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Am J Physiol Heart Circ Physiol 276: H488-H495, 1999;
0363-6135/99 $5.00
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Vol. 276, Issue 2, H488-H495, February 1999

Adenosine-induced activation of ATP-sensitive K+ channels in excised membrane patches is mediated by PKC

Keli Hu1, Gui-Rong Li2,3, and Stanley Nattel1,2,3

2 Department of Medicine and Research Center, Montreal Heart Institute, and 3 Department of Medicine, University of Montreal, and 1 Department of Pharmacology and Therapeutics, McGill University, Montreal, Quebec, Canada H1T 1C8

Both protein kinase C (PKC) and adenosine receptor activation have been shown to enhance ATP-sensitive K+ (KATP) channels. The present studies were designed to determine whether PKC mediates adenosine effects on the KATP channel. The dependence of KATP channel activity (nPo) on intracellular ATP concentration ([ATP]i) was determined in excised rabbit ventricular membrane patches. External adenosine (100 µM in the pipette solution) significantly increased KATP nPo at all [ATP]i between 5 and 50 µM by decreasing channel sensitivity to [ATP]i (dissociation constant increased from 7.4 ± 0.8 to 22.2 ± 3.1 µM, P < 0.001), an effect blocked by the adenosine receptor antagonist 8-phenyltheophylline (10 µM). When the highly selective PKC blocker bisindolylmaleimide (BIM) was included in the internal (bath) solution, the KATP-stimulating action of adenosine was prevented. The addition of BIM to the superfusate rapidly inhibited KATP channels activated by adenosine. Endogenous PKC activation by phorbol 12,13-didecanoate (PDD), but not administration of the inactive congener 4alpha -PDD, enhanced KATP activity. Internal guanosine 5'-O-(2-thiodiphosphate) prevented KATP activation by adenosine, an effect which could be overridden by exposure to PDD. We conclude that PKC mediates adenosine activation of KATP channels in excised membrane patches in a membrane-delimited fashion.

ischemic preconditioning; potassium channels; signal transduction; phorbol esters; protein kinase C


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