Electrical bursting and luminal calcium oscillation in excitable cell models.

It is shown in this paper that electrical bursting and the oscillations in the intracellular calcium concentration, [Ca2+]i, observed in excitable cells such as pancreatic beta-cells and R-15 cells of the mollusk Aplysia may be driven by a slow oscillation of the calcium concentration in the lumen of the endoplasmic reticulum, [Ca2+]lum. This hypothesis follows from the inclusion of the dynamic changes of [Ca2+]lum in the Chay bursting model. This extended model provides answers to some puzzling phenomena, such as why isolated single pancreatic beta-cells burst with a low frequency while intact beta-cells in an islet burst with a much higher frequency. Verification of the model prediction that [Ca2+]lum is a primary oscillator which drives electrical bursting and [Ca2+]i oscillations in these cells awaits experimental testing. Experiments using fluorescent dyes such as mag-fura-2-AM or aequorin could provide relevant information.