Inhibition of phenylephrine induced hypertrophy in rat neonatal cardiomyocytes by the mitochondrial KATP 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.