Inhibition of phenylephrine induced hypertrophy in rat neonatal cardiomyocytes by the mitochondrial K channel opener diazoxide

The effect of the putative mitochondrial KATP channel opener diazoxide (100 μM) was studied in terms of its ability to modulate the hypertrophic effect of 24 h treatment with the α1 adrenoceptor agonist phenylephrine (PE; 10 μM) in cultured neonatal rat ventricular myocytes. PE on its own significantly increased cell size by 40%, 3H leucine incorporation by 37% and produced more than a threefold elevation in both atrial natriuretic peptide and myosin light chain-2 expression. These effects were nearly completely prevented by diazoxide although the inhibitory effect of this agent was generally mitigated by the mitochondrial KATP channel antagonists 5-hydroxydecanoic acid (100 μM) and glibenclamide (50 μM). Although PE produced an early threefold elevation in MAP kinase activation this was generally unaffected by diazoxide. PE also produced a greater than threefold increase in Na–H exchanger isoform 1 (NHE-1) expression which, was prevented by diazoxide treatment. Our study therefore, demonstrates a potential antihypertrophic influence of mitochondrial KATP channel activation which, is related to diminished NHE-1 expression. Mitochondrial KATP channel activation could represent an effective approach to minimize the myocardial hypertrophic process.