1
|
Kondo R, Furukawa N, Deguchi A, Kawata N, Suzuki Y, Imaizumi Y, Yamamura H. Downregulation of Ca 2+-Activated Cl - Channel TMEM16A Mediated by Angiotensin II in Cirrhotic Portal Hypertensive Mice. Front Pharmacol 2022; 13:831311. [PMID: 35370660 PMCID: PMC8966666 DOI: 10.3389/fphar.2022.831311] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2021] [Accepted: 03/01/2022] [Indexed: 12/29/2022] Open
Abstract
Portal hypertension is defined as an increased pressure in the portal venous system and occurs as a major complication in chronic liver diseases. The pathological mechanism underlying the pathogenesis and development of portal hypertension has been extensively investigated. Vascular tone of portal vein smooth muscles (PVSMs) is regulated by the activities of several ion channels, including Ca2+-activated Cl- (ClCa) channels. TMEM16A is mainly responsible for ClCa channel conductance in vascular smooth muscle cells, including portal vein smooth muscle cells (PVSMCs). In the present study, the functional roles of TMEM16A channels were examined using two experimental portal hypertensive models, bile duct ligation (BDL) mice with cirrhotic portal hypertension and partial portal vein ligation (PPVL) mice with non-cirrhotic portal hypertension. Expression analyses revealed that the expression of TMEM16A was downregulated in BDL-PVSMs, but not in PPVL-PVSMs. Whole-cell ClCa currents were smaller in BDL-PVSMCs than in sham- and PPVL-PVSMCs. The amplitude of spontaneous contractions was smaller and the frequency was higher in BDL-PVSMs than in sham- and PPVL-PVSMs. Spontaneous contractions sensitive to a specific inhibitor of TMEM16A channels, T16Ainh-A01, were reduced in BDL-PVSMs. Furthermore, in normal PVSMs, the downregulation of TMEM16A expression was mimicked by the exposure to angiotensin II, but not to bilirubin. This study suggests that the activity of ClCa channels is attenuated by the downregulation of TMEM16A expression in PVSMCs associated with cirrhotic portal hypertension, which is partly mediated by increased angiotensin II in cirrhosis.
Collapse
Affiliation(s)
- Rubii Kondo
- Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan
| | - Nami Furukawa
- Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan
| | - Akari Deguchi
- Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan
| | - Naoki Kawata
- Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan
| | - Yoshiaki Suzuki
- Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan
| | - Yuji Imaizumi
- Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan
| | - Hisao Yamamura
- Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan
| |
Collapse
|
2
|
Dam VS, Boedtkjer DMB, Aalkjaer C, Matchkov V. The bestrophin- and TMEM16A-associated Ca(2+)- activated Cl(–) channels in vascular smooth muscles. Channels (Austin) 2015; 8:361-9. [PMID: 25478625 PMCID: PMC4203738 DOI: 10.4161/chan.29531] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The presence of Ca2+-activated Cl– currents (ICl(Ca)) in vascular smooth muscle cells (VSMCs) is well established. ICl(Ca) are supposedly important for arterial contraction by linking changes in [Ca2+]i and membrane depolarization. Bestrophins and some members of the TMEM16 protein family were recently associated with ICl(Ca). Two distinct ICl(Ca) are characterized in VSMCs; the cGMP-dependent ICl(Ca) dependent upon bestrophin expression and the ‘classical’ Ca2+-activated Cl– current, which is bestrophin-independent. Interestingly, TMEM16A is essential for both the cGMP-dependent and the classical ICl(Ca). Furthermore, TMEM16A has a role in arterial contraction while bestrophins do not. TMEM16A’s role in the contractile response cannot be explained however only by a simple suppression of the depolarization by Cl– channels. It is suggested that TMEM16A expression modulates voltage-gated Ca2+ influx in a voltage-independent manner and recent studies also demonstrate a complex role of TMEM16A in modulating other membrane proteins.
Collapse
|
3
|
Dam VS, Boedtkjer DMB, Nyvad J, Aalkjaer C, Matchkov V. TMEM16A knockdown abrogates two different Ca(2+)-activated Cl (-) currents and contractility of smooth muscle in rat mesenteric small arteries. Pflugers Arch 2013; 466:1391-409. [PMID: 24162234 PMCID: PMC4062836 DOI: 10.1007/s00424-013-1382-1] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2013] [Revised: 10/10/2013] [Accepted: 10/10/2013] [Indexed: 12/30/2022]
Abstract
The presence of Ca2+-activated Cl− channels (CaCCs) in vascular smooth muscle cells (SMCs) is well established. Their molecular identity is, however, elusive. Two distinct Ca2+-activated Cl− currents (ICl(Ca)) were previously characterized in SMCs. We have shown that the cGMP-dependent ICl(Ca) depends on bestrophin expression, while the “classical” ICl(Ca) is not. Downregulation of bestrophins did not affect arterial contraction but inhibited the rhythmic contractions, vasomotion. In this study, we have used in vivo siRNA transfection of rat mesenteric small arteries to investigate the role of a putative CaCC, TMEM16A. Isometric force, [Ca2+]i, and SMC membrane potential were measured in isolated arterial segments. ICl(Ca) and GTPγS-induced nonselective cation current were measured in isolated SMCs. Downregulation of TMEM16A resulted in inhibition of both the cGMP-dependent ICl(Ca) and the “classical” ICl(Ca) in SMCs. TMEM16A downregulation also reduced expression of bestrophins. TMEM16A downregulation suppressed vasomotion both in vivo and in vitro. Downregulation of TMEM16A reduced agonist (noradrenaline and vasopressin) and K+-induced contractions. In accordance with the depolarizing role of CaCCs, TMEM16A downregulation suppressed agonist-induced depolarization and elevation in [Ca2+]i. Surprisingly, K+-induced depolarization was unchanged but Ca2+ entry was reduced. We suggested that this is due to reduced expression of the L-type Ca2+ channels, as observed at the mRNA level. Thus, the importance of TMEM16A for contraction is, at least in part, independent from membrane potential. This study demonstrates the significance of TMEM16A for two SMCs ICl(Ca) and vascular function and suggests an interaction between TMEM16A and L-type Ca2+ channels.
