HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: db07-0026v1 db07-0026v2 56/6/1694    most recent Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Johnson, D. Articles by Dunne, M. J. Search for Related Content PubMed PubMed Citation Articles by Johnson, D. Articles by Dunne, M. J. Social Bookmarking                What's this?

Glucose-Dependent Modulation of Insulin Secretion and Intracellular Calcium Ions by GKA50, a Glucokinase Activator

¹ Faculty of Life Sciences, Core Technology Facility, University of Manchester, Manchester, U.K
² AstraZeneca, Macclesfield, Cheshire, U.K

Address correspondence and reprint requests to Mark Dunne, Faculty of Life Sciences, University of Manchester, Core Technology Facility, 46 Grafton St., Manchester, M13 9NT, U.K. E-mail: mark.j.dunne{at}manchester.ac.uk

Abbreviations: [Ca²⁺]_i, estimated internal calcium concentration; DMEM, Dulbecco's modified Eagle's medium; EC₅₀, half-maximal effective concentration; GKA, glucokinase activator; GKA50, glucokinase activator compound 50; GSIS, glucose-stimulated insulin secretion; K_ATP channel, ATP-sensitive K⁺ channel; KRH, HEPES-balanced Krebs-Ringer phosphate buffer; OMeG, 3-O-methoxyglucose; 5-TG, 5-thioglucose

Because glucokinase is a metabolic sensor involved in the regulated release of insulin, we have investigated the acute actions of novel glucokinase activator compound 50 (GKA50) on islet function. Insulin secretion was determined by enzyme-linked immunosorbent assay, and microfluorimetry with fura-2 was used to examine intracellular Ca²⁺ homeostasis ([Ca²⁺]_i) in isolated mouse, rat, and human islets of Langerhans and in the MIN6 insulin-secreting mouse cell line. In rodent islets and MIN6 cells, 1 µmol/l GKA50 was found to stimulate insulin secretion and raise [Ca²⁺]_i in the presence of glucose (2–10 mmol/l). Similar effects on insulin release were also seen in isolated human islets. GKA50 (1 µmol/l) caused a leftward shift in the glucose-concentration response profiles, and the half-maximal effective concentration (EC₅₀) values for glucose were shifted by 3 mmol/l in rat islets and 10 mmol/l in MIN6 cells. There was no significant effect of GKA50 on the maximal rates of glucose-stimulated insulin secretion. In the absence of glucose, GKA50 failed to elevate [Ca²⁺]_i (1 µmol/l GKA50) or to stimulate insulin release (30 nmol/l–10 µmol/l GKA50). At 5 mmol/l glucose, the EC₅₀ for GKA50 in MIN6 cells was 0.3 µmol/l. Inhibition of glucokinase with mannoheptulose or 5-thioglucose selectively inhibited the action of GKA50 on insulin release but not the effects of tolbutamide. Similarly, 3-methoxyglucose prevented GKA50-induced rises in [Ca²⁺]_i but not the actions of tolbutamide. Finally, the ATP-sensitive K⁺ channel agonist diazoxide (200 µmol/l) inhibited GKA50-induced insulin release and its elevation of [Ca²⁺]_i. We show that GKA50 is a glucose-like activator of ß-cell metabolism in rodent and human islets and a Ca²⁺-dependent modulator of insulin secretion.

CiteULike    Del.icio.us    Digg    Reddit    Technorati    What's this?