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#high temperature

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Properties of Plasma Membrane

What happens when cholesterol is added to a membrane at high temperature?

Dual effect of cholesterol on membrane order described as condensing and fluidity buffering arises from rigid steroid ring system intercalating among phospholipid acyl chains. At temperatures above phospholipid Tm chains highly disordered with many gauche conformers large area per lipid fluid low order. Cholesterol hydroxyl moiety positioned near phospholipid carbonyl oxygen forms hydrogen bond, rigid tetracyclic rings restrict chain isomerization reducing number gauche kinks order parameter S increases from zero point two to zero point five measured deuterium NMR, lateral diffusion coefficient decreases ten to minus eight to ten to minus nine centimeters squared per second, permeability to solutes ions glucose reduced, bilayer thickness increased zero point three nanometers and bending rigidity increased protecting against lysis while still lateral fluid not gel. At low temperature below Tm cholesterol disrupts crystalline packing inserting between chains increasing disorder fluidity preventing gel formation. At high temperature cholesterol rich liquid-ordered rafts with sphingomyelin thicker ordered slower than liquid-disordered unsaturated phospholipid phase recruiting signaling proteins like Src kinases. Cholesterol therefore decreases fluidity at high temperature buffering against hyperfluidity maintaining integrity for protein function and signal compartmentalization.

Ref: Ohvo-Rekila et al., Cholesterol Interactions and Membrane Fluidity Biphasic Effect, Prog Lipid Res 2002.

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