Slow calcium and potassium currents across frog muscle membrane: measurements with a vaseline-gap technique.
1. 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. 2. 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. 3. 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. 4. Ba2+, Sr2+, Ca2+, Mn2+ and Mg2+ can carry current across the membrane; Ni2+ and Co2+ cannot. Ca2+ currents are weakly blocked by external Mg2+.
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology*; D004553:Electric Conductivity; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009132:Muscles / Q000502:physiology*; D011188:Potassium / Q000502:physiology*; D011896:Rana temporaria
D007473:Ion Channels; D008274:Magnesium; D011188:Potassium; D002118:Calcium