AJP - Cell Physiology, Vol 271, Issue 3 C971-C981, Copyright © 1996 by American Physiological Society

ARTICLES

Single-channel basis of slow inactivation of Na+ channels in rat skeletal muscle

R. L. Ruff
Department of Neurology, Cleveland Veterans Affairs Medical Center, Ohio, USA.

This study examined the single-channel basis of slow inactivation of Na+ currents (INa) in rat fast-twitch skeletal muscle fibers. A loose patch voltage clamp monitored changes in the maximum inward INa 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 INa. 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 INa and increased during recovery from slow inactivation of INa. 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.

This article has been cited by other articles:

				D. G. Allen, G. D. Lamb, and H. Westerblad Skeletal Muscle Fatigue: Cellular Mechanisms Physiol Rev, January 1, 2008; 88(1): 287 - 332. [Abstract] [Full Text] [PDF]

				J. N. Edwards, W. A. Macdonald, C. van der Poel, and D. G. Stephenson O2bullet production at 37{degrees}C plays a critical role in depressing tetanic force of isolated rat and mouse skeletal muscle Am J Physiol Cell Physiol, August 1, 2007; 293(2): C650 - C660. [Abstract] [Full Text] [PDF]

				T. L. Dutka and G. D. Lamb Transverse tubular system depolarization reduces tetanic force in rat skeletal muscle fibers by impairing action potential repriming Am J Physiol Cell Physiol, June 1, 2007; 292(6): C2112 - C2121. [Abstract] [Full Text] [PDF]

				K. T. Murphy and T. Clausen The importance of limitations in aerobic metabolism, glycolysis, and membrane excitability for the development of high-frequency fatigue in isolated rat soleus muscle Am J Physiol Regulatory Integrative Comp Physiol, May 1, 2007; 292(5): R2001 - R2011. [Abstract] [Full Text] [PDF]

				W. Ulbricht Sodium Channel Inactivation: Molecular Determinants and Modulation Physiol Rev, October 1, 2005; 85(4): 1271 - 1301. [Abstract] [Full Text] [PDF]

				R. L. Ruff and S. C. Cannon Defective slow inactivation of sodium channels contributes to familial periodic paralysis Neurology, June 13, 2000; 54(11): 2191 - 2192. [Full Text] [PDF]

				R. L. Ruff Effects of temperature on slow and fast inactivation of rat skeletal muscle Na+ channels Am J Physiol Cell Physiol, November 1, 1999; 277(5): C937 - C947. [Abstract] [Full Text] [PDF]