Studies of membrane-associated enzyme activities which are regulated by membrane potential

本实验室的研究表明，KCl诱导的去极化可增强内皮素1（ET-1）引起的收缩成分对Ca^2+的敏感性，而各种高钾通道开放剂（KCO）可降低Ca^2+敏感性，抑制激动剂诱导的猪或犬冠状动脉收缩和IP_3的合成。因此，在高浓度KCl去极化或佛波酯刺激的肌肉中，通过改变生理盐溶液（PSS）中KCl的浓度或KCOs引起的膜电位水平的变化影响Ca^<2+>敏感性，可能存在一些可能的转导机制。（90 K-2.5Ca）、5 mMKCl-2.5mMCaCl_2-PSS（5 K-2.5Ca）产生的复极化或去除细胞外Ca^<2+>（[Ca^<2+]_0）并加入1 mMEGTA（90 K-0 Ca）引起[Ca^<2+]_i降低和舒张。90 K-0 Ca引起的舒张作用比5 K-2.5Ca引起的慢，但对[Ca^2+]i的降低无显著性差异。[Na^+]_0的减少并不减缓0 Ca的弛豫。30 K-0 Ca中的[Ca^<2+>] i-力关系曲线与5 K-0 Ca和90 K-0 Ca中的相似。在2.5 mM CaCl_2-PSS中逐步改变[K^+]_0所得到的[Ca^<2+] i-力关系曲线位于90 mM KCl-PSS中改变[Ca^<2+]_0所得到的曲线的右侧，因此，KCl去极化增加，KCOs引起的超极化降低收缩元件的Ca^2+敏感性。肌膜存在信号转导系统，通过膜电位水平调节收缩元件的Ca^2+敏感性，包括酶活性。

Studies in our laboratory have demonstrated that KCl-induced depolarization potentiates the increased Ca^<2+> sensitivity of contractile elements induced by endothelin-1 and that various K^+ channel openers (KCOs) which hyperpolarize membrane reduce the Ca^<2+> sensitivity and to inhibit agonist-induced contraction and synthesis of IP_3 in porcine or canine coronary artery. Thus, there are some possible transduction mechanisms by which the changes in level of membrane potential by altering KCl concentration in physiological salt solution (PSS) or by KCOs influence the Ca^<2+> sensitivity in high KCl-depolarized or phorbor ester-stimulated muscles.After the perfusion with 90 mM kc1-2.5 Mm CaCl_2 PSS (90K-2.5Ca), repolarization produced by 5 mM KCl-2.5 mM CaCl_2-PSS(5K-2.5Ca) or the removal of extracellualr Ca^<2+> ([Ca^<2+>]_0) and addition of 1 mM EGTA (90K-0Ca) induced decreases in [Ca^<2+>]_i and relaxation. The relaxation induced by 90K-0Ca was slower than induced by 5K-2.5Ca without significant difference in the decrease in [Ca^<2+>]i. The reduction of [Na^+]_0 did not slow down the relaxation in 0Ca. The [Ca^<2+>]i-force relation curve in 30K-0Ca was been that in 5K-0Ca and that in 90K-0Ca. The effect of levcromakalim was blocked by glibenclmide and counteracted by 20 mM -KC1 PSS.The [Ca^<2+>]i-force relationship curve obtained by changing [K^+]_0 stepwise in 2.5 mM CaCl_2-PSS was located to the right of that by changing [Ca^<2+>]_0 in 90 mM KCl-PSS.Thus, KCl-depolarization increases and hyperpolarization induced by KCOs decreases the Ca^<2+> sensitivity of contractile elements. There are signal transduction systems for sarcolemma to regulate the Ca^<2+> sensitivity of contractile elements including with enzyme activities by the level of membrane potential.