Membrane phospholipids of the ocular tunica fibrosa

The authors compared porcine corneal and scleral membrane phospholipids determined with use of 31P nuclear magnetic resonance (NMR). These tissues make up the tunica fibrosa (outer coat) of the eye. Since the sclera, unlike the cornea, does not possess an epithelium or an endothelium, comparative analysis of these tissues included examination of the cornea with and without its epithelium and endothelium. The phospholipids quantified include: phosphatidylcholine, lysophosphatidylcholine, phosphatidylcholine plasmalogen, phosphatidylethanolamine, lysophosphatidylethanolamine, phosphatidylethanolamine plasmalogen, phosphatidylserine, sphingomyelin, phosphatidylinositol, phosphatidylglycerol, cardiolipin, and an uncharacterized phosphatide that accounts for 1.5%-3.5% of the detected phospholipids. Metabolic indices, comprised of individual or grouped metabolites, were calculated to further compare and contrast metabolites and to provide pathway-specific metabolic interrelations for each set of phospholipids from cornea and sclera. Significant differences exist between the corneal stroma and the sclera in 9 of the 12 phospholipids, whereas differences exist between the whole cornea and the sclera in 7 of the 12 phospholipids.