Characterization and localization of high-affinity GABA uptake in slices of the rabbit oviduct.

The characteristics of [3H]gamma-aminobutyric acid (GABA) uptake by slices of the rabbit oviduct were studied, and the GABA-accumulating structures were identified by histoautoradiography. A high-affinity (Km = 5 microM), sodium-dependent GABA uptake system was demonstrated which showed significant segmental variation along the oviduct with a maximal capacity (21 nmol/g tissue per h) at the fimbriated ampullary end of the organ. The uptake showed optimum values at pH 7.4 and 37 degrees C and could be influenced by changes of K+ and Ca2+ concentrations in the medium. Unlabelled GABA, ouabain and beta-alanine completely inhibited the uptake process, whereas known inhibitors of neuronal GABA uptake (L-diaminobutyric acid, nipecotic acid) produced only partial inhibition even at high doses. In autoradiographic experiments, epithelial secretory cells were predominantly labelled by [3H]GABA. These findings indicate the presence of a non-neuronal GABA uptake system in the oviductal epithelium and do not support the earlier hypothesis of GABAergic innervation in the oviduct.