Modulation of human GABAρ1 receptors by taurine

A study was made of the effects of taurine on GABAρ1 receptors expressed in Xenopus oocytes. The EC50 and reversal potentials for GABA, taurine and glycine currents were 2.3 ± 0.4 μM (−25 ± 0.9 mV), 5 ± 0.8 mM (−27 ± 0.4 mV) and 7 ± 0.5 mM (−22 ± 0.6 mV), respectively. Co-application of GABA and taurine, revealed a taurine concentration-dependent biphasic-modulation of the receptor: at 0.3–30 μM taurine potentiated the GABA-currents, whereas at 0.3–30 mM the GABA-currents were reduced. In contrast glycine potentiated the GABA-currents at all concentrations tested. TPMPA, a GABAC specific receptor antagonist, also blocked effectively and reversibly the taurine and glycine currents. Finally, lanthanum and zinc modulated the currents generated by the three amino acids. Taurine is abundant in the retina and our observations suggest that taurine may play an important role modulating the retinal GABAergic transmission.