Na pump and plasma membrane structure in L-cell fibroblasts expressing rat liver fatty acid binding protein

Sandra Incerpi, John R. Jefferson, W. Gibson Wood, W. James Ball, Friedhelm Schroeder

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34 Scopus citations

Abstract

Although the intracellular fatty acid binding proteins have been investigated for nearly two decades and purified proteins are now available, little is known regarding the function of these proteins in intact cells. Therefore, L-cell fibroblasts transfected with cDNA encoding for rat liver fatty acid binding protein (L-FABP) were examined as to whether L-FABP expression in intact cells modifies plasma membrane enzyme activities, fluidity, and lipids. Plasma membrane Na K-ATPase activity was 65.9 ± 18.7 and 38.6 ± 22.8 (P < 0.001) nmol/mg protein × min for control and high-expression transfected cells, respectively. Consistent with this observation, [3H] ouabain binding to whole cells was significantly decreased from 3.7 ± 0.3 to 2.0 ± 0.8 pmol ouabain bound/mg cell protein in control and high-expression cells, respectively, whereas the cell's affinity for ouabain was not significantly altered. Unexpectedly, Western blot analysis indicated that transfected cells had higher levels of Na+, K+-ATPase protein; in contrast, the activities of 5′-nucleotidase and Mg-ATPase were unaltered. The effects of L-FABP expression on plasma membrane Na K-ATPase function appeared to be mediated through alterations in plasma membrane lipids and/or structure. The plasma membrane cholesterol/phospholipid ratio decreased and the bulk plasma membrane fluidity increased in the high-expression cells. In conclusion, plasma membrane Na K-ATPase activity in L cells may be regulated in part through expression of cytosolic L-FABP.

Original languageEnglish (US)
Pages (from-to)35-42
Number of pages8
JournalArchives of Biochemistry and Biophysics
Volume298
Issue number1
DOIs
StatePublished - Oct 1992

Bibliographical note

Funding Information:
This work was supported in part by grants from the USPHS (GM 31651 to F.S.; AA-07292 to W.G.W.; HL-32214 to W.J.B.) and by the Fulbright Foundation (Visiting Fulbright Scholar, S.I.). The technical assistance of Mr. Timothy Hubbell in culturing the transfected cells and of Ms. Purabi Dey with the Western blot analysis was much appreciated.

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