Alpha 1-adrenoceptor regulation of delayed afterdepolarizations and triggered activity in subendocardial Purkinje fibers surviving 1 day of myocardial infarction.
Alpha 1-adrenoceptor agonists were shown to induce delayed afterdepolarizations (DADs) and triggered activity in the presence of elevated extracellular Ca2+. We investigated the effects of alpha 1-adrenoceptor stimulation on DADs and triggered activity in canine Purkinje fibers that survived 1-day of myocardial infarction. Endocardial preparations were studied using standard microelectrode techniques. In quiescent preparations showing no DADs and in presence of propranolol (2 x 10(-7) M), phenylephrine (10(-6) M), an alpha 1-adrenoceptor agonist induced DADs (n = 6) and differentially induced triggered activity in ischemic but not in normal Purkinje fibers (n = 4). In 8 preparations that showed subthreshold DADs, phenylephrine increased the DAD amplitude from 4.0 +/- 2.5 mV to 8.0 +/- 3.3 mV (P less than 0.03) and from 3.2 +/- 1.5 mV to 6.5 +/- 3.7 mV (P less than 0.05) at paced cycle lengths of 800 and 400 ms, respectively. Phenylephrine caused subthreshold DADs to reach threshold and result in triggered activity (n = 6). The effects of phenylephrine were abolished by 10(-6) M prazosin, an alpha 1-adrenoceptor blocker. Our results suggest that alpha 1-adrenoceptor stimulation regulates DADs and triggered activity seen in subendocardial Purkinje fibers surviving 1 day of myocardial infarction and may contribute to the spontaneous ventricular tachycardia seen in vivo at this stage.
Department of Medicine, State University of New York, Brooklyn.
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M
Boutjdir
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el-Sherif
D000200:Action Potentials / Q000187:drug effects; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D004285:Dogs; D006321:Heart / Q000187:drug effects / Q000502:physiology; D009203:Myocardial Infarction / Q000473:pathology / Q000503:physiopathology*; D009206:Myocardium / Q000473:pathology; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011690:Purkinje Fibers / Q000187:drug effects / Q000502:physiology*
D000318:Adrenergic beta-Agonists; D010656:Phenylephrine; D011433:Propranolol; D011224:Prazosin