The enteric nervous system, which regulates multiple aspects of digestive activity, is composed of two major cell types, neurons and glial cells. Enteric glia, but not enteric neurons, respond to bioactive lipids with calcium signaling. The sphingomyelin metabolite sphingosine-1-phosphate (S1P) caused dose-dependent calcium (Ca2+) signaling using extracellular and intracellular Ca2+. The signal transduction cascade was pertussis toxin-insensitive and involved an extracellular receptor since repetitive exposure yielded diminished responsiveness. Inhibition of either phospholipase C or the inositol 1,4,5-trisphosphate receptor abolished S1P effects. RT-PCR analysis demonstrated the presence of S1P-coupled endothelial differentiation gene (EDG) receptor mRNAs (EDG-1, EDG-3, and EDG-5) within the enteric nervous system. Immunocytochemical analysis demonstrated strong expression of both EDG-1 and EDG-3 and weak expression of EDG-5 in enteric glial cells. Other sphingomyelin cycle components, including sphingomyelin, sphingomyelinase, and sphingosine caused Ca2+ transients in enteric glia. Related lipids lysophosphatidic acid and sphingosylphosphorylcholine also induced Ca 2+ signaling in enteric glia, suggesting that multiple lipid-activated signaling mechanisms exist in these cells.
Bibliographical noteFunding Information:
This research was supported by the National Institutes of Health (DK41204 and accompanying Minority Supplemental Grant, and Systems & Integrative Biology training grant GM08322–11) and by a pre-doctoral fellowship from the Horace Rackham School of Graduate Studies, University of Michigan.
- Enteroglial cells
- Nervous system