Alpha and beta adrenergic effects on human atrial specialized conducting fibers

Abstract

The authors determined the effects of epinephrine on automaticity and action potential characteristics of right atrial specialized fibers (RAF) from human atria obtained during cardiac surgery. RAF were studied with standard microelectrode techniques during superfusion with Tyrode's solution at 37°C. A biphasic response to epinephrine was seen, rate slowing at low agonist concentrations and increasing at high concentrations. The epinephrine-induced duced slowing of spontaneous rate was due to a decrease in the slope of phase 4 depolarization. At the high epinephrine concentrations RAF hyperpolarized. The α-adrenergic blocker, phentolamine, shifted the dose-response curve upward and to the left and enhanced the hyperpolarization of RAF. The β blocker, propranolol, shifted the curve to the right and decreased the degree of hyperpolarization. The study they made suggests the presence of α and β receptors in RAF. The α response consists of a slowing of rate, the β response of an acceleration of rate and hyperpolarization of RAF.