Functional receptors in Xenopus oocytes for U-37883A, a novel ATP- sensitive K+ channel blocker: comparison with rat insulinoma cells

E Guillemare, E Honore, J De Weille, M Fosset, M Lazdunski and K Meisheri

Institut de Pharmacologie Moleculaire et Cellulaire, Centre Nationale de la Recherche Scientifique, Valbonne, France.

Follicle-enclosed Xenopus oocytes were used to describe the ATP- sensitive K+ (KATP) channel-blocking properties of U-37883A (4- morpholinecarboximidine-N-1-adamantyl-N'-cyclohexyl), in comparison with glibenclamide. In follicular oocytes, the KATP channel opener P1060 (30 microM), a pinacidil analog, activated a large outward K+ current that was blocked by glibenclamide (IC50 = 0.33 microM) and U- 37883A (IC50 = 0.26 microM). P1060 activation was inhibited by both U- 37883A and glibenclamide in a noncompetitive manner. U-37883A also blocked the KATP channel activation by cAMP (300 microM) and adenosine (10 microM). Single-channel studies on isolated follicular cells showed that U-37883A (10 microM) reduced the open probability of the KATP channel by 76%, without significantly modifying the single-channel current amplitude. Receptor binding studies with [3H]U-37883 in membranes from follicle-enclosed oocytes demonstrated a single class of low affinity binding sites, with a Kd of 450 nM and a Bmax of 17 pmol/mg of protein. Studies with analogs of U-37883A showed that U- 52090A inhibited KATP current and displaced [3H]U-37883 from its binding site with similar potencies. In contrast, U-42069D neither inhibited KATP current nor competed with [3H]U-37883 binding. In RINm5F cells (an insulinoma cell line), U-37883A, unlike glibenclamide, failed to inhibit KATP current. Furthermore, there was no significant specific binding of [3H]U-37883 in RINm5F cell membranes, which displayed high levels of specific binding of [3H]glibenclamide. These data demonstrate the presence of a receptor for U-37883A-type guanidines that controls the activity of the endogenous KATP channels in follicle-enclosed oocytes. The available data collectively suggest that U-37883A is a more selective blocker of the follicular KATP channel, which is very similar to that in smooth muscle, than of the pancreatic beta cell KATP channel.

Volume 46, Issue 1, pp. 139-145, 07/01/1994
Copyright © 1994 by American Society for Pharmacology and Experimental Therapeutics

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