Kinetic analysis about the bidirectional transport of 1-anilino-8-naphthalene sulfonate (ANS) by isolated rat hepatocytes.
The purpose of the present study was to investigate the bidirectional transport of 1-anilino-8-naphthalene sulfonate (ANS) using isolated rat hepatocytes. The initial uptake rate of ANS by isolated hepatocytes was determined. The uptake process of ANS was saturable, with a Km of 29.1 +/- 3.2 microM and Vmax of 2.9 +/- 0.1 mmol/min/mg protein. Subsequently, the initial efflux rate of ANS from isolated hepatocytes was determined by resuspending preloaded cells to 3.0% (w/v) BSA buffer. The efflux process for total ANS revealed a little saturability. The mean value of the efflux clearance was 2.2 +/- 0.1 microL/min/mg protein. The efflux rate of ANS from hepatocytes was markedly decreased at 4 degrees C, indicating that the apparent efflux of ANS might not be attributed to the release of ANS bound to the cell surface, but to the efflux of ANS from intracellular space. The efflux clearance was furthermore corrected for the unbound intracellular ANS concentration on the basis of its binding parameters to cytosol. The relation between efflux rate and unbound ANS concentration was fitted well to the Michaelis-Menten equation with a saturable and a nonsaturable components. The Vmax and Km values were 0.54 mmol/min/mg protein, and 10.0 microM, respectively. Based on the comparison of the ratios of Vmax to Km (Vmax/Km) corresponding to the transport clearance, the influx clearance was two times higher than the efflux clearance. Together with our preliminary studies that ATP suppression in hepatocytes substantially inhibited ANS influx rate, we concluded that the hepatic uptake of ANS is actively taken up into hepatocytes via the carrier mediated transport system.
College of Pharmacy, Chungbuk National University, Cheongju, Chungbuk 361-763, Korea.
Pung Sok
PS
Lee
Im-Sook
IS
Song
Tae Ha
TH
Shin
Suk-Jae
SJ
Chung
Chang-Koo
CK
Shim
Sukgil
S
Song
Youn Bok
YB
Chung
D000817:Anilino Naphthalenesulfonates / Q000378:metabolism* / Q000493:pharmacokinetics*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects*; D002478:Cells, Cultured; D022781:Hepatocytes / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D026901:Membrane Transport Proteins / Q000493:pharmacokinetics*; D051381:Rats; D017207:Rats, Sprague-Dawley
D000817:Anilino Naphthalenesulfonates; D026901:Membrane Transport Proteins; C027132:1-anilino-8-naphthalenesulfonate