Molecular diversity of sphingolipid signalling.

Sphingolipid breakdown products are now being recognized to play a dual role in cellular signalling, acting as intracellular as well as extracellular signalling molecules. Both types of action may even be found with one sphingolipid species. The recent demonstration of G protein-coupled receptors with high affinity for sphingosine 1-phosphate and sphingosylphosphorylcholine has been followed by the discovery of several novel sphingolipid actions, such as regulation of heart rate, oxidative burst, neurite retraction or platelet activation. Ligand profiles and concentration-response relationships suggest the existence of putative sphingolipid receptor subtypes. Against this background, several observations on supposed sphingolipid second messenger actions deserve a new evaluation.