Characterization of taurine uptake in the rat retina.

Abstract

Taurine is a free amino acid found in mammalian tissues and its pharmacological depletion in various animal models has been demonstrated to cause visual deficits and morphological degeneration in the retina1. Taurine is an important modulator of cellular processes whose most unique characteristic is the unusually high mM concentrations in which it is found intracellularly2. In the retina, concentrations as high as 79 mM have been measured3 with most of the taurine being exogenous in nature1. The steep gradient across the cell membrane requires a very efficient transport system that is carefully regulated. Taurine uptake in the retina has been demonstrated, in various species, to have 2 saturable components of differing affinity to taurine2. The transport systems exhibit a 10to 100-fold difference in their affinites for taurine, as measured by the taurine concentration at which a half-maximal velocity is attained (Km). In the retina, visual transduction is initiated in the rod outer segments (ROS) of the photoreceptor cells4 to which the high-affinity taurine uptake component has been specifically linked5,6. However, the kinetics of taurine uptake in the ROS have not been studied in detail. In view of the