Collapse
Affiliation(s)
- Vibeke Secher Dam
- Department of Biomedicine, MEMBRANES, Aarhus University, Ole Worms Alle bygn.4, 1163, Aarhus, C 8000, Denmark
| | | | | | | | | |
Collapse
|
4
|
Matchkov VV, Secher Dam V, Bødtkjer DMB, Aalkjær C. Transport and Function of Chloride in Vascular Smooth Muscles. J Vasc Res 2013; 50:69-87. [DOI: 10.1159/000345242] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2012] [Accepted: 10/16/2012] [Indexed: 12/12/2022] Open
|
5
|
Bautista-Cruz F, Paterson WG. Evidence for altered circular smooth muscle cell function in lower esophageal sphincter of W/Wv mutant mice. Am J Physiol Gastrointest Liver Physiol 2011; 301:G1059-65. [PMID: 21885685 DOI: 10.1152/ajpgi.00020.2011] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Nitrergic neurotransmission to gut smooth muscle is impaired in W/W(v) mutant mice, which lack intramuscular interstitial cells of Cajal (ICC-IM). In addition, these mice have been reported to have smaller amplitude unitary potentials (UPs) and a more negative resting membrane potential (RMP) than control mice. These abnormalities have been attributed to absence of ICC-IM, but it remains possible that they are due to alterations at the level of the smooth muscle itself. Amphotericin-B-perforated patch-clamp recordings and Ca(2+) imaging (fura 2) were compared between freshly isolated single circular smooth muscle cells (CSM) from W/W(v) mutant and control mice lower esophageal sphincter (LES). There was no significant difference in seal resistance, capacitance, or input resistance in response to applied electrotonic current pulses between CSM cells from W/W(v) mutants and controls. Compared with control mice, RMP was more negative and UPs significantly smaller in CSM cells from mutant mice LES. Administration of caffeine induced an inward current in cells from both mutant and control mice, but the current density was significantly larger in cells from W/W(v) mutants. Membrane potential hyperpolarization induced by sodium nitroprusside was larger in cells from control mice vs. W/W(v) mutants. In addition, intracellular Ca(2+) transients induced by caffeine were significantly increased in cells from mutants. These findings indicate that LES CSM is abnormal in W/W(v) mutant mice. Thus some physiological functions attributed to ICC-IM based on experiments in smooth muscle of ICC deficient mice may need to be reconsidered.
Collapse
Affiliation(s)
- Francisco Bautista-Cruz
- Gastrointestinal Diseases Research Unit, Kingston General Hospital, Department of Medicine, Queen's University Kingston, Ontario, Canada
| | | |
Collapse
|
6
|
Patel AC, Brett TJ, Holtzman MJ. The role of CLCA proteins in inflammatory airway disease. Annu Rev Physiol 2009; 71:425-49. [PMID: 18954282 DOI: 10.1146/annurev.physiol.010908.163253] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Inflammatory airway diseases such as asthma and chronic obstructive pulmonary disease (COPD) exhibit stereotyped traits that are variably expressed in each person. In experimental mouse models of chronic lung disease, these individual disease traits can be genetically segregated and thereby linked to distinct determinants. Functional genomic analysis indicates that at least one of these traits, mucous cell metaplasia, depends on members of the calcium-activated chloride channel (CLCA) gene family. Here we review advances in the biochemistry of the CLCA family and the evidence of a role for CLCA family members in the development of mucous cell metaplasia and possibly airway hyperreactivity in experimental models and in humans. On the basis of this information, we develop the model that CLCA proteins are not integral membrane proteins with ion channel function but instead are secreted signaling molecules that specifically regulate airway target cells in healthy and disease conditions.
Collapse
Affiliation(s)
- Anand C Patel
- Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri 63110, USA
| | | | | |
Collapse
|
7
|
Burt RP. Depletion of Ca2+ from intracellular stores potentiates spontaneous contractions of the rat portal vein. Eur J Pharmacol 2005; 496:109-18. [PMID: 15288582 DOI: 10.1016/j.ejphar.2004.05.032] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2004] [Revised: 04/02/2004] [Accepted: 05/20/2004] [Indexed: 10/26/2022]
Abstract
Spontaneous contractions of the rat portal vein were potentiated in magnitude by phenylephrine, cyclopiazonic acid, ryanodine or caffeine. All these drugs can deplete Ca2+ from intracellular stores, which stimulates store-operated cation entry in some tissues. The possibility that depletion of Ca2+ from intracellular stores potentiates the spontaneous contractions was therefore investigated using functional experiments. Phenylephrine or cyclopiazonic acid was added to tissues in Ca2+-free Krebs solution, followed by a 30-min washout. After addition of extracellular Ca2+, the spontaneous contractions were potentiated. This showed the stimulus for potentiating the contractions remained so long as intracellular Ca2+ stores were depleted. Following phenylephrine washout in normal Krebs solution, potentiation of the spontaneous contractions was attenuated with time. This attenuation was abolished by the protein kinase C inhibitor calphostin C. These results show depletion of Ca2+ from intracellular stores potentiates spontaneous contractions of the portal vein. Protein kinase C may inhibit this mechanism.
