P-glycoprotein-mediated drug secretion in mouse proximal tubule perfused in vitro.
To examine the functional significance of drug-transporting P-glycoprotein (P-gp), studies were conducted in the isolated and perfused proximal tubule S2 segment from mice disrupting both mdr1a and mdr1b genes [mdr1a/1b(-)(-)] and their wild-type mice. Efflux of the intracellular fluorescence of rhodamine 123, a fluorescence substrate of P-gp, into the lumen was measured, and the decay half-time of the intracellular fluorescence (T(1/2)) as an index of the drug-transporting P-gp activity was regarded. In the wild-type mice, the T(1/2) was 34 +/- 4 s (n = 36) at the basal period and was increased to 434 +/- 41 s by the addition of luminal verapamil, a P-gp inhibitor. In the mdr1a/1b(-)(-) mice, the T(1/2) was 407 +/- 16 s (n = 10) at the basal period and was no longer affected by the luminal addition of verapamil. The digoxin content in the kidney after a repeated administration of the drug was markedly elevated in the mdr1a/1b(-)(-) mice. In conclusion, P-gp-mediated drug efflux capacity indeed exists in the apical membrane of proximal tubule cells from the wild-type mice, whereas it is absent in that of the mdr1a/1b(-)(-) mice.
Tsuruoka
Shuichi
S
Department of Clinical Pharmacology, Jichi Medical School, Minamikawachi, Tochigi, Japan.
Sugimoto
Koh-Ichi
KI
Department of Clinical Pharmacology, Jichi Medical School, Minamikawachi, Tochigi, Japan.
Fujimura
Akio
A
Department of Clinical Pharmacology, Jichi Medical School, Minamikawachi, Tochigi, Japan.
Imai
Masashi
M
Department of Pharmacology, Jichi Medical School, Minamikawachi, Tochigi, Japan.
Asano
Yasushi
Y
Department of Nephrology, Jichi Medical School, Minamikawachi, Tochigi, Japan.
Muto
Shigeaki
S
Department of Nephrology, Jichi Medical School, Minamikawachi, Tochigi, Japan.
D018435:ATP Binding Cassette Transporter, Subfamily B / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D004077:Digoxin / Q000378:metabolism; D005456:Fluorescent Dyes / Q000493:pharmacokinetics; D019450:Genes, MDR; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D010477:Perfusion; D020112:Rhodamine 123 / Q000493:pharmacokinetics
D018435:ATP Binding Cassette Transporter, Subfamily B; D005456:Fluorescent Dyes; D020112:Rhodamine 123; D004077:Digoxin