Regulation of cardiac myosin synthesis: studies of RNA content in cultured heart cells.

Contraction regulates the myosin content and the rate of myosin synthesis in cultured neonatal rat heart cells. To further explore the mechanism for this regulation we examined various parameters of RNA content and RNA synthesis in contacting versus noncontracting myocytes. While contraction stimulated myosin heavy chain (MHC) synthesis by 72% compared to that of KCl-arrested cells, simultaneous analyses of polysome profiles were no different under the two culture conditions. Incorporation of [3H]uridine monophosphate into cellular RNA revealed no change in the rate of total RNA or ribosomal subunits synthesis. In vitro translation of cellular RNA yielded similar incorporation of [35S]methionine into trichloroacetic acid precipitable protein. Specific transcription of the MHC gene was examined by dot-blot analysis and was unaltered by contraction. Northern blot analysis of the MHC sequences detected by a cDNA probe revealed an mRNA sequence corresponding to a molecular weight of approximately 30 S. These data suggest that RNA synthesis and RNA content are unaltered by contraction in cultured heart cells and therefore the changes in myosin synthesis may be mediated at a post-transcriptional control level.