Effect of Procaine on the Ventricular Muscle of Bullfrog

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  • Effects of Procaine on the Ventricular Muscle of Bullfrog
  • Effect of Procaine on the Ventricular M

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The effects of procaine on the contractility of the bullfrog's ventricular muscle were investigated. The addition of 10-5 g/ml of pro-caine potentiated the twitch tension which was accompanied by an eleva-tion as well as a prolongation of the action potential plateau. This positive inotropism of procaine was not induced by endogenous catecho-lamine because a β-blocking agent did not influence this twitch potentia-tion. The twitch potentiation was increased in proportion to the external Ca concentration, suggesting the possibility of augmentation of Ca influx during the action potential. In normal Ringer solution, procaine sup-pressed potassium contracture which was composed of two components: an initial phasic component and a late tonic one. Potassium contracture after perfusion with Ca-free solution was also suppressed by procaine. However, potassium contracture which had been treated previously with La was composed of only a tonic component and was potentiated by procaine in spite of perfusion with Ca-free solution. The tonic com-ponent of potassium contracture may be considered to occur with in-tracellular Ca. Procaine may increase the Ca inward current, acting on the intracellular Ca storage site and consequently accelerate the excita-tion-contraction coupling in frog ventricular muscle.

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