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Antibody inhibition of synaptosomal protein of 25 kDa (SNAP-25) and syntaxin 1 reduces rapid exocytosis in insulin-secreting cells.

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Author

  • Jenny Vikman
  • Xiaosong Ma
  • Gregory H Hockerman
  • Patrik Rorsman
  • Lena Eliasson

Summary, in English

SNARE-proteins (soluble NSF-attachment protein receptor) are important for Ca2+-dependent exocytosis. We have used capacitance measurements and confocal imaging to dissect the role of synaptosomal protein of 25 kDa (SNAP-25) and syntaxin 1 in rapid exocytosis in insulin-secreting pancreatic ß-cells. Following immunoneutralization of syntaxin 1 and SNAP-25, exocytosis was strongly reduced and associated with a marked reduction in the size of the readily releasable pool (RRP) by 65% and 86% in the presence of the anti-SNAP-25 and anti-syntaxin 1 antibodies respectively. The size of the immediately releasable pool (IRP), a subset of RRP in close association with the voltage-dependent Ca2+-channels, was reduced to an equal extent. The reduction in IRP correlated with slowed release kinetics and the time constant ({tau}) increased from a control value of 16 to 36 ms and 51 ms after inclusion of anti-SNAP-25 and anti-syntaxin 1 antibodies respectively in the pipette solution. We further show that SNAP-25 and syntaxin 1 aggregate in clusters along the plasma membrane. The size of these clusters was estimated to be ~300 nm and every ß-cell contained ~400 SNAP-25/syntaxin 1 clusters. Whereas the inhibitory action of the anti-syntaxin 1 antibody on exocytosis could be attributed almost entirely to suppression of the voltage-dependent Ca2+-current (–40%), the effect of the anti-SNAP-25 antibody was not mediated by decreased Ca2+-entry and is more likely due to a direct interference with the exocytotic machinery. Our data are consistent with the concept that both syntaxin 1 and SNAP-25 are required for rapid exocytosis in ß-cells.

Publishing year

2006

Language

English

Pages

503-515

Publication/Series

Journal of Molecular Endocrinology

Volume

36

Issue

3

Document type

Journal article

Publisher

Society for Endocrinology

Topic

  • Endocrinology and Diabetes

Status

Published

Research group

  • Diabetes - Islet Cell Exocytosis
  • Genomics, Diabetes and Endocrinology
  • Islet cell physiology

ISBN/ISSN/Other

  • ISSN: 1479-6813