1Department of Physiology, The Fourth Military Medical University, Xi'an 710032; 2Institute of Basic Medical Sciences, Medical College, Dalian University, Dalian 116622; and 3Faculty of Medicine, Department of Physiology, The University of Hong Kong, Hong Kong, China
Submitted 11 July 2003 ; accepted in final form 17 February 2004
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
transient outward potassium current; anion channel; actin cytoskeleton; myocyte; potassium ion
Initial studies found that the Ito was reduced in Cl-free solution and concluded that this current was carried primarily by Cl (13, 15, 18). However, later studies revealed that K+, rather than Cl, was the main charge carrier of the current (24, 25). Inhibition of the current induced by less permeant Cl substitutes was thought to be probably the result of a decrease in free Ca2+ concentration, since the Cl substitutes used in those studies might chelate external Ca2+ (Cao2+; see Ref. 23). This notion was supported by the observation that the Ito was less sensitive to replacement of external Cl (Clo) when free Ca2+ was kept at a constant level (24, 25). Further studies also provided some evidence for the dependence of the Ito on Ca2+. Reducing Cai2+ by EGTA inhibits the Ito (41). On the other hand, other studies showed that the current in rat cardiac ventricular myocytes displays a Ca2+-independent property (3, 22), which is also inhibited by less permeant Cl substitutes and anion channel blockers (ACB; see Ref. 30). Heretofore, the mechanism of the influence of less-permeant Cl substitutes on cardiac Ito remains unclear.
In the mammalian heart, several anion channels have been functionally identified for over a decade (19). In the study of cardiac anion channels, a common phenomenon is that Cl substitutes and ACB have profound effects on other channels (1, 8, 16, 31, 43, 44), which is generally attributed to nonspecific effects. However, our primary study suggests that the nonspecific effects of Cl substitutes and ACB on cardiac Ca2+ channel may implicate a channel-channel interaction (46), an important regulating mode found in epithelia (27, 40). It is well accepted that the cystic fibrosis transmembrane conductance regulator (CFTR) may act both as a Cl channel and a regulator of the activity of other epithelial channels via a channel-channel interaction (27, 40), possibly mediated by the cytoskeleton (20). Moreover, studies have found that a variety of channels are regulated by the actin cytoskeleton (2, 7, 17, 20, 33, 34, 36, 45). The Kv4.2, which contributes to the Ito, is found to interact with filamin, a member of the -actinin/spectrin/dystrophin family of actin-binding proteins. Absence of filamin results in suppression of Kv4.2 current (36). In mammalian cardiac ventricular myocyte, there is a possibility that one channel activity may influence other channel(s) via the actin cytoskeleton. Therefore, in the present study, to evaluate the hypothesis that channel-channel interaction might be implicated in the action of Cl substitutes, we reexamined the effects of Cl substitution on Ito. The present data indicate that the effects of anions on Ito are closely related to their permeability, and disruption of the actin microfilament by cytochalasin D (CytD) produced an effect similar to that of less permeant anions on the steady-state inactivation of Ito. The present results provide evidence for the hypothesis that the effects of anions on Ito involve a modulatory action of anion channel(s) on Ito channel, probably mediated by the actin cytoskeleton.
![]() |
MATERIALS AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Whole cell patch-clamp experiments.
Aliquots of cell suspension were transferred to a perfusion chamber on the stage of an inverted microscope. Pipettes had tip resistances of 22.5 M when filled with internal solution. Whole cell recordings were performed at room temperature (23
25°C) using a patch-clamp amplifier and Pulse software (HEKA Elektronik, Lambrecht, Germany). The offset potentials between both electrodes were zeroed before the pipette touched the cell. The liquid junction potential between the Asp-rich pipette and the standard bath solutions for recording Ito was calculated to be 15 mV by using the JPCalc program within Clampex 8.1 (Axon Instruments) and was corrected after the experiments. To minimize changes in liquid junction potentials caused by alteration in Clo, the Ag-AgCl bath ground electrode was placed in a separate pool of 3 M KCl, which was connected to the recording chamber by a 3 M KCl-agar bridge, as reported previously by Zygmunt and Gibbons (47). Whole cell Ito was elicited by 300-ms pulses from a holding potential of 65 mV (after correction of the junction potential) to test potentials ranging from 55 to +45 mV in 10-mV increments. Whole cell basal Cl currents were elicited from a holding potential of 40 mV to test potentials ranging from 100 to +100 mV in 20-mV increments. The pulses were 200 ms in duration and delivered at 1-s interval. The current signals were low-pass filtered at 5 kHz and stored in the hard disk of an IBM-compatible computer. Ito was calculated by subtracting the peak outward current from the current at the end of the test pulse.
