Inhibition of the multidrug efflux pump in isolated hepatocyte couplets by immunosuppressants FK506 and cyclosporine

• Published in: Transplantation Vol. 55; no. 3; p. 646
• Main Authors: Takeguchi, N, Ichimura, K, Koike, M, Matsui, W, Kashiwagura, T, Kawahara, K
• Format: Journal Article
• Language: English
• Published: United States 01.03.1993
• Subjects: Animals; ATP Binding Cassette Transporter, Subfamily B, Member 1; Bile Canaliculi - ultrastructure; Cyclosporine - pharmacology; Daunorubicin - pharmacology; Drug Resistance; Fluoresceins; Fluorescent Dyes; Fura-2; Liver - cytology; Membrane Glycoproteins - antagonists & inhibitors; Microscopy, Fluorescence - methods; Progesterone - pharmacology; Rats; Signal Processing, Computer-Assisted; Tacrolimus - pharmacology; Verapamil - pharmacology; Vinblastine - pharmacology
• DOI: 10.1097/00007890-199303000-00033
• ISSN: 0041-1337

Fluorescence image analysis of isolated rat hepatocyte couplets, which retain a bile canaliculus between them, has shown the presence of transport systems for the bile acid and non-bile acid organic anion in the canalicular membrane. The cells also transported Fura-2 and BCECF, which are fluorescent indicators of intracellular Ca2+ and H+ concentrations, respectively, into the canaliculus. Both Fura-2 and BCECF transports were inhibited by progesterone, verapamil, vinblastine, and daunomycin, indicating that the transports are due to a multidrug efflux pump (P-glycoprotein) in the canalicular membrane. Interestingly, the transport by the multidrug efflux pump was inhibited by immunosuppressants FK506 (tacrolimus) and cyclosporine, their half-maximal inhibitory concentrations in the cell suspension being 10 microM and 0.6 microM, respectively. In contrast, the reported immunosuppressive potency of FK506 is 10- to 100-fold that of cyclosporine. Inhibition by immunosuppressants of the multidrug efflux pump, which is a transporter of cytotoxic and other drugs and present in normal human tissues--such as kidney, liver, the blood-brain barrier, and colon--may, at least partly, explain side effects caused by cyclosporine in these tissues of transplant recipients. FK506 at its clinical concentrations may not inhibit the multidrug efflux pump.