Rate of Penetration of Phosphate into Muscle Cells

Abstract

Summary. Labelled sodium and labelled phosphate are injected simultaneously into the lymph sack of the frog and the distribution of the radioactive sodium and the radioactive phosphate between plasma and muscle of equal weights is determined. A constant partition ratio of the radioactive sodium is obtained after the lapse of about 20 minutes. From this ratio the volume of the interspaces of the muscle can be calculated. In the case of phosphorus, the partition ratio increases even after the lapse of many days because of continued penetration of the labelled phosphate into the cells. The difference of the partition ratio of the radioactive phosphorus and the radioactive sodium permits us to calculate the amount of 32 P which penetrated into the muscle cells. Since all phosphorus atoms present in the plasma can be assumed to show the same behaviour as the 32 P atoms we can compute from the figures obtained the amount of plasma inorganic P which exchanged with cellular P during the experiment. In the course of 4 days at 22°, 0.082 mgm P was found to penetrate into the cells of 1 gm gastroenemius muscle and vice versa. At 0°, 1 / 5 of the above value was found. An alternative method which is independent of the knowledge of the size of the extracellular space is based on the determination of the comparison of the active inorganic phosphorus content of the plasma with the active organic phosphorus content of the muscle. When applying this method, one assumes that the organic phosphorus compounds of the muscle are renewed inside the cells. By this method, the amount of plasma P penetrated into 1 gm muscle in the course of 4 days was found to be 0.088 mgm.