ATP-dependent transport of amphiphilic cations across the hepatocyte canalicular membrane mediated by mdr1 P-glycoprotein.
The ATP-dependent transport of the three 3H-labeled, amphiphilic cations quinidine, N-(n-pentyl)-quinidinium, and N-(4',4'-azo-n-pentyl)-21-deoxyajmalinium was studied in rat canalicular plasma membrane vesicles. N-Alkylation of quinidine with an n-pentyl residue resulted in a permanently charged cationic substrate for ATP-dependent transport which exhibited a 10-fold higher transport rate relative to quinidine. The Km value was 0.4 microM for N-(n-pentyl)-quinidinium and 5 microM for quinidine. The permanently cationic and photolabile derivative of ajmaline, N-(4',4'-azo-n-pentyl)-21-deoxyajmalinium, was also an efficient substrate and served to label canalicular membrane proteins with molecular masses of 143 kDa and 108 kDa. ATP-dependent transport of the permanently charged amphiphilic cations was inhibited by the P-glycoprotein inhibitors and substrates quinidine, verapamil, and daunorubicin. The data demonstrate that N-alkylation of quinidine and ajmaline results in most efficient substrates for mdr1 P-glycoprotein-mediated ATP-dependent transport.
Müller
M
M
Division of Tumor Biochemistry, Deutsches Krebsforschungszentrum, Heidelberg, Germany.
Mayer
R
R
Hero
U
U
Keppler
D
D
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000255:Adenosine Triphosphate / Q000378:metabolism; D000345:Affinity Labels; D000818:Animals; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000378:metabolism*; D002412:Cations / Q000378:metabolism*; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008566:Membranes / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000345:Affinity Labels; D002352:Carrier Proteins; D002412:Cations; D008562:Membrane Glycoproteins; D000255:Adenosine Triphosphate