The maintenance of ionic homeostasis in the tolerant genotypes requires the extrusion of [Na.sup.+] from the cytosol to the vacuole or apoplast through the [Na.sup.+]/[H.sup.+] antiporter
(SHI et al., 2002).
The molecular nature of Na+ sensors is still unclear, the plasma membrane Na+/H+ antiporter
SOS1 (Salt Overly Sensitive1) is a possible candidate because its cytoplasmic end is assumed to be involved in Na+ sensing (Zhu, 2003).
N-acetylcysteine, a drug that stimulates the uptake of cysteine in exchange for glutamate, which is transported to the extracellular milieu through the antiporter
Xc-, reverted the social interaction and anxiety behaviors of autistic rats as a result of presynaptic mGluR2/3 .
To restore the pH, the [Na.sup.+]/[H.sup.+] antiporter
is activated, but it acts inefficiently because Na+ cannot be pumped out of the cell, as the [Na.sup.+]/[K.sup.+] ATPase is inhibited by the absence of intracellular ATP.
The observed calcium transient activity may support the existence of a sodium-calcium antiporter
and the existence of calcium influx induced by depletion of calcium stores.
Immunocal provides the essential GSH precursor, cystine, which is transported into cerebellar granule neurons via the system [x.sub.c.sup.-] antiporter
The influx of a high concentration of glutamate inhibits the conversion of glutamate and cysteine into glutathione (an antioxidant molecule) through the antiporter
system [x.sub.c.sup.-] , which suggests that glutamate excitotoxicity can cause oxidative insults by decreasing the production of antioxidant molecules that can start a chain reaction of free radical attack and eventually result in the disruption of a living cell.
In addition, many other genes, including NHA1 (encoding a [Na.sup.+]/[H.sup.+] antiporter
located at the plasma membrane), TRK1/TRK2 (encoding [K.sup.+] transporters located at the plasma membrane), and NHX1 (encoding a [Na.sup.+]/[H.sup.+] antiporter
localized in the vacuole), also participate in the salt stress response [24, 25].
An ORF (RWLH02992) similar to the chloramphenicol export proton antiporter
(multidrug efflux system protein MtdL) was identified, as in other pathogenic E.
Changes in the cellular [Na.sup.+]/[H.sup.+] antiporter
activity and an increase in intracellular pH have been reported after exposure to estrogen and estradiol (Ediger et al.
(1996) Efflux pump of the proton antiporter
family confers low-level fluoroquinolone resistance in Mycobacterium smegmatis.