Effects of zinc ex vivo on taurine uptake in goldfish retinal cells

BACKGROUND: Taurine and zinc exert neurotrophic effects in the central nervous system. Current studies demonstrate that Na(+)/Cl(-) dependent neurotransmitter transporters, similar to that of taurine, are modulated by micromolar concentrations of zinc. This study examined the effect of zinc sulfate ex vivo on [(3)H]taurine transport in goldfish retina. METHODS: Isolated cells were incubated in Ringer with zinc (0.1–100 µM). Taurine transport was done with 50 nM [(3)H]taurine or by isotopic dilution with taurine (0.001–1 mM) and 50 nM [(3)H]taurine. RESULTS: Zinc reduced the capacity of taurine transport without changes in affinity, and caused a noncompetitive inhibition of high affinity taurine transport, with an EC(50)= 0.072 µM. The mechanism by which zinc affects taurine transport is unknown at the present. CONCLUSIONS: There may be a binding site of zinc in the transporter that affects union or translocation of taurine, or possibly the formation of taurine-zinc complexes, rather than free zinc, could affect the operation of the transporter.