Collapse
Affiliation(s)
- Richard P Burt
- Department of Pharmacology, University College London, Gower Street, London WC1E 6BT, UK.
| |
Collapse
|
8
|
Saleh SN, Greenwood IA. Activation of chloride currents in murine portal vein smooth muscle cells by membrane depolarization involves intracellular calcium release. Am J Physiol Cell Physiol 2005; 288:C122-31. [PMID: 15355851 DOI: 10.1152/ajpcell.00384.2004] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The present study describes the first characterization of Ca2+-activated Cl− currents ( IClCa) in single smooth muscle cells from a murine vascular preparation (portal veins). IClCa was recorded using the perforated patch version of the whole cell voltage-clamp technique and was evoked using membrane depolarization. Generation of IClCa relied on Ca2+ entry through dihydropyridine-sensitive Ca2+ channels because IClCa was abolished by 1 μM nicardipine and enhanced by raising external Ca2+ concentration or by application of BAY K 8644. IClCa was characterized by the sensitivity to Cl− channel blockers and the effect of altering the external anion on reversal potential. Activation of IClCa after membrane depolarization was dependent on Ca2+ release from intracellular stores. Thus the amplitude of IClCa was diminished by the SR-ATPase inhibitor cyclopiazonic acid, the inositol 1,4,5-trisphosphate receptor antagonist 2-aminoethoxydiphenyl borate (2-APB), and the ryanodine receptor blocker tetracaine. The degree of inhibition produced by the application of 2-APB and tetracaine together was significantly greater than the effect of each agent applied alone. In current-clamp mode, injection of depolarizing current elicited a biphasic action potential, with the later depolarization being sensitive to niflumic acid (NFA; 10 μM). In isometric tension recordings, NFA inhibited spontaneous contractions. These data support a role for this conductance in portal vein excitability.
Collapse
Affiliation(s)
- Sohag N Saleh
- Department of Basic Medical Sciences, Pharmacology and Clinical Pharmacology, St. George's Hospital Medical School, London, United Kingdom
| | | |
Collapse
|
9
|
Matchkov VV, Aalkjaer C, Nilsson H. A cyclic GMP-dependent calcium-activated chloride current in smooth-muscle cells from rat mesenteric resistance arteries. J Gen Physiol 2004; 123:121-34. [PMID: 14718479 PMCID: PMC2217427 DOI: 10.1085/jgp.200308972] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2003] [Accepted: 12/29/2003] [Indexed: 11/24/2022] Open
Abstract
We have previously demonstrated the presence of a cyclic GMP (cGMP)-dependent calcium-activated inward current in vascular smooth-muscle cells, and suggested this to be of importance in synchronizing smooth-muscle contraction. Here we demonstrate the characteristics of this current. Using conventional patch-clamp technique, whole-cell currents were evoked in freshly isolated smooth-muscle cells from rat mesenteric resistance arteries by elevation of intracellular calcium with either 10 mM caffeine, 1 microM BAY K8644, 0.4 microM ionomycin, or by high calcium concentration (900 nM) in the pipette solution. The current was found to be a calcium-activated chloride current with an absolute requirement for cyclic GMP (EC50 6.4 microM). The current could be activated by the constitutively active subunit of PKG. Current activation was blocked by the protein kinase G antagonist Rp-8-Br-PET-cGMP or with a peptide inhibitor of PKG, or with the nonhydrolysable ATP analogue AMP-PNP. Under biionic conditions, the anion permeability sequence of the channel was SCN- > Br- > I- > Cl- > acetate > F- >> aspartate, but the conductance sequence was I- > Br- > Cl- > acetate > F- > aspartate = SCN-. The current had no voltage or time dependence. It was inhibited by nickel and zinc ions in the micromolar range, but was unaffected by cobalt and had a low sensitivity to inhibition by the chloride channel blockers niflumic acid, DIDS, and IAA-94. The properties of this current in mesenteric artery smooth-muscle cells differed from those of the calcium-activated chloride current in pulmonary myocytes, which was cGMP-independent, exhibited a high sensitivity to inhibition by niflumic acid, was unaffected by zinc ions, and showed outward current rectification as has previously been reported for this current. Under conditions of high calcium in the patch-pipette solution, a current similar to the latter could be identified also in the mesenteric artery smooth-muscle cells. We conclude that smooth-muscle cells from rat mesenteric resistance arteries have a novel cGMP-dependent calcium-activated chloride current, which is activated by intracellular calcium release and which has characteristics distinct from other calcium-activated chloride currents.
Collapse
Affiliation(s)
- Vladimir V Matchkov
- The Water and Salt Research Center and Department of Physiology, University of Aarhus, Aarhus, Denmark.
| | | | | |
Collapse
|
10
|
Steendahl J, Holstein-Rathlou NH, Sorensen CM, Salomonsson M. Effects of chloride channel blockers on rat renal vascular responses to angiotensin II and norepinephrine. Am J Physiol Renal Physiol 2004; 286:F323-30. [PMID: 14506073 DOI: 10.1152/ajprenal.00017.2003] [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: 11/22/2022] Open
Abstract
The aim of the present study was to investigate the role of Ca2+-activated Cl-channels in the renal vasoconstriction elicited by angiotensin II (ANG II) and norepinephrine (NE). Renal blood flow (RBF) was measured in vivo using electromagnetic flowmetry. Ratiometric photometry of fura 2 fluorescence was used to estimate intracellular free Ca2+concentration ([Ca2+]i) in isolated preglomerular vessels from rat kidneys. Renal arterial injection of ANG II (2-4 ng) and NE (20-40 ng) produced a transient decrease in RBF. Administration of ANG II (10-7M) and NE (5 × 10-6M) to the isolated preglomerular vessels caused a prompt increase in [Ca2+]i. Renal preinfusion of DIDS (0.6 and 1.25 μmol/min) attenuated the ANG II-induced vasoconstriction to ∼35% of the control response, whereas the effects of NE were unaltered. Niflumic acid (0.14 and 0.28 μmol/min) and 2-[(2-cyclopentenyl-6,7-dichloro-2,3-dihydro-2-methyl-1-oxo-1 H-inden-5-yl)oxy]acetic acid (IAA-94; 0.045 and 0.09 μmol/min) did not affect the vasoconstrictive responses of these compounds. Pretreatment with niflumic acid (50 μM) or IAA-94 (30 μM) for 2 min decreased baseline [Ca2+]ibut did not change the magnitude of the [Ca2+]iresponse to ANG II and NE in the isolated vessels. The present results do not support the hypothesis that Ca2+-activated Cl-channels play a crucial role in the hemodynamic effects of ANG II and NE in rat renal vasculature.
