Fig. 2.

OH-Trp is a nontransported inhibitor of PAT1. A, concentration-dependent inhibition of PAT1-mediated [³H]-β-alanine (100 μM) uptake (40 min, pH 5.5) by OH-Trp (0.1–30 mM). Data represent uptake after subtraction of uptake into water-injected control oocytes measured under identical conditions. B, OH-Trp (20 mM) induced no current in PAT1-expressing oocytes but significantly reduced the current associated with β-alanine (β-Ala) (2 mM). ***, p < 0.001 versus β-alanine. C, extracellular OH-Trp (20 mM) did not trans-stimulate PAT1-specific [³H]-β-alanine efflux, whereas the PAT1 substrates GABA and proline (Pro) (both 20 mM) caused significant trans-stimulation. Glutamate (20 mM), which is not a PAT1 substrate, did not trans-stimulate PAT1-specific [³H]-β-alanine efflux. ***, p < 0.001; NS, p > 0.05, versus control. D, inhibition of PAT1-mediated [³H]ALA (100 μM) uptake (pH 5.5) by OH-Trp (20 mM) but not by the PepT1 inhibitor AMBA (30 mM). ***, p < 0.001; NS, p > 0.05, versus control.