Bolton T B, Prestwich S A, Zholos A V, Gordienko D V
Department of Pharmacology and Clinical Pharmacology, St George's Hospital Medical School, London, United Kingdom.
Annu Rev Physiol. 1999;61:85-115. doi: 10.1146/annurev.physiol.61.1.85.
The main contributors to increases in [Ca2+]i and tension are the entry of Ca2+ through voltage-dependent channels opened by depolarization or during action potential (AP) or slow-wave discharge, and Ca2+ release from store sites in the cell by the action of IP3 or by Ca(2+)-induced Ca(2+)-release (CICR). The entry of Ca2+ during an AP triggers CICR from up to 20 or more subplasmalemmal store sites (seen as hot spots, using fluorescent indicators); Ca2+ waves then spread from these hot spots, which results in a rise in [Ca2+]i throughout the cell. Spontaneous transient releases of store Ca2+, previously detected as spontaneous transient outward currents (STOCs), are seen as sparks when fluorescent indicators are used. Sparks occur at certain preferred locations--frequent discharge sites (FDSs)--and these and hot spots may represent aggregations of sarcoplasmic reticulum scattered throughout the cytoplasm. Activation of receptors for excitatory signal molecules generally depolarizes the cell while it increases the production of IP3 (causing calcium store release) and diacylglycerols (which activate protein kinases). Activation of receptors for inhibitory signal molecules increases the activity of protein kinases through increases in cAMP or cGMP and often hyperpolarizes the cell. Other receptors link to tyrosine kinases, which trigger signal cascades interacting with trimeric G-protein systems.
细胞内钙离子浓度（[Ca2+]i）升高和张力增加的主要促成因素包括：通过去极化、动作电位（AP）或慢波放电开启的电压依赖性通道使钙离子内流，以及通过三磷酸肌醇（IP3）的作用或钙诱导的钙释放（CICR）使钙离子从细胞内储存位点释放。动作电位期间钙离子内流触发来自多达20个或更多的亚膜下储存位点（使用荧光指示剂时可见为热点）的CICR；然后钙离子波从这些热点扩散，导致整个细胞内[Ca2+]i升高。先前检测为自发性瞬时外向电流（STOCs）的储存钙离子的自发性瞬时释放，在使用荧光指示剂时可见为钙火花。钙火花出现在某些特定的优选位置——频繁放电位点（FDSs）——这些位点和热点可能代表散布于整个细胞质中的肌浆网聚集物。兴奋性信号分子受体的激活通常使细胞去极化，同时增加IP3（导致钙储存释放）和二酰基甘油（激活蛋白激酶）的产生。抑制性信号分子受体的激活通过增加环磷酸腺苷（cAMP）或环磷酸鸟苷（cGMP）来增加蛋白激酶的活性，并且常常使细胞超极化。其他受体与酪氨酸激酶相连，后者触发与三聚体G蛋白系统相互作用的信号级联反应。