Collapse
Affiliation(s)
- Joen Steendahl
- Division of Renal and Cardiobascular Research, Department of Medical Physiology, The Panum Institute, University of Copenhagen, DK-2200 Copenhagen N, Denmark
| | | | | | | |
Collapse
|
11
|
Jones K, Shmygol A, Kupittayanant S, Wray S. Electrophysiological characterization and functional importance of calcium-activated chloride channel in rat uterine myocytes. Pflugers Arch 2004; 448:36-43. [PMID: 14740218 DOI: 10.1007/s00424-003-1224-7] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2003] [Accepted: 12/01/2003] [Indexed: 10/26/2022]
Abstract
In order to better understand the mechanisms underlying excitation of the uterus, we have elucidated the characteristics and functional importance of Ca(2+)-activated Cl(-) currents ( I(Cl-Ca)) in pregnant rat myometrium. In 101/320 freshly isolated myocytes, there was a slowly inactivating tail current (162+/-48 pA) upon repolarization following depolarising steps. This current has a reversal potential close to that for chloride, and was shifted when [Cl(-)] was altered. It was activated by Ca(2+) (but not Ba(2+)) entry through L-type Ca(2+) channels, enhanced by the Ca(2+) channel agonist Bay K8644 (2 microM), and inhibited by the Cl(-) channel blockers, niflumic acid (10 microM) and anthracene-9-carboxylic acid (9-AC, 100 microM). We therefore conclude that the pregnant rat myometrium contains Ca(2+)-activated Cl(-) channels producing inward current in ~30% of its cells. When these channels were inhibited by niflumic acid or 9-AC in intact tissues, the frequency of spontaneous contractions, was significantly reduced. Niflumic acid was also shown to inhibit oxytocin-induced contractions and Ca(2+) transients. Neither 9-AC nor niflumic acid had any effect on high-K-invoked contractions. Taken together these data suggest that Ca(2+)-activated Cl(-) channels are activated by Ca(2+) entry and play a functionally important role in myometrium, probably by contributing to membrane potential and firing frequency (pacemakers) in these cells.
Collapse
Affiliation(s)
- K Jones
- Department of Physiology, The University of Liverpool, Liverpool, L69 3BX, UK
| | | | | | | |
Collapse
|
12
|
Lee HM, Kim HI, Shin YK, Lee CS, Park M, Song JH. Diclofenac inhibition of sodium currents in rat dorsal root ganglion neurons. Brain Res 2003; 992:120-7. [PMID: 14604780 DOI: 10.1016/j.brainres.2003.08.048] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The effects of diclofenac, a nonsteroidal anti-inflammatory drug (NSAID), on the fast tetrodotoxin-sensitive (TTX-S) and the slow tetrodotoxin-resistant (TTX-R) sodium currents in rat dorsal root ganglion neurons were investigated using the whole-cell patch-clamp method. Diclofenac suppressed both sodium currents in a dose-dependent manner. The apparent dissociation constants for the diclofenac suppression of TTX-S and TTX-R sodium currents were estimated to be 14 and 97 microM, respectively, at a holding potential of -80 mV. Diclofenac had no effect on the kinetic parameters of the activation process in either type of sodium current. However, diclofenac produced shifts of the steady-state inactivation curves in the hyperpolarizing direction in both types of sodium currents in a dose-dependent manner. At sufficiently negative holding potentials, the inhibitory effects of diclofenac on both types of sodium currents were minimal. The results suggested that diclofenac might bind to sodium channels with a greater affinity when they are in the inactivated state than when they are in the resting state. Effects of other NSAIDs (acetylsalicylic acid, antipyrin, indomethacin and flufenamic acid) on sodium currents were tested. Among these, only flufenamic acid suppressed the sodium currents to a considerable extent. Thus, the chemical structure of each NSAID, not the inhibition of cyclooxygenase, seems to be an important determinant in the sodium current inhibition. The suppression of sodium currents in sensory neurons by diclofenac and flufenamic acid would contribute to their analgesic activity in addition to their inhibition of cyclooxygenase.
Collapse
Affiliation(s)
- Hyang Mi Lee
- Department of Pharmacology, Chung-Ang University, College of Medicine, 221 Heuk-Suk Dong, Dong-Jak Ku, Seoul 156-756, South Korea
| | | | | | | | | | | |
Collapse
|
13
|
Burt RP. Phasic contractions of the rat portal vein depend on intracellular Ca2+ release stimulated by depolarization. Am J Physiol Heart Circ Physiol 2003; 284:H1808-17. [PMID: 12586637 DOI: 10.1152/ajpheart.00637.2002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The phasic contraction to phenylephrine of the rat isolated portal vein was investigated using functional studies. Phasic contractions to phenylephrine and caffeine could be produced after several minutes in Ca(2+)-free Krebs solution, which were inhibited by cyclopiazonic acid or ryanodine. The phenylephrine and caffeine contractions were abolished, however, within 10 min in Ca(2+)-free Krebs solution and by nifedipine. This indicated the Ca(2+) stores were depleted in the absence of Ca(2+) influx through voltage-gated channels. The phasic contraction to phenylephrine was also abolished by niflumic acid even in Ca(2+)-free Krebs solution. This showed that the response depended on intracellular Ca(2+) release stimulated directly by depolarization, resulting from opening of Ca(2+)-activated Cl(-) channels, but did not require Ca(2+) influx. In support of this, K(+)-induced phasic contractions were also produced in Ca(2+)-free Krebs solution. The phenylephrine but not K(+)-induced phasic contractions in Ca(2+)-free Krebs solution were inhibited by ryanodine or cyclopiazonic acid. This would be consistent with Ca(2+) release from more superficial intracellular stores (affected most by these agents), probably by inositol 1,4,5-trisphospate, being required to stimulate the phenylephrine depolarization.
