García-Arribas…Goñi {Langmuir 32: 9053}
We have studied lipid bilayers obtained from human red blood cell extracts, and the effect of incorporating a long-chain ceramide (palmitoyl ceramide, pCer) into them. The bilayers have been examined using atomic force microscopy and differential scanning calorimetry. Gel-like phase domains are generated by the presence of pCer at high mol ratios (around 30 mol% pCer) and cause an increase in bilayer thickness and nanomechanical resistance. Furthermore, cholesterol (Chol) depletion of the system causes the domains to stiffen even more, demonstrating that Chol was an integral part of the domains and that no Cer-Chol displacement events were present. These experiments speak in favour of the possibility of lipid gel domains enriched in both Chol and pCer in cellular environments
Ceramide-Induced Lamellar Gel Phases in Fluid Cell Lipid Extracts
García-Arribas AB, Ahyayauch H, Sot J, López-González PL, Alonso A, Goñi FM.
Langmuir 2016 Sep.; 32: 9053.
The effects of increasing amounts of palmitoylceramide (pCer) on human red blood cell lipid membranes have been studied using atomic force microscopy of supported lipid bilayers, in both imaging (bilayer thickness) and force-spectroscopy (nanomechanical resistance) modes. Membranes appeared homogeneous with pCer concentrations up to 10 mol % because of the high concentration of cholesterol (Chol) present in the membrane (∼45 mol %). However, the presence of pCer at 30 mol % gave rise to a clearly distinguishable segregated phase with a nanomechanical resistance 7-fold higher than the continuous phase. These experiments were validated using differential scanning calorimetry. Furthermore, Chol depletion of the bilayers caused lipid domain generation in the originally homogeneous samples, and Chol-depleted domain stiffness significantly increased with higher amounts of pCer. These results point to the possibility of different kinds of transient and noncompositionally constant, complex gel-like phases present in RBC lipid membranes rich in both pCer and Chol, in contrast to the widespread opinion about the displacements between pCer-enriched “gel-like” domains and liquid-ordered “raft-like” Chol-enriched phases. Changes in the biophysical properties of these complex gel-like phases governed by local modulation of pCer:Chol ratios could be a cell mechanism for fine-tuning the properties of membranes as required.
PubMed: 27486830. Doi: 10.1021/acs.langmuir.6b01579.
