Effects of Reduced Ambient pH on Sodium Balance in the Red-Spotted Newt, Notophthalmus viridescens

Abstract

Aspects of electrolyte balance were studied in aquatic red-spotted newt adults (Notophthalmus viridescens). In the laboratory, newts subjected to aged tap water (ATW) at controlpH (6.20-7.40) experienced a slight net Na⁺ loss. However, the rate of net Na⁺ loss after acute exposure to low pH (4.24-4.32) ATW increased significantly. Chronic exposure to low pH, followed by a final transfer to pH 4.22-4.37, reduced the rate of net Na⁺ loss to less than that observed in control animals. Body K⁺ concentration was greater in animals taken from the natural habitat (pH 5.24-7.80) than in animals acclimated to any of the laboratory conditions. Both body mass and body K⁺ concentration were significantly reduced in newts exposed to either low-pH treatment. Total body Na⁺ concentration was virtually unaffected by low-pH exposure. Rates of unidirectional Na⁺ influx and efflux were dramatically altered as a result of the laboratory treatment regimes. The rate of Na⁺ influx was significantly less in newts acutely transferred to low-pHATW than it was in control animals, but chronic low-pH exposure restored the Na⁺ influx to control levels. The rate of Na⁺ eflux was higher in control newts than it was in animals acutely or chronically exposed to low pH. Apparently, red-spotted newt adults possess adaptations permitting a more favorable state of Na⁺ balance than occurs in most teleosts and amphibians exposed to lowpH conditions.