Effects of verapamil on the extracellular K+ rise during myocardial ischaemia in dogs.

The effects of verapamil on the [K+]o rise produced by myocardial ischaemia were assessed in 26 open chest mongrel dogs. Ischaemia was produced by intermittent occlusion of the LAD artery (15 dogs) or by reduction of flow of the cannulated LAD (11 dogs). Specially constructed valinomycin K+ sensitive electrodes were inserted into the mid myocardium in the central zone of ischaemia (CZ); in the margin (MZ) and in the nonischaemic zone (NZ). Occlusion of the coronary artery under controlled conditions produced significant [K+]o rise, greater in the CZ than in the MZ. During the infusion of verapamil the ischaemic [K+]o rise was substantially reduced in both zones. During controlled 75% reduction of coronary flow the [K+]o reached a plateau that remained stable until reperfusion was re-established. During verapamil infusion, the plateau showed a steady decline, both in the CZ and in the MZ. The changes in [K+]o produced by verapamil, during myocardial ischaemia are probably due to: coronary dilatation of the marginal arteries and+or to a reduction of the late cellular K+ conductance due to a decrease in the intracellular Ca2+, produced by verapamil.