Sodium fluxes in fresh-water turtles This investigation was supported in part by grants 5T1-GM-989-03 and 1-F1-GM-18,741-01A1 from NIH, and NASA grants NGR-39-009-015 and Tr. 5994. Portions of this material were submitted to the University of Michigan in partial fulfillment of the requirements for a Ph.D. degree.

Abstract

Fresh-water softshell turtles ( Trionyx spinifer ) showed net uptake of sodium from solutions as dilute as 5 MM. Chloride uptake could be accounted for by passive processes. There was no net uptake of potassium. Net sodium uptake was inhibited by low temperatures. Hibernation resulted in decreases in the sodium concentration and osmotic pressure of the plasma. Influx and efflux of sodium in the fresh-water turtle Pseudemys scripta varied from 0.04 to 10.1 Mmoles/(100 g hour). In hatchling turtles, the exchangeable sodium pool was 96% of the total sodium. The exchangeable pool was subdivided into at least two compartments, one rapidly and the other slowly exchanging. The latter compartment was 19 times larger than the former. Pseudemys scripta , was found to have a system for active uptake of sodium. This involves the membranous lining of the pharynx, the cloacal bursae and the cloaca. Aside from the skin and the shell, these are the only tissues in contact with environmental water. The cloacal region accounted for 48 to 68% of the sodium influx rate.