Myosin-activating protein kinases are possible regulators of nonmuscle myosin in developing human heart.

We studied the localization of myosin-activating protein kinases in cardiomyocytes obtained from fetal human heart at 8-9 weeks gestation. It was found that at this developmental stage, smooth muscle/nonmuscle myosin light chain kinase (MLCK, 108 kDa) and its high-molecular weight isoform (MLCK, 210 kDa), skeletal MLCK and death-associated protein kinase (DAPK) are co-localized with nonmuscle myosin IIB in the premyofibrils. The data obtained suggest that cardiac nonmuscle myosin at 8-9 weeks gestation may serve as the substrate of the studied myosin-activating protein kinases that are likely to cooperatively regulate the formation of myofibrils. We revealed high-molecular weight isoform of smooth muscle/nonmuscle kinase MLCK-210 in developing human heart and determined the ratios of MLCK-108 and MLCK-210 at different gestational stages. In this case, the approximate time period of changes in these isoforms ratio was revealed (between 8-9 and 13 weeks), that can be associated with functional changes in the developing myocardium.