J. Biol. Chem., Vol. 262, Issue 6, 2608-2612, 02, 1987

Increased cytosolic calcium. A signal for sulfonylurea-stimulated insulin release from beta cells

TY Nelson, KL Gaines, AS Rajan, M Berg and AE Boyd 3d

The mechanisms by which glyburide and tolbutamide signal insulin secretion were examined using a beta cell line (Hamster insulin- secreting tumor (HIT) cells). Insulin secretion was measured in static incubations, free cytosolic Ca2+ concentration ([Ca2+]i) was monitored in quin 2-loaded cells, and cAMP quantitated by radioimmunoassay. Insulin secretory dose-response curves utilizing static incubations fit a single binding site model and established that glyburide (ED50 = 112 +/- 18 nM) is a more potent secretagogue than tolbutamide (ED50 = 15 +/- 3 microM). Basal HIT cell [Ca2+]i was 76 +/- 7 nM (mean +/- S.E., n = 141) and increased in a dose-dependent manner with both glyburide and tolbutamide with ED50 values of 525 +/- 75 nM and 67 +/- 9 microM, respectively. The less active tolbutamide metabolite, carboxytolbutamide, had no effect on [Ca2+]i or insulin secretion. Chelation of extracellular Ca2+ with 4 mM EGTA completely inhibited the sulfonylurea-induced changes in [Ca2+]i and insulin release and established that the rise in [Ca2+]i came from an extracellular Ca2+ pool. The Ca2+ channel blocker, verapamil, inhibited glyburide- or tolbutamide-stimulated insulin release and the rise in [Ca2+]i at similar concentrations with IC50 values of 3 and 2.5 microM, respectively. At all concentrations tested, the sulfonylureas did not alter HIT cell cAMP content. These findings provide direct experimental evidence that glyburide and tolbutamide allow extracellular Ca2+ to enter the beta cell through verapamil-sensitive, voltage-dependent Ca2+ channels, causing a rise in [Ca2+]i which is the second messenger that stimulates insulin release.
CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				D. P. Betten, R. B. Vohra, M. D. Cook, M. J. Matteucci, and R. F. Clark Antidote use in the critically ill poisoned patient. J Intensive Care Med, September 1, 2006; 21(5): 255 - 277. [Abstract] [PDF]

				H. A. Spiller and T. S. Sawyer Toxicology of oral antidiabetic medications Am. J. Health Syst. Pharm., May 15, 2006; 63(10): 929 - 938. [Abstract] [Full Text] [PDF]

				L B Hays, B Wicksteed, Y Wang, J F McCuaig, L H Philipson, J M Edwardson, and C J Rhodes Intragranular targeting of syncollin, but not a syncollinGFP chimera, inhibits regulated insulin exocytosis in pancreatic {beta}-cells J. Endocrinol., April 1, 2005; 185(1): 57 - 67. [Abstract] [Full Text] [PDF]

				Y. Miura and H. Matsui Glucagon-like peptide-1 induces a cAMP-dependent increase of [Na+]i associated with insulin secretion in pancreatic {beta}-cells Am J Physiol Endocrinol Metab, November 1, 2003; 285(5): E1001 - E1009. [Abstract] [Full Text] [PDF]

				Y. Miura, M. Kato, K. Ogino, and H. Matsui Impaired Cytosolic Ca2+ Response to Glucose and Gastric Inhibitory Polypeptide in Pancreatic {beta}-Cells from Triphenyltin-Induced Diabetic Hamster Endocrinology, July 1, 1997; 138(7): 2769 - 2775. [Abstract] [Full Text] [PDF]