Studies on the Potentiation of Contractility of Heart Papillary Muscle by Paired Stimulation

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Abstract
The positive inotropic effect of paired stimulation was studied in isolated papillary muscles of the cat. The observations made on isometrically and isotonically contracting preparations show that paired stimulation must be differentiated from a pure frequency potentiation. Paired stimulation potentiation is hardly affected neither by changing initial muscle length, initial tension, stimulation frequency nor bath temperature. It is independent of the catecholamine stores in the heart and is not inhibited by blockade of the β adrenergic receptor mechanism. A close frequency and temperature dependent correlation was found between time to peak tension values, minimal and optimal time intervals during paired stimulation, and absolute and effective electrical refractory period. On transition to paired electrical stimulation the isolated papillary muscle of the cat behaves in a similar fashion as is observed in postcxtrasystolic potentiation. It is concluded that both forms of potentiation can be ascribed to a same fundamental underlying mechanism.

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