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Showing papers on "Cellular compartment published in 1974"


Journal ArticleDOI
TL;DR: In this article, the authors demonstrate the ultrastructural distribution of calcium in smooth muscle cells of the guinea pig taenia coli using a precipitation method with potassium oxalate.
Abstract: In order to demonstrate the ultrastructural distribution of calcium in smooth muscle cells of the guinea pig taenia coli a precipitation method with potassium oxalate has been used. In addition, morphometric assessment (“stereology”) of cell components and direct quantitative estimation of calcium content in isolated subcellular fractions by atomic absorbtion analyses were carried out. After oxalate treatment smooth muscle cells show four major and distinct sites of calcium oxalate deposition: sarcoplasmic reticulum, mitochondria, cell boundaries (sarcolemma, surface microvesicles) and nucleus. Calcium oxalate deposits were frequently found at the level of close associations formed by different cell organelles. Correlating the morphometric analysis of electron micrographs with microchemical measurements of calcium in isolated subcellular fractions an estimation of calcium content in each cell component of one smooth muscle cell was performed. The nucleus has a significantly higher calcium content than that of any other cellular compartment, but the mitochondria are the main calcium-storage sites of smooth muscle cytoplasm. The highest calcium concentration was found in mitochondria. Although the amount of calcium stored in the sarcoplasmic reticulum represents only about a quarter of that accumulated in mitochondria, around 20% might be enough to produce contraction. On the other hand, the surface microvesicles may accommodate the entire amount of calcium translocated during activity. Functional implications of these findings in relation to the contraction-relaxation cycle are considered and the possible role of the surface microvesicles is discussed.

84 citations



Journal ArticleDOI
TL;DR: Increased proliferation in the crypts during recovery after low radiation doses resulted in a marked decrease in both crypt and villus cells of activity of α-glucosidase, and the germ-free state of the intestine also significantly influences the pattern of α, which has little influence on the other enzymes tested.
Abstract: The activity of a number of enzymes involved in carbohydrate metabolism was measured in different cellular compartments of the intestinal epithelium by microchemical techniques. The enzyme activities were related to different cell positions along crypt and villus and to cell age. Enzyme activities in proliferating, differentiating and functional cell compartments of the intestine of normal rats were compared with those in which the cell kinetics had been modified. The effect of increased proliferative activity within the crypt of normal animals was studied in the intestine during recovery after low radiation doses. The effect of increased life-span was investigated in germ-free animals. The specific activity of α-glucosidase, present in microvilli, was found to increase considerably during cell differentiation and subsequent cell migration along the villus. Its specific activity remained unchanged in isolated intestinal loops deprived of dissaccharide substrate for 6 weeks. Lactate dehydrogenase and, to a...

30 citations


Journal ArticleDOI
TL;DR: The membrane system is made up of the nuclear envelopes, rough and smooth endoplasmic reticulum, Golgi apparatus and plasmalemma and it has been shown that the matrix polysaccharides of the wall are formed within the membranes and that the pattern of synthesis of these polymers changes during differentiation of the cells.
Abstract: The membrane system is made up of the nuclear envelopes, rough and smooth endoplasmic reticulum, Golgi apparatus and plasmalemma. Interconnexions between the various parts of the system are shown and these probably represent a flow of membrane from the endoplasmic reticulum through the Golgi apparatus to the plasmalemma. Membrane fractions have been isolated from broken cells and their function in the synthesis of polysaccharides established. It has been shown that the matrix polysaccharides of the wall (pectic substances and hemicelluloses) are formed within the membranes and that the pattern of synthesis of these polymers changes during differentiation of the cells. Cellulose microfibrils are probably synthesized at the plasmalemma which is formed by incorporation of membrane bounded vesicles from the Golgi apparatus. Thus the assembly of the polymers takes place either when the membrane is within the cytoplasm or when it is incorporated as the plasmalemma of the cell.

24 citations