title: Cholesterol heterogeneity in bovine rod outer segment disk membranes.
abstract: Rod outer segment disk membranes have been used to study visual transduction events. Numerous studies have also focused on protein-lipid interactions in these membranes. The possible heterogeneity of the disk membrane composition has not been addressed in such studies. Freeze fracture studies (Andrews, L. D., and Cohn, A. I. (1979) J. Cell Biol. 81, 215-220; Caldwell, R., and McLaughlin, B. (1985) J. Comp. Neurol. 236, 523-537) suggest a difference in cholesterol content between newly formed and old disks. This potential heterogeneity in disk membrane composition was investigated using digitonin. Osmotically intact bovine rod outer segment disk membranes prepared by Ficoll flotation were separated based on the cholesterol content of the disks. The addition of digitonin to disk membrane suspensions in a one-to-one molar ratio with respect to cholesterol produced an increase in the density of the membranes in proportion to the amount of cholesterol present. The digitonin-treated disks were separated into subpopulations using a sucrose density gradient. Disks were shown to vary in cholesterol to phospholipid ratio from 0.30 to 0.05. The ratio of phospholipid to protein remained constant in all disk subpopulations at approximately 65 phospholipids per protein. No significant change in the fatty acid composition of the disks was observed as a function of change in cholesterol content. This work demonstrates compositional heterogeneity in disk membranes which may ultimately affect function.
authors.affiliation: Department of Biochemistry, School of Medicine, State University of New York/Buffalo 14214.
authors.forename: K
authors.initials: K
authors.lastname: Boesze-Battaglia
authors.forename: T
authors.initials: T
authors.lastname: Hennessey
authors.forename: A D
authors.initials: AD
authors.lastname: Albert
mesh_terms: D000818:Animals; D002417:Cattle; D002462:Cell Membrane / Q000032:analysis; D002499:Centrifugation, Density Gradient; D002784:Cholesterol / Q000032:analysis*; D004072:Digitonin / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D005227:Fatty Acids / Q000032:analysis; D010743:Phospholipids / Q000032:analysis; D010786:Photoreceptor Cells / Q000032:analysis*; D011506:Proteins / Q000032:analysis; D012243:Rhodopsin / Q000032:analysis; D012374:Rod Cell Outer Segment / Q000032:analysis* / Q000187:drug effects; D013053:Spectrophotometry
chemical_list: D005227:Fatty Acids; D010743:Phospholipids; D011506:Proteins; D012243:Rhodopsin; D002784:Cholesterol; D004072:Digitonin