Studies of phosphorus metabolism in man; a study of the permeability of the human erythrocyte to inorganic phosphate in vitro by the use of radioactive phosphate (P32).

I T IS A distinct pleasure to dedicate the first published* of a series of articles from this laboratory on the use of radio isotopes in human physiologic studies to Dr. George R. Minot. It was under his direction that our venture into this field was undertaken. Radio phosphorus has been used in the examination of various phases of phosphorus metabolism and the results have been summarized by Hevesy’ ‘ 2 and Kamen.3 Most of the data presented in the literature were obtained in animals, and by use ofdosages of isotopic p32 in excess ofwhat may be considered tracer amounts. Human studies on the metabolism of p32 in tracer amounts are few in number, most of the interest of previous authors having been directed to the therapeutic uses of the isotope. Since normal metabolic processes may be deranged by larger than tracer doses of P3 , it seemed of value to investigate the metabolism of phosphorus in the human body using P’2 as a tracer in doses low enough to cause no demonstrable metabolic disturbance. These studies wil be presented elsewhere.4 The use of p32 in such concentrations immediately imposes problems of revisions of methods and further considerations of accuracy of counting technics. These will be described fully in another communication.5 The first consideration in the attack on phosphorus metabolism was the resolution of the controversy of phosphorus exchange between cells and plasma of the circulating blood. The present communication is concerned with the distribution of phosphorus between red cells and plasma in in vitro studies of the phosphorus exchange between these two media. Eisenmann et al.,#{176} have shown in an in vitro system to which inorganic phosphate together with p32 were added to human whole blood, that at 38 C. phosphate entered the red cells freely, while at 7 C. the exchange was minimal. In their experiments to ioi mg. phosphorus were added to 100 ml. of whole bood. They also stated that, under their experimental conditions, radio phosphorus accumulated in the cells out of proportion to the amount of inorganic phosphate present. Their observations were made on whole blood and plasma and the cell concentrations of phosphorus compounds were calculated using hematocrits. In the present communication no phosphate was added except that represented by the p32 which was negligible, since the specific activity of the isotopic sodium