INFLUENCE OF MECHANICAL-ACTIVITY, ADRENERGIC-STIMULATION, AND CALCIUMON THE EXPRESSION OF MYOSIN HEAVY-CHAINS IN CULTIVATED NEONATAL CARDIOMYOCYTES

It is generally accepted that mechanical stress of cardiomyocytes incr eases RNA and protein synthesis of myosin heavy chain (MHC) quantitati vely but it is still a matter of debate whether MHC gene expression is also changed qualitatively. We investigated expression of MHC genes o f spontaneously contracting neonatal cardiomyocytes experimentally arr ested by permanent depolarization [potassium chloride (KCl)] as well a s by electromechanical uncoupling [2,3 butanedione monoxime (BDM)]. Re lative distribution of MHC mRNA isoforms (alpha and beta) was studied by quantitative polymerase chain reaction. Expression of MHC isoenzyme s was the same in contracting (34.5% beta-MHC) and arrested (40.5% and 33.0% beta-MHC in KCl and BDM, respectively) cardiomyocytes. However, treatment with phenylephrine for the same period increased significan tly beta-MHC expression to 55%. We conclude that hormonal factors rath er than Ca2+ or mechanical stress regulate qualilatively MHC gene expr ession. (C) 1997 Wiley-Liss, Inc.