Protection by verapamil and nifedipine against ischaemia-induced loss of [3H]-(+)-PN 200-110 binding sites in the rat heart.

We have studied the effects of 60 min global ischaemia and 30 min of subsequent reperfusion on the binding of [3H]-(+)-PN 200-110 and [3H]-(-)-devapamil (desmethoxyverapamil or D888) in rat heart membranes. The hearts were perfused in the Langendorff-mode and pretreated with 1 mumol/l verapamil, 30 nmol/l and 1 mumol/l nifedipine. After 60 min of global ischaemia in the absence of drugs, we found a reduction of [3H]-(+)-PN 200-110 binding sites, without changes in the equilibrium dissociation binding constant (Kd). After the subsequent reperfusion maximum specific binding (Bmax) was further reduced, whereas the Kd remained constant. [3H]-devapamil binding sites were influenced to a lower extend and showed only a decrease in Bmax at reperfusion. Pretreatment with 1 mumol/l verapamil completely prevented the changes which were observed for [3H]-(+)-PN 200-110. Pretreatment with a low, vasodilating concentration (30 nmol/l) of nifedipine displayed selective protection against the extra reduction in Bmax which was observed during reperfusion. It is concluded that calcium antagonists show protection against the ischaemia-induced loss of dihydropyridine binding sites in relation to their negative inotropic, energy-saving activity. Furthermore, nifedipine at low, vasodilating but not negative inotropic concentrations protects against further reperfusion-induced injury, which protection may be related to an improved flow during reperfusion.