PKC REGULATION OF CARDIAC CFTR CL- CHANNEL FUNCTION IN GUINEA-PIG VENTRICULAR MYOCYTES

The role of protein kinase C (PKC) in regulating the protein kinase A (PKA)-activated Cl- current conducted by the cardiac isoform of the cy stic fibrosis transmembrane conductance regulator (cCFTR) was studied in guinea pig ventricular myocytes using the whole cell patch-clamp te chnique. Although stimulation of endogenous PKC with phorbol 12,13-dib utyrate (PDBu) alone did not activate this Cl- current, even when intr acellular dialysis was limited with the perforated patch-clamp techniq ue, activation of PKC did elicit a significant response in the presenc e of PKA-dependent activation of the current by the beta-adrenergic re ceptor agonist isoproterenol. PDBu increased the magnitude of the Cl- conductance activated by a supramaximally stimulating concentration of isoproterenol by 21 +/- 3.3% (n = 9) when added after isoproterenol a nd by 36 +/- 16% (n = 14) when introduced before isoproterenol. 4 alph a-Phorbol 12,13-didecanoate, a phorbol ester that does not activate PK C, did not mimic these effects. Preexposure to chelerythrine or bisind olylmaleimide, two highly selective inhibitors of PKC, significantly r educed the magnitude of the isoproterenol-activated Cl- current by 79 +/- 7.7% (n = 11) and 52 +/- 10% (n = 8), respectively. Our results su ggest that although acute activation of endogenous PKC alone does not significantly regulate cCFTR Cl- channel activity in native myocytes, it does potentiate PKA-dependent responses, perhaps most dramatically demonstrated by basal PKC activity, which may play a pivotal role in m odulating the function of these channels.