alpha-Ketoglutarate uptake in human fibroblasts.

Glutamine requirements are increased during injury, in particular to sustain the needs of rapidly growing cells. This includes fibroblasts involved in wound healing. alpha-Ketoglutarate (alpha-KG) has been proved to be a potent precursor of glutamine. However, little is known about the process of its cell uptake. Since this first step could be crucial in alpha-KG metabolism, we have characterized alpha-ketoglutarate uptake in fibroblasts. Total uptake of alpha-ketoglutarate was linear up to 1 mmol and temperature independent. Rate of uptake was independent of the presence of Na+ in the medium. Competition studies with another ketoacid demonstrated the nonspecificity of alpha-ketoglutarate uptake. In addition, 4-hydroxy-alpha-cyanocinnamate, a known inhibitor of anion transport, was ineffective on alpha-ketoglutarate uptake. Taken as a whole, these data provide evidence that alpha-ketoglutarate uptake in fibroblast occurs by an unmediated diffusion process. This suggests that alpha-ketoglutarate uptake is not the controlling step in fibroblasts, i.e. only the availability of extracellular alpha-ketoglutarate. This could be an advantage since during injury, cell membrane depolarization and dissipation of Na+ gradient may limit cellular glutamine uptake.