Bicarbonate exchange kinetics at equilibrium across the erythrocyte membrane by 13C NMR

The rate of exchange of 13C-labelled bicarbonate across the membranes of human erythrocytes in suspension, at thermal and chemical equilibrium, was measured using 13C NMR spectroscopy: the permeability coefficient (3.34 X 10(-4) cm s-1) agrees well with previous values obtained with other methods. Data analysis was complicated by the need to consider the Donnan ratio of the charged species inside and outside the cells. This work appears to be the first, involving the present NMR procedure, for studying fast membrane transport of a molecule other than water.