Effects of temperature on slow and fast inactivation of rat skeletal muscle Na+ channels

• Published in: American Journal of Physiology: Cell Physiology 1999-11, Vol.277 (5), p.C937-C947
• Main Author: Ruff, Robert L
• Format: Article
• Language: English
• ISSN: 0363-6143; 1522-1563
• DOI: 10.1152/ajpcell.1999.277.5.c937

Departments of Neurology and Neuroscience, Case Western Reserve University School of Medicine, Louis Stokes Cleveland Veterans Affairs Medical Center, University Hospitals of Cleveland, Cleveland, Ohio 44106 Patch-clamp studies of mammalian skeletal muscle Na + channels are commonly done at subphysiological temperatures, usually room temperature. However, at subphysiological temperatures, most Na + channels are inactivated at the cell resting potential. This study examined the effects of temperature on fast and slow inactivation of Na + channels to determine if temperature changed the fraction of Na + channels that were excitable at resting potential. The loose patch voltage clamp recorded Na + currents ( I Na ) in vitro at 19, 25, 31, and 37°C from the sarcolemma of rat type IIb fast-twitch omohyoid skeletal muscle fibers. Temperature affected the fraction of Na + channels that were excitable at the resting potential. At 19°C, only 30% of channels were excitable at the resting potential. In contrast, at 37°C, 93% of Na + channels were excitable at the resting potential. Temperature did not alter the resting potential or the voltage dependencies of activation or fast inactivation. I Na available at the resting potential increased with temperature because the steady-state voltage dependence of slow inactivation shifted in a depolarizing direction with increasing temperature. The membrane potential at which half of the Na + channels were in the slow inactivated state was shifted by +16 mV at 37°C compared with 19°C. Consequently, the low availability of excitable Na + channels at subphysiological temperatures resulted from channels being in the slow, inactivated state at the resting potential. mammalian skeletal muscle; sodium channel; sodium current; fast inactivation; slow inactivation; paramyotonia congenita; hyperkalemic periodic paralysis