Na+-Proton Exchanger

Figure 2. Infrared spectra of a Na" and exchanged clays following the uptake of cyclohexylamine. Absorptions at 1585 and 1525 cnT are characteristic of the neutral and protonated amine species, respectively.

Taken together, these results indicate that similar to other proton-translocating membrane proteins, both types of Na /H exchangers contain critical sulfhydryl groups that are involved in the transport mechanism. These sulfhydryl groups do not appear to be present at the external transport site but may be involved in switching from an inactive to an activated state. 

While the lactate-H+ symporter and the K+/H+ exchanger are involved in acidification of the cell, the Na+/H+ exchanger present in the basal cells exports protons out of the cell in exchange for Na+ [139]. It was observed that removal of Na+ from the Ringer s solution decreased intracellular pH by 0.5 unit in basal cells, possibly due to inhibition of the Na+/H+ exchanger. As the basal cells are the precursors for the superficial cells of the corneal epithelium, it is quite likely that similar exchange processes are also present in the superficial layer, the principal barrier to ion and drug transport [99,103],... 

Partially proton-exchanged Na faujasite X, in turn, is the best catalyst for selective monochlorination with tert-butyl hypochlorite.258 NaX, NaY, and NaKL zeolites used in the chlorination of toluene with sulfuryl chloride undergo rapid deactivation because of the accumulation of polychlorinated toluenes in the pores of the catalysts and dealumination.259, 260 Direct electrophilic fluorination of aromatics can be effected by using Selectfluor in the presence of triflic acid.261 Electrophilic fluorination may also be carried out by R2NF and R3N+FA reagents.262 Elemental fluorine may also act as a powerful electrophile in acidic media (sulfuric acid, trifluoroacetic acid, or formic acid), but monosubstituted aromatics give isomeric mixtures.263-265... 

ZHY partially proton-exchanged Y zeolite, supplied by Union Carbide. Si/Al ratio=2.9. The exchange ratio of Na by H" 40%... 

Mechanisms that then restore the basal cytosolic [Ca2+] levels remain unclear. Besides a Ca2+-ATPase on the osteoclast dorsal surface relatively little is known of alternative or parallel methods for Ca2+ extrusion (Zaidi et al., 1993) although there is recent functional, evidence for a Na+/Ca2+ exchanger that, in analogy to the regulation of cytoplasmic [Ca2+] in cardiac muscle could be linked to the proton extrusion that is a primary determinant of the rate and extent of bone resorption (Moonga et al., 2001). 

Sodium bicarbonate reabsorption by the proximal tubule is initiated by the action of a Na+/H+ exchanger located in the luminal membrane of the proximal tubule epithelial cell (Figure 15-3). This transport system allows sodium to enter the cell from the tubular lumen in exchange for a proton from inside the cell. As in all portions of the nephron, Na+/K+ ATPase in the basolateral... 

Like the 5-HT1A receptor (see Section 2.1), the 5-HT2A receptor can regulate several transport processes. The 5-HT2A receptor activates the type 1 sodium-proton exchanger (NHE-1) in renal mesangial cells (187,227) and vascular smooth muscle cells (222), the Na+K+-AIPase (sodium pump) in airway smooth muscle cells (228), and the Na+/K+/2Cr cotransporter when 5-HT2A receptor transfected... 

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