Active Uptake of Sodium by Softshell Turtles ( Trionyx spinifer )

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Abstract
Aquatic softshell turtles ( Trionyx spinifer spinifer ) show a net active uptake of sodium from solutions of this cation as dilute as 5 micromoles per liter. This probably occurs in the pharynx, a site of aquatic respiration. Inhibition of active sodium transport by low temperatures causes an extreme lowering of the sodium concentration in the plasma. Other fresh-water turtles may utilize this mechanism of ionic regulation. The ultrastructure of the pharyngeal villi is similar to that of frog skin and toad bladder.