The stimulatory action of tolbutamide on Ca2+-dependent exocytosis in pancreatic β cells is mediated by a 65-kDa mdr-like P-glycoprotein

Sebastian Barg, Erik Renström, Per Olof Berggren, Alejandro Bertorello, Krister Bokvist, Matthias Braun, Lena Eliasson, William E. Holmes, Martin Köhler, Patrik Rorsman, Frank Thévenod

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67 Scopus citations

Abstract

Intracellular application of the sulfonylurea tolbutamide during whole- cell patch-clamp recordings stimulated exocytosis >5-fold when applied at a cytoplasmic Ca2+ concentration of 0.17 μM. This effect was not detectable in the complete absence of cytoplasmic Ca2+ and when exocytosis was elicited by guanosine 5'-O-(3-thiotriphosphate) (GTPγS). The stimulatory action could be antagonized by the sulfonamide diazoxide, by the Cl-- channel blocker 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), by intracellular application of the antibody JSB1 [originally raised against a 170-kDa multidrug resistance (mdr) protein], and by tamoxifen (an inhibitor of the mdr- and volume-regulated Cl- channels). Immunocytochemistry and Western blot analyses revealed that JSB1 recognizes a 65-kDa protein in the secretory granules. This protein exhibited no detectable binding of sulfonylureas and is distinct from the 140-kDa sulfonylurea high-affinity sulfonylurea receptors also present in the granules. We conclude that (i) tolbutamide stimulates Ca2+-dependent exocytosis secondary to its binding to a 140-kDa high-affinity sulfonylurea receptor in the secretory granules; and (ii) a granular 65-kDa mdr-like protein mediates the action. The processes thus initiated culminate in the activation of a granular Cl- conductance. We speculate that the activation of granular Cl- fluxes promotes exocytosis (possibly by providing the energy required for membrane fusion) by inducing water uptake and an increased intragranular hydrostatic pressure.

Original languageEnglish (US)
Pages (from-to)5539-5544
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume96
Issue number10
DOIs
StatePublished - May 11 1999

Keywords

  • ABC protein
  • Insulin
  • Sulfonyl urea receptor

ASJC Scopus subject areas

  • Genetics
  • General

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    Barg, S., Renström, E., Berggren, P. O., Bertorello, A., Bokvist, K., Braun, M., Eliasson, L., Holmes, W. E., Köhler, M., Rorsman, P., & Thévenod, F. (1999). The stimulatory action of tolbutamide on Ca2+-dependent exocytosis in pancreatic β cells is mediated by a 65-kDa mdr-like P-glycoprotein. Proceedings of the National Academy of Sciences of the United States of America, 96(10), 5539-5544. https://doi.org/10.1073/pnas.96.10.5539