Alpha and beta adrenergic interactions with ouabain-induced delayed afterdepolarizations

Abstract

Standard microelectrode techniques were used to study the effect of alpha and beta adrenergic agonists and antagonists on ouabain-induced delayed afterdepolarizations (DADs) in isolated canine Purkinje fibers. The Purkinje fibers were superfused with ouabain (2 X 10(-7) M) for approximately 30 min to produce afterdepolarizations before superfusion with appropriate adrenergic agonists and antagonists. Propranolol (2 X 10(-7) M), a beta blocking concentration, had no effect on DAD amplitude; higher concentrations of propranolol (2 X 10(-6) reduced DAD and eliminated triggered rhythms. Isoproterenol (5 X 10(-6) M) increased DAD amplitude and triggered activity, an effect which was abolished by pretreatment with propranolol (2 X 10(-7) M). Neither alpha adrenergic blockade with phentolamine nor superfusion with the alpha adrenergic receptor agonist methoxamine had an effect on DAD amplitude or triggered activity. It is concluded that the beta adrenergic stimulation can enhance DAD amplitude and triggered activity in the ouabain-toxic Purkinje fiber. In contrast, alpha adrenergic agonists and blockers do not appear to have significant effects on DAD amplitude or triggered activity.