title: Activation of protein kinases and inhibition of protein phosphatases play a central role in the regulation of exocytosis in mouse pancreatic beta cells.
abstract: The mechanisms that regulate insulin secretion were investigated using capacitance measurements of exocytosis in single beta cells maintained in tissue culture. Exocytosis was stimulated by voltage-clamp depolarizations to activate the voltage-dependent Ca2+ channels that mediate Ca2+ influx into the beta cell. Under basal conditions, the exocytotic responses were small despite large Ca2+ currents. The exocytotic responses were dramatically increased (10- to 20-fold) by conditions that promote protein phosphorylation, such as activation of protein kinases A and C or inhibition of protein phosphatases. The stimulation of secretion was not due to an enhancement of Ca2+ influx and both peak and integrated Ca2+ currents were largely unaffected. Our data indicate that exocytosis in the insulin-secreting pancreatic beta cell is determined by a balance between protein phosphorylation and dephosphorylation. They further suggest that although Ca2+ is required for the initiation of exocytosis, modulation of exocytosis by protein kinases and phosphatases, at a step distal to the elevation of Ca2+, is of much greater quantitative importance. Thus an elevation of Ca2+ may represent a permissive rather than a decisive factor in the regulation of the insulin secretory process.
authors.affiliation: Rolf Luft Centre for Diabetes Research, Department of Endocrinology, Karolinksa Institute, Stockholm, Sweden.
authors.forename: C
authors.initials: C
authors.lastname: Ammälä
authors.forename: L
authors.initials: L
authors.lastname: Eliasson
authors.forename: K
authors.initials: K
authors.lastname: Bokvist
authors.forename: P O
authors.initials: PO
authors.lastname: Berggren
authors.forename: R E
authors.initials: RE
authors.lastname: Honkanen
authors.forename: A
authors.initials: A
authors.lastname: Sjöholm
authors.forename: P
authors.initials: P
authors.lastname: Rorsman
mesh_terms: D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004988:Ethers, Cyclic / Q000494:pharmacology; D005071:Evoked Potentials / Q000187:drug effects; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D007515:Islets of Langerhans / Q000187:drug effects / Q000201:enzymology / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors*; D011493:Protein Kinase C / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D004988:Ethers, Cyclic; D005576:Colforsin; D019319:Okadaic Acid; D011494:Protein Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D010749:Phosphoprotein Phosphatases; D013755:Tetradecanoylphorbol Acetate