Figure 10.

Synaptic depolarization of cardiac muscle is linearly related to burst frequency. A, EJP bursts (4 pulses/burst; interpulse interval, 70 msec) delivered at 0.8 Hz to a quiescent preparation. At the break in the trace, the stimulation frequency was changed to 0.45 Hz. B, The amplitude of the first EJP in the burst is plotted as a function of time, during application of stimuli at different frequencies, as noted below the data points. Stimulus parameters are as in A. C, Amplitude of the first EJP in each burst (normalized to 1 at 0.8 Hz for each preparation) as a function of stimulation frequency. Data were pooled from eight independent preparations, each stimulated at multiple frequencies, as in A and B; the solid line represents a linear regression fit (r² = 0.88; p < 0.001).