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C16:0 sulfatide inhibits insulin secretion in rat beta-cells by reducing the sensitivity of KATP channels to ATP inhibition

Journal article
Authors Karsten Buschard
Maria K. Blomqvist
Jan-Eric Månsson
Pam Fredman
Kirstine Juhl
Jesper Gromada
Published in Diabetes
Volume 55
Issue 10
Pages 2826-34
ISSN 0012-1797 (Print)
Publication year 2006
Published at Institute of Neuroscience and Physiology, Department of Psychiatry and Neurochemistry
Pages 2826-34
Language en
Links dx.doi.org/10.2337/db05-1355
Keywords Adenosine Triphosphate/*pharmacology, Animals, Calcium/metabolism, Cells, Cultured, Exocytosis/drug effects, Glucose/antagonists & inhibitors, Insulin/*secretion, Insulin-Secreting Cells/drug effects/*secretion, Insulinoma/metabolism, Membrane Potentials/drug effects, Oligosaccharides/secretion, Potassium Channels/*drug effects, Rats, Rats, Inbred Lew, Sulfoglycosphingolipids/*pharmacology
Subject categories Neurochemistry

Abstract

Sulfatide (3'-sulfo-beta-galactosyl ceramide) is a glycosphingolipid present in mammalians in various fatty acid isoforms of which the saturated 16 carbon-atom length (C16:0) is more abundant in pancreatic islets than in neural tissue, where long-chain sulfatide isoforms dominate. We previously reported that sulfatide isolated from pig brain inhibits glucose-induced insulin secretion by activation of ATP-sensitive K+ channels (K(ATP) channels). Here, we show that C16:0 sulfatide is the active isoform. It inhibits glucose-stimulated insulin secretion by reducing the sensitivity of the K(ATP) channels to ATP. (The half-maximal inhibitory concentration is 10.3 and 36.7 micromol/l in the absence and presence of C16:0 sulfatide, respectively.) C16:0 sulfatide increased whole-cell K(ATP) currents at intermediate glucose levels and reduced the ability of glucose to induce membrane depolarization, reduced electrical activity, and increased the cytoplasmic free Ca2+ concentration. Recordings of cell capacitance revealed that C16:0 sulfatide increased Ca2+-induced exocytosis by 215%. This correlated with a stimulation of insulin secretion by C16:0 sulfatide in intact rat islets exposed to diazoxide and high K+. C24:0 sulfatide or the sulfatide precursor, beta-galactosyl ceramide, did not affect any of the measured parameters. C16:0 sulfatide did not modulate glucagon secretion from intact rat islets. In betaTC3 cells, sulfatide was expressed (mean [+/-SD] 0.30 +/- 0.04 pmol/microg protein), and C16:0 sulfatide was found to be the dominant isoform. No expression of sulfatide was detected in alphaTC1-9 cells. We conclude that a major mechanism by which the predominant sulfatide isoform in beta-cells, C16:0 sulfatide, inhibits glucose-induced insulin secretion is by reducing the K(ATP) channel sensitivity to the ATP block.

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