Die Myofilamente glatter Muskulatur und ihr Verhältnis zu den Myofilamenten quergestreifter Muskulatur. Eine elektronenmikroskopische Studie an Muskelzellen der Weinbergschnecke

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Abstract
Smooth muscle cells of the edible snail are separated by a basal membrane from the collagenous fibroblast-containing ground substance of the connective tissue. The periphery of their sacroplasm contains tubules of sacro-plasmic reticulum 300 A in diameter, large-lumened vacuoles with very low electron density and a few mitochondria. The interior of the muscle cells is filled with myofilaments, apparently arranged randomly beside one another. Long sections through groups of filaments show cross striations with a periodicity of 220 A which corresponds somewhat to that of myofilaments of skeletal muscle. Most of the filaments are 190 A thick. In addition thinner myofilaments of about 130 A occur. Comparing the thickness of these with that of myofilaments previously known a geometric series with an increase of 2 is obtained for their diameters. This begins with filaments of about 30 A thickness and ends with filaments of about 260 A thickness. This astonishing result, in which the filament thickness of 190 A in the muscle studied here fits into a mathematical progression of diameter size, is discussed in detail with respect to a series of possible consequences and is considered an argument for a gradual increase of the thinnest filament units depending on the kind of muscle and the state of contraction.