ISSN:
1432-2013
Keywords:
Pancreaticβ-cell
;
ATP-sensitive K-channel
;
Sulphonylurea
;
Glibenclamide
;
Tolbutamide
;
Diazoxide
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract ATP-sensitive K-channels in the cloned β-cell line HIT T15 were studied by patch-clamp methods; by measurement of 86Rb efflux; and by [3H]glibenclamide binding to isolated membrane preparations. In inside-out patches a 50 pS K-channel was found which was blocked by ATP or tolbutamide applied to the intracellular membrane surface. A minimum estimate of about 500 channels per β-cell was obtained by combining whole-cell and single-channel data. The rate of efflux of 86Rb from 86RbCl-loaded HIT cells was markedly increased by intracellular ATP-depletion; 86Rb-efflux was progressively inhibited by increasing concentrations of glibenclamide or tolbutamide. In non-ATP-depleted cells, diazoxide elicited a concentration-dependent stimulation of 86Rb-efflux which was completely blocked by 1 μM glibenclamide. Isolated membranes showed dose-dependent saturable binding of [3H]glibenclamide to both high (K d=1.12 nM) and low (K d=136 nM) affinity binding sites. We estimate about 5000 high-affinity binding sites per cell. [3H]-glibenclamide binding was inhibited by tolbutamide (IC50=125 μM) but was not affected by diazoxide. ADP (0.5 or 1.0 mM) markedly reduced binding; other nucleotides tested were ineffective.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00373140
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