SIMULTANEOUS MEASUREMENTS OF CA2+ IN THE INTRACELLULAR STORES AND THE CYTOSOL OF HEPATOCYTES DURING HORMONE-INDUCED CA2+ OSCILLATIONS

Simultaneous Ca2+ measurements in the cytosol and intracellular stores (IS) of rat hepatocytes were performed using two Ca2+-sensitive probes (Fluo-3 and Mag-fura-2), and combined whole-cell patch clamp and fluorescence microscopy. A steady-state Ca2+ concentration of similar to 630 mu M 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 Ca2+-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.