Long-Term Submergence At 3 °C of the Turtle, Chrysemys Picta Bellii, In Normoxic and Severely Hypoxic Water

Plasma [Na+], [K+], and [Cl-] were measured on blood sampled periodically from turtles submerged in Na-equilibrated (low-O2) or air-equilibrated (high-O2) water. Plasma osmolality and total [Ca2+] and [Mg2+] were measured on selected samples. Previously we reported that a severe metabolic acidosis developed under these conditions; in low-O2 turtles, plasma [lactate-], rising to over 200 m-equiv/1, was only partially buffered by [HCO3-], which fell from 40 to 5 m-equiv/1. The balance of the buffering was accomplished by changes in strong ions which included (in low-O2) a fall in [Cl−] from 79·5 ±1·4 m-equiv/1 to below 60 m-equiv/1, a rise in [Ca2+] from 3 to over 100 m-equiv/1, and a rise in [Mg2+] from 3 to over 30 m-equiv/1. Together, all ionic changes balanced the increase in [lactate-], but this analysis is tentative because we do not know the distribution of Ca2+ and Mg2+ between free and bound forms in vivo. Plasma osmolality rose from 233 ±4·1 to 382 ± 12·4 mosmol after 162 days in low-O2, even though the turtles showed a gain in body weight. The ionic changes that occurred in plasma also occurred in the pericardial and peritoneal fluids, suggesting general extracellular fluid participation in lactate buffering. Bladder urine contained significant concentrations of both lactate and calcium, indicating that some acid excretion may have occurred during the submergence.