The State of the Inorganic Components of Human Red Blood Cells*

Under resting conditions-that is, when metabolism is reduced to a minimum by chilling-previous experiments have indicated that sodium, potassium, inorganic phosphorus, and phosphate esters will not traverse the membrane of the red blood cell even when the concentrations of water, sodium, potassium, or inorganic phosphate in the serum are greatly altered (l-3). However, when the metabolic processes in the red blood cells are activated by heating the cells to 37”, inorganic phosphorus may be made to pass in either direction across the cellular membranes (2, 3). Two explanations for the difference in the behavior of the active and resting cells present themselves. The permeability of the red blood cell membrane may vary with the metabolic processes. On the other hand it is possible that in the resting cell sodium, potassium, and phosphate are restrained by combination in undissociable or non-diffusible form with substances of such large molecular size that they cannot penetrate the membrane and that these are broken down in the reactions involved in the metabolic processes of the cells. In an effort to determine the relative importance of physical and chemical restraints in the segregation of the chemical components within the cell, the passage of sodium, potassium, and phosphate of hemolyzed blood across an artificial membrane was compared with their movements across the intact