We summarize here, mainly for mammalian systems, the present knowledge of (a) the membrane CO₂ permeabilities in various tissues; (b) the physiological significance of the value of the CO₂ permeability;
Keywords: CO2 permeability; Rhesus proteins; aquaporin-1-deficient mice; aquaporins; membrane cholesterol; protein CO2 channels.
(c) the mechanisms by which membrane CO₂ permeability is modulated; (d) the role of the intracellular diffusivity of CO₂ for the quantitative significance of cell membrane CO₂ permeability; (e) the available evidence for the existence of CO₂ channels in mammalian and artificial systems, with a brief view on CO₂ channels in fishes and plants; and, (f) the possible significance of CO₂ channels in mammalian systems.