The intensity of acidosis differentially alters the pathways of ammoniagenesis in LLC-PK1 cells

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Utilizing [5-15N] and [2-15N]-labeled glutamine and gas chromatography mass spectrometry methodology, we examined the pathways of ammoniagenesis under basal and acute acidotic conditions of pH 7.0 and pH 6.8, respectively. LLC-PK1 cultures were incubated for one hour with gentle rocking in a bicarbonate buffer of pH 7.4, pH 7.0, or pH 6.8 supplemented either with [5-15N] or [2-15N] glutamine at 37 degrees C in a 5% CO2/95% air incubator atmosphere. Incubation of cultures with [5-15N] glutamine at pH 7.4 resulted in a substantial amount of 15N ammonia formation which was not significantly altered by incubations at pH 7.0. By contrast, exposure to pH 6.8 significantly increased 15N ammonia formation in comparison with its production at pH 7.0 or 7.4. However, 15N ammonia production from [2-15N] glutamine was significantly stimulated at pH 7.0 and was further increased at pH 6.8. Incubation of the cells with [2-15N] glutamine resulted in a substantially lower amounts of 15N ammonia formation than produced with [5-15N] glutamine. Alanine formation from [2-15N] glutamine increased significantly at pH 7.0; but in contrast to 15N ammonia formation, pH 6.8 had no additional stimulatory effect on 15N alanine formation. Cells incubated with [2-15N] glutamine resulted in a significant decrement in 15N glutamate production at both pH 7.0 and 6.8 when compared with pH 7.4. 15N aspartate formation was unaltered by the changes in media pH.(ABSTRACT TRUNCATED AT 250 WORDS)