Characterization and modulation of rat small intestinal brush-border membrane transbilayer fluidity

Area of Science:

• Biochemistry
• Membrane Biology
• Cell Physiology

Background:

• Cell membranes possess distinct leaflets with potentially different properties.
• Understanding membrane fluidity is crucial for cellular functions like transport and enzyme activity.

Purpose of the Study:

• To directly assess the fluidity of the exofacial and cytofacial leaflets of rat small intestinal brush-border membranes.
• To investigate the factors contributing to asymmetric membrane fluidity.
• To examine the effects of agents altering membrane fluidity on enzyme activities and nutrient transport.

Main Methods:

• Utilized selective quenching with trinitrophenyl groups.
• Employed steady-state fluorescence polarization and differential polarized phase fluorescence techniques.
• Assessed phospholipid distribution using phospholipase A2 and trinitrophenylation.

Main Results:

• The exofacial hemileaflet demonstrated greater fluidity than the cytofacial hemileaflet.
• Asymmetric phospholipid distribution (phosphatidylcholine and phosphatidylethanolamine) contributed to the observed fluidity differences.
• In vitro benzyl alcohol preferentially fluidized the exofacial leaflet, decreasing leucine aminopeptidase activity.
• In vivo A2C preferentially fluidized the cytofacial leaflet, enhancing D-glucose transport.

Conclusions:

• Rat intestinal brush-border membranes exhibit inherent asymmetry in leaflet fluidity, influenced by lipid composition.
• Modulating membrane fluidity with specific agents can selectively impact enzyme activities and nutrient transport mechanisms.