CATION EXCHANGE BETWEEN CELLS AND PLASMA OF MAMMALIAN BLOOD : I. 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 K(42). 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 Q (10) of 2.35. Below 15°C. the rate of loss of potassium exceeds the rate of uptake.