The high‐affinity uptake and release of glycine was studied in retinas of Xenopus laevis. In the toad and tadpole retina, 3H‐glycine was accumulated by a population of cells located predominantly in the inner nuclear layer. When retinas preloaded with 3H‐glycine were subjected to high K+‐concentrations, these retinas released large amounts of 3H‐glycine by a Ca++‐dependent mechanism. The appearance and maturation of these putative glycinergic properties was followed during retinal development. Our results indicate that the high‐affinity uptake of glycine first appears around stage 33/34 whereas K+‐stimulated glycine release cannot be detected until stage 42.
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