lab23 - Published July 1, 1964 The Mechanism of Sodium and...

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The Mechanism of Sodium and Chloride Uptake by the Gills of a Fresh-Water Fish, Carassius auratus i. Evidence for an independent uptake of sodium and chloride ions F. GARC~A ROMEU AND J. MAETZ From the D~partement de Biologle, Commissariat ~ l'l~nergie Atomique, Centre d'Etudes Nuel~aires, Saelay, France ABSTRACT Carassius auratus placed in a dilute sodium chloride solution (400 gM) is able to absorb sodium and chloride ions at very different rates, or to absorb one ion and to lose the other. This is the case not only for fish which have been previously kept in choline chloride or sodium sulfate solutions or deionized water, in order to stimulate their absorption processes, but also in control fish which have not been deprived of sodium or chloride. The absorp- tion of sodium or chloride appears to be unaffected by the presence of a non- permeant co-ion such as choline or sulfate. Conductivity measurements of the external medium show that during ion uptake the conductivity is constant or increases slowly. This suggests the existence of exchange processes between the ions absorbed and endogenous ions excreted. It is unlikely that potassium or calcium is exchanged for sodium, because of the low permeability of the gills to these ions. Finally, the flux ratios observed for both sodium and chloride ions in the present investigation can only be explained, in relation to their electro- chemical gradients across the gills, in terms of active transport. Fresh water organisms maintain a concentration gradient between the electro- lytes of their internal medium and those of their very dilute external medium. Invertebrates, fish, and amphibians have been the objects of numerous investi- gations designed to elucidate the processes by which they maintain this gradient. Special attention has been paid to sodium- and chloride-concen- trating mechanisms. In this field diverse experimental techniques on various taxonomic groups yield results which may be classified into two categories: (a) those which indicate the presence of a special transport mechanism for the sodium (active transport) while the chloride follows passively (Ussing, 1954) ~95 The Journal of General Physiology on March 23, 2010 jgp.rupress.org Downloaded from Published July 1, 1964
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xi96 THE JOURNAL OF GENERAL PHYSIOLOGY • VOLUME 47 " t964 and (b) those which suggest independent concentration mechanisms for both sodium and chloride: active transport for both ions according to J6rgensen, Levi, and Zerahn (1954) and Zadunaisky, Candia, and Chiarandini (1963), transport associated with ionic interchange processes which account for the different rates of absorption of the cation and anion, according to Krogh (1937 a, b, 1939) and Shaw (1960 a, b, c). It is of particular interest that the skins of the amphibians Rana esculenta and R. temporaria in vivo (J6rgensen et al., 1954) gave results contradictory to those obtained in vitro (Ussing, 1954). The reasons for these contradictory results re- main to be elucidated. Shaw (1960 a) without underestimating the importance
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lab23 - Published July 1, 1964 The Mechanism of Sodium and...

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