Adaptation to stress exposure prevents the arrhythmogenic and contractile effects of the "calcium paradox"

It was established in experiment on rat papillary muscle that adaptation to stress exposure increased the myocardial resistance to contractile actions and limited the depression of electrophysiologic parameters induced by the excess of intracellular calcium. This adaptation decreased the contracture in 6.5 times and significantly limited the depression of resting potential (RP) induced by low-sodium (9 mM) perfusing solution. It was shown at the next stage that adaptation limited the depression of electrophysiologic parameters of cardiac cells at high calcium concentrations and high pacing rate. Under these factors the resting potential appeared to be significantly more in adaptation than in control (82 mV vs 69 mV respectively) while the action potential (AP) duration was twofold more. Possible mechanism is discussed of the cardioprotective effect of adaptation to stress exposure associated with the limitation of RP and AP in calcium overload.