Fig. 6. (A ) Glycine transporter 1 (GlyT1)-mediated currents recorded in Xenopus laevis  oocytes in response to application of N-ethylglycine (EG) and sarcosine for 30 s were compared. (B ) To investigate the additive effect of EG and glycine at GlyT1, EG was applied to Xenopus laevis  oocytes expressing GlyT1 in mounting concentrations alone or in combination with a fixed concentration of glycine (33.3 μM). Simultaneous application of EG and glycine further increased inducible GlyT1-mediated currents compared with glycine application alone. This under-additive effect further underlines that both substrates compete for transport capacity at GlyT1, as expectable for regular substrates. An asterisk indicates a significant difference compared with glycine-induced currents (P < 0.05). Values are given as a fraction of glycine-induced currents (33.3 μM). Data are presented as mean ± SD (n = 6).