Single apamin-blocked Ca-activated K+ channels of small conductance in cultured rat skeletal muscle.
Action potentials in many excitable cells are followed by a prolonged afterhyperpolarization that modulates repetitive firing. Although it is established that the afterhyperpolarization is produced by Ca-activated K+ currents, the basis of these currents is not known. The large conductance (250 pS) Ca-activated K+ channel (BK channel) is not a major contributor to the afterhyperpolarization in non-innervated skeletal muscle and some nerve cells, because apamin, a neurotoxic component of bee venom, abolishes the afterhyperpolarization but does not block BK channels, and 5 mM extracellular tetraethylammonium ion (TEA) blocks BK channels but does not reduce the afterhyperpolarization. We now report single-channel currents from small conductance (10-14 pS) Ca-activated K+ channels (SK channels) with the necessary properties to account for the afterhyperpolarization. SK channels are blocked by apamin but not by 5 mM external TEA (TEAo). They are also highly Ca-sensitive at the negative membrane potentials associated with the afterhyperpolarization.
D000200:Action Potentials; D000818:Animals; D001030:Apamin / Q000494:pharmacology*; D001514:Bee Venoms / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology*; D002712:Chlorides / Q000378:metabolism; D004553:Electric Conductivity; D004594:Electrophysiology; D007473:Ion Channels / Q000187:drug effects*; D009132:Muscles / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D001514:Bee Venoms; D002712:Chlorides; D007473:Ion Channels; D013757:Tetraethylammonium Compounds; D001030:Apamin; D011188:Potassium; D002118:Calcium