The binding of noradrenaline to human erythrocytes

When human erythrocytes are incubated in a suspension medium containing noradrenaline, they take up noradrenaline in a reaction proceeding in two phases. In a rapid first reaction noradrenaline is bound by the cells by adsorption at pH-values above 6.0; this reaction follows Freundlich's isotherms. Subsequently, noradrenaline is taken up much more slowly by transmembranous diffusion into the cells. Neither reaction can be influenced by inhibitors such as N-ethyl maleinimide, ouabain, alpha- or beta-receptor blockers.