Abstract
The zonal uptake of estrone sulfate (E1S; 1 to 400 μM) was investigated in periportal and perivenous rat hepatocytes and cells isolated from whole liver (regular hepatocytes). Transport of E1S by periportal, perivenous, and regular hepatocytes was described by saturable (Kms of 24 to 26 μM and Vmaxs of 1.8 nmol/min/mg protein) and nonsaturable components (2.5 to 3.2 μl/min/mg protein) that were not different among the zonal regions (p > .05, ANOVA). These kinetic constants represented pooled values for the entire complement of transporters for E1S, including two known transporters of E1S: Ntcp, Na+-taurocholate cotransporting polypeptide, and oatp1, the organic anion transporting polypeptide cloned from rat liver. Uptake of E1S was significantly reduced by estradiol 17β-glucuronide (50 μM) and bumetanide (200 μM), and was inhibited strongly and competitively by pregnenolone sulfate with an inhibition constant of 6.7 μM. Further segregation of the kinetic constants as the sodium-dependent and -independent systems was achieved through simultaneous fitting of data obtained in the presence and absence of sodium from parallel hepatocytic uptake studies. For the periportal, perivenous, and regular hepatocytes, two saturable systems: a sodium-dependent transport system, characterized by similarVmaxs (1.1 to 1.4 nmol/min/mg protein) andKms (49 to 55 μM), a sodium-independent transport system of comparable Vmaxs (0.70 to 0.84 nmol/min/mg protein) and Kms (16 to 22 μM), and a linear clearance of 1.7 to 2.7 μl/min/mg protein (ANOVA, p > .05) were obtained. The data suggest that hepatic uptake of E1S involved sodium-dependent and -independent transporter systems. No heterogeneity in transport was observed.
Footnotes
-
Send reprint requests to: Dr. K.S. Pang, Faculty of Pharmacy, University of Toronto, 19 Russell St., Toronto, Ontario, Canada M5S 2S2. E-mail: pang{at}phm.utoronto.ca
-
This work was supported by the National Institutes of Health (Grant GM-38250) and Medical Research Council of Canada (MA-9104). Eugene Tan was a recipient of the Medical Research Council of Canada graduate fellowship.
- Abbreviations used are::
- E1S
- estrone sulfate
- oatp1 and oatp2
- organic anion transporting polypeptide 1 and 2
- Ntcp
- sodium-dependent taurocholate cotransporting polypeptide
- Received October 15, 1998.
- Accepted December 16, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
DMD articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|