External [K+] and the block of the K+ inward rectifier by external Cs+ in frog skeletal muscle.
Frog skeletal muscle has a K+ channel called the inward rectifier, which passes inward current more readily than outward current. Gay and Stanfield (1977) described a voltage-dependent block of inward K+ currents through the inward rectifier by external Cs+ in frog muscle. Here, frog single muscle fibers were voltage clamped using the vaseline-gap voltage-clamp technique to study the effect of external [K+] on the voltage-dependent block of inward K+ currents through the inward rectifier by external Cs+. The block of inward K+ currents through the channel by external Cs+ was found to depend on external [K+], such that increasing the external concentration of the permeant ion K+ potentiated the block produced by the impermeant external Cs+. These findings are not consistent with a one-ion channel model for the inward rectifier. The Eyring rate theory formalism for channels, viewed as single-file multi-ion pores (Hille and Schwarz, 1978), was used to develop a two-site multi-ion model for the inward rectifier. This model successfully reproduced the experimentally observed potentiation of the Cs+ block of the channel by external K+, thus lending further support to the view of the inward rectifier as a multi-ion channel.
D000818:Animals; D002586:Cesium / Q000494:pharmacology*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D009132:Muscles / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D011898:Ranidae
D007473:Ion Channels; D002586:Cesium; D011188:Potassium