Slow calcium and potassium currents across frog muscle membrane: measurements with a vaseline‐gap technique.

Abstract

A vaseline-gap voltage-clamp technique was used to record slow Ca2+ and K+ currents from frog skeletal muscle fibers loaded with the Ca2+ chelator EGTA [ethyleneglycol-bis(.beta.-aminoethyl ether)N,N,N'',N'',-tetraacetic acid]. K+ currents were increased when Mg2+ replaced external Ca2+. They were abolished when internal K+ was replaced by tetraethylammonium (TEA+). Ca2+ currents could be studied in isolation in fibers loaded with (TEA)2EGTA. Under maintained depolarization, Ca2+ currents slowly increase (half-time of 35 ms or more at 25 mV) and then decline to a steady value. Decline under repolarization is rapid (half-time of 6-7 ms) 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+.