Troponin C isoform composition determines differences in Sr 2 -activation characteristics between rat diaphragm fibers

Abstract

Single fibers of rat diaphragm containing different naturally occuring combinations of myofibrillar protein isoforms were used to evaluate the contribution of troponin C (TnC) isoforms to fiber type-related differences with respect to sensitivity to Sr2+ of the contractile system. Mechanically skinned fibers were studied for their isometric force vs. Sr 2+ concentration ([Sr2+]) relationships and then analyzed electrophoretically for myofibrillar protein isoform composition. Our data demonstrate that fiber-type differences in Sr2+ dependence of contractile activation processes are primarily determined by the TnC isoform composition, with the slow isoform conferring on average a sevenfold gre..