Effect of acute pH change on mitochondrial glutamine transport.

The uptake of [3H]glutamine in submitochondrial particles (SMP) was measured at varying medium pH. Glutamine transport, but not glutamine binding, was inversely related to medium pH (range 6.5-8.5). Glutamine uptake was highest at medium pH of 6.5 (4.59 +/- 0.4 pmol.mg-1.30 s-1) and lowest at medium pH of 8.0 (1.99 +/- 0.3 pmol.mg-1.30 s-1). The effect of medium pH on glutamine transport was rapidly reversible. Changes in pH gradient (delta pH) had no influence on the rate of glutamine transport. Kinetics of mitochondrial glutamine transport was studied at pH 6.5 and 8.5 to further elucidate the mechanism by which pH alters glutamine transport. Glutamine concentration at half-maximal velocity ([S]0.5) was 9.07 and 13.32 mM at pH 6.5 and 8.5, respectively (P less than 0.02). The maximal velocity (Vmax) was 1,417.72 +/- 185.69 pmol.mg-1.15 s-1 at pH 6.5 and 910.95 +/- 192.85 pmol.mg-1.15 s-1 at pH 8.5 (P less than 0.01). Thus both the affinity and the Vmax of the transport system were enhanced in acidic pH. These data imply that intracellular pH has influence over glutamine transport into the mitochondrial matrix and, consequently, renal NH3 production. Glutamine delivery to the matrix via changes in cytosolic pH may be one of the regulators for ammoniagenesis during acute acid-base disorders.