Differential temperature-dependency of electrophysiological and inotropic actions of nifedipine, verapamil and cinnarizine in K+-depolarized ventricular myocardium.

1. Temperature dependency (in the range 27-37 degrees C) of inotropic and electrophysiological effects of equieffective (EC30 at 37 degrees C) concentrations of nifedipine, verapamil and cinnarizine was assessed in potassium depolarized isoprenaline-reactivated guinea-pig ventricular strips. 2. Lowering temperature greatly enhanced nifedipine inhibition of (a) maximal rate of depolarization (Vmax) of slow action potentials and (b) amplitude of contractions. 3. Electrophysiological and inotropic actions of verapamil was virtually unaffected by temperature changes. 4. Negative inotropic action of cinnarizine was greater at 37 degrees C than at lower temperature. At 37 degrees C, but not at 32 degrees C, cinnarizine reduced Vmax of slow action potentials.