Figure 3. The effect of AIP is dependent on cycle length and [Ca²⁺]_i.

A, the experimental protocols are shown at the top. Mean time courses of recovery from I_Ca−L inactivation measured during slow pacing (SP) and fast pacing (FP) conditions are shown with or without 2 μmol l⁻¹ AIP treatment. See inset for symbol assignment. The inset shows the mean I_Ca−L recovery times, T_0.5, of each groups (#P < 0.05; *P < 0.01). B, superimposed I₁ and I₂ traces of I_Ca−L before (a), during fast pacing at 1 Hz (b) and after pacing had slowed to 0.1 Hz (c). The currents were taken at the times marked in panel C (a–c). C, shows average dynamics of I₂/I₁ ratio during abrupt changes in pacing frequency. The experimental protocol is shown in the top panel. The I₁–I₂ interval was fixed at 0.15 s while the interpaired pulse interval was either 10 or 1 s. Two transitions were examined. After more than a 10-s rest, the interpulse interval was increased to 1 Hz for 10 pulses and then abruptly slowed to 0.1 Hz. The dynamics of the transitions of interpulse interval are plotted. *P < 0.01, when compared with the first I₂/I₁.