Tissue Glycogen and Extracellular Buffering Limit the Survival of Red‐Eared Slider Turtles during Anoxic Submergence at 3°C

Abstract

The goal of this study was to identify the factors that limit the survival of the red‐eared slider turtle Trachemys scripta during long‐term anoxic submergence at 3°C. We measured blood acid‐base status and tissue lactate and glycogen contents after 13, 29, and 44 d of submergence from ventricle, liver, carapace (lactate only), and four skeletal muscles. We also measured plasma Ca2+, Mg2+, Na+, K+, Cl−, inorganic phosphate (Pi), lactate, and glucose. After 44 d, one of the six remaining turtles died, while the other turtles were in poor condition and suffered from a severe acidemia (blood pH = 7.09 from 7.77) caused by lactic acidosis (plasma lactate 91.5 mmol L−1). An initial respiratory acidosis attenuated after 28 d. Lactate rose to similar concentrations in ventricle and skeletal muscle (39.3–46.1 μmol g−1). Liver accumulated the least lactate (21.8 μmol g−1), and carapace accumulated the most lactate (68.9 μmol g−1). Plasma Ca2+ and Mg2+ increased significantly throughout submergence to levels comparable to painted turtles at a similar estimated lactate load. Glycogen depletion was extensive in all tissues tested: by 83% in liver, by 90% in ventricle, and by 62%–88% in muscle. We estimate that the shell buffered 69.1% of the total lactate load, which is comparable to painted turtles. Compared with painted turtles, predive tissue glycogen contents and plasma $$\mathrm{HCO}\,^{-}_{3}$$ concentrations were low. We believe these differences contribute to the poorer tolerance to long‐term anoxic submergence in red‐eared slider turtles compared with painted turtles.