Fatty acid composition of Drosophila photoreceptor light-sensitive microvilli

Phototransduction, the mechanism underlying the electrical response to light in photoreceptor cells, has been thoroughly investigated in Drosophila melanogaster, an essential model in signal transduction research. These cells present a highly specialized photosensitive membrane consisting of thousands of microvilli forming a prominent structure termed a rhabdomere. These microvilli encompass the phototransduction proteins, most of which are transmembrane and exclusively rhabdomeric. Rhabdomere membrane lipids play a crucial role in the activation of the transient receptor potential ionic channels (TRP and TRPL) responsible for initiating the photoresponse. Despite its importance, rhabdomere lipid composition has not been established. We developed a novel preparation enriched in rhabdomere membranes to perform a thorough characterization of the lipidomics of Drosophila rhabdomeres. Isolated eyes (500) were homogenized and subjected to a differential centrifugation protocol that generates a fraction enriched in rhabdomere membrane. Lipids extracted from this preparation were identified and quantified by gas chromatography coupled to mass spectrometry. We found an abundance of low sterol esters (C16:0, C18:0), highly abundant and diverse triglycerides, free fatty acids, a moderate variety of mono and diacyglycerols (C:16:0, 18:0, C18:1) and abundant phospholipids (principally C18:2). This preparation opens a new avenue for investigating essential aspects of phototransduction.

Lipid composition of intestinal brush border membrane in alloxan induced acute experimental diabetes.

Several alterations were observed in the rat intestinal brush border membrane (BBM) lipid composition after 7 days old alloxane-induced diabetes as compared to the control animals. There was no change in the total protein contents but a significant increase in the total lipid contents was observed. Glycolipids constituting the major lipid components showed a two-fold increase. No significant difference was observed in the total phospholipid contents. A significant decline in the free cholesterol (CH) level, free fatty acids, triglycerides and sialic acid contents was observed in membranes from diabetic rats. Esterified CH, monoglycerides+diglycerides, phosphatidyl serine+phosphatidyl inositol and phosphatidyl choline levels remained unaffected. A significant increase in sphingomyelin with a parallel decrease in phosphatidyl ethanolamine was observed in BBM preparations from diabetic rats. The observed changes in intestinal BBM might be responsible for altered functions of the diabetic intestines.

Effect of high-fat diet on mice intestinal brush border membrane composition.

Effect of feeding high-fat (26% fat) diet to mice for 21 days on intestinal brush border membrane composition was evaluated by comparing with controls fed 10% fat diet. 125I-labelled lectin binding and chemical analysis of fucose, sialic acid, hexoses and hexosamines revealed essentially similar results in control and test groups. Membrane phospholipids, expressed on dry membrane basis, were significantly reduced while total cholesterol was enhanced in experimental group compared to controls. Triglyceride content was not altered under these conditions. [14C]-acetate incorporation studies showed that decrease in phospholipid content was due to reduced synthesis of phospholipid constituents, in particular, phosphatidylcholine and phosphatidylethanolamine, as a result of feeding high fat diet. The results suggest that high amount of fat in the diet of adult mice does not alter sugar content in brush border membrane but affects membrane lipid composition.