Figure 5. Time course of CICR during continuous Ca²⁺ entry.

A–C, F/F₀ rises elicited by depolarizing pulses to 0 mV with various durations. Pulse durations were 2–10 ms in A, 10–50 ms in B, 100–500 ms in C, respectively. The darker trace was the F/F₀ rise elicited by the pulse of longer duration. F/F₀ traces were obtained at 4 ms linescan⁻¹ from the cytoplasm within 2 μm of the plasma membrane, averaged over 2 traces and smoothed by moving average over 12 ms. The traces in different panels were from different neurons. V_m and I_Ca are shown below. The inset in A shows the correlation of I_Ca at the ends of 2–10 ms depolarizing pulses with the resulting rates of CICR (f_Ca), obtained from 12 neurons. I_Ca and f_Ca were normalized to those evoked by a 10 ms pulse (I_Ca10ms and f_Ca10ms, respectively). The plot was fitted with a straight line (dashed line; slope, 0.89; r² value, 0.68).