Inhibition of Isolated Auricles by Anticholinesterases and Reactivation With Atropine and Epinephrine

¹ From the Department of Embryology, Carnegie Institution of Washington, Baltimore, Maryland

The chronotropic and inotropic responses of spontaneously beating isolated auricles of the guinea pig were studied in vitro during exposure to anticholinesterases. Carcholin and Mecholyl were most effective in arresting or inhibiting the atria, whereas neostigmine, physostigmine and strychnine were less potent. It was possible to overcome the inhibition or arrest in all cases except that of strychnine by means of atropine or epinephrine. After strychninization, atropine failed to induce contractions, whereas epinephrine did restore spontaneous rhythmicity. Reactivation by atropine was characterized by a return of amplitude and rate of contraction to preinhibitory levels. Reactivation by epinephrine was followed by an acceleration of rate and an increase in the amplitude of contraction above preinhibition levels.