Fig. 2.
Interposed hyperpolarization can increase ΔCm. (a) Representative ICa during the four stimulus patterns shown in b. Each cell received patterns A and B, plus one or more of the other patterns. (b) Stimuli A–D are steps to −55 mV, except in a few cells in which the ΔCm responses to stimuli A and B were too small to measure, in which case the depolarization was increased to −50 mV. Step timing: stimulus A, 30 ms; stimulus B, 2 × 10 ms separated by 10 ms; stimulus C, 2 × 14 ms separated by 2 ms; stimulus D, 2 × 2 ms separated by 26 ms. (c) Mean ΔCm responses (±SEM) to the four stimulus patterns. The response to stimulus B was significantly larger than all others (see text). An alternative analysis in which the ΔCm responses in each cell were first normalized by the ΔCm response to stimulus waveform B gave similar results. (d) Individual ΔCm from the 19 cells receiving stimulus patterns A and B. Responses to the first stimulus presentation are shown for waveforms A (solid gray bars) and B (striped bars).