Specificity of OATP and NTCP Transporters

The first studies of specificity were carried out using cholate, the glycine and taurine conjugates and taurine conjugates of the dihydroxy bile acids cheno-deoxycholate and ursodeoxycholate. Kramer and colleagues prepared plasma membrane vesicles from rat liver and compared bile-acid transport with values from CHO cells stably expressing NTCP. This work established that transport by the liver enzyme was maximal when 2 hydroxyls were present, 

Both specificity studies confirmed that bromosulphthalein (BSP) competitively inhibited taurocholate transport by NTCP and OATP. This is in conflict with reports that BSP transport was not sodium dependent, suggesting that OATP was responsible.The reason for this dilference is not clear but may reflect dilferences in the approaches, using isolated rat hepatocytes or transfection to produce cells that stably express the protein. Choice of cell line may also be important as expression of MEH also showed dilferences, with no demonstrable Na -dependent transport of taurocholate in Syrian hamster kidney cells or oocytes but Na -dependent transport was shown in Mardin-Darby canine 

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