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 µm3), and the ratio of cell water volume to membrane surface area was high (VwAm−1 = 1·89). Hence, the apparent Cl– permeability (PCl = kVwAm−1, µm s−1) was close to that in other vertebrates. The plot of lnPCl 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 PCl is similar among animals when compared at their preferred temperatures. Also, Q10 for anion exchange calculated from PCl 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.
Document Type: Regular Paper
Institute of Biology, University of Southern Denmark, Odense, 5230 Odense M, Denmark,
Department of Medical Physiology, University of Copenhagen, 2200 Copenhagen N, Denmark,
School of Biological Sciences, University of Liverpool, Biosciences Building, Liverpool, L69 7ZB, U.K.,
Department of Zoophysiology, Aarhus University, 8000 Aarhus, Denmark and
School of Biosciences, University of Birmingham, B15 2TT, U.K.
Publication date: May 1, 2003