Induction of atrial natriuretic factor and myosin light chain-2 gene expression in cultured ventricular myocytes by electrical stimulation of contraction

While hormonal stimuli and mechanical stretch can induce cardiac-specific gene expression and in some cases cellular hypertrophy, the relationship between myocyte contraction frequency, gene expression, and myocyte growth has not been well characterized. In this study a new model system was developed in which cultures of neonatal rat ventricular myocytes were subjected to long term pacing of contractions with pulsatile electrical stimulation. Myocytes submitted to electrical stimulation for 3 days displayed dramatic increases in cellular size and myofibrillar organization, and a 5-10-fold increase in the expression of the cardiac genes atrial natriuretic factor and myosin light chain-2. Atrial natriuretic factor expression induced by electrical stimulation of contractions was inhibited by nifedipine or W7, indicating a dependence on calcium influx and calmodulin activity. Phosphoinositide hydrolysis and cAMP formation were not affected by electrical stimulation suggesting that gene induction occurred independently of the activation of protein kinases C or A above basal levels. These findings show that the cellular events associated with contraction, such as changes in cytoplasmic free calcium levels and/or cellular stretch, may serve as important determinants of myocyte growth and cardiac gene expression.