Simultaneous Ca2+ measurements in the cytosol and intracellular stores (IS) of rat hepatocytes were performed using two Ca(2+)-sensitive probes (Fluo-3 and Mag-fura-2), and combined whole-cell patch clamp and fluorescence microscopy. A steady-state Ca2+ concentration of approximately 630 microM was estimated in the IS. alpha 1-Adrenergic stimulation induced periodic elevations of cytosolic Ca2+ and parallel synchronized transient declines in the IS. Subsequent application of the intracellular Ca(2+)-pump inhibitor thapsigargin resulted in a release of Ca2+ from the IS to reach a level of Ca2+ depletion much lower than the lowest transient decline observed during the oscillations.