Effect of temperature upon carbon dioxide stores in the snake Coluber constrictor and the turtle Chrysemys scripta

The effect of temperature upon respiratory exchange ratio (R) was measured in snakes (Coluber constrictor) and turtles (Chrysemys scripta). Increasing body temperature produced a transient elevation of R, and lowering body temperature transiently depressed R. These thermal effects resulted from an 'excess' and a 'deficit' CO2 elimination, respectively. Steady-state blood CO2 content (CCO2) in C. constrictor decreased linearly with rising temperature. Plasma bicarbonate concentration, calculated from in vivo arterial PCO2 and pH, followed the same pattern. Also, time courses of blood CCO2 were consistent with the metabolic studies. Less than half of the change in blood CCO2 could be explained by shifts of the in vitro CO2 dissociation curve; the remainder was contributed by other tissues. Blood lactate levels changed little with temperature. Based upon the blood studies, the predicted quantity of CO2 eliminated from the extracellular space when temperature increases is about 29% of the excess CO2 eliminated from the snakes. Thus, CCO2 in other tissues also decreases with rising temperature. It is concluded that reptiles function as open systems with respect to CCO2, which does not agree with alphastat control. Systemic arterial PO2 and PCO2 increased with rising body temperature in C. constrictor. The mechanisms producing these increases are discussed.