[Assessment of the mechanical activity of cardiac isomyosins V1 and V3 by an in vitro motility assay with regulated thin filaments].

ABSTRACT

A series of experiments in an in vitro motility assay with reconstructed thin filaments has been performed to determine the dependence of the velocity of thin filament movement on the concentration of calcium in solution (in the pCa range from 5 to 8) for rabbit cardiac isomyosins V1 and V3. The "pCa-velocity" curves had the sigmoid form. It was found for each isoform that sliding velocities of regulated thin filaments (at the saturating calcium concentration (pCa 5)) and actin filaments did not differ from each other. The Hill coefficient was 1.04 and 0.75 for isomyosins V1 and V3, respectively. The calcium sensitivity of V3 was found to be higher than that of V1. In the framework of the same method, the relationship between the velocity of thin filament sliding and the concentration of the actin-binding protein a-actinin (analog of the "force-velocity" relationship) has been estimated for each isoform V1 and V3 at the saturating calcium concentration. The results obtained suggest that the calcium regulation of the contractile activity of isomyosins V1 and V3 occurs by different mechanisms.