Several pulmonary and neurological conditions, both in the newborn and adult, result in
hypercapnia. This leads to disturbances in normal pH homeostasis. Most mammalian cells maintain tight control of intracellular pH (pH(i)) using a group of transmembrane
proteins that specialize in
acid-base transport. These
acid-base transporters are important in adjusting pH(i) during
acidosis arising from
hypoventilation. We hypothesized that exposure to chronic
hypercapnia induces changes in the expression of
acid-base transporters. Neonatal and adult CD-1 mice were exposed to either 8% or 12% CO(2) for 2 wk. We used Western blot analysis of
membrane protein fractions from heart, kidney, and various brain regions to study the response of specific
acid-base transporters to CO(2). Chronic CO(2) increased the expression of the
sodium hydrogen exchanger 1 (NHE1) and electroneutral
sodium bicarbonate cotransporter (NBCn1) in the cerebral cortex, heart, and kidney of neonatal but not adult mice. CO(2) increased the expression of electrogenic NBC (NBCe1) in the neonatal but not the adult mouse heart and kidney.
Hypercapnia decreased the expression of
anion exchanger 3 (AE3) in both the neonatal and adult brain but increased AE3 expression in the neonatal heart. We conclude that: 1) chronic
hypercapnia increases the expression of the
acid extruders NHE1, NBCe1 and NBCn1 and decreases the expression of the
acid loader AE3, possibly improving the capacity of the cell to maintain pH(i) in the face of
acidosis; and 2) the heterogeneous response of tissues to
hypercapnia depends on the level of CO(2) and development.