title: Bay K 8644 and acetylcholine: different interaction with calcium ions in the rat duodenal muscle.
abstract: The contractile effect of the dihydropyridine analogue Bay K 8644, recently described as a Ca2+-agonist, has been evaluated in the rat isolated duodenal muscle in comparison with that of acetylcholine. Bay K 8644 (3 X 10(-10)-10(-6) mol/l) increased the duodenal motility, whereas it behaved as an inhibitor when tested at high concentrations (greater than 10(-6) mol/l). Bay K 8644 was more potent than acetylcholine (threshold concentration 3 X 10(-10) vs. 10(-8) mol/l) but less efficient. The contractile responses to Bay K 8644 and acetylcholine were reduced in calcium-free medium and abolished by addition of 1 mmol/l EGTA. In some K+-depolarized tissues, however, a contractile response to Bay K 8644 was still observed. The effects of Bay K 8644 and acetylcholine were antagonized by nifedipine and verapamil; however, a competitive antagonism was observed only for the interaction Bay K 8644-nifedipine (pA2 = 9.86). The contraction induced by Bay K 8644 was noncompetitively antagonized by low concentrations of atropine (10(-7) mol/l); Bay K 8644 (10(-7) mol/l) did not modify the response to acetylcholine, while inhibiting it at higher concentration (10(-5) mol/l); in addition, it was able to enhance the response to endogenous acetylcholine, released by field stimulation. The above results indicated that Bay K 8644 and cholinergic stimuli are strong activators of the duodenal motility in vitro. The interference of Bay K 8644 with the cholinergic system, observed in both unstimulated and electrically stimulated strips, suggested a novel site of action of this compound in the gastrointestinal muscle.
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000109:Acetylcholine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D004347:Drug Interactions; D005769:Gastrointestinal Motility / Q000187:drug effects; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009129:Muscle Tonus / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D009543:Nifedipine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D014700:Verapamil / Q000494:pharmacology
chemical_list: D007473:Ion Channels; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D014700:Verapamil; D009543:Nifedipine; D000109:Acetylcholine