CO2 and HCO3- Permeability of the Rat Liver Mitochondrial Membrane

Background/Aims: Across the mitochondrial membrane an exceptionally intense exchange of O-2 and CO2 occurs. We have asked, 1) whether the CO2 permeability, P-M,(CO2), of this membrane is also exceptionally high, and 2) whether the mitochondrial membrane is sufficiently permeable to HCO(3)(-)to make passage of this ion an alternative pathway for exit of metabolically produced CO2. Methods: The two permeabilities were measured using the previously published mass spectrometric O-18 exchange technique to study suspensions of mitochondria freshly isolated from rat livers. The mitochondria were functionally and morphologically in excellent condition. Results: The intramitochondrial CA activity was exclusively localized in the matrix. P-M,(CO2) of the inner mitochondrial membrane was 0.33 (SD +/- 0.03) cm/s, which is the highest value reported for any biological membrane, even two times higher than w ouof the red cell membrane. P(M,HCO3-)was 2.10(-6) (SD +/- 2.10(-6)) cm/s and thus extremely low, almost 3 orders of magnitude lower than P-M,P-HCO3- of the red cell membrane. Conclusion:The inner mitochondrial membrane is almost impermeable to HCO3- but extremely permeable to CO2. Since gas channels are absent, this membrane constitutes a unique example of a membrane of very high gas permeability due to its extremely low content of cholesterol. (C) 2016 The Author(s) Published by S. Karger AG, Basel