Removal of sphingomyelin headgroup inhibits the ligand binding function of hippocampal serotonin1A receptors

Sphingolipids are essential components of eukaryotic cell membranes and are thought to be involved in a variety of cellular functions. Sphingomyelin is the most abundant sphingolipid in the nervous system. In this work, we explored the ligand binding function of the hippocampal serotonin(1A) receptor upon hydrolyzing sphingomyelin to ceramide and phosphocholine using sphingomyelinase. The serotonin(1A) receptor is an important neurotransmitter receptor and belongs to the superfamily of G-protein coupled receptors. It is involved in the generation and modulation of various cognitive, behavioral and developmental functions. We show here that specific agonist binding to serotonin(1A) receptors in native hippocampal membranes is considerably reduced upon sphingomyelinase treatment. Interestingly, the overall membrane order does not exhibit any appreciable change under these conditions. Our results show the importance of sphingomyelin (specifically, the sphingomyelin headgroup) for the function of serotonin(1A) receptors. These novel results constitute the first report on the effect of enzymatic hydrolysis of sphingomyelin on the ligand binding function of this important neurotransmitter receptor in native hippocampal membranes. Our results assume greater relevance in the broader perspective of the influence of the membrane lipid environment on the function of the serotonin(1A) receptor in particular, and other G-protein coupled receptors in general.