COMPARATIVE EFFECTS OF IMIPRAMINE AND PROPRANOLOL ON THE TRANSMEMBRANE POTENTIALS OF THE ISOLATED RABBIT'S ATRIA

Publisher Website
Google Scholar
Abstract
Effects of imipramine and the adrenergic [beta] -receptor blocking drugs such as propranolol and pronethalol on the transmembrane potential of the S-A node and right atrium of the spontaneously beating isolated rabbit heart were investigated by a micro-electrode technique. In concentrations more than 10-6 g/ml, these drugs elicited the similar changes in atrial electrical activities a decrease in atrial rate, an increase in the action potential duration resulting from a decrease in depolarization and repolarization velocity and a diminution of the action potential amplitude in both of the S-A nodal and the atrial fibers, and a decrease in slope of the diastolic depolarization in the S-A nodal fiber. A compete abolition of the atrial electrical activities was produced within 60 min. after the administration of high concentrations (10-5 to 10-4 g/ml) of either compound. The abolished activies due to imipramine were not completely recovered by washing the preparation but were recovered by the addition eplnephrine or noreplnephrine. The atrial activities which had been abolished by the high concentration of propranolol or pronethalol were not regained by eplnephrine or noreplnephrine by washing the preparation. Imipramine did not affect the positive chrono-troplc response to isopropylnoreplnephrine, whereas the B-blocking drugs completely inhibited the response. A shortening of the action potential duration following isopropylnoreplnephrine was markedly antagonized by the [beta]-blocking drugs but slightly by imipramine. Imipramine shows no or only little [beta]-blocking activity in the isolated rabbit atria and the inhibition of the atrial electrical activity by im -ipramine is associated with its quinidine-like and local anesthetic-like actions.