Confocal imaging. Fluorescence labeling of F-actin was performed as previously described (29). Cell suspensions, pretreated with different protocols, were sedimented by centrifugation at 100 g for 1 min. The supernatant was discarded. Cells were then fixed in 4% paraformaldehyde-PBS solution for 10 min and washed three times with PBS by centrifugation. Cell suspensions were transferred to slides and kept in 4°C overnight. The cells were permeabilized with 0.2% Triton X-100 in PBS for 10 min at room temperature. After three washes with PBS, cells were stained with FITC-labeled phalloidin (5 µM in PBS) to localize F-actin for 50 min in a dark room at room temperature and then were washed extensively with PBS. Slides were visualized using an Olympus Fluoview FV300 confocal microscope. FITC was excited at 490 nm and detected at 520 nm. Optical sections (0.6 µm thick) were taken of each sample to eliminate out-of-focus fluorescence of the intensely stained myocytes. To standardize the fluorescence intensity for all the experimental preparations, the time of image capture, the image intensity gain, the image enhancement, and the contrast and brightness settings were optimally adjusted at the outset and kept constant for all experiments.
Solutions. The Tyrode solution contained (in mM) 143 NaCl, 5.4 KCl, 0.5 MgCl2, 1.8 CaCl2, 0.3 NaH2PO4, 5 glucose, and 5 HEPES-NaOH (pH 7.4). The nominally Ca2+-free Tyrode solution was made by omitting CaCl2 from the normal solution. The KB solution contained (in mM) 70 potassium glutamate, 25 KCl, 20 taurine, 10 KH2PO4, 3 MgCl2, 0.5 EGTA, 10 glucose, and 10 HEPES-KOH (pH 7.35).
The pipette solution for recording Ito contained (in mM) 110 potassium aspartate (unless specifically stated in the text), 20 KCl, 1 MgCl2, 5 Na2-phosphocreatine, 0.1 GTP, 5 MgATP, 5 EGTA, and 10 HEPES (pH was adjusted to 7.2 with KOH). In some experiments, intracellular K+ (Ki+; 130 mM) was replaced by equimolar Cs+ (pH = 7.2, adjusted with CsOH). The standard bath solution contained (in mM) 140 NaCl, 5 KCl, 1 MgCl2, 0.4 KH2PO4, 1.8 CaCl2, 1 BaCl2, 0.5 CdCl2, 5 HEPES, and 10 glucose (pH 7.4). BaCl2 and CdCl2 were used to inhibit the inwardly rectifying K+ current, the L-type Ca2+ current, and the Ca2+-activated Cl current (48). In some experiments, external Na+ (Nao+) was replaced by equimolar N-methyl-D-glucamine (NMDG). In Cl substitution experiments, 140 mM Clo was replaced by equimolar Br, F, NO3, aspartate (Asp), glutamate (Glu), or gluconate (Glc). The free Ca2+ concentration in bath solutions was calculated using the CaBuf program (provided by Dr. G. Droogmans, Katholieke Universiteit Leuven, Belgium), as described previously (46). According to the calculation, the free Ca2+ in the bathing solutions after substitution of 140 mM Clo with equimolar Asp, Glu, or Glc was 1.76, 1.78, and 0.57 mM, respectively, when the total Ca2+ was 1.8 mM. Because the presence of other bivalent cations, Cd2+ and Ba2+, could not be taken into account in the calculation, the free Ca2+ concentration after replacement of Clo with less permeant anions may represent an underestimate.
The solutions for recording basal Cl current were as follows. The pipette solution contained (in mM) 135 NMDG-Cl, 2 EGTA, 5 Mg-ATP, 10 HEPES, and 10 mannitol, pH 7.2, with intracellular Cl (Cli) = 135 mM. The standard bath solution contained (in mM) 125 NaCl, 2.5 MgCl2, 2.5 CaCl2, 5 glucose, 10 HEPES, and 30 mannitol, pH 7.4, with Clo = 135 mM. Nifedipine (1 µM) was added to the bath solution to inhibit the L-type Ca2+ current. The membrane potential was depolarized from 70 to 40 mV, where it was held for 100 ms to inactivate the Na+ channels. K+ currents were eliminated by omission of K+ from pipette and bath solutions. In some experiments, 125 mM Clo was replaced by either equimolar Br or Asp.
