Transport of organic ions through lipid bilayers

The transport of a series of charged drugs and other organic ions through lipid bilayers was studied, using single-bilayer liposomes. Monovalent organic cations and organic anions could carry charge into the liposomes independent of the nature of their counter ion. Ion-pair formation, following the addition of an excess of I- or Br-, did not facilitate this transport. However the passage of organic cations and anions across the membrane required the presence of the organic anion tetraphenylborate in the lipid bilayer. This effect of tetraphenylborate is probably due to a lowering of an intra-membrane potential energy hill, the principal barrier for transport, and not to ion-pair formation. It is concluded that organic ions that possess sufficiently lipophilic structures to mask their charged character, can pass lipid bilayers in charged form.