Influence of mechanical activity,adrenergic stimulation,and calcium on the expression of myosin heavy chains in cultivated neonatal cardiomyocytes

It is generally accepted that mechanical stress of cardiomyocytes increases RNA and protein synthesis of myosin heavy chain (MHC) quantitatively but it is still a matter of debate whether MHC gene expression is also changed qualitatively. We investigated expression of MHC genes of spontaneously contracting neonatal cardiomyocytes experimentally arrested by permanent depolarization potassium chloride (KCI)] as well as by electromechanical uncoupling 2,3 butanedione monoxime (BDM)]. Relative distribution of MHC mRNA isoforms (α and β) was studied by quantitative polymerase chain reaction. Expression of MHC isoenzymes was the same in contracting (34.5% β-MHC) and arrested (40.5% and 33.0% β-MHC in KCl and BDM, respectively) cardiomyocytes. However, treatment with phenylephrine for the same period increased significantly β-MHC expression to 55%. We conclude that hormonal factors rather than Ca²⁻ or mechanical stress regulate qualitatively MHC gene expression. J. Cell. Biochem. 64:458–465. © 1997 Wiley-Liss, Inc.