TAURINE ANALOG MODULATION OF TAURINE UPTAKE BY 2 DIFFERENT MECHANISMSIN CULTURED GLIAL-CELLS

Previous data have shown that HEPES, a taurine structural analog, inhi bits the uptake of taurine by cultured cells differently, depending an its addition either to the culture medium or to the Krebs-Ringer buff er used for cell incubation during taurine uptake measurements (Lieu a nd Rebel, J Neurosci Res 23: 78-86, 1989). An extensive study of the e ffect of numerous other taurine structural analogs on taurine uptake b y cultured glial cells was carried out. Our results show that taurine uptake modulation by structural analogs follows two different mechanis ms. For the first mechanism, observable after the simultaneous presenc e of taurine and of its analog during the incubation time of the uptak e experiment (10 min), the amine function on the molecule is essential . The sulfonate group could be replaced either by a sulfinic group or by a carboxylic group. beta-Alanine, hypotaurine, acetyltaurine, guani dinoethanesulfonate and guanidinopropionate are the most potent inhibi tors in this first mechanism. For the second mechanism, which requires the presence of the analog in the culture medium during the 48 hr pre ceeding the taurine uptake measurement, the simultaneous presence of a n amine and of a sulfonate group or of an amine and a sulfinate group is required. Carboxylates are ineffective in modulating taurine uptake in this mechanism. The sulfonate buffers synthesized by Good et al. ( Biochemistry 5: 467-477, 1966) also affect taurine uptake in both mech anisms.