title: Electrophysiological and pharmacological evaluation of the nicotinic cholinergic system in chagasic rats.
abstract: BACKGROUND
  Two theories attempt to explain the changes observed in the nicotinic acetylcholine receptors (nAChRs) in chagasic cardiomyopathy. The neurogenic theory proposes that receptor changes are due to loss of intracardiac ganglia parasympathetic neurons. The immunogenic theory proposes that the nAChRs changes are the result of autoantibodies against these receptors. Both theories agreed that nAChRs functional expression could be impaired in Chagas disease.
  
  
  METHODS
  We evaluated nAChRs functional integrity in 54 Sprague Dawley rats, divided in two groups: healthy and chronic chagasic rats. Rats were subjected to electrocardiographic studies in the whole animal under pentobarbital anesthesia, by isolation and stimulation of vagus nerves and in isolated beating hearts (Langendorff's preparation).
  
  
  RESULTS
  Nicotine, 10 μM, induced a significant bradycardia in both groups. However, rats that had previously received reserpine did not respond to nicotine stimulation. β-adrenergic stimulation, followed by nicotine treatment, induced tachycardia in chagasic rats; while inducing bradycardia in healthy rats. Bilateral vagus nerve stimulation induced a significantly higher level of bradycardia in healthy rats, compared to chagasic rats; physostigmine potentiated the bradycardic response to vagal stimulation in both experimental groups. Electric stimulation (e.g., ≥ 2 Hz), in the presence of physostigmine, produced a comparable vagal response in both groups. In isolated beating-heart preparations 1 μM nicotine induced sustained bradycardia in healthy hearts while inducing tachycardia in chagasic hearts. Higher nicotine doses (e.g.,10 - 100 uM) promoted the characteristic biphasic response (i.e., bradycardia followed by tachycardia) in both groups. 10 nM DHβE antagonized the effect of 10 μM nicotine, unmasking the cholinergic bradycardic effect in healthy rats only. 1 nM α-BGT alone induced bradycardia in healthy hearts but antagonized the 10 μM nicotine-induced tachycardia in chagasic rats. In healthy but not in chagasic hearts, 10 μM nicotine shortened PQ and PR interval, an effect counteracted by MA, DHβE and αBGT CONCLUSION: Our results suggest that cholinergic function is impaired in chronic Chagas disease in rats, a phenomena that could be related to alteration on the nAChR expression.
authors.affiliation: Biochemistry Research Units, Health Sciences School, Universidad Centro Occidental Lisandro Alvarado, Barquisimeto, Lara, Venezuela. rcabarca@ucla.edu.ve
authors.forename: Rafael
authors.initials: R
authors.lastname: Bonfante-Cabarcas
authors.forename: Erlymar
authors.initials: E
authors.lastname: López Hincapié
authors.forename: Eliezer
authors.initials: E
authors.lastname: Jiménez Hernández
authors.forename: Ruth
authors.initials: R
authors.lastname: Fonseca Zambrano
authors.forename: Lady
authors.initials: L
authors.lastname: Ferrer Mancini
authors.forename: Marcos
authors.initials: M
authors.lastname: Durand Mena
authors.forename: Claudina
authors.initials: C
authors.lastname: Rodríguez-Bonfante
mesh_terms: D000818:Animals; D002038:Bungarotoxins / Q000494:pharmacology; D002598:Chagas Cardiomyopathy / Q000503:physiopathology*; D004079:Dihydro-beta-Erythroidine / Q000494:pharmacology; D004195:Disease Models, Animal; D004562:Electrocardiography; D006321:Heart / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D008464:Mecamylamine / Q000494:pharmacology; D009538:Nicotine / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D018733:Nicotinic Antagonists / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011978:Receptors, Nicotinic / Q000502:physiology*; D014630:Vagus Nerve / Q000187:drug effects / Q000502:physiology
chemical_list: D002038:Bungarotoxins; D018722:Nicotinic Agonists; D018733:Nicotinic Antagonists; D011978:Receptors, Nicotinic; D004079:Dihydro-beta-Erythroidine; D008464:Mecamylamine; D009538:Nicotine