Fast transmembrane exchange in red cells studied with NMR.

13C NMR, with two fundamentally different procedures, was used to measure the H13CO3- permeability coefficient (P) of human erythrocytes. The values of P (approximately 3 X 10(-4) cm s-1) were similar to those obtained by other, non-NMR methods. A third procedure was used with 31P NMR to measure the permeability coefficient of human erythrocytes for the non-electrolyte dimethyl methylphosphonate; the effects on transmembrane exchange of varying haematocrit and butanol were studied.