Identification of lipids as the main component of skeletal muscle Z-discs.
The existence of lipids in Z-discs of the vertebrate skeletal muscle was suggested by the results of microscopy using rhodamine 6G reagent, a fluorescent probe. After removal of lipids by treatment of myofibrils with 0.5% Trition X-100, intact configurations of Z-filaments composed of alpha-actinin were clearly visible under an electron microscope. These findings indicated that lipids were amorphous-matrix materials of the Z-disc. Lipids were proved to be the main component of Z-discs by their extraction from I-Z-I brushes with a mixture of methanol and chloroform and by analysing them. The total amount of lipids in Z-discs exceeded that of alpha-actinin and varied from 2.4 to 7.1 g per 100 g of myofibrillar proteins depending on the phenotype of skeletal muscle. The sum of the amounts of lipids and alpha-actinin was 4.5 g per 100 g of myofibrillar proteins in chicken pectoralis profundus muscle (fast type), while it was 10.1 g in chicken soleus muscle (slow type). Lipid classes were phospholipids, triacylglycerols, cholesterol and free fatty acids. Since the lipids extracted from I-Z-I brushes were hardly contaminated with those from the sarcoplasmic reticulum and mitochondria, their amounts and classes were considered to be characteristic of Z-discs. The lipids probably cement neighbouring Z-filaments electrostatically, reinforce the Z-disc structure, and play an important role in the force transmission of skeletal muscle myofibrils.
Takahashi
K
K
Department of Animal Science, Faculty of Agriculture, Hokkaido University, Sapporo, Japan.
Shimada
K
K
Ahn
D H
DH
Ji
J R
JR
D000185:Actinin / Q000032:analysis / Q000648:ultrastructure; D000818:Animals; D002417:Cattle; D002645:Chickens; D008055:Lipids / Q000032:analysis*; D008297:Male; D018482:Muscle, Skeletal / Q000737:chemistry / Q000648:ultrastructure; D009210:Myofibrils / Q000737:chemistry / Q000648:ultrastructure; D010369:Pectoralis Muscles / Q000737:chemistry / Q000648:ultrastructure; D010743:Phospholipids / Q000032:analysis; D011817:Rabbits; D012518:Sarcomeres / Q000737:chemistry* / Q000648:ultrastructure; D013552:Swine
D008055:Lipids; D010743:Phospholipids; D000185:Actinin