Jmari K, Mironneau C, Mironneau J
J Physiol. 1986 Nov;380:111-26. doi: 10.1113/jphysiol.1986.sp016275.
Ca channel currents were recorded in Cs-loaded myometrial strips from pregnant rats after addition of tetraethylammonium chloride and 4-aminopyridine (10 mM each) by means of a double sucrose-gap technique. During a depolarizing pulse, the decay of Ca channel current was slowed down when external Ca was replaced by Ba or Sr. This decay represented an inactivation phenomenon, as assessed by the decreased amplitude of inward tail currents following progressively longer depolarizations, the absence of shift in peak conductance curves against membrane potential, and the stable value of the reversal potential when Ba current was increased during conditioning pulses. Inactivation of Ca and Ba currents through Ca channels was studied using the double-pulse method. Conditioning pulses that produced maximal Ca current induced maximal inactivation; with stronger depolarizations, inactivation decreased but was not completely prevented at the expected Ca reversal potential. Increasing the amount of Ca entering the cell during the pre-pulse reduced both amplitude and kinetics of test Ca currents. These results were not observed with Ba as charge carrier suggesting the participation of different mechanisms in inactivation. With Ca as charge carrier, increasing the external Ca speeded the rate of inactivation. This was not observed with Ba outside. Addition of Co (2.5 mM) reduced the amplitude of both Ca and Ba currents but slowed the inactivation of only the Ca current. Recovery from inactivation was described as a two-exponential process only when the conditioning pulse elicited a Ca inward current. In all other cases, recovery from inactivation was represented as a single exponential curve. It is suggested that inactivation of Ca channels in rat uterine smooth muscle is mediated by both internal Ca-dependent and potential-dependent mechanisms.
采用双蔗糖间隙技术，在添加四乙铵氯化物和4-氨基吡啶（各10 mM）后，记录怀孕大鼠经铯负载的子宫肌条中的钙通道电流。在去极化脉冲期间，当外部钙被钡或锶取代时，钙通道电流的衰减减慢。这种衰减代表一种失活现象，这是通过逐渐延长去极化后内向尾电流幅度的降低、峰值电导曲线相对于膜电位无偏移以及在条件脉冲期间钡电流增加时反转电位的稳定值来评估的。使用双脉冲方法研究了通过钙通道的钙和钡电流的失活。产生最大钙电流的条件脉冲诱导最大失活；随着更强的去极化，失活减少，但在预期的钙反转电位下并未完全阻止。增加预脉冲期间进入细胞的钙量会降低测试钙电流的幅度和动力学。以钡作为载流子未观察到这些结果，表明失活中存在不同机制的参与。以钙作为载流子，增加外部钙会加快失活速率。在外部使用钡时未观察到这种情况。添加钴（2.5 mM）会降低钙和钡电流的幅度，但仅减缓钙电流的失活。仅当条件脉冲引发钙内向电流时，失活的恢复才被描述为双指数过程。在所有其他情况下，失活的恢复表现为单指数曲线。提示大鼠子宫平滑肌中钙通道的失活由内部钙依赖性和电位依赖性机制介导。
