[Ca2+]i oscillations from internal stores sustain exocytic secretion from the chromaffin cells of the rat

A large (65%) fraction of in vitro cultured rat chromaffin cells exhibit spontaneous [Ca2+]i oscillations, and the rest can be recruited to oscillate by appropriate stimulations. Based on fura‐2 single cell [ca2+]i measurements, evidence is provided that these oscillation originate, via the activation of Ca2+‐induced Ca2+‐release, from intracellular Ca2+ stores in rapid equilibrium with extracellular Ca2+. By combining [Ca2+]i measurements with a specific plaque secretion assay we demonstrate that oscillating cells exhibit a spontaneous exocytic secretory activity whereas the cells with stable [Ca2+]i do not, [Ca2+]i oscillations appear therefore to account for the high unstimulated catecholamine release, an activity typical of the chromaffin cells of the rat.