HIGH-AFFINITY UPTAKE OF GAMMA-AMINOBUTYRIC ACID IN CULTURED GLIAL AND NEURONAL CELLS

Glial and neuronal cells maintained in primary culture from cerebral hemispheres in newborn rats accumulate [3H]GABA by an efficient high-affinity uptake system (apparent Km = 9 .mu.M, Vmax = 0.018 and 0.584 nmol/mg per min, respectively) which required Na ions and was inhibited by 1 mM ouabain. Strychnine and parachloromercuriphenylsulfonate (pCS) (both at 1 mM) also strongly inhibited uptake of [3H]GABA, but metabolic inhibitors (2,4-dinitrophenol, potassium cyanide and malonate) were without effect. Only 3 structural analogs of GABA (nipecotate, .beta.-alanine and 2,4-diaminobutyrate) inhibited uptake of [3H]GABA, while several other compounds with structural similarities to GABA (e.g., glycine, L-proline and taurine) did not interact with the system. The kinetic studies indicated presence of a 2nd uptake (Km = 92 .mu.M, Vmax = 0.124 nmol/mg per min) in the primary cultures containing predominantly glioblasts. Only 1 of the neuronal cell lines transformed by simian virus SV40 appeared to accumulate [3H]GABA against a concentration gradient. Apparent Km of this uptake was relatively high (819 .mu.M), and it was only weakly inhibited by 1 mM ouabain and 1 mM pCS. The structural specificity also differed from that of the uptake observed in the primary cultures. Significantly, none of the nontransformed continuous cell lines of tumoral (glioma, C6; neuroblastoma, Ml; MlNN) or normal (NN; I6) origin actively accumulated [3H]GABA. For the neurochemical studies related to GABA and requiring homogeneous cell populations, the primary cultures offer a better experimental model than the continuous cell lines.