Kehl S J
Department of Physiology, University of British Columbia, Vancouver, B.C., Canada, V6T 1Z3.
Pflugers Arch. 1996 Aug;432(4):623-9. doi: 10.1007/s004240050178.
The block of large-conductance calcium-activated potassium (BK) channels by internal and external alkali metal ions was studied in adult rat melanotrophs. Internal but not external 20 mM Na+ produced a strongly voltage-dependent, flickery block that was well-fitted to the Woodhull model by using a value of 140 mM for the dissociation rate constant at 0 mV [Kd(0)] and an equivalent valence (zdelta) of 0.9. At a concentration of 20 mM external K+, Cs+ and Rb+, but not Li+, caused a rightward shift of the voltage dependence of the intracellular Na+ (Na+i ) block. This effect of K+, Cs+ and Rb+ was modelled by an equilibrium knock-out mechanism in which the block-relieving ion binds to a site located within the voltage field and consequently increases the off-rate of Na+. Internal Li+ caused little or no block whereas internal Cs+ caused a voltage-dependent block [Kd(0) approximately 150 mM]. Flickery channel block observed in cell-attached patches was consistent with a cytoplasmic Na+ activity between 1 and 10 mM.
在成年大鼠黑素细胞中研究了内部和外部碱金属离子对大电导钙激活钾（BK）通道的阻断作用。内部而非外部的20 mM Na +产生了强烈的电压依赖性闪烁阻断，通过使用0 mV时解离速率常数为140 mM [Kd(0)]和等效价（zdelta）为0.9的值，该阻断作用与伍德胡尔模型拟合良好。在20 mM的外部K +、Cs +和Rb +浓度下，但不是Li +，导致细胞内Na +（Na+i）阻断的电压依赖性向右移动。K +、Cs +和Rb +的这种作用通过平衡敲除机制进行建模，其中解除阻断的离子与位于电压场中的位点结合，从而增加Na +的解离速率。内部Li +几乎不产生或不产生阻断，而内部Cs +产生电压依赖性阻断[Kd(0)约为150 mM]。在细胞贴附膜片上观察到的闪烁通道阻断与细胞质Na +活性在1至10 mM之间一致。
