Effect of neutral lipids on fluidity of corpora lutea plasma membranes and the accessibility of LH/hCG receptor.

Porcine corpora lutea plasma membranes were treated with neutral lipids from hen egg yolk and a special mixture consisting of 70% neutral lipids, 20% phosphatidylcholine and 10% phosphatidylethanolamine. Membrane fluidity, as determined by fluorescence polarization of DPH, significantly increased already after 30 min of incubation of the membranes with lipids. The fluidization effect of neutral lipids increased with the increasing concentration of lipids up to a concentration of 1 mg.ml-1. In experiments with plasma membranes labelled with [3H]cholesterol the increase in membrane fluidity was found to be partially due to a decrease of membrane cholesterol concentration. The most potent concentration of neutral lipids in extracting cholesterol was 2 mg.ml-1. The increase in fluidity of plasma membranes caused by neutral lipids and lipid mixture decreased the accessibility of the LH/hCG receptor.