Effects of K+ channel blockers and openers on antinociception induced by agonists of 5-HT1A receptors

The modulation by K+ channel-acting drugs of the antinociceptive effect of several 5-HT1A receptor agonists was examined with the hot plate test in mice. All the 5-HT1A receptor agonists tested induced dose-dependent antinociception, the order of potency being (+/-)-8-hydroxy-2-(di-n-propyl-amino)tetralin (8-OH-DPAT) > buspirone greater than or equal to lesopitron greater than or equal to tandospirone. The blockers of ATP-sensitive K+ channels (K-ATP) gliquidone and glipizide (1-4 and 16-64 mu g/mouse i.c.v., respectively) reduced the antinociceptive effect of 8-OH-DPAT, whereas cromakalim (32-64 mu g/mouse i.c.v.), an opener of K-ATP channels, enhanced the effect. In contrast, 4-aminopyridine (25-250 ng/mouse i.c.v.) and tetraethylammonium (10-20 mu g/mouse i.c.v.), which antagonize several non-ATP-dependent K+ conductances, were inactive. The same results were found with other agonists of 5-HT1A receptors (lesopitron, buspirone and tandospirone): gliquidone inhibited whereas cromakalim increased their antinociceptive effects. None of the K+ channel-acting drugs modified the binding of [H-3]8-OH-DPAT to hippocampal membranes, whereas all the 5-HT1A receptor agonists displaced the ligand. These results suggest that ATP-sensitive K+ conductances are involved in the antinociception induced by agonists of 5-HT1A receptors.