THE EFFECTS OF DIGITOXIN AND POTASSIUM ON STRIATED MUSCLE

¹ From the Department of Pharmacology, Cornell University Medical College, New York

On the assumption that the reversible state of inexcitability of the isolated frog's sartorius muscle which supervenes when the muscle is maintained outside a liquid environment, following treatment with one of the digitalis glucosides, is due to the presence of extracellular potassium which has escaped from the cell (Cattell, 1), a detailed study has been carried out in which the effects of digitoxin and those of potassium excess have been compared.

In muscles maintained in oxygen (or air) after treatment with ouabain or digitoxin there is at first a period in which the twitch tension is increased, but this is soon followed by loss of excitability. On returning to the solution containing the glucoside or to unmodified Ringer's solution recovery occurs within a few minutes. These effects are indistinguishable from those following treatment with Ringer's solution containing an excess of potassium, except that in the latter case recovery does not occur unless the muscle is treated with Ringer's solution containing the normal amount of potassium. Ouabain and digitoxin are equally effective and in concentration of 1 part per million their effects correspond approximately to that of a Ringer's solution modified to contain about 50 mgm. per 100 cc. of potassium.

There is a persistence of the effect of the digitalis glucosides—demonstrated by recurrence of the characteristic changes when the muscle is maintained in air following repeated soaking in Ringer's solution.

During the period of declining twitch tension caused by potassium excess, the ratio of tension to initial heat remains approximately constant, thus contrasting with the results previously reported for ouabain treated muscles, in which the decline in response was accompanied by a fall in the T/H ratio. The fall in efficiency resulting from treatment with the digitalis glucosides is therefore not due to the extracellular potassium.