Intrinsic CO2 Permeability of Cell Membranes and Potential Biological Relevance of CO2 Channels

The past dozen years has seen a series of papers that come to the conclusion that CO2 passes through certain aquaporins and Rhesus proteins. The past three years has seen another series of papers that come to the conclusion that protein channels could not make a meaningful contribution to overall CO2 membrane permeability because of a combination of: 1) a high CO2 permeability of membrane lipids and 2) large unstirred layers, which would render their CO2 resistance much higher than that of a biological membrane. Is this also true for a membrane crowded with proteins? This comment summarizes the current status of the debate.