D. Sterling et Jr. Casey, Transport activity of AE3 chloride/bicarbonate anion-exchange proteins andtheir regulation by intracellular pH, BIOCHEM J, 344, 1999, pp. 221-229
Plasma membrane Q-/HCO3- anion-exchange (AE) proteins contribute to regulat
ion of intracellular pH (pH(i)). We characterized the transport activity an
d regulation by pH(i) of full-length AE3 and the cardiac isoform, AE3c, bot
h of which are expressed in the heart. AE3c is an N-terminal variant of AE3
. We also characterized AE1, AE2 and a deletion construct (AE3tr) coding fo
r the common region of AE3 and AE3c. AE proteins were expressed by transien
t transfection of HEK-293 cells, and transport activity was monitored by fo
llowing changes of intracellular pH or intracellular chloride concentration
associated with anion exchange. Transport activities, measured as proton f
lux (mM H+ . min(-1)), were as follows: AE1, 24; AE2, 32; full-length AE3,
9; AE3c, 4 and AE3tr, 4. The wide range of transport activities is not expl
ained by variation of cell surface processing since approx. 30% of each iso
form was expressed on the cell surface. pH(i) was clamped at a range of val
ues from 6.0-9.0 to examine regulation of AE proteins by pH(i). Whereas AE2
was steeply inhibited by acid pH(i), AE1, AE3 and AE3c were essentially in
sensitive to changes of pH(i). We conclude that AE3 and AE3c can contribute
to pH(i) recovery after cellular-acid loading.