The role of sodium current in the radial spread of contraction in frog muscle fibers.
The membrane potential of isolated muscle fibers was controlled with a two-electrode voltage clamp, and the radial extent of contraction elicited by depolarizing pulses of increasing magnitude was observed microscopically. Depolarizations of the fiber surface only 1-2 mv greater than the contraction threshold produced shortening throughout the entire cross-section of the muscle fiber. The radial spread of contraction was less effective in fibers exposed to tetrodotoxin or to a bathing medium with a greatly reduced sodium concentration. The results provide evidence that depolarization of a muscle fiber produces an increase in sodium conductance in the T tubule membrane and that the resultant sodium current contributes to the spread of depolarization along the T system.
D000818:Animals; D001001:Anura; D002118:Calcium / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D066298:In Vitro Techniques; D008564:Membrane Potentials; D009119:Muscle Contraction; D009132:Muscles / Q000166:cytology / Q000502:physiology*; D012964:Sodium / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology
D013779:Tetrodotoxin; D012964:Sodium; D002118:Calcium