Satin L S, Cook D L
Department of Physiology, University of Washington School of Medicine, Seattle 98105.
Pflugers Arch. 1989 May;414(1):1-10. doi: 10.1007/BF00585619.
Inactivation of voltage-dependent calcium currents was studied in single, dissociated insulin-secreting HIT cells voltage-clamped by the whole-cell patch-clamp method at room temperature. Na and K currents were suppressed by tetrodotoxin, tetraethylammonium, ATP, 4-aminopyridine and Cs. Ca currents activated in less than 10 ms by depolarizations beyond -50 mV from a holding potential of -100 mV and were identified, as in previous studies, by their sensitivity to divalent cation blockade and permeability to Ba as a charge carrier. Sustained depolarization revealed two kinetically distinct phases of inactivation: a rapid phase inactivated approximately 50% of the current in less than 100 ms while the remaining current was inactivated over the next 10-20 s. Rapid inactivation appeared to be due to Ca2+ influx since it was slowed markedly when Ba2+ was used as the current carrier, while the degree of inactivation increased and decreased with increasing depolarization in direct parallel with the U-shaped current-voltage relationship for inward Ca current. Slow inactivation appeared to be voltage-dependent since current could be inactivated (by approximately 20%) by 10 s long depolarizations to potentials below the threshold for activating Ca current, slow time constants of inactivation were voltage-dependent and slow inactivation persisted when Ca was replaced with Ba. Ca currents with low activation thresholds (in the -50 to -30 mV range) appeared to be preferentially inactivated by the rapid Ca-dependent mechanism. Recovery of slowly inactivated Ca current was very slow and currents inactivated by larger depolarizations required longer recovery time than those elicited by smaller depolarizations. Rapid and slow inactivation mechanisms may be important in understanding the fast spiking and slow plateau depolarizations seen in pancreatic B-cells exposed to stimulatory levels of glucose.
采用全细胞膜片钳技术在室温下对单个分离的胰岛素分泌型HIT细胞进行电压钳制，研究电压依赖性钙电流的失活情况。用河豚毒素、四乙铵、ATP、4-氨基吡啶和铯抑制钠电流和钾电流。从-100 mV的钳制电位去极化超过-50 mV时，钙电流在不到10 ms内激活，并且如先前研究一样，根据其对二价阳离子阻断的敏感性以及对作为电荷载体的钡的通透性来识别。持续去极化揭示了失活的两个动力学不同阶段：快速阶段在不到100 ms内使约50%的电流失活，而其余电流在接下来的10 - 20 s内失活。快速失活似乎是由于Ca2+内流，因为当用Ba2+作为电流载体时它明显减慢，而失活程度随着去极化增加而增加和减少，与内向钙电流的U形电流-电压关系直接平行。缓慢失活似乎是电压依赖性的，因为通过长达10 s的去极化到低于激活钙电流阈值的电位可使电流失活（约20%），缓慢的失活时间常数是电压依赖性的，并且当Ca被Ba取代时缓慢失活持续存在。具有低激活阈值（在-50至-30 mV范围内）的钙电流似乎优先通过快速的钙依赖性机制失活。缓慢失活的钙电流的恢复非常缓慢，并且由较大去极化失活的电流比较小去极化引发的电流需要更长的恢复时间。快速和缓慢失活机制可能对于理解暴露于刺激水平葡萄糖的胰腺β细胞中所见的快速尖峰和缓慢平台去极化很重要。
