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-/HCO3- 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 mum(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), mum s(-1)) was close to that in other vertebrates. The plot of InPCl 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 CO2 production and transport in ectothermic vertebrates. (C) 2003 The Fisheries Society of the British Isles.