The uptake of amines by human erythrocytes in vitro.
1. Human erythrocytes incubated at 37 degrees C in Krebs bicarbonate solution at pH 7.5 took up 5-hydroxytryptamine, histamine and (-)-noradrenaline at slow rates which were proportional to the concentration of the amines in the medium at least up to 16 mug/ml., in accordance with a simple diffusion process.2. The initial velocity of uptake was greatest for 5-hydroxytryptamine, about 4 times less for histamine and about 20 times less for (-)-noradrenaline; (+)-noradrenaline was not taken up.3. Comparison of uptake measurements by bio-assay and by radioactivity indicated that, after 1 hr, about 10% of each amine taken up had been inactivated.4. At 2 degrees C the uptake of all three amines was greatly diminished. The presence of the antagonists cocaine, chlorpromazine, lysergic acid diethylamide, mepyramine and pronethalol (at 10(-6) or 10(-5) g/ml.) did not affect uptake of the amines.5. In the steady state the ratios of concentration of the amines between cells and medium were greater than could be accounted for by a Donnan distribution.6. Cells which had taken up amines lost most but not all of them into amine-free medium, at rates which were slower than the corresponding rates of uptake. It was concluded that the amines are partially bound in the cells, noradrenaline most and histamine least.7. The slow diffusion of amines into, and the small amounts retained by, erythrocytes indicate that they do not contribute significantly to the rapid termination of the pharmacological actions of these amines in vivo.