Lipid phase of transverse tubule membranes from skeletal muscle. An electron paramagnetic resonance study

Abstract

The lipid phase of transverse tubule membrane was probed with a variety of fatty acid spin labels. The motion of the probe increased as the distance between the spin label and polar head group increased, in agreement with results reported in other membranes. The value of the order parameter at 37 degrees C for a fatty acid spin label containing the label attached to its fifth carbon atom was closer to values reported for bacterial membranes than to the lower values reported for other mammalian membranes. Order parameters for spin labels containing the label nearer to the center of the bilayer were closer to the values reported in other mammalian membranes than to values reported for bacterial membranes. These results indicate that the lipid segments in the vicinity of the polar head group, and less so those near the center of the bilayer, are motionally more restricted in transverse tubules than in other mammalian membranes. In particular, the lipid phase of the transverse tubule membrane is less fluid than that of the sarcoplasmic reticulum membrane. A possible role of the high cholesterol content of transverse tubules in generating the lower fluidity of its lipid phase is discussed.

The cholesterol-lowering agent methyl-β-cyclodextrin promotes glucose uptake via GLUT4 in adult muscle fibers and reduces insulin resistance in obese mice

“…Earlier reports indicate that mammalian T-tubule membranes are highly enriched in cholesterol compared with the sarcolemma (49,56). This feature likely contributes to the unusual physical properties of the T-tubule membrane system, which in its low fluidity at 37°C resembles more the membrane properties of a halophilic archaebacteria than those of other mammalian membranes (21). In response to insulin, the GLUT4 transporters translocate to the sarcolemma (46) and especially to the T-tubule system (38), a process that likely occurs in the cholesterol-enriched T-tubule lipid environment.…”

“…Biochemical and structural studies have indicated that the T-tubule and the surface plasma membrane of mammalian skeletal muscle differ in lipid composition, with fourfold higher cholesterol content in the T-tubules relative to the plasma membrane (34,49,56). At physiological temperature, the lipid phase of T-tubules is significantly less fluid than in most mammalian plasma membranes (21), a feature that may arise from its high cholesterol content. Previous reports indicate that feeding both mice and Ossabaw swine a high-fat diet (HFD) increases cholesterol levels in skeletal muscle plasma membranes (19).…”

Common structural domains in the sarcoplasmic reticulum Ca-ATPase and the transverse tubule Mg-ATPase.

“…It is not known what role, if any, the TT Mg-ATPase plays in excitation-contraction coupling; however, it is quite interesting not only that the Mg-ATPase is structurally related to the Ca-ATPase, but that the Mg-ATPase displays such significantly different catalytic properties compared with the Ca-ATPase. Although the TT Mg-ATPase is glycosylated, has a more acidic isoelectric point (34), and is embedded in a substantially different lipid environment compared with the SR Ca-ATPase (15,20,43), it is possible that the Mg-ATPase and the SR Ca-ATPase are products of the same gene or gene family, and that, as a result of selective co-or posttranslational processing, the Mg-ATPase is routed into the T tubules rather than into the SR membrane during membrane assembly. Further, as a result of the glycosylation itself, or because of the different lipid environment in which it resides, the Mg-ATPase may exhibit completely different catalytic properties.…”

Cholesterol removal from adult skeletal muscle impairs excitation–contraction coupling and aging reduces caveolin-3 and alters the expression of other triadic proteins

“…Reports regarding T-tubule lipid composition from vertebrate muscles have revealed some unusual features, characterized by high cholesterol and sphingolipid contents (Lau et al, 1979 ; Rosemblatt et al, 1981 ; Hidalgo et al, 1986 ), which endow T-tubule membranes with an unusually rigid lipid environment similar to that present in thermophilic bacteria (Hidalgo, 1985 ). The high cholesterol and sphingolipid levels of T-tubule membranes, which are significantly higher than those present in plasma membranes, are comparable to those reported in lipids rafts and caveolae (Smart et al, 1999 ).…”