RESUMO
The degree of detergent insolubility of cell membranes is a useful parameter to test the strength of lipid-lipid interactions relative to lipid-detergent interactions. Thus, solubility studies could give insights about lipid-lipid interactions relevant in domain formation. In this work we perform a detailed study of the solubilization of four different erythrocyte membrane systems: intact human and bovine erythrocytes, and human and bovine erythrocytes depleted in cholesterol with methyl-beta-cyclodextrin. Each system was incubated with different concentrations of the non-ionic detergent Triton X-100, and the insoluble fraction was characterized by determining cholesterol and phosphorus content. A distinct solubilization behavior was obtained for the four systems, which was quantified by a "detergent resistance parameter" obtained from the fit of the solubility curves. In order to correlate these findings with membrane structural parameters, we quantify the degree of acyl chain order/rigidity of the original membranes by EPR spectroscopy, finding that detergent resistance is higher when acyl chains are more rigid. Regarding compositional properties, we found a good correlation between detergent resistance parameters and the total amount of cholesterol plus sphingomyelin in the original membranes. Our results suggest that a high degree of acyl chain packing is the determinant membrane factor for resistance to the action of Triton X-100 in erythrocytes.
