ISSN:
1432-2013
Keywords:
Liver
;
Hepatocytes
;
Membrane vesicles
;
Dicarboxylate transport
;
Krebs-cycle intermediates
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract The mechanisms involved in the hepatocellular uptake of Krebs-cycle intermediates were investigated in isolated basolateral (sinusoidal and lateral) rat liver plasma membrane (blLPM) vesicles. An inwardly directed Na+ gradient markedly stimulated uptake of 2-oxoglutarate and succinate into voltage- and pH-clamped blLPM vesicles. This Na+-dependent portion of the dicarboxylate uptake was characterized by (a) saturability with increasing substrate concentrations (K m= 6.4–10 mM; V max≈0.2 nmol min−1 mg protein−1), (b) cisinhibition by lithium (10 mM), other Krebs-cycle dicarboxylates (1 mM) and DIDS (4,4′-diisothiocyanostilbene-2,2′-disulfonic acid; 1 mM) but not by sulphate, monocarboxylates, oxalate, acidic amino acids, bile salts and probenecid, (c) stimulation by an intravesicular negative K+-diffusion potential indicating electrogenic [(Na+) n〉2-succinate] cotransport, and (d) a pH optimum for transport between 7.0 and 7.5. In the absence of Na+, an inside alkaline pH gradient also markedly stimulated 2-oxoglutarate uptake. This pH-gradient-driven 2-oxoglutarate uptake was insensitive to lithium, but could also be inhibited by DIDS and succinate. Furthermore, saturation kinetics demonstrated K m (≈ 34 mM) and V max (≈ 0.8 nmol min−1 mg protein−1) values that were clearly different from those of the Na+-dependent uptake system. These results indicate the occurrence of two separate dicarboxylate transport systems along the sinusoidal border of hepatocytes, one being a Na+-dicarboxylate symporter and the other representing an anion-exchange system.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00374220
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