Transfection by eukaryotic expression vector pcDNA3-HERG inhibits the cultured neonatal rabbit ventricular myocyte hypertrophy induced by phenylephrine

ObjectiveProlonged action potential and decreased outward K⁺ currents are consistent findings in hypertrophic myocardium. The relation between action potential prolongation and myocyte hypertrophy has remained unclear. The present study investigated the temporal relation between action potential prolongation and myocyte hypertrophy, and the effect of enhancing repolarization on myocyte hypertrophy induced by phenylephrine.MethodsNeonatal rabbit ventricular myocytes were cultured and treated with 10 μmol/l phenylephrine. At 6 and 48 h after phenylephrine stimulation, myocyte hypertrophic parameters (including myocyte volume, total protein content, and membrane capacitance), action potential duration (APD), and calcineurin activity were measured; meanwhile, the effect of human-ether-a-go-go–related gene (HERG; encoding the αsubunit of rapidly activating delayed rectifier potassium channel) transfection on the above parameters at 48 h of phenylephrine stimulation was also measured.ResultsAt 6 h after phenylephrine treatment, APD at 90% repolarization of neonatal rabbit ventricular myocytes was prolonged by 14.3% (P<.05), but myocyte hypertrophy was not found. At 48 h after phenylephrine stimulation, APD at 90% repolarization of neonatal rabbit ventricular myocytes was furthermore prolonged by 18.8% (P<.05); at the same time, myocyte volume, total protein content, membrane capacitance, and calcineurin activity were increased by 40.0%, 41.8%, 36.4%, and 124.1%, respectively (P<.01). Neonatal rabbit ventricular myocytes transfected by pcDNA3-HERG overexpressed I_HERG,tail current, which was about fourfold higher than I_Kr (rapidly activating delayed rectifier K⁺ current) of neonatal rabbit ventricular myocytes without transfection of HERG. HERG overexpression could accelerate repolarization and shorten APD at 90% repolarization prolonged by phenylephrine and partially inhibit myocyte hypertrophy and calcineurin activation.ConclusionsDuring the myocyte hypertrophy induced by phenylephrine, prolongation of APD at 90% repolarization is not secondary to but precedes myocyte hypertrophy. HERG overexpression could enhance the repolarization and inhibit the calcineurin activation and myocyte hypertrophy induced by phenylephrine.