Boyett M R, Honjo H, Harrison S M, Zang W J, Kirby M S
Department of Physiology, University of Leeds, UK.
Pflugers Arch. 1994 Aug;428(1):39-50. doi: 10.1007/BF00374750.
L-type Ca2+ current, iCa, has been recorded in guinea-pig ventricular myocytes at 36 degrees C using the whole cell patch clamp technique. Intracellular Ca2+ was buffered with ethylenebis(oxonitrilo)tetraacetate (EGTA). An increase in the rate of stimulation from 0.5 to 3 Hz resulted in an abrupt decrease in iCa in the first beat at the high rate, followed by a progressive decrease (tau approx. 7 s) over the next 30 s. The changes were not the result of Ca(2+)-dependent inactivation, because similar changes occurred with either Ba2+ or Na+ as the charge carrier. During 20-s voltage clamp pulses there was an ultra-slow phase of inactivation of Ba2+ or Na+ current through the Ca2+ channel (tau approx. 6 s at 0 mV). This was confirmed by applying test pulses after conditioning pulses of different duration: the Ba2+ current during the test pulse decreased progressively when the duration of the conditioning pulse was increased progressively to 20 s. Ultra-slow inactivation of Ba2+ current was voltage dependent and increased monotonically at more positive potentials. Recovery of Ba2+ current from ultra-slow inactivation occurred with a time constant of 3.7 s at -40 mV and 0.7 s at -80 mV. The gradual decrease in iCa on increasing the rate to 3 Hz may have been the result of the development of ultra-slow voltage-dependent inactivation.
采用全细胞膜片钳技术，在36℃下记录了豚鼠心室肌细胞中的L型钙电流（iCa）。细胞内钙用乙二胺四乙酸（EGTA）缓冲。刺激频率从0.5 Hz增加到3 Hz时，快速刺激的第一个搏动中iCa会突然下降，随后在接下来的30 s内逐渐下降（时间常数约为7 s）。这些变化不是钙依赖性失活的结果，因为当Ba2+或Na+作为载流子时会出现类似变化。在20 s的电压钳制脉冲期间，通过钙通道的Ba2+或Na+电流存在超慢失活阶段（在0 mV时时间常数约为6 s）。通过在不同持续时间的预处理脉冲后施加测试脉冲得以证实：当预处理脉冲的持续时间逐渐增加到20 s时，测试脉冲期间的Ba2+电流逐渐下降。Ba2+电流的超慢失活依赖于电压，且在更正的电位下单调增加。在-40 mV时，Ba2+电流从超慢失活恢复的时间常数为3.7 s，在-80 mV时为0.7 s。将刺激频率增加到3 Hz时iCa的逐渐下降可能是超慢电压依赖性失活发展的结果。
