Ceramides are an important group of sphingolipids that modulate several cellular events. The mechanisms underlying biological actions of ceramides are not fully known, but evidence suggests that ceramides can act through regulation of the biophysical properties of the membrane. However, ceramide-induced changes on membrane properties are complex and depend on several factors. To gain further insight into this subject, we characterized the biophysical impact of very-long acyl chain C24-ceramide in a fluid model membrane under thermodynamic equilibrium and non-equilibrium conditions. Our results show that C24-ceramide readily forms two types of gel domains with distinct properties, likely corresponding to different interdigitated metastable gel phases. Upon reaching thermodynamic equilibrium, only partially interdigitated gel phase coexists with the fluid phase. In addition, C24-ceramide promotes strong changes in the shape of the vesicles, including domains with sharp edges and tubule-like structures. The results suggest that the formation of very long acyl chain ceramides in response to stress stimuli will initially induce a multitude of changes in the organization and fluidity of biological membranes that might be responsible for the activation of different cellular processes.
Keywords: Ceramide gel domains; Confocal microscopy; Giant unilamellar vesicles; Lipid interdigitation; Lipid tubules; Metastable gel phase.
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