The Comparative Physiology of Diving in North American Freshwater Turtles. II. Plasma Ion Balance during Prolonged Anoxia

Abstract

Plasma ionic composition was measured during submergence in anoxic water ($P_{O_{2}} < 2 mmHg$) at 10 C of four species of North American freshwater turtles (Chrysemys picta, Chelydra serpentina, Sternotherus odoratus, and Trionyx spiniferus). As we reported in the previous paper, the species rank in the order listed in their capacity to survive prolonged anoxia at this temperature. The objectives of this study were to examine the changes in plasma ions in response to the anoxia and to relate these responses to the overall blood acid-base picture. The qualitatively similar pattern of ionic changes in each species included a primary increase in [lactate⁻] and decrease in [HCO₃⁻]. In addition, there were increases in [K⁺], total [Ca⁺⁺], and total [Mg⁺⁺] and decrease in [Cl⁻]. These latter strong ion changes are interpreted as compensatory changes that served to balance the lactate charge and that were associated with exchanges of weak ions that buffered the H⁺. The overall importance of these ionic changes ...