RT Journal Article
SR Electronic
T1 Kinetic Analysis of the Primary Active Transport of Conjugated Metabolites Across the Bile Canalicular Membrane: Comparative Study of<em>S</em>-(2,4-Dinitrophenyl)-glutathione and 6-Hydroxy-5,7-dimethyl-2-methylamino4-(3-pyridylmethyl)benzothiazole Glucuronide
JF Journal of Pharmacology and Experimental Therapeutics
JO J Pharmacol Exp Ther
FD American Society for Pharmacology and Experimental Therapeutics
SP 866
OP 872
VO 282
IS 2
A1 Niinuma, Kayoko
A1 Takenaka, Osamu
A1 Horie, Toru
A1 Kobayashi, Kazuo
A1 Kato, Yukio
A1 Suzuki, Hiroshi
A1 Sugiyama, Yuichi
YR 1997
UL http://jpet.aspetjournals.org/content/282/2/866.abstract
AB Eisai hyperbilirubinemic rat (EHBR) is a mutant strain with a hereditary defect in canalicular multispecific organic anion transporter (cMOAT). We examined the uptake and mutual inhibition of S-(2,4-dinitrophenyl)-glutathione (DNP-SG), which is a typical substrate for cMOAT, and 6-hydroxy-5,7-dimethyl-2-methylamino-4-(3-pyridylmethyl) benzothiazole (E3040) glucuronide (E-glu) with canalicular membrane vesicles (CMV) prepared from Sprague-Dawley (SD) and EHBR rats to investigate the multiplicity of the organic anion transporter. The ATP-dependent uptake by CMV from SD rats had an apparent Km of 17.6 μM for DNP-SG and 5.7 μM for E-glu, whereas the corresponding uptake by CMV from EHBR had an apparent Km of 44.6 μM for E-glu. The effects of E-glu, 4-methylumbelliferone glucuronide (4 MUG), E3040 sulfate (E-sul) and 4-methylumbelliferone sulfate (4 MUS) on the uptake of [3H]DNP-SG were also examined. The uptake of [3H]DNP-SG was inhibited by glucuronides (E-glu and 4 MUG) in a concentration-dependent manner, although it was enhanced by the sulfate conjugates (E-sul and 4 MUS). This enhancement was shown to be caused by an increased DNP-SG affinity for the transporter. In CMV from SD rats, although ATP-dependent uptake of [3H]DNP-SG was almost completely inhibited by E-glu, that of [14C]E-glu was only reduced to about 30% of controls by DNP-SG. On the other hand, in CMV from EHBR, the ATP-dependent uptake of [14C]E-glu was not inhibited at all by DNP-SG. Kinetic analysis indicated that E-glu inhibited DNP-SG uptake competitively. In conclusion: 1) cMOAT recognizes both DNP-SG and E-glu, and another transporter present in SD rats is also involved in E-glu transport along with cMOAT; 2) the latter transporter is kinetically similar to the E-glu transporter present in EHBR; 3) E-sul enhances the uptake of DNP-SG by increasing the affinity of glucuronide for the transporter. The American Society for Pharmacology and Experimental Therapeutics