Single Na+ channel currents observed in cultured rat muscle cells

Abstract

The voltage- and time-dependent conductance of membrane Na+ channels is responsible for the propagation of action potentials in nerve muscle cells. In voltage-step-clamp experiments on neurone preparations containing 104-107 Na+ channels, the membrane conductance shows smooth variations in time but analysis of fluctuations and other evidence suggests that the underlying single-channel conductance changes are stochastic, rapid transitions between closed and open states as seen in other channel types. Reported here are the 1st observations of currents through individual Na+ channels under physiological conditions using an improved version of the extracellular patch-clamp technique on cultured rat muscle cells. These observations support earlier inferences about channel gating and show a single-channel conductance of .apprx. 18 pS [pioosiemens].