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A moderate degree of lead intoxication was observed in male rats after repeated intraperitoneal injections with two doses of lead acetate three times a week during 5 (12.5 mg of Pb per kg body mass) and 6 (6.01 mg of Pb per kg body mass) weeks. Using an in vitro motility assay, we investigated the impact of this intoxication on the characteristics of actin-myosin interaction and its regulation in the atria, right, and left ventricles. Both lead doses exposure decreased the maximum sliding velocity of reconstituted thin filaments over myosin and fraction of motile filaments in all heart chambers, caused the myosin isoforms shift towards slower β-myosin heavy chains in ventricles and decreased regulatory light chain phosphorylation in atria. No statistically significant difference was found in force and calcium regulation of actin-myosin interaction. A dose-dependent effect of lead on myosin functional characteristics was …