Differences in uptake kinetics of cis-3-aminocyclohexane carboxylic acid into neurons and astrocytes in primary cultures

Abstract

The uptake of [ 3H]ACHC and [ 3H]GABA into cultured neurons and astrocytes was studied. [ 3H]ACHC uptake was less efficient than that of GABA in both cell types and K m values for ACHC uptake into neurons and astrocytes were 40.3 μM and 210.8 μM, respectively. The corresponding V max values were 0.321 and 0.405 nmol·min −1·mg −1 cell protein, respectively. Kinetic studies of the effects of GABA on ACHC uptake and vice versa showed that GABA is a linear competitive inhibitor of ACHC uptake in both cell types with a K i value of 15 μM. On the other hand, ACHC turned out to be a complex inhibitor of astrocytic GABA uptake being competitive at lower concentrations and non-competitive at higher concentrations. ACHC inhibited GABA uptake into neurons competitively with a K i of 69 μM. It is concluded that ACHC acts primarily on neuronal GABA uptake sites but its uptake is much more complicated than hitherto anticipated.