Calcium mobilizing hormones activate the plasma membrane Ca2+ pump of pancreatic acinar cells |
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Authors: | Shmuel Muallem Stephen J Pandol Timothy G Beeker |
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Institution: | (1) Laboratory of Membrane Biology, Research Institute, Cedars-Sinai Medical Center, and University of California, School of Medicine, 90048 Los Angeles, California;(2) Department of Medicine, Veterans Administration Medical Center and University of California, 92161 San Diego, California |
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Abstract: | Summary
45Ca fluxes and free-cytosolic Ca2+ (Ca2+]
i
) measurements were used to study the effect of Ca2+-mobilizing hormones on plasma membrane Ca2+ permeability and the plasma membrane Ca2+ pump of pancreatic acinar cells. We showed before (Pandol, S.J., et al., 1987.J. Biol. Chem.
262:16963–16968) that hormone stimulation of pancreatic acinar cells activated a plasma membrane Ca2+ entry pathway, which remains activated for as long as the intracellular stores are not loaded with Ca2+. In the present study, we show that activation of this pathway increases the plasma membrane Ca2+ permeability by approximately sevenfold. Despite that, the cells reduce Ca2+]i back to near resting levels. To compensate for the increased plasma membrane Ca2+ permeability, a plasma membrane Ca2+ efflux mechanism is also activated by the hormones. This mechanism is likely to be the plasma membrane Ca2+ pump. Activation of the plasma membrane Ca2+ pump by the hormones is time dependent and 1.5–2 min of cell stimulation are required for maximal Ca2+ pump activation. From the effect of protein kinase inhibitors on hormone-mediated activation of the pump and the effect of the phorbol ester 12-0-tetradecanoyl phorbol, 13-acetate (TPA) on plasma membrane Ca+ efflux, it is suggested that stimulation of protein kinase C is required for the hormone-dependent activation of the plasma membrane Ca2+ pump. |
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Keywords: | hormones plasma membrane Ca2+ permeability Ca2+ pump |
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