Ca(2+)- and GTP-dependent exocytosis in mouse pancreatic beta-cells involves both common and distinct steps.
1. The effects of GTP and Ca2+ on secretion from single pancreatic beta-cells were studied using capacitance measurements as an indicator of exocytosis. 2. GTP or GTP gamma S produced a concentration-dependent increase in cell capacitance in the absence of intracellular calcium. There was no effect of cyclic AMP or BAPTA an GTP-induced secretion. 3. In the absence of GTP, the relationship between intracellular calcium concentration and the maximum rate of secretion was fitted by the Hill equation with a slope factor of 2.5 and half-maximal activation at 1.6 microM intracellular Ca2+. Similar values were obtained in the presence of GTP gamma S, suggesting GTP does not alter the sensitivity of the secretory machinery to Ca2+. 4. GDP beta S alone had no effect on cell capacitance but caused a dose-dependent inhibition of exocytosis induced by infusion of either GTP gamma S or Ca2+, suggesting both stimuli involve G-protein activation. GDP beta S was without effect on exocytosis evoked by depolarization-mediated Ca2+ entry. 5. The time course of exocytosis following rapid elevation of GTP gamma S by photolysis of a caged precursor was dependent on the intracellular Ca2+ and cyclic AMP concentrations. 6. Our results are interpreted in terms of a model in which the secretory pathways stimulated by Ca2+ and GTP contain both common and separate parts.
University Laboratory of Physiology, Oxford, UK.
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Proks
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Eliasson
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Ammälä
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Rorsman
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Ashcroft
D000818:Animals; D002118:Calcium / Q000502:physiology*; D004594:Electrophysiology; D005089:Exocytosis / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology / Q000502:physiology*; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D018408:Patch-Clamp Techniques; D013873:Thionucleotides / Q000494:pharmacology
D013873:Thionucleotides; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C023427:guanosine 5'-O-(2-thiodiphosphate); D006160:Guanosine Triphosphate; D002118:Calcium