Surface Density Of Endoplasmic Reticulum Research Articles

Resolution effect on the stereological estimation of surface and volume and its interpretation in terms of fractal dimensions.

Estimating surface and volume density of subcellular membrane systems at different magnifications yield different results. As the magnification is increased from x 18,000 to x 130,000 the estimates of surface density of endoplasmic reticulum and inner mitochondrial membranes increase by a factor of 3, whereas that for outer mitochondrial membranes increase only by 20%. The estimate of volume density of endoplasmic reticulum also increases by a factor of 3. No further increase is observed at magnifications above x 130,000 which is therefore called critical magnification. The findings are interpreted on the basis of the concept of fractals proposed by Mandelbrot, and the fractal dimensions of the membrane systems considered are estimated. This can lead to the derivation of resolution correction factors which permit measurements obtained at any magnification to be converted to estimates at critical magnification. These findings may explain, at least in part, the large discrepancy in the estimates of the surface of cytomembranes found in the literature.

Variations cytoplasmiques dans l'épithelium pigmenté en fonction du cycle lumineux; observations préliminaires*

Cytochemical and stereological studies on frog (rana ridibunda) RPE during a 12 hrs dark/12 hrs light cycle. Rapid changes in surface density of endoplasmic reticulum and in volume density of myeloid bodies shortly after the onset of light. Numerical and volumetric density of microperoxisomes increased after the fourth hour of light, with a concomitant decrease in the volume of phagosomes.

Environmentally induced changes in mitochondria and endoplasmic reticulum of Saccharomyces carlsbergensis yeast.

The effects of culture environment on the volume density and surface density of mitochondria and endoplasmic reticulum in a facultative yeast were studied. When compared with cells grown aerobically on a nonrepressive substrate, cells grown in the absence of oxygen showed a sharp reduction in both volume density of mitochondria and surface density of the inner mitochondrial membrane (imm) in the remaining mitochondrial profiles. Use of fermentable (repressive) substrates under aerobic conditions restricted the volume density of mitochondria to a much greater extent than the surface density of imm. The range of mitochondrial volume densities in these experiments was 4-11%. Surface density of endoplasmic reticulum (ER) was sensitive to growth rate and in particular to changes in oxygen tension, showing large fluctuations during both anaerobic and aerobic adaptation. These fluctuations in ER are discussed in relation to the known role of this organelle in lipid metabolism.

Ultrastructural alterations produced in rat adrenal by aminoglutethimide. A stereologic and cytochemical study.

The ultrastructure of the zona fasciculata cells of the rat adrenal was examined after aminoglutethimide (Elipten) administration. Eight male adult rats were injected with 20-25 mg/kg per day; five control rats were injected with an equal volume of saline. The rats were sacrificed after 7 days of treatment and adrenal pieces were processed for morphological and cytochemical electron microscopic studies. The volume density and surface density of the cell organelles of treated and control animals were determined by the stereologic methods of Weibel et al. and the values were statistically compared. The identification of cholesterol was carried out in treated and control animals by the Scallen and Dietert method. In Elipten treated rats there was a significant decrease in the volume fraction and surface density of mitochondria, a significant increase in the volume fraction and surface density of endoplasmic reticulum and the Golgi complex. The volume fraction of lipid droplets was increased significantly; their number and surface density were also increased. Peroxisomes were more numerous than in controls but their small number and size did not allow a stereologic study. A greater amount of cholesterol was visible in treated than in control rats, namely in the Golgi complex. The number of lysosomes with acid phosphatase activity was not increased in treated rats when compared with controls. The variations observed were interpreted as due to the inhibition of the conversion of cholesterol to pregnenolone, a step of the steroidogenic pathway. (Endocrinology90: 444, 1972)