284 POTASSIUM 



Typical Methods. About 60 X 10*^ counts/min of K''^ in 0.15 milli- 

 equivaleiit KCl was injected into rabbits. Untreated plasma was meas- 

 ured directly into counting planchets, mixed with 2 to 4 drops of 5 per cent 

 trichloroacetic acid, dried under a heat lamp, and counted with a 2-mg/ 

 cm^ end-window Geiger tube. The trichloroacetic acid reduces produc- 

 tion of dry protein flakes. Tissues were digested in HNO3, and dilutions 

 thereof dried for counting (K-1). In another study with rabbits, 5 ml 

 solution containing 30 nc in 0.5 milliequivalent potassium was injected 

 intravenously (K-4). Tissue samples (1 to 3 g) were digested in concen- 

 trated H2SO4 and made up to 20 ml, and an aliquot counted with a 

 dipping tube. The potassium concentration in the urine was determined 

 by flame photometry. In a study with dogs, 150 to 1000 jjlc was injected, 

 and plasma and spinal fluid carefully evaporated for measurement with a 

 Lauritsen electroscope (K-5). 



Methods used for study of exchange between plasma and red cells may 

 be described as follows (K-6) : Venous blood was heparinized with 10 mg 

 of heparin in 1 ml of 0.15 M NaCl per 50 ml of blood. Fifty milliliters of 

 blood was placed in a 200-ml round-bottom paraffin-coated flask fitted 

 with a top, allowing gas flow and sample removal. About 2 X 10^ 

 counts/min of K^^ and about 1 X 10* counts/min of Rb*^ were incor- 

 porated in 1 to 2 ml of plasma and mixed with the whole blood at zero 

 time. Glucose was also added to raise the initial blood glucose by 

 250 mg %. There was some indication that the original K'*- preparation 

 contained a trace of radiocontamination, probably Rb*®. The flasks were 

 rotated mechanically, and small aliquots taken for measurement at given 

 time intervals. Potassium was estimated chemically using the flame 

 photometer w^th diluted plasma and hemolyzed red cells. Radioactivity 

 was determined by the pipetting of solutions onto filter-paper disks. 

 Whole blood was hemolyzed by freezing before pipetting, and a detergent 

 solution (1.7 per cent Hemosol) was used to facilitate even distribution of 

 the red cells. K"*- and Rb^*^ were determined in the same sample by meas- 

 urement initially, and again after the K^- had decayed away. 



In a study of relationships of electrolyte accumulation and tissue 

 metabolism, about 300 mg of rabbit kidney slices were suspended in 2.5 ml 

 of medium in a Warburg vessel (K-7). About 0.2 /xc K''^ in 0.2 ml of 

 medium was placed in the side compartment. At termination of the 

 incubation and gas measurements, the tissues were digested in HNO3, and 

 aliquots of the ash solution as well as of the medium were counted. Total 

 Na and K were estimated by flame photometry. Similar methods have 

 been described for estimation of the exchange rate of K in brain and retina 

 tissue (K-8). 



Potassium absorption has been studied using barley roots from seed- 

 lings grown in the dark at a uniform temperature to give reproducible 



