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

To evaluate shell and bone buffering of lactic acid during acidosis at 3 de grees C, turtles were submerged in anoxic or aerated water and tested at in tervals for blood acid-base status and plasma ions and for bone and shell p ercent water, percent ash, and concentrations of lactate, Ca2+, Mg2+, P-i, 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 a nimals was stable after 25 days of submergence. Plasma calcium concentratio n ([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 lact ate to concentrations of 135.6 +/- 35.2 and 163.6 +/- 5.1 mmol/kg wet wt, r espectively, after 125 days anoxia. Shell and bone [Na+] both fell during a noxia but the fate of this Na+ is uncertain because plasma [Na+] also fell. No other shell ions changed significantly in concentration, although the c oncentrations 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%) rema ined unchanged, but bone ash (41.0 +/- 1.0%) fell significantly. We conclud e that bone, as well as shell, accumulate lactate when plasma lactate is el evated, and that both export sodium carbonate, as well as calcium and magne sium carbonates, to supplement ECF buffering.