Abstract
We have previously observed the functional differences in myocardial contraction between normal control (F1B strain) and cardiomyopathic hamsters (Bio TO-2 strain). To understand the mechanisms underlying myocardial contractile dysfunction in TO-2 hamster, we compared the composition of myosin isoforms and the concentration of myosin heavy chain (MHC) and actin in ventricular muscles of F1B and TO-2 hamsters. Myosin isoforms were separated with pyrophosphate / polyacrylamide gel electrophoresis and their relative proportions were densitometrically quantified. Ventricular myosin from TO-2 consisted of three isoforms, V1 (∼50%), V2 (∼30%) and V3 (∼20%), while F1B myosin contained mostly V1 isoform, accounting for our previous observation that under unloaded conditions, the maximum shortening velocity was lower in TO-2 than in F1B cardiomyocytes. The concentrations of MHC and actin relative to those of total ventricular protein were lower in TO-2 than in F1B hamster, being consistent with our previous finding, the lower isometric peak force in TO-2 than in F1B cardiomyocytes. These results suggest that the shift of myosin isoform from V1 to V2 and V3 and the decrease in contractile protein concentration may contribute to myocardial contractile dysfunction in dilated cardiomyopathic hamster (TO-2). [Jpn J Physiol 55 Suppl:S95 (2005)]
