Combination of Insulin With Frog Skeletal Muscle

¹ From the Department of Pharmacology, University of Virginia Medical School, Charlottesville, Virginia

Isolated intact frog skeletal muscles, equilibrated for a brief period of time in a solution of insulin and then rinsed thoroughly, showed an increased consumption of oxygen and an increased potassium uptake compared to controls when incubated for 6 hours without insulin. This has been interpreted as a firm binding of insulin to special reactive sites at the muscle cell surfaces. An equilibration period of 1 minute and an insulin concentration of 0.5 U/ml were sufficient conditions for saturating all of the sites concerned with oxygen consumption but not for all of those concerned with potassium transfer. In addition an aged insulin solution lost its ability to stimulate potassium uptake before the effect on oxygen consumption was altered. It is therefore concluded that there is one type of reactive site concerned with oxygen consumption with which insulin combines rapidly and another type of reactive site concerned with potassium transfer with which insulin combines relatively more slowly.

Note:
with the technical assistance of Nancy J. Lee