PHOSPHOLIPID FATTY ACYL SPATIAL-DISTRIBUTION IN BOVINE ROD OUTER SEGMENT DISK MEMBRANES

The distribution of fatty acids within the phospholipid headgroup clas ses was investigated as a function of the age/spatial distribution of bovine rod outer segment disk membranes. The disks were separated into subpopulations based upon the cholesterol content in their membranes. Because disk membrane cholesterol content decreases as the disks are apically displaced in the rod outer segment, this separation yields di sk subpopulations of different ages and from age-dependent spatial loc ations within the outer segment. The phospholipids, phosphatidylcholin e (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS) and pho sphatidylinositol (PI), of each of these subpopulations were separated and the fatty acid composition of each was determined. These data ind icated that while most of the fatty acids show little or no change wit h age/spatial location, some pronounced changes can be observed in cer tain classes. Within the PC class, 16:0 dramatically decreases with di sk age while the 22:6 increases with disk age. While the PE class exhi bits some fatty acid changes, they are small. The PS class exhibits no significant changes in fatty acid composition. The PI class which con stitutes less than 2% of the total phospholipid exhibits age-related c hanges in each of the fatty acids which could be measured. Most notabl e of these is an increase in 20:4 as the disks are apically displaced. These changes indicate a remodeling of the disk membranes which may b e related to the phototransduction process or to preparation for event ual disk phagocytosis. (C) 1998 Elsevier Science B.V.