Selective uptake of tritiated glycine, GABA and D-aspartate by retinal cells in culture: a study using autoradiography and simultaneous immunofluorescence.

Autoradiographic studies on the uptake of 3 tritiated amino acids by cell cultures of rat retina are reported. At 0.2 microM [3H]-GABA is taken up with great selectivity by a minority of medium to large multipolar cells. At 2 microM [3H]glycine is taken up with slightly less selectivity by a similar proportion of multipolar cells; the proportions of cells labeled by either amino acid are additive which indicates that they are separate populations. In simultaneous autoradiographical and indirect immunofluorescence experiments, both of these cell classes were found to bind tetanus toxin and are therefore presumably neurons. At 0.4 microM [3H]D-aspartate is preferentially taken up by virtually all small spheroid cells which lack long processes (putative immature photoreceptors), as well as by a minority of larger multipolar cells. All 3 tritiated amino acids also label flattened cells which include retinal glia. The results are discussed in relation to similar experiments performed on undissociated retina and we conclude that these experiments allow us to identify and quantify immature photoreceptors and certain sub-types of amacrine cells in these cultures.