[Cholinergic action of Bay K-8644 on the rat heart sinus node automaticity].
The actions of different concentrations of a dihydropyridine agonist (Bay K-8644) on rat heart sinus node automaticity and their interactions with atropine, were studied. The experiments were performed using a portion of the right atrium that contained the sinus node, perfused with Tyrode's solution at 37 degrees C and registering the action potentials with intracellular microelectrodes (Ag-KCL). The series of Bay K with or without atropine were perfused during 10 min. Atropine, 1 x 10(-5) M, did not change sinus frequency after 30 min of perfusion (237 +/- 6 to 229 +/- 7 action potentials/min; n = 24). Bay K, 2.8 x 10(-8) M (10 ug/L) did not change sinus frequency (240 +/- 9 to 246 +/- 12; n = 8, but in the presence of atropine, caused an increment (225 +/- 7 to 256 +/- 12 p < 0.05). Bay K, 7 x 10(-8) M (25 ug/L) and 1.4 x 10(-7) M (50 ug/L, caused an increase in sinus frequency (237 +/- 5 to 279 +/- 15; n = 9 p < 0.05 and 254 +/- 6 to 291 +/- 6; n = 6 p < 0.05 respectively) that occurred sooner in the presence of atropine. It is concluded that Bay-K has a cholinergic effect that interferes with its positive chronotropic action, specially at low concentrations.
Standen
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Departamento de Ciencias Preclínicas, Facultad de Medicina Universidad de la Frontera, Temuco, Chile.
Schulz
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Cabezas
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Torres
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Salvatici
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D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology*; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D012849:Sinoatrial Node / Q000187:drug effects*; D013268:Stimulation, Chemical; D013997:Time Factors
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D001285:Atropine