Plasma ion balance of submerged anoxic turtles at 3 degrees C: the role of calcium lactate formation

Distribution of systemic blood flow during anoxia in the turtle, Chrysemys scripta

Hypoxia causes a reflex redistribution of regional blood flow in mammals that maintains delivery of oxygen to vital organs such as the brain during periods of decreased oxygen availability. The present study was performed to test if this response is developed in lower vertebrates. Regional organ blood flow and arterial blood gases were measured during normoxia (room air) and anoxia (nitrogen breathing) in anesthetized turtles, Chrysemys scripta. Organ blood flow was measured by the distribution of radioactive microspheres injected into the left atrium. The concentration of the microspheres in the organ is directly related to the blood flow rate. By knowing the reference blood flow rate, the reference microsphere concentration, and the total counts in the tissue, the tissue blood flow rate can be calculated. Anoxia caused a redistribution of blood flow away from the kidneys and splanchnic bed to the brain. Coronary blood flow and skeletal muscle blood flow remained constant. Brain blood flow increased approximately 260%. Blood flow to the kidneys and stomach was reduced approximately 50%. Blood flow to the pancreas, small intestine, and liver decreased almost to zero. The observation of anoxia-induced reflex redistribution of organ blood flow in a lower vertebrate suggests that this mechanism could be characteristic of vertebrates in general.

The kinetic properties and sensitivity to pyruvate inhibition of tissue lactate dehydrogenase in diving and nondiving reptiles

The kinetic properties and susceptibility to pyruvate inhibition of lactate dehydrogenase (LDH) were examined in three tissues of the freshwater turtle, Pseudemys scripta, and two snake species, Elaphe obsoleta and Nerodia rhombifera. Brain and heart LDH activity of the snakes surpassed that of Pseudemys at pyruvate concentrations between 0.03 and 0.50 mM. The snakes also had lower apparent Km and higher Vmax values than Pseudemys. Liver LDH activity, apparent Km, and Vmax were highest in Elaphe, and there were no differences between Km or Vmax values of Nerodia and Pseudemys. In each tissue, snake LDH was less susceptible to pyruvate inhibition than was Pseudemys LDH. The results indicate that Pseudemys LDH is no better adapted to withstand anaerobic conditions than is that of Nerodia or Elaphe.

Patterns of energy metabolism in the stone crab, Menippe mercenaria, during severe hypoxia and subsequent recovery

Specimens of the stone crab, Menippe mercenaria, survived severe hypoxia (PO2 less than 8mm Hg) for at least 12 hr at 28-30 degrees C. During the time course of 12 hr of hypoxia, hemolymph L-lactate levels rose to 30-50 mumoles/g wet wt. There was a slight elevation of L-alanine levels, whereas succinate was found in only trace quantities in the hemolymph. Pronounced metabolic changes took place in the heart, cheliped closer, and leg socket muscles during severe hypoxia. L-lactate accumulated to levels ranging from 16-20 mumoles/g wet wt. There were pronounced changes in high-energy phosphate levels in the cheliped closer and leg socket muscles. Taking into account expected intra- and extracellular water content, the calculated intracellular lactate content in the three muscles investigated is substantially less than the hemolymph lactate concentrations. Part of this reverse concentration gradient may be accounted for by the reduction in lactate activity due to cation-lactate complex formation. Hemolymph calcium and magnesium concentrations rose considerably during severe hypoxia. During recovery from severe hypoxia, approximately 50% of the accumulated lactate in the hemolymph was cleared in 6 hr. Hemolymph lactate and alanine levels returned to near control levels after 24 hr of recovery. This study shows that the stone crab, M. mercenaria, survives severe hypoxia by a reliance on glycogen fermentation to lactate. This species is capable of tolerating high levels of accumulated lactate.

The viability of nearctic freshwater turtles submerged in anoxia and normoxia at 3 and 10 degrees C

Survival times of temperature-acclimated freshwater turtles submerged in normoxic and anoxic water were determined. Juvenile Chrysemys scripta from Alabama and adult Chrysemys picta bellii from Wisconsin exhibited the maximal survival times of the 10 species and subspecies investigated, both being able to survive at least a half-year of submergence at 3 degrees C in normoxic water. Minimal viability was exhibited by Sternotherus odoratus and Trionyx spiniferus submerged in anoxia at 10 degrees C (5.2 and 2.6 days, respectively). All species lived longer in normoxic water than in anoxic water, attesting to the importance of extrapulmonary gas exchange during submergence at low temperature. While freshwater turtles are often reputed to overwinter buried in mud, which is an anoxic microenvironment, this behaviour seems unlikely for southern Trionyx and Sternotherus, although it may be possible for northern Chrysemys.

Intracellular and extracellular acid-base and electrolyte status of submerged anoxic turtles at 3 degrees C

Specimens of fresh water turtles (Chrysemys picta bellii) were acclimated to 3 degrees C and then submerged in completely anoxic water for time periods of up to 12 weeks. Blood withdrawn via indwelling arterial catheters was analysed for plasma pH, PCO2, bicarbonate concentration, [lactate], [Na+], [K+], [Ca2+] and [Mg2+], and tissue samples of skeletal muscle, liver and cardiac muscle were excised. Samples of skeletal muscle were analysed for intracellular pH (DMO), [lactate], [Na+], [K+], [Ca2+], and [Mg2+], and samples of liver and cardiac muscle for intracellular pH and [lactate] during normoxia and after 1, 2, 4, 8 and 12 weeks of anoxia. Arterial plasma pH fell from 8.0 during normoxia to lower than 7.2 concomitant with a reduction in plasma [HCO3-] after 12 weeks of anoxia due to the production of large amounts of lactic acid. The intracellular pH (pHi) of heart muscle and liver dropped in parallel or even more than plasma pH, whereas pHi in skeletal muscle changed less resulting in a delta pHi/delta pHe value of less than 0.6. Intracellular [lactate] and [Ca2+] increased considerably, but attained concentrations much smaller than those observed in the extracellular compartment. The intracellular concentrations of K+, Na+ and Mg2+ were also significantly affected, the changes, however, were small in comparison with those observed for Ca2+ and lactate concentration. The water distribution between intra- and extracellular compartments remained essentially unaffected by anoxia. It is concluded that the considerable increase in extracellular Mg2+ and Ca2+ cannot be the result of release from muscle cells and has to be attributed to release from skeleton and shell.(ABSTRACT TRUNCATED AT 250 WORDS)