Cytosolic nucleotides enhance the tolbutamide sensitivity of the ATP- dependent K+ channel in mouse pancreatic B cells by their combined actions at inhibitory and stimulatory receptors

C Schwanstecher, C Dickel and U Panten

Institute of Pharmacology and Toxicology, University of Gottingen, Germany.

In the plasma membrane of pancreatic B cells, a K+ channel (K-ATP channel) has been identified that is regulated by cytoplasmic nucleotides. This channel is inhibited by sulfonylureas. We have previously shown that the potency of tolbutamide is much lower in excised membrane patches than in intact cells, unless the internal side of the membrane is exposed to the Mg2+ complex of ADP (MgADP). In the present study, the mechanism of this interactive control by sulfonylureas and nucleotides was examined using the inside-out configuration of the patch-clamp technique. When test solutions containing Mg2+ ions were applied, the opening activity of the K-ATP- channels was strongly stimulated by 2'-deoxyadenosine-5'-diphosphate (dADP) or GDP, slightly stimulated by ADP, and inhibited by adenosine- 5'-O-(2-thiodiphosphate) (ADP beta S) or adenylyl-imidodiphosphate (AMP- PNP). In the presence of Mg2+, not only ADP but also its analogues dADP (1 mM) and ADP beta S (0.1 mM) enhanced the potency of tolbutamide for channel inhibition; dADP at a low concentration (0.2 mM), GDP (0.2-1 mM), and AMP-PNP (0.2 mM) did not alter the potency of tolbutamide. The particular feature of the test solutions that enhanced the potency of tolbutamide was the presence of Mg(2+)-bound and free nucleotides at channel-stimulating and channel-inhibiting concentrations, respectively. In the presence of Mg2+ and 0.2 mM dADP or 0.2-1 mM GDP, 0.2 mM AMP-PNP intensified the response to tolbutamide by serving as channel-inhibiting component. MgAMP-PNP did not stimulate the opening activity of the K-ATP channel. The sensitivity to tolbutamide that was enhanced by a submaximally effective ADP concentration was further increased by AMP-PNP or ATP but not by GDP. The sensitivity to the sulfonylurea analogue meglitinide was also enhanced by ADP. It is concluded that nucleotides inhibit and activate the K-ATP channel by interaction with two separate receptor sites at the cytoplasmic face of the B cell membrane. Effective inhibition of the channel openings by sulfonylureas results from the simultaneous occupation of both sites by appropriate nucleotides.

Volume 41, Issue 3, pp. 480-486, 03/01/1992
Copyright © 1992 by American Society for Pharmacology and Experimental Therapeutics

This article has been cited by other articles:

				M. Chachin, M. Yamada, A. Fujita, T. Matsuoka, K. Matsushita, and Y. Kurachi Nateglinide, a D-Phenylalanine Derivative Lacking Either a Sulfonylurea or Benzamido Moiety, Specifically Inhibits Pancreatic beta -Cell-Type KATP Channels J. Pharmacol. Exp. Ther., March 1, 2003; 304(3): 1025 - 1032. [Abstract] [Full Text] [PDF]

				P. Proks, F. Reimann, N. Green, F. Gribble, and F. Ashcroft Sulfonylurea Stimulation of Insulin Secretion Diabetes, December 1, 2002; 51(90003): S368 - 376. [Abstract] [Full Text] [PDF]

				L Aguilar-Bryan, C. Nichols, S. Wechsler, J. Clement 4th, A. Boyd 3rd, G Gonzalez, H Herrera-Sosa, K Nguy, J Bryan, and D. Nelson Cloning of the beta cell high-affinity sulfonylurea receptor: a regulator of insulin secretion Science, April 21, 1995; 268(5209): 423 - 426. [Abstract] [PDF]