EFFECT OF ADENOSINE AND INTRACELLULAR GPT ON K-ATP CHANNELS OF MAMMALIAN SKELETAL-MUSCLE

We investigated the action of adenosine and GTP on K-ATP channels, usi ng inside-out patch clamp recordings from dissociated single fibers of rat flexor digitorum brevis (FDB) skeletal muscle. In excised patches , K-ATP channels could be activated by a combination of an extracellul ar adenosine agonist and intracellular Mg2+-ATP and GTP or GTP-gamma-S . The activation required hydrolyzable ATP and could be partially reve rsed with Mg2+, suggesting that it may involve a G-protein dependent p hosphorylation of K-ATP channels. We found that K channels of the rat FDB could not be activated by Mg2+-ATP alone or by Mg2+-ATP in the pre sence of extracellular adenosine. Patches whose channel activity had b een 'rundown' by Ca2+ could not be recovered by adenosine, GTP or Mg2-ATP. K-ATP channels activated by adenosine receptor agonists had a si milar ATP sensitivity to those under control conditions; but adenosine appears to be able to switch these K-ATP channels from an inactive to an active mode.