Bone and shell contribution to lactic acid buffering of submerged turtles Chrysemys picta bellii at 3°C

Abstract

To evaluate shell and bone buffering of lactic acid during acidosis at 3°C, turtles were submerged in anoxic or aerated water and tested at intervals for blood acid-base status and plasma ions and for bone and shell percent water, percent ash, and concentrations of lactate, Ca2+, Mg2+, Pi, Na+, and K+. After 125 days, plasma lactate concentration rose from 1.6 ± 0.2 mM (mean ± SE) to 155.2 ± 10.8 mM in the anoxic group but only to 25.2 ± 6.4 mM in the aerated group. The acid-base state of the normoxic animals was stable after 25 days of submergence. Plasma calcium concentration ([Ca2+]) rose during anoxia from 3.2 ± 0.2 to 46.0 ± 0.6 mM and [Mg2+] from 2.7 ± 0.2 to 12.2 ± 0.6 mM. Both shell and bone accumulated lactate to concentrations of 135.6 ± 35.2 and 163.6 ± 5.1 mmol/kg wet wt, respectively, after 125 days anoxia. Shell and bone [Na+] both fell during anoxia but the fate of this Na+ is uncertain because plasma [Na+] also fell. No other shell ions changed significantly in concentration, although the concentrations of both bone calcium and bone potassium changed significantly. Control shell water (27.8 ± 0.6%) was less than bone water (33.6 ± 1.1%), but neither changed during submergence. Shell ash (44.7 ± 0.8%) remained unchanged, but bone ash (41.0 ± 1.0%) fell significantly. We conclude that bone, as well as shell, accumulate lactate when plasma lactate is elevated, and that both export sodium carbonate, as well as calcium and magnesium carbonates, to supplement ECF buffering.