Curves describing the loss of K from human red cells as a function of time can be interpreted in terms of an equation which treats the K content of the cell (φ) as the result of an accumulation process occurring at a rate P and an outward diffusion process regulated by a constant a. The equation is useful for describing the observations and for exploring the mechanisms which may be responsible for the K losses, although it cannot be used for analyzing the experimental data in a strict sense in the absence of independent metabolic data because P and a may both be functions of time. The applicability of the equation is illustrated by its use in connection with experimental curves showing K loss as a function of time at 4°, 25°, and 37°C. for systems containing human red cells in isotonic NaCl or NaCl-buffer.
At 4°C., the K loss follows an exponential curve approaching an asymptote in the neighborhood of φ = 0.50 ± 0.15. The corresponding value of P implies that the cells are able to accumulate about 0.6 per cent of their initial K per hour under these conditions.
At 25°C., the K loss starts exponentially but becomes roughly linear with time after 24 to 48 hours. The change of form is probably due to the appearance of autolysins in the system. Curves of a similar mixed or intermediate form may be obtained even at 4°C. if the observations are sufficiently extended and if spontaneous hemolysis becomes appreciable.
At 37°C., the K loss is exponential for the first 24 to 36 hours, the curves approaching asymptotes which, translated into terms of P, indicate that the cells can accumulate about 7 ± 3 per cent of their initial K per hour. After this time autolysis begins to affect the shape of the curves, the rate of K loss increasing rapidly.
The effect of adding fluoride or iodoacetate is to lower the position of the asymptote to which the curves proceed; i.e., to decrease the accumulation rate P, to increase the diffusion constant a, or both. Cyanide has almost no effect. Hypotonicity has little effect on the rate of K loss at 37°C.; at 4°C., the rate of loss is somewhat less in hypotonic NaCl.
The observation that the K loss in systems at 4°C. and containing as much as 0.086 M NaF does not become complete, but proceeds exponentially towards an asymptote between φ = 0.2 and 0.4, suggests that 20 to 40 per cent of the cell K is much less diffusible than the remainder at low temperatures and in the absence of lytic substances. A similar conclusion is suggested by the form of the curve for K loss into saline at 4°C., an accumulation rate of 0.6 m. eq./litre of cells/hour at the end of 100 hours or more being improbably great for a system at such a low temperature and containing no added glucose.