Delayed afterdepolarizations and triggered activity induced in feline Purkinje fibers by alpha-adrenergic stimulation in the presence of elevated calcium levels.
We studied the ability of alpha-adrenergic stimulation to induce delayed afterdepolarizations and triggered activity in Purkinje fibers from cat hearts in the presence of an elevated Ca++ concentration. Delayed afterdepolarizations could not be induced at drive cycle lengths of 200 to 500 msec in the presence of extracellular Ca++ concentrations of 2.7 to 8.1 mM. However, the addition of 10(-5)M phenylephrine in the presence of 5 X 10(-7)M propranolol elicited delayed afterdepolarizations in eight of 10 preparations at a Ca++ concentration of 8.1 mM; nondrive-triggered action potentials were recorded from three of the preparations. These afterpotentials were completely suppressed by 5 X 10(-7)M prazosin or 10(-6)M phentolamine. In the presence of 5 X 10(-7)M propranolol, 10(-5)M phenylephrine prolonged action potential duration and this effect was suppressed by 5 X 10(-7)M prazosin. Methoxamine, at a concentration of 5 X 10(-6)M, was also observed to potentiate delayed afterdepolarizations in all of three preparations studied. These results demonstrate that alpha-adrenergic stimulation can induce afterpotentials in the presence of elevated Ca++ levels in cat hearts. Stimulation of alpha-adrenoceptors may be responsible for arrhythmias under Ca++-loaded conditions such as ischemia and coronary reperfusion.
D000200:Action Potentials / Q000187:drug effects; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002415:Cats; D005260:Female; D006329:Heart Conduction System / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D008729:Methoxamine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011690:Purkinje Fibers / Q000187:drug effects / Q000378:metabolism*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D011943:Receptors, Adrenergic, beta / Q000187:drug effects; D013997:Time Factors
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D010656:Phenylephrine; D011433:Propranolol; D008729:Methoxamine; D002118:Calcium