Houle MS, Altschuld RA, Billman GE. Enhanced in vivo and in vitro contractile responses to beta(2)-adrenergic receptor stimulation in dogs susceptible to lethal arrhythmias.
J Appl Physiol (1985) 2001;
91:1627-37. [PMID:
11568144 DOI:
10.1152/jappl.2001.91.4.1627]
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Abstract
The response to beta-adrenergic receptor (beta-AR) stimulation was evaluated in both isolated cardiomyocytes (video edge detection) and the intact animal (echocardiography) in dogs either susceptible (S) or resistant (R) to ventricular fibrillation induced by a 2-min coronary occlusion during the last minute of exercise. In the intact animal, velocity of circumferential fiber shortening (Vcf) was evaluated both before (n = 27, S = 12 and R = 15) and after myocardial infarction. Before infarction, increasing doses of isoproterenol provoked similar contractile and heart rate responses in each group of dogs. Either beta(1)-AR (bisoprolol) or beta(2)-AR (ICI-118551) antagonists reduced the isoproterenol response, with a larger reduction noted after the beta(1)-AR blockade. In contrast, after infarction, isoproterenol induced a significantly larger Vcf and heart rate response in the susceptible animals that was eliminated by beta(2)-AR blockade. The single-cell isotonic shortening response to isoproterenol (100 nM) was also larger in cells obtained from susceptible compared with resistant dogs and was reduced to a greater extent by beta(2)-AR blockade in the susceptible dog myocytes (S, -48%, n = 6; R, -15%, n = 9). When considered together, these data suggest that myocardial infarction provoked an enhanced beta(2)-AR response in susceptible, but not resistant, animals.
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