Biomaterial Database

Ultrastructural aspects of activation and contraction of vascular smooth muscle. 1976

A P Somlyo, and A V Somlyo

Ultrastructural studies of potential intracellular calcium storage sites and of the organization of contractile proteins in vascular smooth muscle are reviewed. The sarcoplasmic reticulum (SR) is a system of closed tubules present in every smooth muscle examined. The volume of the SR varies in different smooth muscles (from approximately 2.0 to 7.5% of cytoplasmic volume) and correlates with the ability of a given smooth muscle to contract in calcium-free media. The SR accumulates the divalent cation strontium and forms couplings with the surface membrane. Mitochondria are other potential sites of calcium accumulation in vascular smooth muscle, as indicated by the respiration supported accumulation of calcium (with a Km of approximately 17 muM) by isolated mitochondria and by the energy dependent accumulation of barium by mitochondria in situ. The presence of barium in mitochondrial granules in tissues contracted with barium and the presence of strontium and calcium in appropriately incubated preparations have been verified with electron probe microanalysis. Calcium has also been demonstrated in mitochondrial granules in frozen dried cardiac muscle sections and in cultured vascular smooth muscle cells. This technique appears suitable for eventual quantitation of mitochondrial calcium content in vascular and other smooth muscles. Thin (actin, 50-80 A), thick (myosin, approximately 155 A), and intermediate (approximately 100 A) filaments are present in suitably fixed vascular smooth muscle. In rabbit portal anterior mesenteric vein intermediate high voltage stereo electron microscopy shows the myosin filaments to be tapered and approximately 2.2 mum long: significantly longer than the myosin filaments in vertebrate striated muscle. Actin filaments insert on dense bodies. The ultrastructural findings are compatible with physiological evidence suggesting the contributions of intracellular organelles to the regulation of cytoplasmic free calcium levels and the operation of a sliding filament mechanism of contraction in vertebrate smooth muscle.

UI	MeSH Term	Description	Entries
D008642	Mesenteric Veins	Veins which return blood from the intestines; the inferior mesenteric vein empties into the splenic vein, the superior mesenteric vein joins the splenic vein to form the portal vein.	Mesenteric Vein,Vein, Mesenteric,Veins, Mesenteric
D008931	Mitochondria, Muscle	Mitochondria of skeletal and smooth muscle. It does not include myocardial mitochondria for which MITOCHONDRIA, HEART is available.	Sarcosomes,Mitochondrion, Muscle,Muscle Mitochondria,Muscle Mitochondrion,Sarcosome
D009119	Muscle Contraction	A process leading to shortening and/or development of tension in muscle tissue. Muscle contraction occurs by a sliding filament mechanism whereby actin filaments slide inward among the myosin filaments.	Inotropism,Muscular Contraction,Contraction, Muscle,Contraction, Muscular,Contractions, Muscle,Contractions, Muscular,Inotropisms,Muscle Contractions,Muscular Contractions
D009130	Muscle, Smooth	Unstriated and unstriped muscle, one of the muscles of the internal organs, blood vessels, hair follicles, etc. Contractile elements are elongated, usually spindle-shaped cells with centrally located nuclei. Smooth muscle fibers are bound together into sheets or bundles by reticular fibers and frequently elastic nets are also abundant. (From Stedman, 25th ed)	Muscle, Involuntary,Smooth Muscle,Involuntary Muscle,Involuntary Muscles,Muscles, Involuntary,Muscles, Smooth,Smooth Muscles
D002118	Calcium	A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol Ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes.	Coagulation Factor IV,Factor IV,Blood Coagulation Factor IV,Calcium-40,Calcium 40,Factor IV, Coagulation
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D001158	Arteries	The vessels carrying blood away from the heart.	Artery
D012519	Sarcoplasmic Reticulum	A network of tubules and sacs in the cytoplasm of SKELETAL MUSCLE FIBERS that assist with muscle contraction and relaxation by releasing and storing calcium ions.	Reticulum, Sarcoplasmic,Reticulums, Sarcoplasmic,Sarcoplasmic Reticulums