心肌细胞晚钠通道的四种开放模式及其对动作电位的影响

应用膜片箝技术记录豚鼠游离心室肌细胞钠通道电流，发现晚钠通道电流可分为四种开放模式；单个短暂开放，散在开放，长时间长放和爆发型开放。它们的开放机率不一样，其中爆发型的机率为１／２０００，其开放时间常数比前三种大。离细胞体的小片膜电压箝制实验中，亦可观察到晚钠通道的这四种开放模式，它们均可被ＴＴＸ使波动现象基本消失，动作电位时程和有效不应期缩短，静息电位增加，表明晚钠通道的活动在动作电位平台期的形成

FOUR TYPES OF LATE Na CHANNEL CURRENT IN ISOLATED VENTRICULAR MYOCYTES WITH REFERENCE TO THEIR CONTRIBUTION TO THE LASTINGNESS OF ACTION POTENTIAL PLATEAU

Patch clamp technique was employed to record single Na channel current in isolated guinea-pig ventricular myocytes. Four types of late Na channel currents were observed with whole cell and inside-outrecording, which are (1) isolated brief openings, (2) scattered openings, (3) long openings and (4 )bursts. The occurrence frequencies of the four type were different. Bursts appeared about 1 in every2000 depolarizations, with an open time constant longer than others. However, all the four types of latecurrent openings, as well as the early openings occurring immediately upon depolarization, could beblocked by tetrodotoxin. It was also found that at a certain stimulation frequency, normal action Potentialduration (APD) was not invariable as supposed before, but varied from stimulation to stimulation. SPecial Na channel blocker, TTX, shortened the APD and refractory period and abolished the dispersion. Theabove results suggest that the activities of the various types of late Na channel play an important role inthe formation of action potential plateau.