Anion exchange in the giant erythrocytes of African lungfish

Carbon dioxide transport in African lungfish Protopterus aethiopicus blood conformed to the typical vertebrate scheme, implying a crucial and rate‐limiting role of erythrocyte Cl – /HCO 3 – exchange. The rate coefficient for unidirectional Cl – efflux via the anion exchanger ( k , s −1 ) increased with temperature in African lungfish, but values were well below those reported in other species. The erythrocytes of African lungfish were, however, very large (mean cellular volume = 6940 µm 3 ), and the ratio of cell water volume to membrane surface area was high ( V w A m −1 = 1·89). Hence, the apparent Cl – permeability ( P Cl = kV w A m −1 , µm s −1 ) was close to that in other vertebrates. The plot of ln P Cl against the inverse absolute temperature was left‐shifted in the tropical African lungfish compared to the temperate rainbow trout Oncorhynchus mykiss , which supports the idea that P Cl is similar among animals when compared at their preferred temperatures. Also, Q 10 for anion exchange calculated from P Cl values in African lungfish was 2·0, supporting the idea that the temperature sensitivity of erythrocyte anion exchange matches the temperature sensitivity of CO 2 production and transport in ectothermic vertebrates.