Lactate accumulation in the shell of the turtle Chrysemys picta bellii during anoxia at 3&deg;C and 10&deg;C
Lactate concentrations were measured in the shell and plasma of the turtle Chrysemys picta bellii after 3 months of submergence anoxia at 3&deg;C and during and after 9 days of submergence anoxia at 10&deg;C. Liver and skeletal muscle lactate levels were also measured in control and anoxic animals at each temperature. At 3&deg;C, mean shell lactate concentration (N=4) reached 133mmolkg-1shellmass and plasma lactate levels were 144mmoll-1; at 10&deg;C, shell and plasma lactate concentrations (N=5) rose in parallel during anoxic exposure, to 70.8mmolkg-1shellmass and 78.9mmoll-1, respectively, and returned in parallel to control levels during 9 days of recovery. At the end of the anoxic periods, an estimated 44% of the total body lactate resided in the shell at 3&deg;C and 43% at 10&deg;C, and indirect evidence suggests that the shell buffered these same fractions of the acid load. Because of the high lactate concentration per kilogram of shell water (416mmolkg-1 at 3&deg;C; 221mmolkg-1 at 10&deg;C) and the known formation of calcium lactate complexes, it is postulated that most of the lactate existed in the shell in combined form. I conclude that sequestration of lactate within the shell represents a potentially major adaptation to anoxic acidosis for this animal and, together with the previously described release of shell carbonates, may account for up to two-thirds of the total lactic acid buffering in this animal.
Jackson
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