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

LI CI-ZHEN, WANG XING-DE, WANG HONG-WEI, BIAN Yu-Tu, LIU YUAN-Mou

(Department of Physiology, Shanghai Second Medical University, Shanghai 200025)

Abstract

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-out recording, which are (1) isolated brief openings, (2) scattered openings, (3) long openings and (4)
bursts. The occurrence frequencies of the four types were different. Bursts appeared about 1 in every 2 000 depolarizations, with an open time constant longer than others. However, all the four types of late current openings, as well as the early openings occurring immediately upon depolarization, could be
blocked by tetrodotoxin. It was also found that at a certain stimulation frequency, normal action potential duration (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. The above results suggest that the activities of the various types of late Na channel play an important role in the formation of action potential plateau.

Key words: isolated ventricular myocytes; patch clamp; late Na channel current; model

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Citing This Article：

LI CI-ZHEN, WANG XING-DE, WANG HONG-WEI, BIAN Yu-Tu, LIU YUAN-Mou . FOUR TYPES OF LATE Na CHANNEL CURRENT IN ISOLATED VENTRICULAR MYOCYTES WITH REFERENCE TO THEIR CONTRIBUTION TO THE LASTINGNESS OF ACTION POTENTIAL PLATEAU . Acta Physiol Sin 1997; 49 (2): (in Chinese with English abstract).