Sodium and Chloride Regulation in Uca Adapted to 175% Sea Water

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Abstract
Various aspects of the regulation of Na⁺ and Cl⁻ were studied in fiddler crabs adapted to 175% sea water. Turnover rate for both ions averaged 28% h⁻¹. Total fluxes were partitioned into renal route, intestinal route, and the remainder which was presumed to occur across the general body surface. With urine produced at a rate of 0.5% body weight day⁻¹, renal losses contributed 0.1% total flux for Na⁺ and 0.3% for Cl⁻. Intestinal route provided approximately 5% total influx of both ions assuming complete absorption of all ingested salts. The transepithelial potential (TEP) was - 1.3 ± 0.6 mV. In the absence of Na⁺ the TEP was -8.9 ± 1.3 mV; in the absence of Cl⁻ it was +11.7 ± 0.6 mV. Deletion of Na⁺ or Cl⁻ from the bathing medium reduced efltux of the corresponding ion, an effect associated with exchange diffusion. But other results indicate such effects could also be due to permeability changes in the absence of Na⁺ or Cl⁻. Whether or not exchange diffusion occurs flux ratio analysis indicated both Na⁺ and Cl⁻ were actively pumped from crabs in 175% sea water. Hypotonicity is discussed in relation to estuarine environment the crabs inhabit.

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