High-affinity taurine uptake in developing retina.

A specific system for taurine transport is present at the early stages of development in both chick and rat retinas. The results obtained with taurine analogs indicate a high degree of specificity of taurine uptake. Two transport systems were detected for the adult rat retina: a high-affinity (Km 21 microM) and a low-affinity transport system (Km 312 microM). On the other hand, in the adult chick retina, only a low-affinity transport system (Km 580 microM) could be detected. Nevertheless, embryo chick retina accumulated [3H]taurine by two different kinetic mechanisms with Kms of 242 microM and 21 microM for the low- and high-affinity processes, respectively. Taurine uptake systems were absolutely Na+ dependent. The sodium-dependence curve for taurine uptake was sigmoid. These mechanisms appear not to be mediated by a Na+ cotransport system. In spite of the differences observed in taurine uptake in both species, in each of them it closely parallels the changes brought about by the morphological and functional maturation of the retina.