| Zdroj: |
Journal of Experimental Biology; May2003, Vol. 206 Issue 10, p1657, 11p, 5 Black and White Photographs, 1 Diagram, 1 Chart, 18 Graphs |
| Abstrakt: |
Rafts are cholesterol- and sphingolipid-enriched microdomains of the plasma membrane (PM) that organize many signal transduction pathways. Interactions between cholesterol and saturated lipids lead to patches of liquid-ordered membrane (rafts) phase-separating from the remaining PM. Phase behavior is temperature sensitive, and acute changes in temperature experienced by poikilotherms would be expected to perturb raft structure, necessitating an acclimatory response. Therefore, with thermal acclimation, we would expect compositional changes in the raft directed to offset this perturbation. Using differential and density gradient centrifugation, we separated PM from the livers of rainbow trout acclimated to 5°C and 20°C into raftenriched (raft) and raft-depleted PM (RDPM). Compared with RDPM, the raft fractions were enriched in cholesterol, the β[sub 2]-adrenergic receptor and adenylyl cyclase, which are commonly used markers for this microdomain. Furthermore, cholesterol was enriched in all fractions from warm- compared with cold-acclimated animals, but this increase was 3.4 times greater in raft than in PM. We developed a novel approach for measuring membrane molecular interaction strength (and thus the tendency to stabilize raft structure) based on the susceptibility of membranes to detergent. Specifically, studies with model vesicles demonstrated that the capacity of a membrane to accommodate detergent prior to solubilization (saturation point) was a good index of this property. The saturation point of the isolated membrane preparations was temperature sensitive and was significantly different in 5°C- and 20°C-acclimated RDPM when assayed at 5°C and 20°C, respectively. By contrast, this comparison in rafts was not significantly different, suggesting compensation of this property. These data suggest that compositional changes made in the PM during thermal acclimation act to offset thermal perturbation of the raft but not the RDPM... [ABSTRACT FROM AUTHOR] |
