KINETICS OF CHLORIDE TRANSPORT ACROSS FISH RED-BLOOD-CELL MEMBRANES

The continuous flow tube method was used to investigate the kinetics o f chloride transport, and its potential oxygenation-dependency, in red blood cells (RBCs) from four teleost fish species and man. A signific ant interspecific variation in Cl- transport kinetics was found. At 15 degrees C, the rate constant k for unidirectional Cl-36(-) efflux was significantly lower in RBCs from eel and carp than in RBCs from rainb ow trout and Atlantic cod. The values of k of cod RBCs at 15 degrees C and of human RBCs at 37 degrees C were not significantly different. T he volume and surface area of the RBCs were evaluated and used to calc ulate the apparent membrane permeability to Cl- (P-Cl). The magnitude of P-Cl followed the sequence: eel<carp<trout less than or equal to co d. Pa values in trout and cod at 15 degrees C were similar to human va lues at 37 degrees C. An extrapolation of human values to 15 degrees C revealed that the Cl- shift at this temperature was considerable fast er in all four teleosts than in man. This illustrates appropriate adap tion of band-3-mediated anion transport to the different temperature r egimes encountered by fish and mammals. The Cl- transport kinetics did not differ significantly between oxygenated and deoxygenated RBCs in any of the species examined. The apparent absence of any effect of a c hange in haemoglobin oxygen-saturation may be related to the presence of a flexible link which results in minimal interaction between the me mbrane domain (mediating Cl- transport) and the cytoplasmic domain (to which oxygenation-dependent haemoglobin binding occurs) of band 3. In carp, Cl- transport kinetics were not influenced by pH over the extra cellular pH (pHe) range 7.6-8.36, which spans the in vivo pile range. The data are discussed in relation to the rate-limiting role of red bl ood cell HCO3-/Cl- exchange for CO2 excretion.