[Voltage dependence of late Na channel with burst mode in isolated cardiac myocytes]

Patch clamp technique was employed to record single Na channel currents in isolated guinea-pig ventricular myocytes. Burst mode could be elicited by step depolarization and terminates immediately after repolarization. The unitary current of burst mode was not only dependent on Na concentration in the pipettes but also on the test voltage. The open time constant increased as testing voltage becomes more positive. The results from stepwise-depolarization and ramp depolarization experiments showed that the more steps or the faster the upstroke velocity of depolarization used, the more the burst mode would occure.