Interstitial buffer capacity influences Na+/H+ exchange kinetics and oxyntic cell pHi in intact frog gastric mucosa

Abstract

We studied the influence of interstitial buffer capacity and CO2-HCO3- on oxyntic cell intracellular pH (pHi) in intact frog gastric mucosa. Oxyntic cells in stripped gastric mucosa of Rana esculenta were loaded with the pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein, and pHi was assessed fluorometrically. In the presence of a constant serosal and luminal pH, oxyntic cell pHi was dependent on the serosal but not the luminal concentration of cell-impermeable buffer ions such as N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES), tris(hydroxymethyl)aminomethane, N-tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid, and 3-(N-morpholino)propanesulfonic acid. The stepwise increase in oxyntic cell pHi from 6.74 +/- 0.05 with 1 mM HEPES to 7.23 +/- 0.08 was almost completely inhibited by removal of serosal Na+ and by amiloride and dimethyl amiloride, suggesting that it was largely due to Na+/H+ exchange. Increasing the serosal concentration of a CO2-HCO3- buffer from 1% CO2-4 mM HCO3- to 10% CO2-40 mM HCO3- increased oxyntic cell pHi from 7.03 +/- 0.06 to 7.39 +/- 0.07. This CO2-HCO(3-)-dependent pHi increase was also Na+ and amiloride sensitive, but high HCO3- concentrations increased pHi even in the absence of Na+, K+, or Cl-, and in the presence of omeprazole, bafilomycin A1, or acetazolamide. We suggest that in intact frog gastric mucosa, cellular proton extrusion acidifies the interstitial pH immediately adjacent to the basolateral membrane of the oxyntic cells in the absence of a high interstitial buffer capacity.(ABSTRACT TRUNCATED AT 250 WORDS)

Recent advances in the molecular and functional characterization of acid/base and electrolyte transporters in the basolateral membranes of gastric and duodenal epithelial cells

“…Apical localization would lead to proton extrusion into the lumen, which is not observed in Ussing chamber experiments where acid secretion is completely inhibited by omeprazole (P. Song, unpublished observations). Other theoretical considerations and functional results are supportive of basolateral NHE2 expression: NHE2 is strongly upregulated by extracellular alkalinity, which likely occurs in the interstitial space during acid secretion (Seidler et al 1995). As a possible correlate, Na + /H + exchange activity is increased in frog gastric mucosa upon serosal alkalization.…”

“…While Waisbren et al (1994) microdissected and luminally perfused gastric glands and found a very low apical proton permeability, Kaneko et al (1991) observed a rather profound decrease in surface cell pH i upon luminal acid perfusion in the rat stomach in vivo, which was further enhanced by Na + /H + exchange inhibition with an amiloride analogue (Kaneko et al 1992). Interestingly, this pH i decline was strongly dependent on interstitial buffer capacity, and a high interstitial buffer capacity was essential for the gastric epithelial cells to regulate their pH i (Stumpf et al 1993, Seidler et al 1995. We stepwise decreased luminal pH in isolated frog gastric mucosa and found no change in pH i down to a luminal pH of 3, but at pH 2, surface cell pH i decreased slightly to a new pH.…”

Genetic ablation of carbonic anhydrase IX disrupts gastric barrier function via claudin‐18 downregulation and acid backflux

“…33,34 We had previously noticed that a high interstitial buffer capacity is essential for proper pH i control of the gastric surface cells, because protons that are extruded through the basolateral membrane, via the Na + /H + exchange, need to be rapidly removed from that location. 35 The effect of interstitial buffer capacity on pH i was detected even with a neutral pH in the lumen, but was strongly enhanced when the luminal pH was decreased. We had therefore hypothesized that cellular pH i regulatory mechanisms are necessary for gastric acid resistance, but can only function optimally in the presence of high interstitial buffering capacity, augmented by bloodborne CO 2 /HCO À 3 .…”

“…We had previously noticed that a high interstitial buffer capacity is essential for proper pH i control of the gastric surface cells, because protons that are extruded through the basolateral membrane, via the Na + /H + exchange, need to be rapidly removed from that location 35. The effect of interstitial buffer capacity on pH i was detected even with a neutral pH in the lumen, but was strongly enhanced when the luminal pH was decreased.…”

Demonstration of a functional apical sodium hydrogen exchanger in isolated rat gastric glands

“…More recent work identified at least isoforms 1-4 in mucous, endocrine, and parietal cells of the rabbit, rat, and mouse stomach (2,17,19,22). Whereas the role of the NHE-1, -2, and -4 isoforms in the stomach have been addressed in several studies (2,19,21), the role and localization of the NHE-3 isoform has not been examined in detail.…”