Chemicals. 4-AP, nifedipine, CytD, phalloidin, and FITC-phalloidin were purchased from Sigma. Stock solutions of CytD (50 mM) and phalloidin (50 mM) in DMSO were diluted to the desired final concentrations immediately before use.
Statistical analysis. Data are presented as means ± SE. Statistical differences in the data were evaluated by Student's t-test or ANOVA as appropriate and were considered significant at values of P < 0.05.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
|
|
|
|
|
|
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The cardiac Ito was initially thought to be carried by Cl because it decreased in Cl-free solution (13, 15, 18). However, subsequent studies indicated that this current was primarily carried by K+ (24). The effects of Cl substitution on the Ito are usually attributed to altered Cao2+, since less permeant Cl substitutes may reduce the free Ca2+ concentration (23) and consequently inhibit a Ca2+-activated Cl current (47). However, in rat cardiac ventricular myocytes, the Ito, as a matter of fact, is a sole current carried by K+ (Ito), which is independent of Cai2+ and sensitive to blockade by 4-AP (3, 14, 22). Both biochemical and functional evidence shows that Kv4.2 and Kv4.3 contribute to the cardiac Ito (10, 11, 35). Although rat cardiac Ito is also inhibited by less permeant anions, Lefevre et al. (30) have demonstrated that the inhibitory effect of the anions is not significantly altered when Cao2+ is removed and Cai2+ is buffered with a high concentration of EGTA. In the present study, it is unlikely that the effect of less permeant anions was the result of changes in free Cao2+ because Asp and Glu, which only cause a slight decrease in free Cao2+ (<2.3%, see MATERIALS AND METHODS), induce a more markedly inhibitory effect than Glc does. The latter markedly decreased the free Cao2+ by 68.3%. These unparallel effects of the less permeant anions on the free Cao2+ and Ito suggest that their action may involve a mechanism other than chelation of Ca2+. It may be argued that a fraction of Ito may be carried by Cl. If Cl can pass through the Ito channel, then the residual Ito carried by Cl should remain after removing Ki+. However, when the myocytes were dialyzed with the pipette solution in which 130 mM K+ was replaced by equimolar Cs+, Ito decreased progressively and disappeared within 4 min, although the concentrations of both Clo and Cli remained unchanged (n = 4, data not shown). This is similar to the observation reported by Lefevre et al. (30). Therefore, it is unlikely that Cl is a carrier of Ito. In the present study, a KCl-agar bridge electrode was used to minimize the junction potential caused by alteration in Clo concentration. If the KCl-agar bridge electrode failed to effectively reduce the liquid junction potentials, changes in liquid junction potentials should alter the activation of both Ito and the sustained component of outward K+ current. However, less permeant anions, like the specific Ito inhibitor 4-AP, only inhibited Ito, whereas the sustained component of outward K+ current was not significantly affected. Thus it is unlikely that inhibition of Ito by less permeant anions is caused by changes in liquid junction potentials. The present data suggest that the effects of Cl and its substitutes on cardiac Ito involve an anion-related factor.
In cardiac myocytes, the physiological K+ gradient is maintained by a combination of outward K+ movement through K+ channels and an inward movement via the Na+-K+-2Cl cotransporter (32) and the activity of Na+-K+-ATPase. Inhibition of Na+-K+-2Cl cotransport may cause accumulation-depletion of K+ in situ, i.e., an increase in the external K+ (Ko+) and a decrease in the Ki+, thereby reducing the driving force for K+. Thus the inhibition of Ito by less permeant anions may be the result of an inhibition of Na+-K+-2Cl cotransport, as proposed by Lefevre et al. (30). However, in contrast to the less permeant anions, substitution of Cl by some permeant anions, which should also impair Na+-K+-2Cl cotransport, was found to facilitate Ito rather than inhibit it. Moreover, the driving force for K+ is not expected to be significantly altered in Cl substitution conditions because the Ki+ concentration is clamped at a constant level in the whole cell patch-clamp configuration, and the Ko+ is maintained constant by continual perfusion. Na+ is also an important factor for stimulating Na+-K+-2Cl cotransport and Na+-K+-ATPase; substitution of Nao+ with an impermeant cation should eliminate Na+-K+-2Cl cotransport. However, removal of Nao+ does not affect the inhibitory action of less permeant anions (Fig. 2). Furthermore, intracellular Na+ has also been found to have no effects on Ito (14). Inhibition of the Na+-K+-ATPase with its specific inhibitor ouabain (0.5 µM) does not markedly influence the action of the less permeant anion Asp (n = 5, data not shown). Therefore, it seems unlikely that the inhibitory effect of less permeant anions on Ito is caused by either an impairment of Na+-K+-2Cl cotransport or alteration of the activity of Na+-K+-ATPase.
Anion channels exist ubiquitously in cells, including rat ventricular myocytes (12, 26, 42), and display distinct anionic selectivity and permeability sequences (21). Studies have revealed that external anions may modulate the gating of some anion channels (38, 39). In the present study, a basal Cl channel activity was observed. The Cl channel had an anion permeability sequence of Cl Br >> Asp, which matched the action of these anions on Ito. Thus the present results could not rule out the possibility that the Ito channel may be modulated by anion channel(s) via a channel-channel interaction. Recent evidence reveals that the actin cytoskeleton is implicated in the regulation of a variety of ion channels, including voltage-gated K+ channels (17, 33, 34, 36) and anion channels (2, 6, 7, 37, 45). A previous study on epithelial anion channels has suggested that actin plays a role in channel-channel interaction (20). The present study found that disrupting the actin microfilaments with CytD produced an effect similar to that induced by less permeant anions. Confocal imaging revealed that CytD induced a disruption of actin microfilaments. In contrast, less permeant anion Asp did not affect the structure of the actin cytoskeleton. It is unlikely that less permeant anions affect Ito by directly acting on the actin cytoskeleton. These results suggest that the actin cytoskeleton may play a linkage role in the interaction between the anion channel and the Ito channel. Although the present study suggests that Cl channel may be involved in the modulation of the Ito channel in rat cardiac ventricular myocytes, direct evidence for the interaction between the Cl channel and Ito channel is lacking. Further work is required to test this hypothesis.
In many mammalian hearts, including humans, Ito is mainly responsible for the initial rapid phase of the action potential repolarization. Defects of the Ito channel may result in both abnormal electrical activities (28, 35) and morphological changes in the heart (5, 28). Therefore, investigation into the regulation of cardiac Ito is of clinical importance. The present study provides new insight into the regulation of cardiac Ito.
![]() |
GRANTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
ACKNOWLEDGMENTS |
---|
![]() |
FOOTNOTES |
---|
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
2. Ahmed N, Ramjeesingh M, Wong S, Varga A, Garami E, and Bear CE. Chloride channel activity of ClC-2 is modified by the actin cytoskeleton. Biochem J 352: 789794, 2000.[CrossRef][ISI][Medline]
3. Apkon M and Nerbonne JM. Characterization of two distinct depolarization-activated K+ currents in isolated adult rat ventricular myocytes. J Gen Physiol 97: 9731011, 1991.[Abstract]
4. Barry DM and Nerbonne JM. Myocardial potassium channels: electrophysiological and molecular diversity. Annu Rev Physiol 58: 363394, 1996.[CrossRef][ISI][Medline]
5. Barry DM, Xu H, Schuessler RB, and Nerbonne JM. Functional knockout of the transient outward current, long-QT syndrome, and cardiac remodeling in mice expressing a dominant-negative Kv4 subunit. Circ Res 83: 560567, 1998.
6. Cantiello HF. Role of the actin cytoskeleton in the regulation of the cystic fibrosis transmembrane conductance regulator. Exp Physiol 81: 505514, 1996.[Abstract]
7. Chasan B, Geisse NA, Pedatella K, Wooster DG, Teintze M, Carattino MD, Goldmann WH, and Cantiello HF. Evidence for direct interaction between actin and the cystic fibrosis transmembrane conductance regulator. Eur Biophys J 30: 617624, 2002.[CrossRef][ISI][Medline]
8. Conforti L, Sumii K, and Sperelakis N. Diphenylamine-2-carboxylate blocks voltage-dependent Na+ and Ca2+ channels in rat ventricular cardiomyocytes. Eur J Pharmacol 259: 215218, 1994.[CrossRef][ISI][Medline]
9. Cooper JA. Effects of cytochalasin and phalloidin on actin. J Cell Biol 105: 14731478, 1987.[ISI][Medline]
10. Dixon JE and McKinnon D. Quantitative analysis of potassium channel mRNA expression in atrial and ventricular muscle of rats. Circ Res 75: 252260, 1994.[Abstract]
11. Dixon JE, Shi W, Wang HS, McDonald C, Yu H, Wymore RS, Cohen IS, and McKinnon D. Role of the Kv4.3 K+ channel in ventricular muscle. A molecular correlate for the transient outward current. Circ Res 79: 659668, 1996.
12. Duan D, Ye L, Britton F, Horowitz B, Hume JR. A novel anionic inward rectifier in native cardiac myocytes. Circ Res 86: E63E71, 2000.[ISI][Medline]
13. Dudel J, Peper K, Rudel R, and Trautwein W. The dynamic chloride component of membrane current in Purkinje fibers. Pflügers Arch 295: 197212, 1967.
14. Dukes ID and Morad M. The transient K+ current in rat ventricular myocytes: evaluation of its Ca2+ and Na+ dependence. J Physiol 435: 395420, 1991.[Abstract]
15. Fozzard HA and Hiraoka M. The positive dynamic current and its inactivation properties in cardiac Purkinje fibres. J Physiol 234: 569586, 1973.[ISI][Medline]
16. Frace AM, Maruoka F, and Noma A. Control of the hyperpolarization-activated cation current by external anions in rabbit sino-atrial node cells. J Physiol 453: 307318, 1992.[Abstract]
17. Hattan D, Nesti E, Cachero TG, and Morielli AD. Tyrosine phosphorylation of Kv1.2 modulates its interaction with the actin-binding protein cortactin. J Biol Chem 277: 3859638606, 2002.
18. Hiraoka M and Hiraoka M. The role of the positive dynamic current on the action potential of cardiac Purkinje fibers. Jpn J Physiol 25: 705717, 1975.[ISI][Medline]
19. Hume JR, Duan D, Collier ML, Yamazaki J, and Horowitz B. Anion transport in heart. Physiol Rev 80: 3181, 2000.
20. Ismailov II, Berdiev BK, Shlyonsky VG, Fuller CM, Prat AG, Jovov B, Cantiello HF, Ausiello DA, and Benos DJ. Role of actin in regulation of epithelial sodium channels by CFTR. Am J Physiol Cell Physiol 272: C1077C1086, 1997.
21. Jentsch TJ, Stein V, Weinreich F, and Zdebik AA. Molecular structure and physiological function of chloride channels. Physiol Rev 82: 503568, 2002.
22. Josephson IR, Sanchez-Chapula J, and Brown AM. Early outward current in rat single ventricular cells. Circ Res 54: 157162, 1984.[Abstract]
23. Kenyon JL and Gibbons WR. Effects of low-chloride solutions on action potentials of sheep cardiac Purkinje fibers. J Gen Physiol 70: 635660, 1977.
24. Kenyon JL and Gibbons WR. Influence of chloride, potassium, and tetraethylammonium on the early outward current of sheep cardiac Purkinje fibers. J Gen Physiol 73: 117138, 1979.[Abstract]
25. Kenyon JL and Gibbons WR. 4-Aminopyridine and the early outward current of sheep cardiac Purkinje fibers. J Gen Physiol 73: 139157, 1979.[Abstract]
26. Komukai K, Brette F, Pascarel C, Orchard CH. Electrophysiological response of rat ventricular myocytes to acidosis. Am J Physiol Heart Circ Physiol 283: H412H422, 2002.
27. Kunzelmann K. CFTR: interacting with everything? News Physiol Sci 16: 167170, 2001.
28. Kuo HC, Cheng CF, Clark RB, Lin JJ, Lin JL, Hoshijima M, Nguyen-Tran VT, Gu Y, Ikeda Y, Chu PH, Ross J, Giles WR, and Chien KR. A defect in the Kv channel-interacting protein 2 (KChIP2) gene leads to a complete loss of Ito and confers susceptibility to ventricular tachycardia. Cell 107: 801813, 2001.[ISI][Medline]
29. Lader AS, Kwiatkowski DJ, and Cantiello HF. Role of gelsolin in the actin filament regulation of cardiac L-type calcium channels. Am J Physiol Cell Physiol 277: C1277C1283, 1999.
30. Lefevre T, Lefevre IA, Coulombe A, and Coraboeuf E. Effects of chloride ion substitutes and chloride channel blockers on the transient outward current in rat ventricular myocytes. Biochim Biophys Acta 1273: 3143, 1996.[ISI][Medline]
31. Liu J, Lai ZF, Wang XD, Tokutomi N, and Nishi K. Inhibition of sodium current by chloride channel blocker 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) in guinea pig cardiac ventricular cells. J Cardiovasc Pharmacol 31: 558567, 1998.[CrossRef][ISI][Medline]
32. Liu S, Jacob R, Piwnica-Worms D, and Lieberman M. Na+-K+-2Cl cotransport in cultured embryonic chick heart cells. Am J Physiol Cell Physiol 253: C721C730, 1987.
33. Mason HS, Latten MJ, Godoy LD, Horowitz B, and Kenyon JL. Modulation of Kv1.5 currents by protein kinase A, tyrosine kinase, and protein tyrosine phosphatase requires an intact cytoskeleton. Mol Pharmacol 61: 285293, 2002.
34. Nakahira K, Matos MF, and Trimmer JS. Differential interaction of voltage-gated K+ channel -subunits with cytoskeleton is mediated by unique amino terminal domains. J Mol Neurosci 11: 199208, 1998.[CrossRef][ISI][Medline]
35. Oudit GY, Kassiri Z, Sah R, Ramirez RJ, Zobel C, and Backx PH. The molecular physiology of the cardiac transient outward potassium current (Ito) in normal and diseased myocardium. J Mol Cell Cardiol 33: 851872, 2001.[CrossRef][ISI][Medline]
36. Petrecca K, Miller DM, and Shrier A. Localization and enhanced current density of the Kv4.2 potassium channel by interaction with the actin-binding protein filamin. J Neurosci 20: 87368744, 2000.
37. Prat AG, Cunningham CC, Jackson GR Jr., Borkan SC, Wang Y, Ausiello DA, and Cantiello HF. Actin filament organization is required for proper cAMP-dependent activation of CFTR. Am J Physiol Cell Physiol 277: C1160C1169, 1999.
38. Pusch M, Jordt SE, Stein V, and Jentsch TJ. Chloride dependence of hyperpolarization-activated chloride channel gates. J Physiol 515: 341353, 1999.
39. Pusch M, Ludewig U, Rehfeldt A, and Jentsch TJ. Gating of the voltage-dependent chloride channel CIC-0 by the permeant anion. Nature 373: 527531, 1995.[CrossRef][ISI][Medline]
40. Schwiebert EM, Benos DJ, Egan ME, Stutts MJ, and Guggino WB. CFTR is a conductance regulator as well as a chloride channel. Physiol Rev 79, Suppl 1: S145S166, 1999.
41. Siegelbaum SA and Tsien RW. Calcium-activated transient outward current in calf cardiac Purkinje fibres. J Physiol 299: 485506, 1980.[Abstract]
42. Thiemann A, Grunder S, Pusch M, and Jentsch TJ. A chloride channel widely expressed in epithelial and non-epithelial cells. Nature 356: 5760, 1992.[CrossRef][ISI][Medline]
43. Walsh KB and Wang C. Effect of chloride channel blockers on the cardiac CFTR chloride and L-type calcium currents. Cardiovasc Res 32: 391399, 1996.[CrossRef][ISI][Medline]
44. Wang HS, Dixon JE, and McKinnon D. Unexpected and differential effects of Cl channel blockers on the Kv4.3 and Kv4.2 K+ channels. Implications for the study of the Ito2 current. Circ Res 81: 711718, 1997.
45. Zhang J, Larsen TH, and Lieberman M. F-actin modulates swelling-activated chloride current in cultured chick cardiac myocytes. Am J Physiol Cell Physiol 273: C1215C1224, 1997.
46. Zhou SS, Gao Z, Dong L, Ding YF, Zhang XD, Wang YM, Pei JM, Gao F, and Ma XL. Anion channels influence excitation-contraction coupling by modulating L-type Ca2+ channel in ventricular myocytes. J Appl Physiol 93: 16601668, 2002.
47. Zygmunt AC and Gibbons WR. Calcium-activated chloride current in rabbit ventricular myocytes. Circ Res 68: 424437, 1991.[Abstract]
48. Zygmunt AC, Goodrow RJ, and Antzelevitch C. Sodium effects on 4-aminopyridine-sensitive transient outward current in canine ventricular cells. Am J Physiol Heart Circ Physiol 272: H1H11, 1997.