398 



ADVENTURES IN RADIOISOTOPE RESEARCH 



Table 18. — Specific Activity or Phosphorus Frac- 

 tions Isolated prom Different Organs of a Frog. 

 AFTER Administration of Labelled Phosphate 

 During 45 Hours at 20° 



Fraction 



Specific aotiTity 



Plasma P 



Corpuscle P 



Gastrocnemius inorganic P 



Gastrocnemius creatine -\- pyrophosphate P 



Liver P 



Epiphysis P 



Diaphysis P 



100 

 3.6 

 4.9 

 5.3 

 10.1 

 0.35 

 0.20 



Table 19. — Specific Activity of Phosphorus Frac- 

 tions Isolated from Different Organs of a Frog 

 AFTER Administration of Labelled Phosphate 

 During 4 Days at 22° 



phorus extracted from the compound in question. In the following, 

 we shall discuss the interaction of the plasma phosphate with the cellu- 

 lar phosphate. This is clearly a very different problem, the rate of inter- 

 action between the plasma phosphate and the cellular phosphate being 

 determined by the permeability of the cell membrane. 



The low rate at which phosphate ions migrate through the membrane 

 of the cells of the gastrocnemius is seen in Tables 18 and 19. In the course 

 of 4 days at 22° only somewhat less than 1/10 of the P atoms present in 

 the labile P compounds got replaced by plasma P. The molecules of the 

 labile P compounds were repeatedly renewed during this interval and 

 many P atoms present in the muscle cells interchanged lively; however, 

 the interchange between cellular and extracellular P took only place 

 on a restricted scale. 



The results of further experiments in which the activity of the plasma 

 was compared with the activity of the muscle is seen in Table 20. 



To keep the plasma activity at an approximately constant level 

 throughout the experiment, 0.4 cc. solution was injected at the start 

 of the experiment and further 0.08 cc. every hour. As seen in Table 20, 

 within 1 hour and 4 hours the activity of the plasma changes only 



