Smooth muscle fiber, structure

Figure 3.11. Structure of uterus. The uterus contains two layers the endometrium and the myometrium. Endometrium contains columnar epithelium, lamina propria, uterine glands, and arteries. Myometrium contains smooth muscle fibers, interstitial collagen, and arteries.

Palytoxin (PTX) is one of the most potent marine toxins known and the lethal dose (LD q) of the toxin in mice is 0.5 Mg/kg when injected i.v. The molecular structure of the toxin has been determined fully (1,2). PTX causes contractions in smooth muscle (i) and has a positive inotropic action in cardiac muscle (4-6). PTX also induces membrane depolarization in intestinal smooth (i), skeletal (4), and heart muscles (5-7), myelinated fibers (8), spinal cord (9), and squid axons (10). PTX has been demonstrated to cause NE release from adrenergic neurons (11,12). Biochemical studies have indicated that PTX causes a release of K from erythrocytes, which is followed by hemolysis (13-15). The PTX-induced release of K from erythrocytes is depress by ouabain and that the binding of ouabain to the membrane fragments is inhibited by PTX (15). 

When solutions of directly acting choUnomimetics are applied to the eye (i.e., conjunctival sac), they cause contraction of the smooth muscle in two important structures, the iris sphincter and the ciliary muscles (Fig. 12.3). Contraction of the iris sphincter decreases the diameter of the pupil (miosis). Contraction of the circular fibers of the ciliary muscle, which encircles the lens, reduces the tension on the suspensory ligaments that normally stretch and flatten the lens, allowing the highly elastic lens to spontaneously round up and focus for near vision (accommodation to near vision). 

When I started as a novice in the field of cardiac electrophysiology, the dogma was that gap junctions are specialized membrane structures present in the cardiac and smooth muscle of vertebrates where they serve to propagate the action potential from cell to cell. Purkinje fibers and muscular trabeculae were the preferred cardiac preparations. These multicellular preparations were suitable to perform cable analyses and diffusion studies. At that time, my mentor, Silvio Weidmann, had already accomplished his elegant functional studies. 

The bronchus is a tubular structure that brings air into the alveoli. It is lined with pseudostratified columnar epithelium surrounded by a thin lamina propria containing fine collagen and elastic fibers. A thin layer of smooth muscle surrounds the lamina propria. Glands are found in the submucosa and hyaline cartilage and the pulmonary arteries are found in the outer layer (adventitia). 

Blood vessels include capillaries, arterioles, arteries, and veins. Each of these structures is composed of three layers the intima, media, and adventitia (Figure 3.12). For example, in elastic arteries the wall consists of an intimal layer containing endothelial cells and connective tissue a media containing smooth muscle cells, collagen, and elastic fibers and an adventitia containing collagen fibers, nerves, and blood vessels. In cross-section,... 

Elastin, a stmctural protein with mbber-like elastic properties. It is the main component of the elastic yellow connective tissue occurring, e.g., in the lungs and aorta. The amount of elastin is rather low in the inelastic white connective tissue of tendons. Elastin consists of 850-870 aa with a high content of Gly (27%), Ala (23%), Val (17%), and Pro (12%). It forms a three-dimensional network of fibers crosslinked by desmosine, lysinonor-leucine, and isodesmosine. It has been reported that elastin has an unanticipated regulatory function during arterial development, controlling the proliferation of smooth muscle and stabilizing arterial structure [L. Robert, W. Hornebeck (Eds.), Elastin and Elastases, Volume 1, CRC Press, Boca Raton, EL, 1989 D. R. Eyre et al, Annu. Rev. Biochem. 1984, 53, 717 D. Y. Li et al., Nature 1998, 393, 276]. 

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