Collapse
Affiliation(s)
- Richard P Burt
- Department of Pharmacology, University College London, Gower Street, London WC1E 6BT, United Kingdom.
| |
Collapse
|
14
|
Zhang Y, Paterson WG. Role of Ca2+-activated Cl- channels and MLCK in slow IJP in opossum esophageal smooth muscle. Am J Physiol Gastrointest Liver Physiol 2002; 283:G104-14. [PMID: 12065297 DOI: 10.1152/ajpgi.00052.2002] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The possible contribution of Ca2+-activated Cl- channel [I(Cl(Ca))] and myosin light-chain kinase (MLCK) to nonadrenergic, noncholinergic slow inhibitory junction potentials (sIJP) was studied using conventional intracellular microelectrode recordings in circular smooth muscle of opossum esophageal body and guinea pig ileum perfused with Krebs solution containing atropine (3 microM), guanethidine (3 microM), and substance P (1 microM). In opossum esophageal circular smooth muscle, resting membrane potential (MP) was -51.9 +/- 0.7 mV (n = 89) with MP fluctuations of 1-3 mV. A single square-wave nerve stimulation of 0.5 ms duration and 80 V induced a sIJP with amplitude of 6.3 +/- 0.2 mV, half-amplitude duration of 635 +/- 19 ms, and rebound depolarization amplitude of 2.4 +/- 0.1 mV (n = 89). 9-Anthroic acid (A-9-C), niflumic acid (NFA), wortmannin, and 1-(5-chloronaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine (ML-9) abolished MP fluctuations, sIJP, and rebound depolarization in a concentration-dependent manner. A-9-C and NFA but not wortmannin and ML-9 hyperpolarized MP. In guinea pig ileal circular smooth muscle, nerve stimulation elicited an IJP composed of both fast (fIJP) and slow (sIJP) components, followed by rebound depolarization. NFA (200 microM) abolished sIJP and rebound depolarization but left the fIJP intact. These data suggest that in the tissues studied, activation of I(Cl(Ca)), which requires MLCK, contributes to resting MP, and that closing of I(Cl(Ca)) is responsible for sIJP.
Collapse
Affiliation(s)
- Yong Zhang
- Gastrointestinal Disease Research Unit and Departments of Medicine, Biology, and Physiology, Queen's University, Kingston, Ontario, Canada K7L 5G2
| | | |
Collapse
|
15
|
Pallone TL, Huang JMC. Control of descending vasa recta pericyte membrane potential by angiotensin II. Am J Physiol Renal Physiol 2002; 282:F1064-74. [PMID: 11997323 DOI: 10.1152/ajprenal.00306.2001] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Using nystatin perforated-patch whole cell recording, we investigated the role of Cl(-) conductance in the modulation of outer medullary descending vasa recta (OMDVR) pericyte membrane potential (Psi m) by ANG II. ANG II (10(-11) to 10(-7) M) consistently depolarized OMDVR and induced Psi m oscillations at lower concentrations. The Cl(-) channel blockers anthracene-9-decarboxylate (1 mM) and niflumic acid (10 microM) hyperpolarized resting pericytes and repolarized ANG II-treated pericytes. In voltage-clamp experiments, ANG II-treated pericytes exhibited slowly activating currents that were nearly eliminated by treatment with niflumic acid (10 microM) or removal of extracellular Ca(2+). Those currents reversed at -31 and -10 mV when extracellular Cl(-) concentration was 152 and 34 mM, respectively. In pericytes held at -70 mV, oscillating inward currents were sometimes observed; the reversal potential also shifted with extracellular Cl(-) concentration. We conclude that ANG II activates a Ca(2+)-dependent Cl(-) conductance in OMDVR pericytes to induce membrane depolarization and Psi m oscillations.
Collapse
Affiliation(s)
- Thomas L Pallone
- Division of Nephrology, School of Medicine, University of Maryland, Baltimore, Maryland 21201-1595, USA.
| | | |
Collapse
|
16
|
Criddle DN, Meireles A, Macêdo LB, Leal-Cardoso JH, Scarparo HC, Jaffar M. Comparative inhibitory effects of niflumic acid and novel synthetic derivatives on the rat isolated stomach fundus. J Pharm Pharmacol 2002; 54:283-8. [PMID: 11848293 DOI: 10.1211/0022357021778321] [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] [Indexed: 10/31/2022]
Abstract
Novel derivatives of 2-[3-(trifluoromethyl)-analino]nicotinic acid (niflumic acid) were synthesized. The compounds were compared for their inhibitory effects on 5-hydroxytryptamine (5-HT)- and KCI-induced contraction of the rat fundus. The aim was to assess structure-activity relationships regarding the selectivity and potency of these compounds. Niflumic acid (1-100 microM) concentration-dependently inhibited 5-HT-induced tonic contractions with an IC50 value (concentration reducing the control contractile response by 50%, calculated from semi-log graphs) of 0.24 x 10(4) M (n = 9). In contrast, it was significantly less potent at inhibiting KCl-induced responses (IC50 = 1.49 x 10(4) M, n = 9). The methyl ester (NFAme) and amido (NFAm) analogues showed no selectivity between 5-HT- and KCl-induced contractions with IC50 values of 1.64 x 10(-4) M (n = 8) and 1.87 x 10(-4) M (n = 9) for 5-HT responses, and 2.61 x 10(-4) M (n = 8) and 2.55 x 10(-4) M (n = 7) for KCl-induced responses, respectively. Our results suggest that alteration of the carboxylic acid moiety of niflumic acid reduces the selectivity and potency of its inhibitory action on 5-HT-induced contractile responses of the rat fundus, possibly via a reduced interaction with calcium-activated chloride channels.
Collapse
Affiliation(s)
- David N Criddle
- Departamento de Ciências Fisiológicas, CCS, Universidade Estadual do Ceará, Fortaleza, Brazil.
