Cation exchange between cells and plasma of mammalian blood; methods and application to potassium exchange in human blood

The exchange of potassium between cells and plasma of heparinized human blood has been studied in vitro using the radioactive isotope K⁴². The changes in cell and plasma specific activity are characteristic of a simple two-compartment system. The mean of seven determinations of the exchange rate at 38°C. is 1.8 per cent of the cellular potassium per hour. The results indicate that at 38°C. the rate is relatively insensitive to oxygenation or reduction of the hemoglobin, and to 1200 r of gamma radiation. With varying temperature the rate follows pseudo first order kinetics with a Q₁₀ of 2.35. Below 15°C. the rate of loss of potassium exceeds the rate of uptake.