Jacob T J
Department of Physiology, University of Wales, Cardiff, United Kingdom.
Am J Physiol. 1991 Dec;261(6 Pt 1):C1055-62. doi: 10.1152/ajpcell.1991.261.6.C1055.
Pigmented ciliary epithelial cells were studied using the whole cell voltage-clamp technique. Depolarizing steps from a holding potential of -80 mV resulted in a small initial inward current followed by a large outward current. Prolonged depolarizing voltage steps revealed inactivating and noninactivating components of outward current. Outward current was sensitive to the level of Ca2+ in the pipette and was increased by the calcium ionophore A23187; it was blocked by tetraethylammonium (TEA+), quinine, and 4-aminopyridine (4-AP). 4-AP blocked 70% of the outward current with a Ki of 7 x 10(-5) M, and part of the remaining current was abolished by Ni2+. Ni2+ caused a reduction in outward current by blocking IK(Ca) indirectly via decreasing Ca2+ entry through T-type Ca2+ channels. Separating Ni(2+)-sensitive from -insensitive outward conductance gives components that correspond notionally to IK(Ca) and IK(V), respectively. On this basis IK(Ca) represents approximately 28% of K+ outward current. Charybdotoxin blocked 26% of the outward conductance at very depolarized voltage steps as calculated from the slope of the current-voltage curve in this region. It is concluded that there are two major components to the outward current: IK(V), an inactivating voltage-sensitive K+ current, and IK(Ca), which is dependent on the entry of Ca2+ through T-type Ca2+ channels and comprises approximately a quarter of the total K+ outward current under the conditions described. Because of their relative voltage-activation properties, IK(Ca) will be the more important in terms of K+ transport and the secretion of aqueous humor by the ciliary epithelium.
使用全细胞电压钳技术对色素性睫状上皮细胞进行了研究。从 -80 mV 的钳制电位进行去极化步骤，首先会产生一个小的内向电流，随后是一个大的外向电流。长时间的去极化电压步骤揭示了外向电流的失活和非失活成分。外向电流对移液管中的 Ca2+ 水平敏感，并被钙离子载体 A23187 增强；它被四乙铵（TEA+）、奎宁和 4-氨基吡啶（4-AP）阻断。4-AP 以 7×10(-5) M 的 Ki 值阻断了 70% 的外向电流，剩余电流的一部分被 Ni2+ 消除。Ni2+ 通过减少 Ca2+ 通过 T 型 Ca2+ 通道的内流间接阻断 IK(Ca)，从而导致外向电流减少。将 Ni(2+) 敏感的外向电导与不敏感的外向电导分离，得到的成分分别大致对应于 IK(Ca) 和 IK(V)。在此基础上，IK(Ca) 约占 K+ 外向电流的 28%。根据该区域电流 - 电压曲线的斜率计算，在非常去极化的电压步骤下，大蝎毒素阻断了 26% 的外向电导。得出的结论是，外向电流有两个主要成分：IK(V)，一种失活的电压敏感性 K+ 电流；以及 IK(Ca)，它依赖于 Ca2+ 通过 T 型 Ca2+ 通道的内流，在所描述的条件下约占总 K+ 外向电流的四分之一。由于它们相对的电压激活特性，就 K+ 转运和睫状上皮分泌房水而言，IK(Ca) 将更为重要。
