Effect of amiodarone on the dynamics of mechanical restitution of rat papillary muscles

We studied the effect of amiodarone (class III antiarrhythmic drug) on the dynamics of mechanical restitution of rat papillary muscle. Amiodarone produced a weak negative inotropic effect and stimulated potentiation of contractility of the muscle preparation after short-term (4-60 sec) cessation of its electrical stimulation. On the other hand, the time of attaining half-maximum amplitude of contractions after amiodarone treatment did not differ from the control. Analysis of curves presenting the drop of potentiation of muscle preparation contractility after resumption of regular electrical stimulation after 60-sec arrest until attaining a stable level showed that the amplitude returned to the initial level by the 9thcontraction-relaxation cycle both in the control and after amiodarone treatment. Coefficient of the drop of contraction amplitude potentiation was virtually the same in the two groups. Presumably, amiodarone does not modulate calcium-binding capacity of the sarcoplasmic reticulum, but improves Ca retention in the sarcoplasmic reticulum stores.