A vaseline-gap voltage-clamp technique was used to record slow Ca2+ and K+ currents from frog skeletal muscle fibres loaded with the Ca2+ chelator EGTA. K+ currents were increased when Mg2+ replaced external Ca2+, and they were abolished when internal K+ was replaced by tetraethylammonium (TEA+). Ca2+ currents could be studied in isolation in fibres loaded with (TEA)2EGTA. Under maintained depolarization, Ca2+ currents slowly increase (half-time of 35 msec or more at 25 mV) and then decline to a steady value. Decline under repolarization is rapid (half-time of 6-7 msec) and complete. During an action potential, the Ca2+ influx through this system is probably less than the influx observed with tracers. Ba2+, Sr2+, Ca2+, Mn2+ and Mg2+ can carry current across the membrane; Ni2+ and Co2+ cannot. Ca2+ currents are weakly blocked by external Mg2+.
|Original language||English (US)|
|Number of pages||18|
|Journal||Journal of Physiology|
|Publication status||Published - 1981|
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