The structure of detergent-resistant membrane vesicles from rat brain cells

The size and the bilayer thickness of detergent-resistant membranes isolated from rat brain neuronal membranes using Triton X-100 or Brij 96 in buffers with or without the cations, K+/Mg2+ at a temperature of either 4 degrees C or 37 degrees C were determined by dynamic light scattering and small-angle neutron scattering. Regardless of the precise conditions used, isolated membrane preparations consisted of vesicles of approximately 100 to 200 nm diameter as determined by dynamic light scattering methods, equating to an area of the lipid based membrane microdomain size of 200 to 400 nm diameter. By means of small angle neutron scattering it was established that the average thickness of the bilayers of the complete population of detergent-resistant membranes was similar to that of the parental membrane at between 4.6 and 5.0 nm. Detergent-resistant membranes prepared using buffers containing K+/Mg2+ uniquely formed unilamellar vesicles while membranes prepared in the absence of K+/Mg2+ formed a mixture of uni- and oligolamellar structures indicating that the arrangement of the membrane differs from that observed in the presence of cations. Furthermore, the detergent-resistant membranes prepared at 37 degrees C were slightly thicker than those prepared at 4 degrees C, consistent with the presence of a greater proportion of lipids with longer, more saturated fatty acid chains associated with the Lo (liquid-ordered) phase. It was concluded that the preparation of detergent-resistant membranes at 37 degrees C using buffer containing cations abundant in the cytoplasm might more accurately reflect the composition of lipid rafts present in the plasma membrane under physiological conditions.