452 ADVENTURES IN RADIOISOTOPE RESEARCH 



rate. It is quite conceivable that a decomposition of other still more 

 labile phosphorus compounds during extraction cannot be avoided. But 

 the existence of the great difference in the inorganic phosphate con- 

 centration of plasma and cell water can be explained in a very different 

 way as well. 



The muscle cells take up when formed a comparatively large amount 

 of inorganic P. This high inorganic P content is maintained all through 

 life, the cell walls being impermeable to phosphate ions or, as far as 

 a restricted permeability is present, the phosphate lost by the cells is 

 compensated by a secretion of an equal amount of phosphate from the 

 plasma into the muscle cells. Numerous examples of such active sec- 

 retion are reported by Krogh (1939), and the application of his views 

 to the present problem leads to the last mentioned explanation. 



It is not possible at present to decide which of the explanations men- 

 tioned above is the correct one ; the application of radioactive P as 

 an indicator leads, however, to the result that a restricted permeability 

 of the muscle cell wall to phosphate ions is actually present. Professor 

 Kbogh has kindly drawn our attention to a possibility of deciding 

 which of these explanations is the right one. According to his view, 

 the primary process is the loss of some cellular phosphate by leakage 

 through the cell wall. The extent of the active secretion into the cells 

 is that necessary to compensate for the loss by leakage and is determin- 

 ed by the extent of the latter. Let us increase the phosphate concen- 

 tration of the plasma by administering large amounts of phosphate for 

 example. This increase should, according to the view cited above, not 

 influence the amount of labelled phosphate penetrating into the cells 

 while, in the case that the entrance of labelled phosphate into the cells 

 is due to diffusion, the amount entering the cells from a plasma con- 

 taining more phosphate should be larger than from one containing less. 



Summary 



Labelled sodium and labelled phosphate arc 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 

 phosphorvis and the radioactive sodium permits us to calculate the amount of 

 32P which penetrated into the muscle cells. Since all phosphorus atoms present in 

 the plasma can be assumed to show the same behaviour as the ^ap 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° 



