Studies of tissue permeability. IV. The distribution of glucose between plasma and muscle.

Recent studies have focused attention on the process of sugar entry into the muscle cell as a possible point of regulatory control of carbohydrat,e metabolism. In previous reports the penetration of a variet,y of nonmetabolizable sugars into mammalian muscle has been characterized and the responsiveness of these sugars to insulin and muscle work has been confirmed (1, 2). However, the fact that these sugars are poorly metabolized limits their usefulness in clarifying the interrelationship between penetration and utilization. Such information is required in order to support the concept that glucose entry is a rate-limiting process and the site of insulin action. Since the rates of penetration and utilization of glucose in muscle cannot be determined separately with present techniques, another experimental approach was used. The distribution of free glucose between the extracellular and intracellular tissue water reflects the balance between the rates of penetration and utilization. Measurements of this distribution were carried out under a variety of experimental conditions. Experiments report,ed in this paper indicate that the processes of penetration and utilization, although intimately geared, can be dissociated under certain physiological conditions so that free glucose is accumulated inside the muscle cell.