DIGITALIS AND CALCIUM

Digitalis glucosides administered to isolated frog hearts filled with Ringer solution cause in time a decrease of the amplitude of contractions and eventually a standstill. The character of the decrease of the amplitudes and the time elap-sing until the standstill depends on the dosage; with large doses the diastolic relaxation is diminished and after a short while a standstill in systolic contracture occurs. With minimal effective doses the systolic contractions very slowly decrease and eventually the heart stands still in diastole. Doses lying between these extremes produce effects lying between the aforementioned (Straub (1) and others). We know that calcium is involved in the systolic effect of digitalis (Clark (2), Loewi (3), and others). The present paper deals with the part calcium may play in the diastolic effect of threshold doses of digitalis. The experiments were performed on isolated frog hearts (rana pipiens) attached to a Straub cannula. The Ringer solution had the following composition: 0.65 grains of NaCI, 0.01 grams of KC1, 0.01 grams of CaC12, 0.02 grams of NaHCO3 and water to make 100 cc. solution. The digitalis preparations used were