Imaizumi Y, Muraki K, Takeda M, Watanabe M
Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Nagoya City University, Japan.
Am J Physiol. 1989 Apr;256(4 Pt 1):C880-5. doi: 10.1152/ajpcell.1989.256.4.C880.
An attempt was made to obtain electrophysiological evidence for continuous influx of Ca ion through voltage-dependent Ca channel (VDCC) in smooth muscle during long depolarization, for example in high K solution. Noninactivated Ca current [ICa(ni)] remaining after the accomplishment of voltage-dependent inactivation by prolonged depolarization for approximately 1 min was detected by three means under whole cell voltage clamp in several types of smooth muscle cells. The measurement of ICa(ni) was performed by micropuff application of Cd2+ or Ca2+ in the presence or absence of 5 mM extracellular Ca, respectively, or jump of extracellular Ca concentration [( Ca]o). The current-voltage relationship of ICa(ni) evaluated by these means had a peak at approximately -10 mV. The peak amplitude ranged from 5 to 25 pA, depending on whether the cells were isolated from guinea pig urinary bladder, ureter, vas deferens, taenia caecum, or rabbit portal vein. The ICa(ni) may be large enough to explain sustained contraction in high K solution, at least in these smooth muscle tissues. A window current simulated from the steady-state activation and inactivation curves and the maximum conductance of Ca current (ICa) in these cells suggests a theoretical basis for the observed ICa(ni).
有人试图获取电生理证据，以证明在长时间去极化过程中，例如在高钾溶液中，钙离子通过电压依赖性钙通道（VDCC）持续流入平滑肌。在几种类型的平滑肌细胞中，通过全细胞膜片钳技术，采用三种方法检测了在约1分钟的长时间去极化使电压依赖性失活完成后剩余的非失活钙电流[ICa(ni)]。分别在存在或不存在5 mM细胞外钙的情况下，通过微量喷射Cd2+或Ca2+，或细胞外钙浓度[(Ca]o)的跃升来测量ICa(ni)。通过这些方法评估的ICa(ni)的电流-电压关系在约-10 mV处有一个峰值。峰值幅度在5至25 pA之间，这取决于细胞是从豚鼠膀胱、输尿管、输精管、盲肠带还是兔门静脉分离得到的。至少在这些平滑肌组织中，ICa(ni)可能大到足以解释在高钾溶液中的持续收缩。从这些细胞中钙电流（ICa）的稳态激活和失活曲线以及最大电导模拟得到的窗电流为观察到的ICa(ni)提供了理论基础。
