Molecular Basis of Multiple Open States in Smooth Muscle Calcium Channels and Related Intracellular Signalling

已知一些平滑肌同时具有低电压激活(LVA)和高电压激活(HVA)钙通道电流，并且HVA电流分量在所有的平滑肌肉中占主导地位。在此之前，我们已经提出，钙通道构象从正常开放状态(O1)到第二开放状态(O2)的转换与钙通道激动剂诱导的长通道开放不同，这两种机制是独立运行的。因此，DHP钙通道激动剂和去极化的组合在天然平滑肌钙通道上至少产生四种开放状态。在本研究项目《平滑肌钙通道中多个开放状态的分子基础及相关的细胞内信号传递》期间，我们首先考察了多个开放状态模型是否能系统地解释CHO细胞经验…中U型失活和缓慢失活的特征应用膜片钳技术，进一步研究了L型钙通道(Ca，1.2b)的平滑肌_1亚基。实验表明，单靠平滑肌_1亚基就可以再现“U形失活”和“缓慢失活”的特性，以及高度正的条件反射步骤和钙激动剂的相互作用。结果表明，分子内结构变化和/或相互作用在_1亚基蛋白中起着核心作用。此外，我们利用多种开放状态模型的计算机计算重建了克隆的平滑肌钙通道的缓慢失活和U型失活特性。综上所述，L钙通道_1亚基的构象可以通过电压依赖的方式从O_1态转变为O_2态。根据Hodgkin&Huxley描述的门控模型，无法预测这种转换。我们建议对这个基本模型进行一些修改，以便在更一般的条件下描述浇注动力学。较少

It is known that some smooth muscles possess both low- (LVA) and high voltage-activated (HVA) Ca^<2+> channel currents, and that the HVA current component is predominant in all smooth muscles. Previously, we have suggested that the conversion of the Ca^<2+> channel conformation from normal open (O1) to a second open state (O2) during large depoalrization is distinct from the long channel opening induced by Ca^<2+> channel agonists, and that these two mechanisms operate separately. As a result, a combination of DHP Ca^<2+> channel agonists and depolarization produces at least four open states in native smooth muscle Ca^<2+> channels.During the tenure of the present research project entitled 'Molecular Basis of Multiple Open States in Smooth Muscle Calcium Channels and Related Intracellular Signalling', we have first examined whether the multiple open state model can systematically account for the characteristic features of 'U-shaped inactivation' and 'slow deactivation' in CHO cells exp … More ressing only smooth muscle _1 subunit of L-type Ca^<2+> channel (Ca,1.2b), using patch clamp techniques. The experiments have revealed that smooth muscle _1 subunit alone can reproduce 'U-shaped inactivation' and 'slow deactivation' properties, and also interaction of highly positive conditioning steps and Ca^<2+> agonists. The results imply that intramolecular structural changes and/or interactions in _1 subunit protein play the central roles. Furthermore, we have reconstructed the slow deactivation and U-shaped inactivation properties seen in cloned smooth muscle Ca^<2+> channels using computer calculation with multiple open state models. Taken Together, it is concluded that that the conformation of _1 subunit of L-type Ca2+ channel can be converted from O1 to O2 state in a voltage-dependent manner. This conversion is not predicted from the gating model described by Hodgkin & Huxley. We would like to propose that some modification in this basic model is presumably necessary to describe gating kinetics under more general conditions. Less