Characterization of the transport of the nonelectrolyte dimethyl methylphosphonate across the red cell membrane

We have refined the method for measuring the equilibrium exchange of the neutral phosphoryl compound dimethyl methylphosphonate across the human red cell membrane using ³¹P NMR spectroscopy. Using this improved technique we measured a permeability coefficient of dimethyl methylphosphonate of 9.47 ± 1.01 × 10^–5cm s^–1 at a concentration of 164 mM, at 25 °C. The transport at 25 °C was not saturable up to a concentration of 600 mM and was not inhibited by 4,4′‐diisothiocyano‐2,2′‐disulfonic acid, p‐chloromercuriphenyl sulfonic acid, copper ions or phloretin, or by thiourea or urea at 16 °C. The permeability was enhanced by butanol and phloretin.