Single-channel basis of slow inactivation of Na+ channels in rat skeletal muscle
Ruff, R.L.
American Journal of Physiology 271(3 Pt 1): C971-C981
1996
ISSN/ISBN: 0002-9513 PMID: 8843728 Document Number: 459172
This study examined the single-channel basis of slow inactivation of Na+ currents (I-Na) in rat fast-twitch skeletal muscle fibers. A loose patch voltage clamp monitored changes in the maximum inward I-Na as the holding potential of the membrane patch changed. On a neighboring region of extrajunctional membrane of the same fiber, a gigaohm seal patch voltage clamp recorded single-channel I-Na. The maximum number of simultaneously open Na+ channels among a group of current traces indicated the maximum number of excitable channels. The holding potentials of the two voltage clamps were the same. Slow inactivation did not affect the open time or conductance of single Na+ channels. The number of excitable Na+ channels reversibly decreased during development of slow inactivation of I-Na and increased during recovery from slow inactivation of I-Na. Different stimulation protocols examined whether Na+ channels had to be in the closed, open, or fast-inactivated states to enter the slow-inactivated state. Na+ channels appear to be able to enter the slow-inactivated state from the closed, open, or fast-inactivated state.