Ceramide Channels.

Are ceramide molecules capable of self-assembling in biological and phospholipid membranes to form ceramide channels: membrane channels capable to translocating proteins through said membranes? A number of papers have been published which support the conclusion that ceramide forms these large channels in membranes. The evidence is extensive and consisting of: flux studies using isolated mitochondria, liposomes and planar membranes; visualization by electron microscopy; elastic deformation studies; and regulation by Bcl-2 family proteins. The evidence supports a structural model of the channel shown to be stable by molecular dynamic simulations and having structural and mechanical properties consistent with multiple experiments. Yet the novelty of this claim raises legitimate questions. Indeed, a recent report questions the existence of ceramide channels based on liposome experiments. This review presents both a comprehensive description of the major observations supporting the case that ceramide channels do exist and addresses the issues raised in the skeptical report.