Figure 9. Effect of caffeine on [Ca²⁺]_i and R_rel evoked using different pulse durations.

A-C, calcium transients ([Ca²⁺]_i) and the underlying SR calcium release elicited using 10, 15, 40 and 100 ms depolarizing pulses to 0 mV. The pulse protocol is shown below the records. The measurement was carried out in control (A), in the presence of caffeine (B) and after the removal of the drug (C). Calibration bars for [Ca²⁺]_i and for R_rel are, respectively: vertical, 0.5 μm and 15 μm ms⁻¹; horizontal, 100 and 50 ms. D, time-to-peak (TTP) values of the calcium transients and the calculated SR calcium release for the 10, 15 and 40 ms depolarizations in control (○), after the addition of caffeine (•) and after wash (□). Values were calculated from the transients shown in A-C. Note that caffeine did not influence the TTP. [APIII]= 995-1403 μm, [fura-2]= 97.6–149.6 μm. Parameters of the removal model: k_off,Mg-P = 14.5 s⁻¹, PV_max = 1.6 mm s⁻¹, k_on,Ca-E = 2.2 μm⁻¹ s⁻¹ and k_off,Ca-E = 1.9 s⁻¹.