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The aim of the present study was to investigate if basic GABA-mimetics interact with the taurine transporter (TauT, Slc6a6), and to find a suitable cell based model that is robust towards extracellular changes in osmolality during uptake studies. Taurine uptake was measured in human Caco-2 cells, porcine LLC-PK1 cells, and rat SKPT cells using radiolabelled taurine. Hyperosmotic conditions were obtained by incubation with raffinose (final osmolality of 500 mOsm) for 24 h prior to the uptake experiments. Expression of the taurine transporter, TauT, was investigated at the mRNA level by real-time PCR. Uptake of the GABA-mimetics gaboxadol and vigabatrin was investigated in SKPT cells, and quantified by liquid scintillation or HPLC-MS/MS analysis, respectively. The uptake rate of [ 3H]-taurine was Na + and Cl - and concentration dependent with taurine with an apparent V max of 6.3 ± 1.6 pmol cm - 2 min - 1 and a K m of 24.9 ± 15.0 μM. β-alanine, nipecotic acid, gaboxadol, GABA, vigabatrin, δ-ALA and guvacine inhibited the taurine uptake rate in a concentration dependent manner. The order of affinity for TauT was β-alanine > GABA > nipecotic acid > guvacine > δ-ALA > vigabatrin > gaboxadol with IC 50-values of 0.04, 1.07, 2.02, 4.19, 4.94, 31.4 and 39.9 mM, respectively. In conclusion, GABA mimetics inhibited taurine uptake in hyperosmotic rat renal SKPT cells. SKPT cells, which seem to be a useful model for investigating taurine transport in the short-term presence of high concentrations of osmolytes. Furthermore, analogues of β-alanine appear to have higher affinities for TauT than GABA-analogues.

In the present study, we have investigated ibuprofen transport in renal cell cultures with the aim of characterizing a recently proposed ibuprofen transporter. We here show that hyperosmolarity upregulates an ibuprofen transporter in dog renal MDCK I cells via increased mRNA and protein synthesis, while the transporter was not upregulated by hyperosmolarity in porcine and rat renal cell lines. The transport of ibuprofen in MDCK I cells was inhibited by ibuprofen metabolites such as 1- and 3-hydroxyibuprofen, and to a lesser extent by 2-hydroxyibuprofen. Other non-steroidal anti-inflammatory drugs such as naproxen, ketoprofen, flurbiprofen, diclofenac, and piroxicam also inhibited ibuprofen transport while no effect was observed from acetylsalicylic acid. The transporter was functionally detected in both the apical and basolateral membranes of MDCK 1 cells, and may control intracellular concentrations of ibuprofen.

Ibuprofen is a widely used drug. It has been identified as an inhibitor of several transporters, but it is not clear if ibuprofen is a substrate of any transporter itself. In the present work, we have characterized a transporter of ibuprofen, which is upregulated by hyperosmotic culture conditions in Madin-Darby canine kidney I (MDCK I) renal cells. [(3)H]-Ibuprofen uptake rate was measured in MDCK I cell cultured under normal (300 mOsm) and hyperosmotic (500 mOsm) conditions. Hyperosmotic conditions were obtained by supplementing urea, NaCl, mannitol, or raffinose to culture medium. The effect of increased osmolarity was investigated for different incubation times. [(3)H]-Ibuprofen uptake in MDCK I cells was upregulated by hyperosmotic culture condition, and was saturable with a Km value of 0.37 ± 0.08 μM and a Vmax of 233.1 ± 17.2 pmol· cm(-2)· min(-1). Racemic [(3)H]-ibuprofen uptake could be inhibited by (R)-(-)- and (S)-(+)-ibuprofen with IC50 values of 19 μM (Log IC50 1.39 ± 0.34) and 0.47 μM (Log IC50 -0.36 ± 0.41), respectively. Furthermore, the [(3)H]-ibuprofen uptake rate was increased by decreased extracellular pH but not dependent on Na(+) or Cl(-) ions. The mRNA of Mct1, -2, -4, and -6 as well as Oat1 and -3 were not upregulated by hyperosmolarity. Our findings present strong evidence for the presence of a yet unknown ibuprofen transporter in MDCK I cells. The transporter was upregulated under hyperosmotic culture conditions, and the present study is therefore a starting point for identification of the molecular correlate and potential impact on ibuprofen disposition.