Orientation change of cardiocytes induced by cyclic stretch stimulation: Time dependency and involvement of protein kinases

Mechanical stress has been implicated as one of the growth regulators in th e heart. We investigated the effect of cyclic stretch stimulation on morpho logy and orientation of cultured cardiocytes. Embryonic rat (17 days postco ital) cardiomyocytes cultured on silicone dishes were cyclically stretched to 120% in length at a frequency of 30 cycles/min. After 12 h, in the initi al stage of cultivation, cardiocytes and intracellular myofibrils oriented parallel to the stretch direction. When the stretch stimulus was prolonged to 24-48 h, myofibrils that oriented perpendicular to the stretch direction emerged. Furthermore. when the cells were stretched only in the later stag e (after 24 h of cultivation). both cells and myofibrils tended to orient p erpendicular to the stretch direction. Next we examined the effects of chem ical compounds on these phase related changes in myofibril orientation None of the drugs tested (H-7, HA-1004, staurosporine, herbimycin A, genistein, GdCl3, and EGTA) blocked the parallel orientation of myofibrils induced by the initial-stage stretch. By contrast, H-7, staurosporine, herbimycin A, and genistein did inhibit almost completely the perpendicular orientation o f the myofibrils induced by the late-stage stretch, but HA-1004, GdCl3, or EGTA did not, Immunoblotting study using anti-phsophotyrosine antibody indi cated that tyrosine phosphorylation of a protein of about 125 kDa was enhan ced in a time-dependent manner by the late-stage stretch, but not by the in itial-stage stretch. In conclusion: the alignment change induced by cyclic stretch depends on the stage of cultivation: with stretch in the initial st age (within 12 h), cells and myofibrils orient parallel to the stretch; wit h stretch in the later stage (after 24 h), they orient perpendicular to the stretch. The effect of stretch in the later stage is likely mediated by pr otein kinase C and tyrosine kinase pathways. (C) 1999 Academic Press.