| | | | | | | | | | | |
Collapse
|
17
|
Jury J, Patel M, Bowes T, Daniel EE. Actions of putative chloride channel blocking agents on canine lower esophageal sphincter (LES). Can J Physiol Pharmacol 2001. [DOI: 10.1139/y01-086] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Niflumic acid (NA), a putative Cl-channel blocker, has provided pharmacological evidence that Cl-channel closures mediate hyperpolarization caused by NO in gastrointestinal smooth muscle. However, NA caused concentration- dependent relaxation of canine lower esophageal sphincter (LES) and failed to inhibit NO-mediated relaxations. DIDS also did not inhibit NO-mediated relaxations, but did abolish them when present with 20 mM TEA (tetraethyl ammonium ion), which was also ineffective alone. TEA reversed NA-induced relaxations, but with NA it did not inhibit NO-mediated relaxations. We investigated the modes of action of these agents further. Neither nerve-function block nor block of NOS activity affected the inhibition of LES tone by NA. In patch-clamp studies, NA increased outward currents from 30 to + 90 mV when [Ca2+]pipette was 50 nM. This was prevented by 20 mM TEA, but not by prior inhibition of NOS. At 200 nM [Ca2+]pipette, TEA markedly reduced outward currents, but did not prevent the increase from subsequent NA. In contrast, under similar conditions, application of DIDS after 20 mM TEA further reduced outward currents. When the patch pipette contained CsCl and TEA to block K+ currents, NA had no significant effect on currents between 50 and +90 mV. Thus, NA acted by opening K+ channels: some TEA-sensitive and some not. It had no detectable effect on currents when K+ channels were blocked. We conclude that NA is an unreliable pharmacological tool to evaluate Cl-channel contributions to smooth muscle function. DIDS did not open K+ channels. Decreases in outward currents from DIDS may result from inhibition of K+ currents or currents carried by Cl at depolarized membrane potentials.Key words: DIDS, niflumic acid, NO actions, smooth muscle.
Collapse
|
18
|
Wu SN, Jan CR, Chiang HT. Fenamates stimulate BKCa channel osteoblast-like MG-63 cells activity in the human. J Investig Med 2001; 49:522-33. [PMID: 11730088 DOI: 10.2310/6650.2001.33629] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
BACKGROUND The fenamates, a family of nonsteroidal anti-inflammatory drugs that are derivatives of N-phenylanthranilic acid, are the inhibitors of cyclo-oxygenase. The ionic mechanism of actions of these compounds in osteoblasts is not well understood. METHODS The effects of the fenamates on ionic currents were investigated in a human osteoblast-like cell line (MG-63) with the aid of the whole-cell and inside-out configurations of the patch-clamp technique. RESULTS In MG-63 cells, niflumic acid and meclofenamic acid increased K+ outward currents (IK). The niflumic acid-stimulated IK was reversed by subsequent application of iberiotoxin or paxilline, yet not by that of glibenclamide or apamin. In the inside-out configuration, niflumic acid (30 micromol/L) added to the bath did not modify single-channel conductance but increased the activity of large-conductance Ca2+-activated K+ (BKCa) channels. The EC50 values for niflumic acid- and meclofenamic acid-induced channel activity were 22 and 24 micromol/L, respectively. Niflumic acid (30 micromol/L) and meclofenamic acid (30 micromol/L) shifted the activation curve of BKCa channels to less positive membrane potentials. Membrane stretch potentiated niflumic acid-stimulated channel activity. The rank order of potency for the activation of BKCa channels in these cells was niflumic acid = meclofenamic acid > tolfenamic acid > flufenamic acid > nimesulide. Evans blue and nordihydroguaiaretic acid increased channel activity; however, indomethacin, piroxicam, and NS-398 had no effect on it. CONCLUSIONS The fenamates can stimulate BKCa channel activity in a manner that seems to be independent of the action of these drugs on the prostaglandin pathway. The activation of the BKCa channel may hyperpolarize the osteoblast, thereby modulating osteoblastic function.
Collapse
Affiliation(s)
- S N Wu
- Department of Medical Education and Research, Kaohsiung-Veterans General Hospital, Kaohsiung City, Taiwan, ROC.
| | | | | |
Collapse
|
19
|
Zhang Z, Huang JM, Turner MR, Rhinehart KL, Pallone TL. Role of chloride in constriction of descending vasa recta by angiotensin II. Am J Physiol Regul Integr Comp Physiol 2001; 280:R1878-86. [PMID: 11353695 DOI: 10.1152/ajpregu.2001.280.6.r1878] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We investigated the dependence of ANG II (10−8 M)-induced constriction of outer medullary descending vasa recta (OMDVR) on membrane potential (Ψm) and chloride ion. ANG II depolarized OMDVR, as measured by fully loading them with the voltage-sensitive dye bis[1,3-dibutylbarbituric acid-(5)] trimethineoxonol [DiBAC4(3)] or selectively loading their pericytes. ANG II was also observed to depolarize pericytes from a resting value of −55.6 ± 2.6 to −26.2 ± 5.4 mV when measured with gramicidin D-perforated patches. When measured with DiBAC4(3) in unstimulated vessels, neither changing extracellular Cl− concentration ([Cl−]) nor exposure to the chloride channel blocker indanyloxyacetic acid 94 (IAA-94; 30 μM) affected Ψm. In contrast, IAA-94 repolarized OMDVR pretreated with ANG II. Neither IAA-94 (30 μM) nor niflumic acid (30 μM, 1 mM) affected the vasoactivity of unstimulated OMDVR, whereas both dilated ANG II-preconstricted vessels. Reduction of extracellular [Cl−] from 150 to 30 meq/l enhanced ANG II-induced constriction. Finally, we identified a Cl−channel in OMDVR pericytes that is activated by ANG II or by excision into extracellular buffer. We conclude that constriction of OMDVR by ANG II involves pericyte depolarization due, in part, to increased activity of chloride channels.
Collapse
Affiliation(s)
- Z Zhang
- Division of Nephrology, University of Maryland School of Medicine, Baltimore, Maryland 21201-1595, USA
| | | | | | | | | |
Collapse
|
20
|
Zhang Y, Miller DV, Paterson WG. Opposing roles of K(+) and Cl(-) channels in maintenance of opossum lower esophageal sphincter tone. Am J Physiol Gastrointest Liver Physiol 2000; 279:G1226-34. [PMID: 11093945 DOI: 10.1152/ajpgi.2000.279.6.g1226] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The ionic basis underlying the maintenance of myogenic tone of lower esophageal sphincter circular muscle (LES) was investigated in opossum with the use of standard isometric tension and conventional intracellular microelectrode recordings in vitro. In tension recording studies, nifedipine (1 microM) reduced basal tone to 27.7 +/- 3.8% of control. The K(+) channel blockers tetraethylammonium (TEA, 2 mM), charybdotoxin (100 nM), and 4-aminopyridine (4-AP, 2 mM) enhanced resting tone, whereas apamin and glibenclamide were without affect. Cl(-) channel blockers DIDS (500 microM) and 5-nitro-2-(3-phenylpropylamino)-benzoic acid (500 microM), as well as niflumic acid (0.1-300 microM), decreased basal tone, but tamoxifen was without effect. Intracellular microelectrode recordings revealed ongoing, spontaneous, spike-like action potentials (APs). Nifedipine abolished APs and depolarized resting membrane potential (RMP). Both TEA and 4-AP significantly depolarized RMP and augmented APs, whereas niflumic acid dose-dependently hyperpolarized RMP and abolished APs. These data suggest that, in the opossum, basal tone is associated with continuous APs and that K(+) and Ca(2+)-activated Cl(-) channels have important opposing roles in the genesis of LES tone.
