CO 2 gradients and acidification by transport of HCO - in turtle bladders

SCHILB, THEODORE P., AND WILLIAM A. BRODSKY. CO, gradients and acidicfication by transport of HCO, in turtle bladders. Am. J. ‘Physiol. 222(Z) : 272-281. 1972.-During acidification of the mucosal fluid in turtle bladder sacs, the final mucosal [COJ and transmural gradient of [CO,] are dependent on: the serosal [CO,], the transport rate and clearance of bicarbonate, the buffer “poise” of the mucosal fluid, and the metabolic production of COZ. When the serosal [COJ and the clearance of bicarbonate are high, mucosal [CO,] decreases to levels below those of serosal fluid. Concomitant reductions in [CO,], [HCO& and pH of the mucosal fluid are explained only by the transport of bicarbonate ions from the mucosal to serosal fluid. Although bicarbonate ion absorption is the unique explanation for the decreases in [CO,], hydrogen ion secretion is not the unique explanation for increases in [COJ during acidification. Increases in mucosal [COZ] are inevitable whenever the rate of leak of metabolic CO, from cell to mucosal fluid exceeds the concomitant rate of hydration of CO, in the mucosal fluid; and accumulation of mucosal CO, does indeed occur when bicarbonate ions are transported from an alkaline mucosal fluid wherein the buffer poise requires that several molecules of bicarbonate must be removed in order to cause the hydration of 1 molecule of Cop.