Phase responses of a model islet oscillator to a single pulse of IP3.
Unperturbed model islet oscillations are shown in black. The red trace shows the model islet perturbed with a single 10 sec IP3 pulse applied at 20 min. (A) When applied during a burst active phase the IP3 pulse terminates the burst and there is an advance in the timing of the next active pase. (B) When applied early in a silent phase there is little effect on the phase of the islet oscillator. (C) When applied late in a silent phase there is a delay in the next burst. (D) A phase response curve showing the effect of an IP3 pulse on the phase of the islet oscillator. Phase 0 is the beginning of a burst active phase, while phase 1 is the end of the subsequent silent phase. The abscissa shows the phase at which the stimulus was applied, while the ordinate shows the effect the perturbation has on the phase as determined by the difference in timing of the unperturbed nadir (black circle in panels above) and the perturbed nadir (red circle). A negative phase difference means a phase advance, while a positive difference means a phase delay.