BIOASSAY FOR CARDIAC ACTIVE PRINCIPLES BASED ON THE STAIRCASE PHENOMENON OF THE FROG HEART

¹ National Heart Institute, National Institutes of Health, Bethesda, Maryland

A bioassay using the isolated frog ventricle for the measurement of cardiac active principles is described. It is based upon the effect of such substances on the staircase phenomenon; from this it is inferred that the effect is probably exerted upon the reentry of potassium lost by the fiber during contraction. Since the reentry of potassium across the cell membrane is influenced by calcium, potassium, temperature and seasonal variations, these effects are also discussed.

If the assay is made with both frog aad toad hearts, it is possible to distinguish cardiac glycosides with a lactone ring specifically among several groups of substances with activity in the frog preparation.