title: Differential modulation of human small intestinal brush-border membrane hemileaflet fluidity affects leucine aminopeptidase activity and transport of D-glucose and L-glutamate.
abstract: The fluidity of the exofacial (outer) and cytofacial (inner) leaflets of human proximal small intestinal brush-border membrane vesicles was studied by selective quenching by trinitrophenyl groups, steady-state fluorescence polarization, and differential polarized phase fluorometry techniques, utilizing the lipid soluble fluorophore 1,6-diphenyl-1,3,5-hexatriene. Differences in the hemileaflet's phospholipid composition were also analyzed by trinitrophenylation of aminophospholipids and phospholipase A2 treatment of these preparations. The results of these studies demonstrated that the inner leaflet of these membranes was less fluid than its outer counterpart. Phosphatidylserine was located mainly in the inner hemileaflet, whereas phosphatidylethanolamine and phosphatidylcholine were more symmetrically distributed between the hemileaflets of this membrane. Moreover, in vitro addition of 2-[(2-methoxyethoxy)ethyl]-cis-8-(2-octylcyclopropyl)octanoate (final concentration, 7.5 microM) preferentially fluidized the cytofacial leaflet and concomitantly increased Na(+)-gradient-dependent D-glucose uptake, but decreased Na+, K+-dependent L-glutamic acid uptake in these membrane vesicles. In vitro addition of benzyl alcohol (final concentration, 25 mM) preferentially fluidized the exofacial leaflet and decreased leucine aminopeptidase activity in these preparations. These results, therefore, demonstrate that the hemileaflets of human small intestinal brush-border membranes have different phospholipid compositions and fluidities. Alterations of either the exofacial or cytofacial leaflet fluidity, moreover, modulate protein-mediated activities in a distinct manner.
authors.affiliation: Department of Medicine, University of Chicago, Pritzker School of Medicine, Illinois 60637.
authors.forename: P K
authors.initials: PK
authors.lastname: Dudeja
authors.forename: J M
authors.initials: JM
authors.lastname: Harig
authors.forename: R K
authors.initials: RK
authors.lastname: Wali
authors.forename: S M
authors.initials: SM
authors.lastname: Knaup
authors.forename: K
authors.initials: K
authors.lastname: Ramaswamy
authors.forename: T A
authors.initials: TA
authors.lastname: Brasitus
mesh_terms: D000293:Adolescent; D000328:Adult; D019905:Benzyl Alcohol; D001592:Benzyl Alcohols / Q000494:pharmacology; D001692:Biological Transport; D004161:Diphenylhexatriene; D005947:Glucose / Q000378:metabolism*; D005971:Glutamates / Q000378:metabolism*; D018698:Glutamic Acid; D006801:Humans; D007421:Intestine, Small / Q000378:metabolism / Q000648:ultrastructure; D007931:Leucyl Aminopeptidase / Q000378:metabolism*; D008051:Lipid Bilayers / Q000737:chemistry*; D008297:Male; D008560:Membrane Fluidity / Q000187:drug effects; D008875:Middle Aged; D010713:Phosphatidylcholines / Q000032:analysis; D010714:Phosphatidylethanolamines / Q000032:analysis; D010718:Phosphatidylserines / Q000032:analysis; D010743:Phospholipids / Q000032:analysis*; D013050:Spectrometry, Fluorescence; D013228:Stearates / Q000494:pharmacology; D014301:Trinitrobenzenes / Q000494:pharmacology
chemical_list: D001592:Benzyl Alcohols; D005971:Glutamates; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D010718:Phosphatidylserines; D010743:Phospholipids; D013228:Stearates; D014301:Trinitrobenzenes; D004161:Diphenylhexatriene; D018698:Glutamic Acid; C023714:A(2)C; D007931:Leucyl Aminopeptidase; D005947:Glucose; D019905:Benzyl Alcohol