Collapse
Affiliation(s)
- Y Zhang
- Gastrointestinal Diseases Research Unit and Departments of Medicine and Physiology, Queen's University, Kingston, Ontario, Canada K7L 5G2
| | | | | |
Collapse
|
21
|
Mukerji MS, Leathard HL, Huddart H. The effects of potassium channel blockers on progesterone-induced suppression of rat portal vein contractility. J Pharm Pharmacol 2000; 52:983-90. [PMID: 11007070 DOI: 10.1211/0022357001774705] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022]
Abstract
The suppression of contractility of rat portal vein caused by progesterone appears to be due to the potassium (K+) channel opening effect of this hormone. The identity of the specific K+ channels involved has been investigated using a variety of K+ channel blockers. Incubation with 100 nM iberiotoxin antagonised the progesterone-induced inhibition of spontaneous and 20 mM K+-induced phasic activity of the portal vein such that the contractions resembled those of the non-progesterone, non-iberiotoxin control tissues treated with the corresponding solvent vehicles. Incubation with barium chloride (20 and 100 microM), 4-aminopyridine (1 mM), tetraethylammonium chloride (1 mM), glibenclamide (1 microM) or apamin (1 microM) did not, however, have the same antagonistic effect. These results suggest that progesterone's selective suppression of rat portal vein contractility is mediated by the opening of BKCa channels.
Collapse
Affiliation(s)
- M S Mukerji
- Department of Nursing Studies, St. Martin's College, Lancaster, UK
| | | | | |
Collapse
|
22
|
Scarparo HC, Santos GCM, Leal-Cardoso JH, Criddle DN. Selective inhibitory effects of niflumic acid on 5-HT-induced contraction of the rat isolated stomach fundus. Br J Pharmacol 2000; 130:678-84. [PMID: 10821798 PMCID: PMC1572096 DOI: 10.1038/sj.bjp.0703331] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
The effects of niflumic acid (NFA), an inhibitor of calcium-activated chloride currents I(Cl(Ca)), were compared with the actions of the voltage-dependent calcium channel (VDCC) blocker nifedipine on 5-hydroxtryptamine (5-HT)- and acetylcholine (ACh)-induced contractions of the rat isolated fundus. NFA (1 - 30 microM) elicited a concentration-dependent inhibition of contractions induced by 5-HT (10 microM) with a reduction to 15. 5+/-6.0% of the control value at 30 microM. 1 microM nifedipine reduced 5-HT-induced contraction to 15.2+/-4.9% of the control, an effect not greater in the additional presence of 30 microM NFA. In contrast, the contractile response to ACh (10 microM) was not inhibited by NFA in concentrations </=100 microM, although this response was partly inhibited by nifedipine (1 microM) to 67.6+/-11. 8% of the control value. NFA (1 - 30 microM) did not affect contraction induced by either 20 mM or 60 mM KCl, suggesting that this drug was not acting via blockade of VDCCs or activation of potassium channels. In contrast, 3, 5-dichlorophenylamine-2-carboxylic acid and 4, 4'-diisothiocyanatostilbene-2,2'-disulphonic acid were less selective in their inhibitory effects, inducing reductions of 60 mM KCl-induced contraction at concentrations >/=10 microM. Our results show that NFA can exert selective inhibitory effects on the chloride-dependent 5-HT-induced contractions of the rat fundus. The data support the hypothesis that activation of Cl((Ca)) channels leading to calcium entry via VDCCs is a mechanism utilized by 5-HT, but not by ACh, to elicit contraction of the rat fundus.
Collapse
Affiliation(s)
- H C Scarparo
- Departamento de Farmacologia e Fisiologia, Faculdade de Medicina, Universidade Federal do Ceará, Cel. Nunes de Melo 1127, Porangabussu, Fortaleza, CE, Brazil
| | - G C M Santos
- Laboratório de Eletrofisiologia, Departamento de Ciências Fisiológicas, CCS, Universidade Estadual do Ceará, Av. Paranjana 1700, Fortaleza CE 60740-000, Brazil
| | - J H Leal-Cardoso
- Laboratório de Eletrofisiologia, Departamento de Ciências Fisiológicas, CCS, Universidade Estadual do Ceará, Av. Paranjana 1700, Fortaleza CE 60740-000, Brazil
| | - D N Criddle
- Laboratório de Eletrofisiologia, Departamento de Ciências Fisiológicas, CCS, Universidade Estadual do Ceará, Av. Paranjana 1700, Fortaleza CE 60740-000, Brazil
- Author for correspondence:
| |
Collapse
|
23
|
Teixeira MC, Coelho RR, Leal-Cardoso JH, Criddle DN. Comparative effects of niflumic acid and nifedipine on 5-hydroxytryptamine- and acetylcholine-induced contraction of the rat trachea. Eur J Pharmacol 2000; 394:117-22. [PMID: 10771043 DOI: 10.1016/s0014-2999(00)00089-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The effects of niflumic acid, an inhibitor of Ca(2+)-activated Cl(-) (Cl((Ca))) channels, were compared with those of the voltage-dependent Ca(2+) channel (VDCC) blocker nifedipine on 5-hydroxytryptamine (5-HT)- and acetylcholine-induced contractions of the rat isolated trachea. Niflumic acid (3-100 microM) induced a concentration-dependent inhibition of 5-HT (10 microM)-induced contractions, with a reduction to 37.0+/-9.5% of the control at the highest concentration. One micromolar nifedipine, which completely blocked 60 mM KCl-induced contractions, reduced the response to 5-HT similarly to 39.2+/-11.5% of the control. The inhibition of the 5-HT response was not significantly different from that produced by the combined presence of nifedipine (1 microM) and niflumic acid (100 microM), suggesting that their effects were not additive. In contrast, neither niflumic acid (3-100 microM) nor nifedipine (1 microM) inhibited acetylcholine-induced contractions. The contraction to 5-HT (10 microM) in Cl(-)-free solution was decreased by more than approximately 85% of the control, whilst that of acetylcholine was reduced only by approximately 36%. Our data show that niflumic acid exerts selective inhibitory effects on 5-HT-induced contraction, and suggest that activation of Cl((Ca)) channels may be a mechanism whereby 5-HT (but not acetylcholine) induces Ca(2+) entry via VDCCs to elicit contraction.
