiliation(s)
- Mei Hong Zhu
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada
| | - Tae Sik Sung
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada
| | - Masaaki Kurahashi
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada
| | - Lauren E. O'Kane
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada
| | - Kate O'Driscoll
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada
| | - Sang Don Koh
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada
| | - Kenton M. Sanders
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada
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Problems with extracellular recording of electrical activity in gastrointestinal muscle. Nat Rev Gastroenterol Hepatol 2016; 13:731-741. [PMID: 27756919 PMCID: PMC8325940 DOI: 10.1038/nrgastro.2016.161] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Motility patterns of the gastrointestinal tract are important for efficient processing of nutrients and waste. Peristalsis and segmentation are based on rhythmic electrical slow waves that generate the phasic contractions fundamental to gastrointestinal motility. Slow waves are generated and propagated actively by interstitial cells of Cajal (ICC), and these events conduct to smooth muscle cells to elicit excitation-contraction coupling. Extracellular electrical recording has been utilized to characterize slow-wave generation and propagation and abnormalities that might be responsible for gastrointestinal motility disorders. Electrode array recording and digital processing are being used to generate data for models of electrical propagation in normal and pathophysiological conditions. Here, we discuss techniques of extracellular recording as applied to gastrointestinal organs and how mechanical artefacts might contaminate these recordings and confound their interpretation. Without rigorous controls for movement, current interpretations of extracellular recordings might ascribe inaccurate behaviours and electrical anomalies to ICC networks and gastrointestinal muscles, bringing into question the findings and validity of models of gastrointestinal electrophysiology developed from these recordings.
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