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

Abstract

Single fibers of rat diaphragm containing different naturally occurring 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 Sr(2+) of the contractile system. Mechanically skinned fibers were studied for their isometric force vs. Sr(2+) concentration ([Sr(2+)]) relationships and then analyzed electrophoretically for myofibrillar protein isoform composition. Our data demonstrate that fiber-type differences in Sr(2+) dependence of contractile activation processes are primarily determined by the TnC isoform composition, with the slow isoform conferring on average a seven..