Phorbol Ester-Induced Ventricular Fibrillation in the Langendorff-Perfused Rabbit Heart: Antagonism by Staurosporine and Glibenclamide

Using a paced Lagendorff-perfused rabbit heart paradigm, we investigated the role of protein kinase C (PKC) in the development of ventricular fibrillation (VF)in hearts subjected to hypoxia (12 min) and re-oxygenation (40 min). We studied the effect of putative activators and inhibitors of PKC on the incidence of VF. Hearts exposed to 4β-phorbol, 12, 13-dibutyrate (PDBu), isophorbol or the membrane permeant diacylglycerol analog, t-oleoyl-2-accetyl-acetyl-rac-glycerol (OAG), during the prehypoxic phase had an increased incidence of VF during the hypoxic and reoxygenation periods. The incidence of VF was 90%, 83% and 75% in hearts exposed to PDBu, isophorbol and OAG, respectively (P < 0.05 vs control). Perfusion of hearts with PDBu was associated with a significant increase in the membrane fraction of cardiac PKC activity. In the presence of the inactive phorbol ester 4α-phorbol didecanoate, the incidence of VF was 17% (P > 0.05 vs control). PKC activators were profibrillatory at concentrations that did not affect cardiac function: neither left ventricular developed pressure nor coronary perfusion pressure were affected. The effect of PDBu was antagonized by staurosporine: the incidence of VF was 17% in PDBu + staurosporine treated hearts (P < 0.05 vs control). To further study the porfibrillatory effect of PDBu, hearts were exposed to PDBu in the presence of the ATP-dependent potassium channel antagonist glibenclamide. The latter prevented PDBu-induced VF. The results show that under the conditions employed, PDBu-induce activation of PKC induces redistribution of PKC activity and is associated with the development of VF.