Kawano S, DeHaan R L
Department of Anatomy and Cell Biology, Emory University Health Sciences Center, Atlanta, Georgia 30322.
J Membr Biol. 1990 Jun;116(1):9-17. doi: 10.1007/BF01871667.
T-type calcium channels (IT channels) were studied in cell-attached patch electrode recordings from the ventricular cell membrane of 14-day embryonic chick heart. All experiments were performed in the absence of Ca2+ with Na+ (120 mM) as the charge carrier. IT channels were distinguished from L-type calcium channels (IL) by their more negative activation and inactivation potential ranges; their smaller unitary slope conductance (26 pS), and their insensitivity to isoproterenol or D600. Inactivation kinetics were voltage dependent. The time constant of inactivation was 37 msec when the membrane potential was depolarized 40 mV from rest (R + 40 mV), and 20 msec at R + 60 mV. The frequency histogram of channel open times (tau o) was fit by a single-exponential curve while that of closed times (tau c) was bi-exponential. tau o was the same at R + 40 mV and R + 60 mV whereas tau c was shortened at R + 60 mV. The open-state probability (P o) increased with depolarization: 0.35 at R + 40 mV, 0.8 at R + 60 mV and 0.88 at R + 80 mV. This increase in Po at depolarized potentials could be accounted for by the decrease in tau c.
在14日龄鸡胚心脏心室细胞膜的细胞贴附式膜片钳记录中对T型钙通道（IT通道）进行了研究。所有实验均在无Ca2+的情况下进行，以Na+（120 mM）作为载流子。IT通道与L型钙通道（IL）的区别在于其激活和失活电位范围更负；其单位斜率电导较小（26 pS），且对异丙肾上腺素或D600不敏感。失活动力学是电压依赖性的。当膜电位从静息电位去极化40 mV（R + 40 mV）时，失活时间常数为37毫秒，在R + 60 mV时为20毫秒。通道开放时间（tau o）的频率直方图由单指数曲线拟合，而关闭时间（tau c）的频率直方图为双指数曲线。在R + 40 mV和R + 60 mV时，tau o相同，而在R + 60 mV时，tau c缩短。开放状态概率（P o）随去极化而增加：在R + 40 mV时为0.35，在R + 60 mV时为0.8，在R + 80 mV时为0.88。去极化电位下P o的这种增加可以用tau c的减少来解释。
