The polycationic compound gentamicin inhibits the calcium paradox in guinea-pig hearts

The calcium paradox was induced by perfusion, for 50 s, with Ca super(2+)-free solution containing EGTA. Nifedipine and verapamil in concentrations which reduced the equilibrium contractile force by 50% only mitigated the extent of the calcium paradox, whereas gentamicin applied in a concentration also reducing the contractile amplitude by 50% was able to suppress the calcium paradox completely. The dose-response curves for nifedipine, with respect to the reduction of contractile force and contracture, were identical. In contrast, gentamicin was more effective in attenuating the contracture of the paradox than in reducing the equilibrium contractile force. The large gain of Na super(+) during the Ca super(2+)-lack period was diminished by both nifedipine and gentamicin.