title: Membrane order conservation in raft and non-raft regions of hepatocyte plasma membranes from thermally acclimated rainbow trout.
abstract: Homeoviscous adaptation (HVA), the thermal conservation of membrane fluidity/order at different body temperatures, has been observed to varying degrees in different membranes. However, HVA has not been studied in raft and non-raft regions of the plasma membrane (PM) separately. Rafts are ordered PM microdomains implicated in signal transduction, membrane traffic and cholesterol homeostasis. Using infrared spectroscopy, we measured order in raft-enriched PM (raft) and raft-depleted PM (RDPM) isolated from hepatocytes of rainbow trout (Oncorhynchus mykiss) acclimated to 5 and 20 degrees C. We found approximately 130% and 90% order compensation in raft and RDPM, respectively, suggesting their independent regulation. Raft was more ordered than RDPM in the warm-acclimated trout, a difference fully explained by a 58% enrichment of cholesterol, compared to RPDM. Unexpectedly, raft and RDPM from cold-acclimated trout did not differ in cholesterol content or order. Freezing the membrane samples during preparation had no effect on order. Treatment with cyclodextrin depleted cholesterol by 36%, 56%, and 55%, producing significant decreases in order in raft and RDPM from warm-acclimated trout and RDPM from cold-acclimated trout, respectively. However, a 69% depletion of cholesterol from raft from cold-acclimated trout had no significant effect on order. This result, and the lack of a difference in order between raft and RDPM, suggests that raft and non-raft PM in cold-acclimated trout are not spatially segregated by phase separation due to cholesterol.
authors.affiliation: School of Life Sciences, Arizona State University,Tempe, AZ 85287, USA. john.zehmer@utsouthwestern.edu
authors.forename: John K
authors.initials: JK
authors.lastname: Zehmer
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Hazel
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D002784:Cholesterol / Q000737:chemistry / Q000378:metabolism; D003080:Cold Temperature; D004305:Dose-Response Relationship, Drug; D005615:Freezing; D022781:Hepatocytes / Q000378:metabolism*; D006706:Homeostasis; D008055:Lipids / Q000737:chemistry; D021962:Membrane Microdomains / Q000737:chemistry* / Q000378:metabolism; D017686:Oncorhynchus mykiss; D017434:Protein Structure, Tertiary; D015398:Signal Transduction; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature
chemical_list: D008055:Lipids; D002784:Cholesterol