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British Journal of Pharmacology
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January 1999, Volume 126, Issue 1, Pages 87 - 92 |
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| Original Article |
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Taurine modulates IKr but not IKs in guinea-pig ventricular cardiomyocytes
Hiroyasu Satoh1 Department of Pharmacology, Division of Molecular and Cellular Biology, Nara Medical University, Kashihara, Nara 634-8521, Japan1Author for correspondence: E-mail: hysat@naramed-u.ac.jp |
| Keywords |
| Taurine;
E-4031;
293B;
action potential duration;
delayed rectifier K+ current;
IKr;
IKs;
patch clamp;
guinea-pig ventricular myocytes |
| Abstract |
1 Effects of taurine on the delayed rectifier K+ current (IK) in isolated guinea-pig ventricular cardiomyocytes were examined at different intracellular Ca2+ concentration ([Ca2+]i), using whole-cell voltage and current clamp techniques. Experiments were performed at 36°C. 2 Addition of taurine (10 - 20 mM) decreased the action potential duration (APD) at pCa 8, but increased the APD at pCa 6. Taurine (20 mM) enhanced IK at 70 mV by 22.4±3.1% (n=6, P<0.01) at pCa 8, whereas taurine inhibited the IK by 27.1±2.7% (n=6, P<0.01) at pCa 6. These responses behaved in a concentration-dependent manner. 3 The IK is composed of the rapid and slow components (IKr and IKs). When [Ca2+]i was pCa 6, taurine at 20 mM reduced the tail current of IKr at 70 mV by 16.5±2.7% (n=5, P<0.05) and that of IKs at 70 mV by 27.1±2.8% (n=6, P<0.01). In contrast, at pCa 8, the tail currents of IKr and IKs at 70 mV were enhanced by 13.4±3.2% (n=7, P<0.05) and by 22.4±3.1% (n=7, P<0.01), respectively. The voltages of half-maximum activation (V1/2) for IKr and IKs were not modified by taurine. 4 Addition of E-4031 (5 µM) to taurine had a complete blockade of the tail current of IKr, but not IKs. The remained tail current (IKs) in the presence of E-4031 (5 µM) was not affected by taurine (20 mM), but was blocked by 293B (30 µM). 5 These results indicate that taurine modulates IKr but not IKs, depending on [Ca2+]i, resulting in regulation of the APD. |
Received 27 July 1998; Revised 14 October 1998; Accepted 20 October 1998
