EXPRESSION OF THE HUMAN SODIUM-PROTON EXCHANGER NHE-1 IN XENOPUS-LAEVIS OOCYTES ENHANCES SODIUM-PROTON EXCHANGE ACTIVITY AND ESTABLISHES SODIUM-LITHIUM COUNTERTRANSPORT
S. Busch et al., EXPRESSION OF THE HUMAN SODIUM-PROTON EXCHANGER NHE-1 IN XENOPUS-LAEVIS OOCYTES ENHANCES SODIUM-PROTON EXCHANGE ACTIVITY AND ESTABLISHES SODIUM-LITHIUM COUNTERTRANSPORT, Pflugers Archiv, 429(6), 1995, pp. 859-869
We investigated whether the human sodium/proton (Na+/H+) exchanger iso
form 1 (NHE-1) can mediate sodium/lithium (Na+/Li+) countertransport.
Using the Xenopus laevis oocyte expression system we determined amilor
ide-sensitive Lif uptake, a measure of Na+/H+ exchange, in oocytes inj
ected with water or NHE-1 cRNA. Amiloride-sensitive Li+ uptake was thr
ee- to tenfold enhanced over control in NHE-1 cRNA-injected cells and
was selectively inhibited by 0.01 mu M HOE 694 [i.e. (3-methylsulphony
l-4-piperidinobenzoyl) guanidine methanesulphonate]. The endogenously
present Na+/H+ exchanger was insensitive to HOE 694. After acidificati
on of oocytes from pH 7.7 to 6.8, amiloride-sensitive Li+ uptake was f
our- to tenfold higher in NHE-1 cRNA-injected cells than in controls.
Li+ efflux from control oocytes was independent of extracellular Na+,
indicating that these cells expressed no measurable Na+/Li+ countertra
nsport activity. In NHE-1 cRNA-injected oocytes, Li+ efflux was distin
ctly enhanced by extracellular Na+ ions. This Na+-dependent Li+ efflux
was inhibited by ethylisopropylamiloride, phloretin and by cytosolic
acidification. The data show that expression of the NHE-1 in X. laevis
oocytes induces the expression of Na+/Li+ countertransport. The data
confirm that Na+/H+ exchange and Na+/Li+ countertransport are mediated
by the same transport system.