title: Effect of 4-aminopyridine and verapamil on the inhibitory action of normorphine on the guinea-pig ileum.
abstract: The ability of normorphine to inhibit the muscular twitches elicited by electrical stimulation of the longitudinal muscle of the guinea-pig ileum was antagonized by 4-aminopyridine (4-AP). Incubation with 4-aminopyridine (4-AP) caused a marked increase of the normorphine IC50 and this effect was not modified by naloxone or by the Ca2+ channel blocker, verapamil. Although verapamil caused a significant decrease of the normorphine IC50 it also caused a potent reduction of the contractile effect of acetylcholine. The results suggest that 4-AP and verapamil act on different Ca2+ pools and that verapamil does not primarily affect the presynaptic Ca2+ pool involved in opiate action.
mesh_terms: D015761:4-Aminopyridine; D000109:Acetylcholine / Q000494:pharmacology; D000631:Aminopyridines / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004347:Drug Interactions; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D009022:Morphine Derivatives / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D014700:Verapamil / Q000494:pharmacology*
chemical_list: D000631:Aminopyridines; D009022:Morphine Derivatives; D015761:4-Aminopyridine; D014700:Verapamil; D000109:Acetylcholine; D002118:Calcium; C010616:normorphine