title: Reversion by calcium but not by Bay K 8644 of neuromuscular blockade induced by nicardipine.
abstract: We compared the effects of nicardipine on indirectly and directly elicited twitches in phrenic-hemidiaphragm preparations from rats, and the effects of calcium and Bay K 8644 on nicardipine-induced neuromuscular blockade. Nicardipine (5-250 microM) decreased both directly and indirectly elicited muscular contractions in a concentration-dependent way. The inhibitory effect was greater when the preparation was indirectly stimulated. Nicardipine antagonism of indirectly elicited contractions was reversed in an apparently competitive way by calcium (1-4 mM). In contrast, the calcium channel agonist Bay K 8644 (0.1 and 1 microM) had no effects per se, nor did it reverse neuromuscular blockade induced by nicardipine. Interestingly, Bay K 8644, at 10 microM, decreased the height of indirectly elicited muscular contractions. These results suggest that the calcium antagonist nicardipine affects neuromuscular transmission to a greater degree than muscular contraction, this effect being antagonized by calcium. In contrast, the calcium agonist Bay K 8644 was unable to produce any effect as stimulator of calcium channels at the neuromuscular level, indicating that this drug may exhibit tissue specificity.
authors.affiliation: Department of Pharmacology, School of Medicine, University of Granada, Spain.
authors.forename: E
authors.initials: E
authors.lastname: Del Pozo
authors.forename: J M
authors.initials: JM
authors.lastname: Baeyens
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D003964:Diaphragm / Q000187:drug effects; D005260:Female; D066298:In Vitro Techniques; D007700:Kinetics; D009466:Neuromuscular Blocking Agents; D009529:Nicardipine / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D010791:Phrenic Nerve / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D009466:Neuromuscular Blocking Agents; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009529:Nicardipine; D002118:Calcium