576 ADVEXTURES IX RADIOISOTOPE RESEARCH 



PARD et al. taking 60 min or more, it follows that the red corpuscles 

 lose 2 per cent only of their ^^K content in the course of 1 hour. These 

 and our results indicate the presence of a small rapidly interchanging 

 potassium fraction in the blood corpuscles. These may partly or wholly 

 be due to a rapid interchange between the potassium of the plasma and 

 that of those corpuscles which accumulate in the buffy coat. For canine 

 blood where the rapidly exchanging potassium fraction is very conspi- 

 cuous, Sheppard et al. succeeded in showing that at least an appre- 

 ciable part of their rapidly interchanging potassium is to be looked for 

 in the buffy coat of the isolated blood corpuscles. In experiments of very 

 short duration the amount of ^^K entering from the plasma into the 

 corpuscles during centrifugation furthermore may not be negligible. 

 Lesion of some erythrocytes during the labelling process may also lead 

 to some 42K loss. A removal of the buffy coat which may reduce the ^^K 

 loss of the erythrocytes observed shortly after their injection into the 

 circulation, cannot be considered to be a practical proposition in routine 

 blood volume determinations. 



DISCUSSION 



Different methods exist which permit to determine the rate of loss of 

 ^2K by the red corpuscles. We can activate erythrocytes, and after washing 

 them to remove the adhering plasma, shake the active red corpuscles 

 with inactive plasma, for example for 1 hr, and subsequently determine the 

 .activity of the last mentioned plasma. The figure obtained indicates the 

 loss of *2K by the corpuscles in the course of 1 hr. This procedure has the 

 disadvantage that washing may harm the mechanism responsible for 

 the permeation of potassium into the erythrocytes. The permeability of 

 potassium is known to be of a different type from that of phosphate. 

 The strong concentration of potassium in the red corpuscles in among 

 •others easily influenced by addition of glucose to the plasma or by 

 temperature changes. Therefore we preferred another method which is 

 based on the following consideration. 



If during a certain time a percentage of the ^SR of negligible weight 

 Added to the blood sample penetrated into the corpuscles, we can assume 

 that a corresponding fraction of all potassium ions present at the start 

 of the experiment in the plasma moved into the corpuscles as well. 

 As the potassium concentration of the red corpuscles remains constant 

 during the experiment (a minor deviation of this assumption would not 

 :significantly influence the result arrived at) a corresponding amount of 

 potassium must have moved in the opposite direction, hence from the 

 corpuscles into the plasma. We can thus determine the percentage of 

 corpuscle potassium which moves from the corpuscles into the plasma 



