Characterization of glycine uptake in plasma membrane vesicles isolated from cultured glioblastoma cells.

C6 glioblastoma cells in culture were employed to isolate plasma membrane vesicles. After disruption of the glioblastoma cells by homogenization, membrane fractions were obtained by centrifugation on a discontinuous Ficoll density gradient. Fragmented membranes were found mainly in vesicular form. Transport of glycine has been demonstrated in membrane vesicles, using artificially imposed ion gradients as the sole energy source. The uptake of glycine is strictly dependent on the presence of Na+ and Cl- in the medium, and the process can be driven either by an Na+ gradient (out greater than in) or by a Cl- gradient (out greater than in) when the other essential ion is present. The process is stimulated by a membrane potential (negative inside) as demonstrated by the effect of ionophore valinomycin and anions with different permeabilities. The kinetic analysis shows that glycine is accumulated by two systems with different affinities.