Sulfatide is associated with insulin granules and located to microdomains of a cultured beta cell line

Previous studies using pancreas from various mammals and freshly isolated islets from rat pancreas have provided evidence supporting possible involvement of the glycosphingolipid sulfatide in insulin processing and secretion. In this study, sulfatide expression and metabolism in the beta cell line RINr1046-38 (RIN-38), commonly used as a model for beta cell functional studies, were investigated and compared with previous findings from freshly isolated islets. RIN-38 cells expressed similar amounts (2.7 +/- 1.1 nmol/mg protein, n = 19) of sulfatide as isolated rat islets and also followed the same metabolic pathway, mainly through recycling. Moreover, in agreement with findings in isolated islets, the major species of sulfatide isolated from RIN-38 cells contained C16:0 and C24:0 fatty acids. By applying subcellular isolations and electron microscopy and immunocytochemistry techniques, sulfatide was shown to be located to the secretory granules, the plasma membrane and enriched in detergent insoluble microdomains. In the electron microscopy studies, Sulph I staining was also associated with mitochondria and villi structures. In conclusion, RIN-38 cells might be an appropriate model, as a complement to isolated islets where the amount of material often limits the experiments, to further explore the role of sulfatide in insulin secretion and signal transduction of beta cells.