Modulation of Na+/H+ exchange activity by Cl-.
Na+/H+ exchanger (NHE) activity is exquisitely dependent on the intra- and extracellular concentrations of Na+ and H+. In addition, Cl- ions have been suggested to modulate NHE activity, but little is known about the underlying mechanism, and the Cl- sensitivity of the individual isoforms has not been established. To explore their Cl- sensitivity, types 1, 2, and 3 Na+/H+ exchangers (NHE1, NHE2, and NHE3) were heterologously expressed in antiport-deficient cells. Bilateral replacement of Cl- with nitrate or thiocyanate inhibited the activity of all isoforms. Cl- depletion did not affect cell volume or the cellular ATP content, which could have indirectly altered NHE activity. The number of plasmalemmal exchangers was unaffected by Cl- removal, implying that inhibition was due to a decrease in the intrinsic activity of individual exchangers. Analysis of truncated mutants of NHE1 revealed that the anion sensitivity resides, at least in part, in the COOH-terminal domain of the exchanger. Moreover, readdition of Cl- into the extracellular medium failed to restore normal transport, suggesting that intracellular Cl- is critical for activity. Thus interaction of intracellular Cl- with the COOH terminus of NHE1 or with an associated protein is essential for optimal activity.
Aharonovitz
O
O
Cell Biology Program, Hospital for Sick Children, Toronto M5G 1X8, Canada H3G 1Y6.
Kapus
A
A
Szászi
K
K
Coady-Osberg
N
N
Jancelewicz
T
T
Orlowski
J
J
Grinstein
S
S
D000818:Animals; D016466:CHO Cells; D048429:Cell Size; D002712:Chlorides / Q000378:metabolism*; D002918:Chymotrypsin / Q000378:metabolism; D006224:Cricetinae; D005452:Fluoresceins / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009994:Osmolar Concentration; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D051381:Rats; D012964:Sodium / Q000378:metabolism; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors
D002712:Chlorides; D005452:Fluoresceins; D005456:Fluorescent Dyes; D008565:Membrane Proteins; D020033:Protein Isoforms; C513110:Slc9a2 protein, rat; C000613387:Slc9a3 protein, rat; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D012964:Sodium; D002918:Chymotrypsin