The role of Na+/H+ exchange in norepinephrine-induced protein synthesis in neonatal cultured rat cardiomyocytes.

Abstract
It is reported that Na+ influx contributes to stretch-induced cardiac hypertrophy. Na influx may also be involved in cardiac hypertrophy induced by catecholamine. In the present study, to test whether Na+/H+ exchange plays an important role in norepinephrine-induced cardiac hypertrophy, the effect of Na+/H+ exchange inhibitor, amiloride on protein systhesis was studied in cultured neonatal rat cardiomyocytes in serum free medium. [3H]Phenylalanine uptake was determined 24 and 48 hours after administration of norepinephrine with and without amiloride. In the control, norepinephrine increased [3H]phenylalanine uptake in a dose dependent manner (10-5-10-7 M). Prazosin (10-7 M) and amiloride (10-5-10-4M) significantly attenuated the norepinephrine mediated protein synthesis. These results indicate that α1-adrenergic stimulation enhances the protein synthesis through activation of Na+/H+ exchange. Therefore, Na+ influx and/or PH increase may play a key role in cardiac hypertrophy.

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