Magnitude of length-dependent changes in contractile properties varies with titin isoform in rat ventricles

Abstract

The effects of differential expression of titin isoforms on sarcomere length (SL)-dependent changes in passive force, maximum Ca2+-activated force, apparent cooperativity in activation of force ( nH), Ca2+ sensitivity of force (pCa50), and rate of force redevelopment ( ktr) were investigated in rat cardiac muscle. Skinned right ventricular trabeculae were isolated from wild-type (WT) and mutant homozygote (Ho) hearts expressing predominantly a smaller N2B isoform (2,970 kDa) and a giant N2BA-G isoform (3,830 kDa), respectively. Stretching WT and Ho trabeculae from SL 2.0 to 2.35 μm increased passive force, maximum Ca2+-activated force, and pCa50, and it decreased nH and ktr. Compared with WT trabeculae, the magnitude of SL-dependent changes in passive force, maximum Ca2+-activated force, pCa50, and nH was significantly smaller in Ho trabeculae. These results suggests that, at least in rat ventricle, the magnitude of SL-dependent changes in passive force, maximum Ca2+-activated force, pCa50, nH, and ktr is defined by the titin isoform.