Sodium gradient- and sodium plus potassium gradient-dependentl-glutamate uptake in renal basolateral membrane vesicles

Abstract

A membrane preparation enriched in the basolateral segment of the plasma membrane was isolated from the rat renal cortex by a procedure that included separation of particulates on a self-generating Percoll gradient. The uptake of L-glutamate by the basolateral membrane vesicles was studied. A Na+ gradient (Na+]o greater than [Na+]i) stimulated the uptake of L-glutamate and provided the driving force for the uphill transport of the acidic amino acid, suggesting a Na+-L-glutamate cotransport system in the basolateral membrane. A K+ gradient ([K+]i greater than [K+]o) increased the uptake additionally. This effect was specific for K+(Rb+). The action of the K+ gradient in enhancing the uptake of L-glutamate had an absolute requirement for Na+. In the presence of Na+, but in the absence of a Na+ gradient. i.e., [Na+]o = [Na+]i, the K+ gradient also energized the concentrative uptake of L-glutamate. This effect of the K+ gradient was not attributable to an alteration in membrane potential. The finding of a concentrative uptake system for L-glutamate energized by both Na+ ([Na+]o greater than [Na+]i and K+ ([K+]o) gradients in the basolateral membrane, combined with previous reports of an ion gradient-dependent uphill transport system for this amino acid in the brush border membrane, suggests a mechanism by which L-glutamate is accumulated intracellularly in the renal proximal tubule to extraordinarily high concentrations.

Pharmacologically different Na/H antiporters on the apical and basolateral surfaces of cultured porcine kidney cells (LLC-PK1).

“…The Na-dependent glucose transporter serves as an appropriate marker for the apical surface based on previously published results with proximal tubule cells (18) and LLC-PK1 cells (19,20). The Na-dependent L-glutamate transporter is also apically located in LLC-PK1 cells (14), although distributed on both surfaces in the proximal tubule (21). Once again, the results of the present experiments were consistent with expectations, since 99%o of methyl a-[14Clglucoside uptake (Fig.…”

Renal angiotensin II AT2receptors promote natriuresis in streptozotocin-induced diabetic rats

“…After a midline incision, the kidneys were excised and cut sagitally. The outer cortices were used for the preparation of the basolateral (BLM) and brush-border (BBM) membranes (16,28). Briefly, the cortices were homogenized in Trissucrose buffer A (50 mM Tris, 250 mM sucrose, 2 mM PMSF, pH 7.4).…”

Fatty acyl chain composition in the determination of renal membrane order.

“…al. (8); cortical tissue was homogenized in 250 mM sucrose and 10 mM Tris (pH 7.6). The purities of these membranes were determined by enzyme markers and were similar to values previously reported from this laboratory (1,9).…”