Three, non-cytosolic Ca2+ pools were characterized in intact PC12 cells. The first pool, sensitive to both inositol 1,4,5-trisphosphate and caffeine (Zacchetti, D., Clementi, E., Fasolato, C., Zottini, M., Grohovaz, F., Fumagalli, G., Pozzan, T., and Meldolesi, J. (1991) J. Biol. Chem. 266, 20152-20158) accounts for ≅200 μM of Ca2+/liter of cell water (<30% of total exchangeable Ca2+) and takes up Ca2+ from the cytosol via a Ca2+-ATPase, blocked by thapsigargin. A second pool, ≅400 μM/liter, is insensitive to both inositol 1,4,5-trisphosphate, caffeine, and thapsigargin and is released by the Ca2+ ionophore ionomycin. This pool is probably heterogeneous and its intracellular localization and physiological roles remain undefined. The third pool, ≅170 μmoles of Ca2+/liter, was discharged by the combination of ionomycin together with a substance that collapsed intracellular pH gradients, such as monensin or NH4C1. This indicates that the pool is acidic, at variance with the first two. When exocytosis was stimulated, the size of this pool declined, indicating its primary residence within secretory granules. In the conditions of our experiments no major transfer of Ca2+ among the pools seemed to occur. This is the first comprehensive description of non-cytosolic Ca2+ pools investigated in intact neurosecretory cells by non-invasive procedures.
|Number of pages||9|
|Journal||Journal of Biological Chemistry|
|Publication status||Published - 1991|
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