INOTROPIC SYNERGISM OF CARDIAC GLUCOSIDE WITH CALCIUM ACTING ON THE FROG’S HEART IN ARTIFICIAL MEDIA1

The relation of calcium ion concentration to the effect of cardiac glucosides has been studied by many investigators, among them Loewi (1); Lloyd (2); Konschegg (3); La Barre and van Heerswynghels (4); Smith, Winkler and Hoff (5); and Baker (6). A high proportion of these studies have concerned the poison-ing of intact animals, without regard to inotropic (i.e., “therapeutic”) action as related to the concentration of the applied glucoside. In addition, however, the hypocalcic heart under appropriate conditions affords a useful means of evaluat-ing the “therapeutic ” effectiveness of a cardiac glucoside in restoring the con-traction of such a hypodynamic frog heart. It is the purpose of this report to formulate quantitatively the relationship of 1) the percentile contractile response of the myocardium referred to maximal concentration; 2) the concentration of calcium ion; and 3) the concentration of cardiac glucoside. METHODS. Procecure. The technique employed was based upon that used by McLean and Hastings (7). Male frogs (Rana pipiens) weighing about 30 gin. were used. The bicarbonate-phosphate buffered Krebs-Henseleit solution (8) employed as a medium had the followin