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Journal of Experimental Biology 53,75-92 (1970)
Published by Company of Biologists 1970

Chloride Regulation at Low Salinities by Nereis Diversicolor (Annelida, Polychaeta) : I. Uptake and Exchanges of Chloride

RALPH I. SMITH ¹

¹ Department of Zoology and Dove Marine Laboratory (Cullercoats), University of Newcastle upon Tyne; Department of Zoology, University of California, Berkeley, California, 94720, U.S.A.

1. N. diversicolor from estuarine conditions in north-eastern England can be adapted to a chloride concentration in a pond water (PW) medium at least as low as 0.9 mM/l, and shows a net uptake of chloride when returned to a medium 3-10 mM/l more concentrated. But in comparable transfers after adaptation at a chloride concentration of 10 mM/l, net uptake is not measurable.

2. Net uptake of chloride is demonstrable in the lowest salinities, where coelomic chloride concentration drops below the regulatory plateau. Net uptake reaches 3.5 µM/g wet weight/h.

3. Chloride loss is well correlated with weight loss after adaptation in 10 mM/l, but poorly so after adaptation in PW, suggesting that the urine is very hypotonic to body fluid in PW, and isotonic (or less hypotonic) at environmental chloride concentrations of 10 mM/l or higher.

4. Uptake of chloride occurs against both electrical and chemical-concentration gradients over the lower third of the environmental salinity range, which is the range in which hyperosmotic and hyperionic regulation are most pronounced.

5. The electrical potential across the body wall is maximal in PW (17 mV, inside-negative), and decreases to zero in 50 % SW.

6. Chloride influx (as measured with ³⁶Cl) is highest in SW, and decreases in proportion to chloride concentration down to 50-25% SW, rises to a secondary maximum in 10% SW or less, and decreases as fresh water is approached.

7. Urinary chloride loss is low, and proportional to external chloride concentration in higher salinities, maximal in the c. 10% SW range of salinities, and apparently decreases to a minimum in FW. This may be in part the consequence of recovery of chloride from an hypotonic urine, in part the consequence of a reduction in urine volume. Evidence for these last two possibilities will be given in the papers which follow.