Abstract
Species differences in the transport activity mediated by canalicular multispecific organic anion transporter (cMOAT) were examined using temocaprilat, an angiotensin-converting enzyme inhibitor whose biliary excretion is mediated predominantly by cMOAT, and 2,4-dinitrophenyl-S-glutathione, a typical substrate for cMOAT, in a series of in vivo and in vitro experiments. Temocaprilat was infused to examine the biliary excretion rate at steady-state. The in vivo transport clearance values across the bile canalicular membrane, defined as the biliary excretion rate divided by the hepatic unbound concentrations, were 9.8, 39.2, 9.2, 1.1, and 0.8 ml/min/kg for mouse, rat, guinea pig, rabbit, and dog, respectively. TheKm and Vmaxvalues for ATP-dependent uptake of 2,4-dinitrophenyl-S-glutathione into canalicular membrane vesicles were 15.0, 29.6, 16.1, 55.8, and 30.0 μM and 0.38, 1.90, 0.15, 0.47, and 0.23 nmol/min/mg protein, yielding the in vitro transport clearance across the bile canalicular membrane (Vmax/Km) of 25.5, 64.2, 9.4, 8.4, and 7.7 for mouse, rat, guinea pig, rabbit, and dog, respectively. A close in vivo and in vitro correlation was observed among animal species for the transport clearance across the bile canalicular membrane. These results suggest that the uptake experiments with canalicular membrane vesicles can be used to quantitatively predict in vivo excretion across the bile canalicular membrane.
Footnotes
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Send reprint requests to: Dr. Hitoshi Ishizuka, Analytical and Metabolic Research Laboratories, Sankyo Co., Ltd., 2-58, Hiromachi 1-chome, Shinagawa-ku, Tokyo 140-8710, Japan. E-mail:ishizu{at}shina.sankyo.co.jp
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↵1 This work was supported in part by a grant-in-aid for Scientific Research on Priority Areas “ABC proteins” (10044243) from the Ministry of Education, Science and Culture of Japan and the Core Research for Evolutional Sciences and Technology of the Japan Sciences and Technology Corporation.
- Abbreviations:
- CMV
- canalicular membrane vesicles
- cMOAT
- canalicular multispecific organic anion transporter
- SD
- Sprague-Dawley
- EHBR
- Eisai hyperbilirubinemic rat
- DNP-SG
- 2,4-dinitrophenyl-S-glutathione
- ALP
- alkaline phosphatase
- LAP
- leucine aminopeptidase
- γ-GTPase
- γ-glutamyl transpeptidase
- GST
- glutathione S-transferase
- CLbile(plasma)
- biliary excretion clearance defined by plasma concentration
- CLbile(liver)
- biliary excretion clearance defined by the liver concentration
- CLbile(u,liver)
- biliary excretion clearance defined by the liver unbound concentration
- Cplasma
- plasma concentration
- Cliver
- liver concentration
- Cu,liver
- liver unbound concentration
- fu,plasma
- the plasma unbound fraction
- fu,liver
- the liver unbound fraction
- MRP
- multidrug resistance-associated protein
- BSEP
- bile salt export pump
- Received November 10, 1998.
- Accepted May 21, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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