title: Agents that promote protein phosphorylation inhibit the activity of the Na+/Ca2+ exchanger and prolong Ca2+ transients in bovine chromaffin cells.
abstract: The Na+/Ca2+ exchanger is an important element in the maintenance of calcium homeostasis in bovine chromaffin cells. The Na+/Ca2+ exchanger from other cell types has been extensively studied, but little is known about its regulation in the cell. We have investigated the role of reversible protein phosphorylation in the activity of the Na+/Ca2+ exchanger of these cells. Cells treated with 1 mM dibutyryl cyclic AMP (dbcAMP), 1 microM phorbol 12,13-dibutyrate, 1 microM okadaic acid, or 100 nM calyculin A showed lowered Na+/Ca2+ exchange activity and prolonged cytosolic Ca2+ transients caused by depolarization. A combination of 10 nM okadaic acid and 1 microM dbcAMP synergistically inhibited Na+/Ca2+ exchange activity. Conversely, 50 microM 1-(5-isoquinolinyl-sulfonyl)-2-methylpiperazine, a protein kinase inhibitor, enhanced Na+/Ca2+ exchange activity. Moreover, we used cyclic AMP-dependent protein kinase and calcium phospholipid-dependent protein kinase catalytic subunits to phosphorylate isolated membrane vesicles and found that the Na+/Ca2+ exchange activity was inhibited by this treatment. These results indicate that reversible protein phosphorylation modulates the activity of the Na+/Ca2+ exchanger and suggest that modulation of the exchanger may play a role in the regulation of secretion.
authors.affiliation: Program in Molecular and Cellular Biology, University of Massachusetts, Amherst.
authors.forename: L F
authors.initials: LF
authors.lastname: Lin
authors.forename: L S
authors.initials: LS
authors.lastname: Kao
authors.forename: E W
authors.initials: EW
authors.lastname: Westhead
mesh_terms: D000818:Animals; D003994:Bucladesine / Q000494:pharmacology*; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism / Q000502:physiology*; D002417:Cattle; D002838:Chromaffin System / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D004357:Drug Synergism; D004988:Ethers, Cyclic / Q000494:pharmacology*; D016257:Fura-2; D008387:Marine Toxins; D019319:Okadaic Acid; D010080:Oxazoles / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D010766:Phosphorylation; D011506:Proteins / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger
chemical_list: D002352:Carrier Proteins; D004988:Ethers, Cyclic; D008387:Marine Toxins; D010080:Oxazoles; D011506:Proteins; D019831:Sodium-Calcium Exchanger; D019319:Okadaic Acid; D003994:Bucladesine; C059041:calyculin A; D010749:Phosphoprotein Phosphatases; D002118:Calcium; D016257:Fura-2