Gas Transport Mediated by Proteins in Cell Membranes

Abstract

Transports of water and gases through cell membranes have conventionally been considered to diffuse across the lipid bilayer. Recently, however, it was reported that water transport was mediated by water channel, aquaporin (AQP). Gas permeation, such as CO₂ and NH₃, was greatly restricted by the apical membrane in epithelia of the urinary tract or colon crypt, a restriction not explained by diffusion. The reason for this low permeation rate was considered to be the difference in lipid composition of the cell membranes. On the other hand, band 3 and AQP have been suggested as possible gas or CO₂ channels. In 1998, several reports indicated that AQP1 enhanced CO₂ permeation of cell membranes or might be the CO₂ channel, although other study disagreed. Recent studies on gas permeation of the cell membrane mediated by protein or an as yet unspecified channel were reviewed.