Comparative analysis of the ontogeny of a sodium-dependent bile acid transporter in rat kidney and ileum

An apical sodium-dependent bile acid transporter (ASBT) has recently been cloned and characterized in the rat ileum. Northern and Western blotting revealed both the ASBT mRNA and protein in rat kidney. The coding sequence of the kidney transcript was found to be identical to the previously cloned ileal ASBT. Indirect immunofluorescence studies localized the ASBT protein to the apical membrane of the renal proximal convoluted tubule. Kinetic analysis of sodium-dependent taurocholate uptake using membrane vesicles revealed a similar Michaelis-Menten constant value for taurocholate in the kidney and intestine. ASBT protein and function were present in the kidney but not the ileum from 7-day-old rats. On postnatal day 7, there was a sevenfold increase in ASBT steady-state mRNA levels in the kidney relative to the ileum, yet nuclear run-on assays revealed that the nascent transcription rates at this age were virtually the same. This suggests that the difference in the neonatal expression of the ASBT gene in the kidney and ileum may be in part due to differences in mRNA stability.

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Molecular analysis of the differential regulation of the apical sodium-dependent bile acid transporter (ASBT) in postnatal rat kidney and ileum

Gastroenterology ◽

10.1016/0016-5085(95)27191-0 ◽

1995 ◽

Vol 108 (4) ◽

pp. A720

Keyword(s):

Bile Acid ◽

Molecular Analysis ◽

Rat Kidney ◽

Differential Regulation ◽

Sodium Dependent ◽

Bile Acid Transporter ◽

Acid Transporter

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Increased expression of ileal apical sodium-dependent bile acid transporter in postpartum rats

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00309.2001 ◽

2002 ◽

Vol 282 (1) ◽

pp. G41-G50 ◽

Cited By ~ 15

Author(s):

Aldo D. Mottino ◽

Tim Hoffman ◽

Paul A. Dawson ◽

Marcelo G. Luquita ◽

Juan A. Monti ◽

...

Keyword(s):

Small Intestine ◽

Bile Acid ◽

Membrane Vesicles ◽

Proximal Region ◽

Unit Weight ◽

Intestinal Loop ◽

Loop Model ◽

Sodium Dependent ◽

Bile Acid Transporter ◽

Acid Transporter

The expression and activity of the apical ileal sodium-dependent bile acid transporter (asbt) was examined in the small intestine of control, pregnant, and lactating postpartum rats 2, 12, and 21 days after delivery. Western blot analysis of brush border membrane vesicles (BBMV) prepared from different regions of the small intestine demonstrated that expression of asbt was maximal in the most distal segments for all experimental groups, was not substantially affected in pregnant and 2-day postpartum rats, and was significantly increased in 12- and 21-day postpartum rats. Analysis of mRNA suggested that asbt protein was regulated at the posttranscriptional level in postpartum rats. Increased expression of asbt protein postpartum was maximal (∼2-fold) in the proximal region of the ileum, consistent with a 60% increase in taurocholate (TC) transport in BBMV from the proximal ileum in 14- to 21-day postpartum rats relative to control rats. Absorption of TC, determined from the intact proximal ileum using an intestinal loop model, demonstrated a 30% increase in TC uptake per unit weight of tissue in 14- to 21-day postpartum rats relative to control rats. Together with the marked increase in intestinal mass observed at peak lactation, these data indicate a significant increase in asbt-mediated reclamation of bile acids in the intestine of lactating rats.

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