Possible involvement of [Ca2+]i level in the modulation of the current-voltage relationship for the fast Na+ current in late embryonic chick cardiomyocytes.
Modulation by intracellular Ca2+ concentration ([Ca2+]i) of the reversal potential for the fast Na+ current (INa) in 17-day-old embryonic chick ventricular cardiomyocytes was examined using a whole-cell voltage-clamp technique. Experiments were performed at room temperature (22 degrees C). Test pulses were applied between -60 to +50 mV from a holding potential of -90 mV. The INa was TTX-sensitive, and the reversal potential was +47.3+/-2.2 mV (n = 20) at pCa 10. Neither pCa 7 or pCa 10 caused any effect on the peak amplitudes of INa, but the reversal potential at pCa 7 shifted in the hyperpolarizing direction by 10.5+/-2.8 mV (n = 10, p < 0.05), as compared with that at pCa 10. The hyperpolarizing shift was also observed by application of taurine, and behaved in a concentration-dependent manner; by 10.4+/-2.3 mV (n = 8, p < 0.05) at 10 mM, and by 12.1+/-2.3 mV (n = 8, p < 0.05) at 20 mM. Even when taurine at low concentration (5 mM) enhanced INa, the similar shift of the reversal potential occurred. These results suggest that the shift of reversal potential of the INa in embryonic chick cells would be involved with somewhat cellular mechanism dependent on [Ca2+]i, which may play an important role for cardiac functions of the embryonic cells.[1]References
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