Mg2+-dependent inhibition of KATP by sulphonylureas in CRI-G1 insulin-secreting cells

K. Lee, S. E. Ozanne, C. N. Hales, M. L. J. Ashford

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    24 Citations (Scopus)

    Abstract

    1 Patch-clamp recording techniques were used to examine the effects of tolbutamide, glibenclamide, meglitinide and thiopentone on KATP in CRI-GI insulin-secreting cells in the presence and absence of Mg2+. 2 In the absence of Mg2+ in the intracellular bathing solution, tolbutamide was significantly less effective when applied either to the intracellular or to the extracellular surfaces of cell-free patches. Removal of extracellular Mg2+ did not alter the effectiveness of tolbutamide provided that Mg2+ was present at the intracellular surface of the patch. 3 Tolbutamide was also significantly less effective when applied to the intracellular surface of cell-free patches when Mn2+ was used as a replacement for Mg2+. 4 Both the sulphonylurea, glibenclamide and the non-sulphonylurea derivative, meglitinide also showed Mg2+ dependent inhibitory effects in cell-free patches. In contrast, the barbiturate thiopentone inhibited KATP in a Mg(2+)-independent manner. 5 Whole-cell IK(ATP) were used to quantify the effects of tolbutamide and glibenclamide in the presence and absence of intracellular Mg2+. Concentration-inhibition curves, in the presence of intracellular Mg2+, resulted in IC50 values of 12.1 microM and 2.1 nM for tolbutamide and glibenclamide, respectively. In the absence of intracellular Mg2+, the corresponding IC50 values were 25.3 mM and 3.6 microM, respectively. The values of IC50 for thiopentone in the presence and absence of intracellular Mg2+ were 69.4 microM and 69.2 microM, respectively. 6 With respect to the high affinity binding sites for [3H]-glibenclamide in CRI-G1 membranes, no significant differences were found between the dissociation constants for, or the maximal binding capacities of, [3H]-glibenclamide in the presence or absence of Mg2+. 7. In the CRI-G1 insulin-secreting cell line, it is concluded that intracellular Mg2+ does not influence the affinity of the sulphonylureas for the sulphonylurea receptor but that this ion is critically important for the interaction between the sulphonylurea receptor and KATP.
    Original languageEnglish
    Pages (from-to)632-640
    Number of pages9
    JournalBritish Journal of Pharmacology
    Volume111
    Issue number2
    Publication statusPublished - Feb 1994

    Keywords

    • Glyburide
    • Animals
    • Thiopental
    • Sulfonylurea Compounds
    • Islets of Langerhans
    • Electrophysiology
    • Benzamides
    • Potassium Channels
    • Rats
    • Hypoglycemic Agents
    • Cell Membrane
    • Tolbutamide
    • Adenosine Triphosphate
    • Magnesium
    • Cell Line
    • Ligands

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