Pathways of water through erythrocyte membranes. Routes along defect structures

A new model for the passive (diffusional) permeation of water and for the transfer of protons across membranes from mammalian erythrocytes is presented. The proton transfer is anion-coupled through the action of the band3 protein. Inhibition studies reveal that the pathways for the anion- and water-exchange are independent. Dynamic grain boundaries and defect structures in thermodynamic equilibrium (steady state in the general case) with the membrane are considered to be the major routes for the water permeation. Modulators of membrane functions may either act only locally or may lead to a reordering of the membrane. The specific inhibitor of the anion-exchange, 4,4'-diisothiocyanatostilbene-2-2'-disulfonic acid (DIDS), is considered to induce only local effects by closing the anion-transfer gate. The more unspecific binding of the mercurial p-chloromercuribenzenesulfonic acid (pCMBS) should change the membrane aggregational states. Thus pCMBS can reduce the water permeation and at the same time stimulate the passive proton translocation as is experimentally observed.