1. The effect of thiocyanate on chloride and sodium fluxes across the gill was studied in the goldfish Carassius auratus. At low external chloride concentrations, addition of SCN− to the bathing solution markedly inhibited chloride influx and efflux, the net flux being reversed. SCN− injection was without effect. SCN− had no effect on sodium fluxes when injected or added to the external medium.

  2. The inhibition of chloride influx by SCN− was of a mixed type involving simultaneous modifications of the affinity constant of the carrier for Cl− and of the maximal Cl− influx. The affinity constant of the carrier for SCN− was 10 times lower than that for Cl−.

  3. The gill of the goldfish was found to be practically impermeable to SCN−.

  4. In the presence of external SCN−, the C1−/HCO3− exchange was reversed : Cl− was lost against HCO3− which is absorbed. This suggests an obligatory exchange.

  5. Exchange diffusion for chloride was also demonstrated.

  6. A kinetic model is proposed to explain chloride and bicarbonate transport across the gill of Carassius auratus.

© 1975 by Company of Biologists
1975
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