Effects of Ryanodine on Ouabain-induced spontaneous mechanical and electrical oscillations in guinea-pig heart

Abstract The effects of ryanodine on ventricular arrhythmias in guinea-pigs in vivo , on delayed afterpotentials and aftercontractions, and on spontaneous oscillations of the membrane potential (SOP) and of resting tension (SOT) of guinea-pig papillary muscle under ouabain intoxication were studied After addition of ouabain (1 μ m ) the afterpotentials, aftercontractions, and SOP and SOT amplitude were significantly increased. The power spectra of SOT and SOP under these conditions had a resonance harmonic with the frequency of about 5 Hz. Three to 5 mins after the addition of ryanodine (0.1–0.5 μ m ), the afterpotentials, aftercontractions, and SOP and SOT were abolished, suggesting a close relationship between these oscillations and the oscillatory activity of sarcoplasmic reticulum. In in vivo experiments, ouabain-induced (75–115 μg/kg) ventricular arrhythmias were terminated 4 to 5 min after intravenous injection of ryanodine (15 μg/kg), within 8–10 min, sinus rhythm was completely restored. We attribute the antiarrhythmic effect of ryanodine to a cellular effect and alteration of SR function, rather than to effects that are secondary to this.