Collapse
Affiliation(s)
- M C Teixeira
- Laboratório de Eletrofisiologia, Departamento de Ciências Fisiológicas, CCS, Universidade Estadual do Ceará, Fortaleza, Brazil
| | | | | | | |
Collapse
|
24
|
Putney LK, Vibat CR, O'Donnell ME. Intracellular Cl regulates Na-K-Cl cotransport activity in human trabecular meshwork cells. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 277:C373-83. [PMID: 10484324 DOI: 10.1152/ajpcell.1999.277.3.c373] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The trabecular meshwork (TM) of the eye plays a central role in modulating intraocular pressure by regulating aqueous humor outflow, although the mechanisms are largely unknown. We and others have shown previously that aqueous humor outflow facility is modulated by conditions that alter TM cell volume. We have also shown that the Na-K-Cl cotransport system is a primary regulator of TM cell volume and that its activity appears to be coordinated with net efflux pathways to maintain steady-state volume. However, the cellular mechanisms that regulate cotransport activity and cell volume in TM cells have yet to be elucidated. The present study was conducted to investigate the hypothesis that intracellular Cl concentration ([Cl]i) acts to regulate TM cell Na-K-Cl cotransport activity, as has been shown previously for some other cell types. We demonstrate here that the human TM cell Na-K-Cl cotransporter is highly sensitive to changes in [Cl]i. Our findings reveal a marked stimulation of Na-K-Cl cotransport activity, assessed as ouabain-insensitive, bumetanide-sensitive K influx, in TM cells following preincubation of cells with Cl-free medium as a means of reducing [Cl]i. In contrast, preincubation of cells with media containing elevated K concentrations as a means of increasing [Cl]i results in inhibition of Na-K-Cl cotransport activity. The effects of reducing [Cl]i, as well as elevating [Cl]i, on Na-K-Cl cotransport activity are concentration dependent. Furthermore, the stimulatory effect of reduced [Cl]i is additive with cell-shrinkage-induced stimulation of the cotransporter. Our studies also show that TM cell Na-K-Cl cotransport activity is altered by a variety of Cl channel modulators, presumably through changes in [Cl]i. These findings support the hypothesis that regulation of Na-K-Cl cotransport activity, and thus cell volume, by [Cl]i may participate in modulating outflow facility across the TM.
Collapse
Affiliation(s)
- L K Putney
- Department of Human Physiology, School of Medicine, University of California, Davis, California 95616-8644, USA
| | | | | |
Collapse
|
25
|
White R, Hiley CR. The actions of some cannabinoid receptor ligands in the rat isolated mesenteric artery. Br J Pharmacol 1998; 125:533-41. [PMID: 9806337 PMCID: PMC1565654 DOI: 10.1038/sj.bjp.0702111] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. The actions of a number of cannabinoid receptor ligands were investigated using the myograph-mounted rat isolated mesenteric artery. Anandamide, CP 55,940, HU-210, palmitoylethanolamide and WIN 55,212-2 all caused concentration-dependent relaxations of methoxamine-precontracted vessels which were not affected by removal of the endothelium. 2. Precontracting vessels with 60 mM KCl instead of methoxamine greatly reduced the vasorelaxant effects of anandamide and palmitoylethanolamide. High K+ solution caused a modest decrease in the relaxant potency of CP 55,940 and HU-210, and had no effect on relaxations induced by WIN 55,212-2. 3. Relaxations of methoxamine-induced tone by anandamide, CP 55,940 and HU-210, but not palmitoylethanolamide and WIN 55,212-2, were attenuated by the cannabinoid receptor antagonist, SR 141716A. Relaxation of vessels contracted with 60 mM KCl by CP 55,940 was also sensitive to SR 141716A. 4. Anandamide and CP 55,940 caused small but concentration-dependent contractions in resting vessels in the absence of extracellular calcium. These were not sensitive to SR 141716A. Palmitoylethanolamide and WIN 55,212-2 produced smaller contractions only at higher concentrations. 5. Anandamide and CP 55,940, but not palmitoylethanolamide and WIN 55,212-2, caused concentration-dependent inhibition of the phasic contractions induced by methoxamine in calcium-free conditions, but only anandamide caused inhibition of contractions to caffeine under such conditions. These inhibitory effects were not antagonised by SR 141716A. 6. The present study provides the first detailed investigation of the actions of cannabinoid agonists on vascular smooth muscle. Our results show that these compounds exert both receptor-dependent and -independent effects on agonist-induced calcium mobilization in the rat isolated mesenteric artery.
Collapse
Affiliation(s)
- R White
- Department of Pharmacology, University of Cambridge
| | | |
Collapse
|
26
|
Edwards G, Weston AH. Recent advances in potassium channel modulation. PROGRESS IN DRUG RESEARCH. FORTSCHRITTE DER ARZNEIMITTELFORSCHUNG. PROGRES DES RECHERCHES PHARMACEUTIQUES 1997; 49:93-121. [PMID: 9388385 DOI: 10.1007/978-3-0348-8863-9_3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- G Edwards
- School of Biological Sciences, University of Manchester, UK
| | | |
Collapse
|