RESULTS

Extracellular Transfer of Glucose-The following experiments indicated that extracellular transfer of glucose from the capillary to the muscle cell membrane was not a significant rate-limiting step for glucose uptake in the diabetic muscle. As described earlier (9), the rate of sorbitol distribution in the extracellular space was taken as an index of glucose transfer. Sorbitol does not penetrate the cell membrane and has the same equilibrium distribution in the diabetic as in the normal heart (9). Table I shows that sorbitol reached more than 80 y0 of its final distribution in the extracellular water (360~ 1 per g) within 30 seconds. The rate of equilibration was essentially the same as that found in the normal heart (9) and suggested that the same calculations of glucose transfer could be applied. On this basis, it was estimated that the extracellular transfer was so rapid as