(1) Maleate stimulates glutamine uptake, NH3 production, and glutamate production while inhibiting gluconeogenesis by renal cortical slices from control and acidotic rats incubated in a Krebs-Ringer bicarbonate buffer. (2) Levels of glutamate decrease and levels of 2-oxoglutarate increases in slices incubated with maleate and glutamine 2.0 mm as substrate. (3) NH3 production and gluconeogenesis from glutamate are inhibited by maleate. (4) In a "sodium-free" buffer (2.5 mm Na+) maleate also stimulates uptake of glutamine and NH3 production. (5) In Krebs-Ringer bicarbonate buffer the effect of maleate on uptake of glutamine and NH3 production is abolished when acetoacetate is added to the incubation medium but there is no effect on acetoacetate in a sodium-free buffer. (6) Uptake of [14C]glutamine by luminal brush border vesicles is stimulated by maleate in the absence of sodium. (7) The stimulation of the deamidation of glutamine by maleate may be mediated through a reduction in intracellular glutamate, but there is also stimulation of sodium-independent transport of glutamine probably mediated through γ-glutamyl transpeptidase (EC 188.8.131.52.). (8) Stimulation of the deamidation of glutamine occurs in the presence of increased levels of 2-oxoglutarate.
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