[The modulation of anomalous automatism in ischemic Purkinje fibers by a specific subclass of alpha 1-adrenoblockers].

In the present study, the authors used two specific blockers of alpha 1-adrenergic receptor subtypes (chloroethyclonidine and WB-4101) to determine the mechanisms responsible for automatic rhythm occurring during simulated ischemia and reperfusion of isolated canine Purkinje fibers. In the control situation, all fibers showed membrane potentials greater than -90 mV and normal automatic rhythm. During simulated ischemia, the membrane potential depolarized to the -60 mV range. Abnormal automaticity was seen in 20% of fibers untreated with phenylephrine and in 50% of those supervised with 10(-7) M phenylephrine. The incidence of abnormal automaticity was reduced to 0% with WB-4101 and increased to 90% with chloroethylclonidine. Moreover, the ischemic fibers were significantly more hyperpolarized during superfusion with WB-4101 than with chloroethylclonidine. It is concluded that automatic arrhythmias induced by alpha 1-adrenergic stimulation during simulated ischemia may be attributed to a specific alpha 1-adrenergic receptor subtype that is blocked by WB-4101.