Membrane solubility of chlorpromazine. Hygroscopic desorption and centrifugation methods yield comparable results.

Binding of the positively charged drug chlorpromazine to artificial and erythrocyte bilayer membranes was investigated by the filtration method called hygroscopic desorption [Conrad & Singer (1979) Proc. Natl. Acad. Sci. U.S.A. 76, 5202-5206] and by the conventional centrifugation method. Only minor differences in the partition coefficients were observed using the two methods. Our finding is not consistent with the observation of Conrad & Singer that amphipaths are completely excluded from biological membranes. However, the partition coefficient is dependent on membrane composition, which means dependent on the physical properties of a membrane.