Non-ionic diffusion of pentobarbital across human chorion laeve.

Diffusion of the weak organic acid, pentobarbital, across human chorion laeve in vitro shows an inverse correlation with pH, when corrected for extracellular space permeation by the concurrent measurement of membrane permeability to the lipid insoluble molecule, p-aminohippurate. The temperature dependence of pentobarbital diffusion at different pHs supports the concept that the additional net flux of solute at lower pH occurs by transcellular permeation by the non-ionized moiety, the observed increase corresponding roughly to the dissociation curve for pentobarbital.