Carl A, Lee H K, Sanders K M
Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno 89557, USA.
Am J Physiol. 1996 Jul;271(1 Pt 1):C9-34. doi: 10.1152/ajpcell.1996.271.1.C9.
Intracellular Ca2+ concentration ([Ca2+]i) plays a central role in regulating tone and contractility of smooth muscle cells. In contrast to the "classic" model of electromechanical coupling where membrane potential determines [Ca2+]i, it is now well established that [Ca2+]i in turn may also affect membrane potential by modulating open probabilities of ion channels. Activation by [Ca2+]i of large-conductance K+ channels, Cl- channels, and nonselective cation channels has been described, as well as block of delayed rectifier K+ channels by [Ca2+]i and [Ca2+]i-induced inactivation of Ca2+ channels. Therefore, a network consisting of positive- and negative-feedback loops regulates [Ca2+]i as well as membrane potential. In this context, we review the properties of Ca(2+)-dependent ion channels and their functional role in vascular and visceral smooth muscles. Any alteration of the "Ca2+ sensitivity" of ion channels is expected to have a profound effect on the reciprocal relationship between membrane potential and [Ca2+]i. Already several molecular factors determining Ca2+ sensitivity of Ca(2+)-activated K+ channels have been identified. We provide a working definition for Ca2+ sensitivity.
细胞内钙离子浓度（[Ca2+]i）在调节平滑肌细胞的张力和收缩性方面发挥着核心作用。与膜电位决定[Ca2+]i的“经典”机电偶联模型不同，现在已经明确，[Ca2+]i反过来也可能通过调节离子通道的开放概率来影响膜电位。已经描述了[Ca2+]i对大电导钾通道、氯通道和非选择性阳离子通道的激活，以及[Ca2+]i对延迟整流钾通道的阻断和[Ca2+]i诱导的钙通道失活。因此，一个由正反馈和负反馈回路组成的网络调节着[Ca2+]i以及膜电位。在此背景下，我们综述了钙依赖性离子通道的特性及其在血管和内脏平滑肌中的功能作用。离子通道“钙敏感性”的任何改变预计都会对膜电位和[Ca2+]i之间的相互关系产生深远影响。已经确定了几种决定钙激活钾通道钙敏感性的分子因素。我们给出了钙敏感性的实用定义。
