title: Inositol 3,4,5,6-tetrakisphosphate inhibits insulin granule acidification and fusogenic potential.
abstract: ClC Cl(-) channels in endosomes, synaptosomes, lysosomes, and beta-cell insulin granules provide charge neutralization support for the functionally indispensable acidification of the luminal interior by electrogenic H(+)-ATPases (Jentsch, T. J., Stein, V., Weinreich, F., and Zdebik, A. A. (2002) Physiol. Rev. 82, 503-568). Regulation of ClC activity is, therefore, of widespread biological significance (Forgac, M. (1999) J. Biol. Chem. 274, 12951-12954). We now ascribe just such a regulatory function to the increases in cellular levels of inositol 3,4,5,6-tetrakisphosphate (Ins(3,4,5,6)P(4)) that inevitably accompany activation of the ubiquitous Ins(1,4,5)P(3) signaling pathway. We used confocal imaging to record insulin granule acidification in single mouse pancreatic beta-cells. Granule acidification was reduced by perfusion of single cells with 10 microm Ins(3,4,5,6)P(4) (the concentration following receptor activation), whereas at 1 microm ("resting" levels), Ins(3,4,5,6)P(4) was ineffective. This response to Ins(3,4,5,6)P(4) was not mimicked by 100 microm Ins(1,4,5,6)P(4) or by 100 microm Ins(1,3,4,5,6)P(5). Ins(3,4,5,6)P(4) did not affect granular H(+)-ATPase activity or H(+) leak, indicating that Ins(3,4,5,6)P(4) instead inhibited charge neutralization by ClC. The Ins(3,4,5,6)P(4)-mediated inhibition of vesicle acidification reduced exocytic release of insulin as determined by whole-cell capacitance recordings. This may impinge upon type 2 diabetes etiology. Regulatory control over vesicle acidification by this negative signaling pathway in other cell types should be considered.
authors.affiliation: Department of Physiological Sciences, Lund University, BMC F11 SE-221 84 Lund, Sweden. erik.renstrom@mphy.lu.se
authors.forename: Erik
authors.initials: E
authors.lastname: Renström
authors.forename: Rosita
authors.initials: R
authors.lastname: Ivarsson
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Shears
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D018118:Chloride Channels / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D007295:Inositol Phosphates / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D007515:Islets of Langerhans / Q000378:metabolism; D051379:Mice; D018613:Microscopy, Confocal; D022142:Secretory Vesicles / Q000187:drug effects; D015398:Signal Transduction; D013997:Time Factors
chemical_list: D018118:Chloride Channels; D002712:Chlorides; D007295:Inositol Phosphates; D007328:Insulin; C081652:inositol-3,4,5,6-tetrakisphosphate