Modulation of taurine uptake in the goldfish retina and axonal transport to the tectum - Effect of crushing the optic nerve or axotomy

Although there are a great number of studies concerning the uptake of tauri ne in several tissues, the regulation of taurine transport has not been stu died in the retina after lesioning the optic nerve. In the present study, i solated retinal cells of the goldfish retina were used either immediatly af ter cell suspension or in culture. The high-affinity transport system of [H -3]taurine in these cells was sodium-, temperature- and energy-dependent, a nd was inhibited by hypotaurine and beta -alanine, but not by gamma -aminob utyric acid. There was a decrease in the maximal velocity (V-max) without m odifications in the substrate affinity (K-m) after optic axotomy. These cha nges were mantained for up to 15 days after the lesion. The results might b e the summation of mechanisms for providing extracellular taurine to be tak en up by other retinal cells or eye structures, or regulation by the substr ate taurine, which increases after lesioning the optic nerve. The in vivo a ccumulation of [H-3]taurine in the retina after intraocular injection of [H -3]taurine was affected by crushing the optic nerve or by axotomy. A progre ssive retinal decrease in taurine transport was observed after crushing the optic nerve, starting at 7 hours after surgery on the nerve. The uptake of [H-3]taurine by the tectum was compensated in the animals that were subjec ted to crushing of the optic nerve, since the concentration of [H-3]taurine was only different from the control value 24 hours after the lesion, indic ating an efficient transport by the remaining axons. On the contrary, the l ow levels of [H-3]taurine in the tectum after axotomy might be an index of the non-axonal origin of taurine in the tectum. Axonal transport was illust rated by the differential presence of [H-3]taurine in the intact or crushed optic nerve. The uptake of [H-3]taurine into retinal cells in culture in t he absence or in the presence of taurine might indicate the existence of an adaptive regulation of taurine transport in this tissue, however taurine t ransport probably differentially occurs in specific populations of retinal cells. The use of a purified preparation of cells might be useful for futur e studies on the modulation of taurine transport by taurine in the retina a nd its role during regeneration.