Active Chloride Transport by the Gills of Rainbow Trout (salmo Gairdneri)

Active sodium uptake from dilute media has been described extensively in a number of aquatic vertebrates, and we have some understanding of the cellular mechanisms involved (Koefoed-Johnsen & Ussing, 1958; Ussing & Windhager, 1964; Biber, Chez & Curran, 1966). While chloride transport has been neglected by comparison, chloride uptake systems are found in diverse groups of animals and deserve more attention. Krogh (1937) reported that several teleosts were able to absorb Cl~ from dilute media, and he also showed that this could occur without simultaneous transfer of an accompanying cation (Krogh, 1938). More recent work has provided values for Cl~ exchange in a number of fish (Mullins, 1950; Gordon, 1963; Motais, 1967; Potts & Evans, 1967). But the mechanism of chloride transport in teleosts has received little attention. Because of its independence of simultaneous cation transport, Krogh (1938) suggested that exchange with another anion, perhaps bicarbonate, preserved electrostatic neutrality. Garcia-Romeu & Maetz (1964) confirmed the report that Cl~ uptake was independent of Na transport in the goldfish. They also provided some evidence for a C1~/HCO3~ exchange by showing that injections of NaHCO3 stimulated Cl~ absorption in Carassius. Such an exchange would also explain the observation by Dejours (1969) thai CO2 excretion by Carassius decreased temporarily when the animal was placed in a low-Cl~ medium and increased when the Cl~ concentration was raised. We have recently shown that ion transport across the teleost gill could be studied with a small volume system which, in effect, externally isolates the gill (Kerstetter, Kirschner & Rafuse, 1970). In the present work we have used the same system to evaluate the kinetics of Cl~ transfer and to study the characteristics of the transport system in rainbow trout.