THE RECOVERY OF CONTRACTILITY AFTER CONTRACTION IN CARDIAC MUSCLE

Abstract

Ventric-ular strips from the turtle were rendered quiescent in Ringer''s solution by addition of Mg, and rhythmically stimulated by induction shocks. The amplitude of contraction is constant in these muscles for a constant rate of stimulation, but varies with rate of stimulation. Obviously the amplitude of contraction is dependent on the velocity of recovery from the refractory period and on the interval between contractions. Since the velocity of recovery was altered by varying the interval between preceding contractions, this is apparently a combined function of the amplitude of the preceding contraction and the reciprocal of the interval between the 2 preceding contractions. The phenomenon of alteration of the rate of recovery as the interval between rhythmical stimuli changes may be one factor in the production of the "treppe" phenomenon. Similar results were obtained with muscles in moist O, in N, and in CO2. This indicates that the phenomenon is not due to the presence of Mg in the bathing fluid.