Coordinate induction of Na(+)-dependent transport systems and Na+,K(+)-ATPase in the liver of obese Zucker rats.
Solute uptake into liver plasma membrane vesicles from either lean or obese Zucker rats was monitored. D-Glucose and L-leucine uptakes at physiological concentrations of the substrate were not different in lean and obese Zucker rats. In agreement with a previous report (Ruiz et al. (1991) Biochem. J. 280, 367-372) L-alanine uptake was significantly enhanced in those preparations from obese animals. Na(+)-coupled uridine transport was markedly enhanced also in obese rats. The effect was due to an increase in Vmax (5.5 +/- 0.6 vs. 2.1 +/- 0.2 pmol/mg protein per 3 s, P < 0.01) without any significant change in Km (11.0 +/- 2.8 vs. 9.0 +/- 2.7 microM for obese and lean rats, respectively). Na+,K(+)-ATPase activity was also higher in liver plasma membrane vesicles from rat liver and it correlated with a higher amount of alpha 1-subunit protein in both, plasma membrane vesicles and homogenates from obese rat livers. In summary, in the hypertrophic liver of obese Zucker rats a coordinate induction of several Na(+)-dependent transport systems occurs and, in order to sustain the metabolic pressure associated with this adaptation, a significant induction of the Na+,K(+)-ATPase expression is also found. These data also provide new evidence for regulation of the recently characterized Na(+)-dependent nucleoside transporter.
Ruiz-Montasell
B
B
Departament de Bioquímica i Fisiologia, Universitat de Barcelona, Facultat de Biologia, Spain.
Ferrer-Martinez
A
A
Casado
F J
FJ
Felipe
A
A
Pastor-Anglada
M
M
D000818:Animals; D002352:Carrier Proteins / Q000096:biosynthesis*; D004790:Enzyme Induction; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008565:Membrane Proteins / Q000096:biosynthesis; D033703:Nucleoside Transport Proteins; D009765:Obesity / Q000378:metabolism*; D051381:Rats; D011924:Rats, Zucker; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000096:biosynthesis*
D002352:Carrier Proteins; D008565:Membrane Proteins; D033703:Nucleoside Transport Proteins; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase