The effect of maleate on glutamine metabolism by rat kidney

(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 2.3.2.2.). (8) Stimulation of the deamidation of glutamine occurs in the presence of increased levels of 2-oxoglutarate.