AJP - Cell Physiology, Vol 256, Issue 2 C420-C427, Copyright © 1989 by American Physiological Society

ARTICLES

Influence of fiber type and muscle source on Ca2+ sensitivity of rat fibers

B. Laszewski-Williams, R. L. Ruff and A. M. Gordon
Department of Physiology, University of Washington, Seattle 98195.

This study investigated the influence of muscle source and fiber type on the calcium sensitivity of skinned rat skeletal muscle fibers from predominantly slow muscles [soleus (SOL) and adductor longus (AL)], mixed muscle [posterior gracilis (PG)], and predominantly fast-twitch muscle [extensor digitorum longus (EDL)]. Fibers were characterized histochemically and by one-dimensional protein gel electrophoresis, and calcium-tension relationships were determined. Fiber type and muscle source had significant effects on the negative log of the calcium concentration associated with half-maximal tension (pCa1/2). Slow-twitch fibers had larger values of pCa1/2 than did fast-twitch fibers. Slow-twitch fibers from the predominantly slow muscles, SOL and AL, had similar values of pCa1/2 but slightly smaller values than from the mixed muscle, PG. Fast-glycolytic (FG) fibers from the predominantly fast muscle, EDL, had a higher pCa1/2 than fibers from the mixed fiber type muscle, PG. There were no differences between the pCa1/2 associated with FG and fast-oxidative-glycolytic fibers.

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