The Na+/H+ exchanger in transitional cells of the inner ear.
The cytosolic pH (pHi) of transitional cells from the ampulla of the gerbil was measured micro-fluorometrically with the pH-sensitive dye 2',7'-bicarboxyethyl-5(6)-carboxyfluorescein (BCECF) to assess the possible contribution of a Na+/H+ exchanger to the regulation of pHi. All experiments were conducted in virtually HCO3(-)-free solutions. Under control conditions, pHi was 7.19 and addition of 10(-5) M ethylisopropylamiloride (EIPA), a blocker of Na+/H+ exchange, caused a small but significant acidification of pHi. A transient exposure to 21.4 mM NH4Cl caused a rapid cytosolic alkalinization followed by a brisk acidification and prompt recovery of pHi to its control value. The cytosolic buffer capacity (Bi) was determined in the absence of Na+ from changes in pHi which were elicited by [NH4+] steps. Bi was 4.7 mM/pH at pHi 7.19 and varied with pHi. The initial net proton flux JH, representative of Na+/H+ exchange activity, was calculated from the product of the initial rate of alkalinization after an NH4(+)-prepulse and Bi at the corresponding pHi. JH was dependent on the extracellular Na+ with an apparent Km of 64 mM, sensitive to the cytosolic [H+] with an apparent Km of 2.7 * 10(-7) M (i.e. pH 6.6), and inhibited by EIPA with an IC50 of 5 * 10(-7) M. These data suggest that transitional cells contain in the basolateral membrane a Na+/H+ exchanger of the amiloride-sensitive subtype.
Wangemann
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P
Cell Physiology Laboratory, Boys Town National Research Hospital, Omaha, NE 68131.
Shiga
N
N
Marcus
D C
DC
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002138:Calibration; D003600:Cytosol / Q000378:metabolism; D007758:Ear, Inner / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005452:Fluoresceins; D005456:Fluorescent Dyes; D005849:Gerbillinae; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
D005452:Fluoresceins; D005456:Fluorescent Dyes; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; C039614:ethylisopropylamiloride