Transport of organic ions through lipid bilayers. The barbiturates

In a previous article [Naunyn-Schmiedeberg's Arch Pharmacol (1981) 316:266-272] transport of a number of organic ions across lipid bilayers was investigated using single bilayer liposomes. In this investigation the translocation of structurally closely related barbiturates across lipid bilayers is studied. The anionic form of the barbiturates can pass lipid bilayers, provided that the lipophilicity of the 5,5-disubstituted side chain is high enough. This permeability of barbiturates in the ionized form explains their uncoupling action of the oxidative phosphorylation and the deviations from the pH-partition theory found in absorption processes.