title: Effect of changes in transmural pressure on contraction frequency of the isolated right atrium of the rabbit.
abstract: Experiments were made on preparations of the rabbit right atrium maintained at 37 degrees C in oxygenated Krebs-Henseleit solution. Baseline diastolic transmural pressure was held at 2 mmHg. A step increase in diastolic pressure was accompanied by an immediate and rapid increase in atrial rate (fast response), followed by a slower increase (t1/2 approximately 0.5 min) (slow response). The slow response to pressure steps was graded, approaching a maximum increase after a 12 mmHg step (44 +/- 4 min-1 from a baseline of 196 +/- 5 min-1; mean +/- SEM; n = 7; P < 0.01). In preparations where baseline atrial rate had been reduced 50% by application of carbamylcholine, the slow response to an increase in pressure was augmented (n = 7; P < 0.01); an increase of 55 +/- 9 min-1 for a 12 mmHg step in atrial pressure. In preparations where baseline rate had been increased 63% by the application of isoprenaline, the slow response was attenuated (n = 5, P < 0.01), an increase of 22 +/- 7 min-1 for a 12 mmHg step. During sinusoidal pressure forcing (0.002-1.0 Hz), rate responses of control and carbamylcholine-treated preparations had a high gain at frequencies < or = 0.02 Hz. Carbamylcholine-treated preparations also showed a high gain at frequencies > or = 0.2 Hz. There appear to be two distinct intrinsic responses to changes in right atrial pressure; a rapid response which is augmented by cholinergic stimulation, and a slower response which is augmented by cholinergic stimulation and reduced by beta-adrenergic stimulation.
authors.affiliation: Department of Physiology, University of Otago, Dunedin, New Zealand.
authors.forename: C P
authors.initials: CP
authors.lastname: Bolter
mesh_terms: D000818:Animals; D016275:Atrial Function; D002217:Carbachol / Q000494:pharmacology*; D005260:Female; D006321:Heart / Q000502:physiology; D006325:Heart Atria / Q000187:drug effects*; D006339:Heart Rate / Q000502:physiology*; D007545:Isoproterenol / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D011312:Pressure; D011817:Rabbits
chemical_list: D002217:Carbachol; D007545:Isoproterenol