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It has been shown that Y-27632, an inhibitor of Rho-associated kinase, delays sarcomere assembly in rat neonatal cardiomyocytes pretreated with angiotensin II. Y-27632 affects the beat rate of cardiomyocytes; however, this effect is only observed at high cell density and, therefore, seems to be related to the formation of gap junctions between adjacent cardiomyocytes. Consistent with this suggestion, we established that Rho-associated kinase is localized in myofibrillar Z-discs of human myocardium and intercalated discs, the structures enriched in gap junctions. We propose that Rho-associated kinase participates in the maturation of the myocardial contractile system through phosphorylation of its molecular targets in Z-discs and intercalated discs.

The skeletal myosin light chain kinase (skMLCK) was identified in human and chicken embryo myocardium but not in embryo and adult rat heart using western blotting. The content of skMLCK and myosin-activating protein kinases: RhaA-activated protein kinase (ROCK), integrin-linked protein kinase (ILK), and zipper-interacting protein kinase (ZIPK) was compared in normal human myocardium and the hearts of patients with dilated cardiomyopathy (DCM). It was demonstrated that the content of skMLCK, ROCK and ILK increases in DCM whereas the content of ZIPK decreases. The results obtained may reflect compensatory processes in cardiomyocytes in DMC, which are aimed at increasing their viability and contractility.