lab24-2 - Published July 1, 1964 T he Mechanism of Sodium...

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The Chloride Uptake by a Fresh-Water Fish, Mechanism of Sodium and the Gills of Carassius auratus 1 i. Evidence for NH[ / NA + and HCO[ / Cl- exchanges J. MAETZ ~D F. GARCfA ROMEU From the D~partement de Biologie, Commissariat a l']~nergie Atomlque, Centre d'~tudes Nucl~aires, Saclay, France A~STRaCT The addition of ammonium ions to the external medium results in an inhibition of the sodium influx and net uptake in Carassius auratus, while in- traperitoneal injection of ammonium produces the opposite effect. The simul- taneous chloride balance is not significantly affected by these treatments. The addition of bicarbonate ions to the external medium results in a reduction of the influx and net flux of chloride, while injection of bicarbonate produces the op- posite effect. The simultaneous sodium balance is not significantly altered. The effects of the external additiom are reversible after elimination of the excess am- monium or bicarbonate ions by rinsing. Inhibition of carbonic anhydrase in the gill by injection of acetazoleamide produces a simultaneous inhibition of both sodium and chloride exchanges. These results confirm the hypothesis of an ex- change of sodium for ammonium, and of bicarbonate for chloride across the gill. A tentative schematic representation of the ionic absorption mechanisms in the branchial cell of the fresh-water teleosts is given. Similarities with other biologi- cal membranes and especially with the renal tubule are pointed out. In the preceding publication (Garcla Romeu and Maetz, 1964) substantial evidence was advanced to show that in Carassius auratus the absorption of so- dium and chloride ions by the gill is independent. Such independence can only be explained by the assumption that these ions are independently ex- changed with endogenous ions. Krogh (1937, 1939) has suggested that the NH + and HCO~ ions might play this role. The work presented here is an attempt to verify this hypothesis. In support of the postulated sodium-ammonium exchange is the fact that the gill is the principal site for nitrogenous excretion in teleosts (Smith, 1929; I~o 9 The Journal of General Physiology on March 23, 2010 Downloaded from Published July 1, 1964
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1210 THE JOURNAL OF GENERAL PHYSIOLOGY • VOLUME 47 I964 Delaunay, 1929), and that this excretion is mainly in the form of ammonia. More recent work by Wolbach, Heinemann, and Fishman (1959) on Ameiurus, Goldstein and Forster (1961) on Myoxocephalus and Anguilla, and Thornburn and Matty (1963) on Carassius Salmo gives figures for branchial ammonia excretion which, at 15 to 100 (#Eq/hr.)/100 gin, are of the same order of magnitude as those which we have found for the net flux of sodium. Goldstein and Forster (1961) have also shown that the major part of the endogenous ammonia is produced in the branchial cells by the activity of enzymes such as glutaminase and glutamic acid dehydrogenase, blood ammonia clearance by the gills accounting for only about 10 per cent of the total output. In support of the postulated chloride-bicarbonate exchange is the fact that
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This note was uploaded on 09/12/2010 for the course BIOLOGY 225 taught by Professor Pavgi during the Winter '10 term at University of Michigan.

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lab24-2 - Published July 1, 1964 T he Mechanism of Sodium...

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