Abstract
Sudden increase in tension on the quiescent isolated cat papillary muscle from 1 to 5 or 10 g lowered the threshold concentration of epinephrine needed to induce automaticity. The threshold was lowered for no longer than 30 seconds. Slow changes in tension did not lower the threshold. Sustained tension of 5 or 10 g did not change the threshold, nor prolong the lowering of threshold resulting from sudden increase in tension. Contractions of muscles after a sudden rise to 10 g tension or sustained at this level were irregular in rhythm and strength, in contrast to the contractions of muscles under 1 g tension. Sensitization of cardiac muscle to epinephrine by tension changes progressively increasing with each successive beat may account for the effects of elevation of arterial blood pressure in cyclopropane-epinephrine and other arrhythmias.
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