The Contribution of the Alkaline Pericardial Fluid of Freshwater Turtles to Acid Buffering During Prolonged Anoxia

The role of buffering of the high pericardial fluid [HCO₃⁻] of the turtle, Chrysemy spicta bellii Gray, was evaluated during prolonged anoxia at 3 and 10°C. At 3°C, pericardial fluid samples were collected from groups of animals after 0, 1, 2, 4 and 8 weeks of anoxia, and the ionic composition of these samples was compared to plasma values from the same animals. At 10 °C, pericardial and plasma samples were taken from normoxic turtles and from turtles after 11 days of anoxia. The samples were analysed for total CO₂⁠, [Cl⁻] and [lactate^-]. At 3°C, the fall in pericardial [HCO₃⁻] and the rise in [lactate⁻] lagged behind the same changes in the plasma, until after about 8 weeks of anoxia the composition of pericardial fluid became identical with that of plasma. At 10 °C, pericardial [HCO₃⁻] fell significantly after 11 days of anoxia but was still above plasma [HCO₃⁻], while [lactate^-] was essentially the same in both fluids. We conclude that the pericardial fluid does participate in the buffering of lactic acid during prolonged anoxia. However, its involvement is delayed, possibly until the energy supply for the active carrier-mediated transfer processes responsible for the high [HCO₃⁻] gradient breaks down as a consequence of the prolonged anoxia. Analysis of the overall buffering in the body reveals that the contribution of the pericardial fluid is minor.