Atmospheric chemistry of CF3CH=CH2 and C4F9CH=CH2: products of the gas-phase reactions with Cl atoms and OH radicals.

FTIR-smog chamber techniques were used to study the products of the Cl atom and OH radical initiated oxidation of CF3CH=CH2 in 700 Torr of N2/O2, diluent at 296 K. The Cl atom initiated oxidation of CF3CH=CH2 in 700 Torr of air in the absence of NOx gives CF3C(O)CH2Cl and CF3CHO in yields of 70+/-5% and 6.2+/-0.5%, respectively. Reaction with Cl atoms proceeds via addition to the >C=C< double bond (74+/-4% to the terminal and 26+/-4% to the central carbon atom) and leads to the formation of CF3CH(O)CH2Cl and CF3CHClCH2O radicals. Reaction with O2 and decomposition via C-C bond scission are competing loss mechanisms for CF3CH(O)CH2Cl radicals, kO2/kdiss=(3.8+/-1.8)x10(-18) cm3 molecule-1. The atmospheric fate of CF3CHClCH2O radicals is reaction with O2 to give CF3CHClCHO. The OH radical initiated oxidation of CxF2x+1CH=CH2 (x=1 and 4) in 700 Torr of air in the presence of NOx gives CxF2x+1CHO in a yield of 88+/-9%. Reaction with OH radicals proceeds via addition to the >C=C< double bond leading to the formation of CxF2x+1C(O)HCH2OH and CxF2x+1CHOHCH2O radicals. Decomposition via C-C bond scission is the sole fate of CxF2x+1CH(O)CH2OH and CxF2x+1CH(OH)CH2O radicals. As part of this work a rate constant of k(Cl+CF3C(O)CH2Cl)=(5.63+/-0.66)x10(-14) cm3 molecule-1 s-1 was determined. The results are discussed with respect to previous literature data and the possibility that the atmospheric oxidation of CxF2x+1CH=CH2 contributes to the observed burden of perfluorocarboxylic acids, CxF2x+1COOH, in remote locations.

Collagen fibril diameter in the common carotid artery of the rat.

The diameter of collagen fibrils has been measured in electron micrographs of the tunica media and adventitia of the common carotid artery of 14 rats (19,262 counts). The fibrils of the media were measured in each of its three interlamellar spaces. The mean fibril diameters in the innermost space and the middle space are not different (29.7 and 30.7 nm). However, the diameter of the fibrils is larger in the outermost space of the media than in the inner two spaces. With a diameter of 37.4 nm, the difference from the other medial spaces is highly significant. The adventitial fibril diameter of 66.1 nm is significantly different from the values for any of the medial spaces. The only cells present in all three spaces of the tunica media of the rat common carotid artery are smooth muscle cells, which presumably synthesize similar procollagen throughout the media. The larger diameter collagen fibrils of the outer interlamellar space may be an adaptation to greater mechanical stress in the outer media, or possibly the activity of the fibroblasts in the adjoining adventitia may affect fibril growth in this space of the media.

Ultrastructure of conjunctival epithelium replacing corneal epithelium.

After corneas of mice had been totally denuded of their epithelium by the application of n-heptanol, the new epithelium which grew over the corneas was studied by electron microscopy at intervals up to 7 months. The purpose was to compare the basal attachment of the new cells, derived from conjunctiva, with that of true corneal epithelial cells growing on the same type of substratum, and studied previously. Goblet cells appeared after 2 weeks amid the squamous type of epithelial cells which had resurfaced the cornea in about 1 week. Goblet cells increased up to at least 6 weeks, but had decreased by 3 months. They persisted, however, for the entire 7 months of the study. Goblet cells had only a small area of contact with the basal lamina, and they had few desmosomes or hemidesmosomes. Basal cells of the squamous type had complex features of their basal attachment quite different from those of normal or repairing corneal epithelial cells studied previously. Flat cytoplasmic extensions of squamous cells underlay most of the goblet cell basal pole which therefore had only a small area on the basal lamina. Numerous filaments inserted into desmosomes and hemidesmosomes of squamous cells, and prominent bundles of these filaments lay just above the basal plasma membrane. They were orientated parallel to the radial axis of the cornea. Closely spaced corrugations of the basal plasma membrane were also orientated in this axis, as well as rows of hemidesmosomes. Even after a period of 7 months, the morphological features of conjunctival cells did not come to resemble those of normal corneal epithelium. The radial arrangement of fibers, hemidesmosome rows, and corrugations is interpreted as a reflection of the continued centripetal migration of the epithelium.

Ultrastructural features of rectal epithelium of the mouse during the early phases of migration to repair a defect.

Observations were made by scanning and transmission electron microscopy on the migrating epithelial cells of the mouse rectum at intervals up to 24 h after stripping the epithelium off the mucosa. Resurfacing of the denuded basal lamina proceeded by the centrifugal migration of the columnar cells of the crypts. Changes in these cells occurred very rapidly. In less than 20 min a flat leading lamella developed and extended out on the basal lamina. The leading lamella could be recognized easily in scanning electron micrographs by the absence of microvilli, although these were retained on the cell body, gradually getting less regular and sparser than normal. Many zeiotic blebs appeared on the free margin of these cells. The features of migrating epithelium which are displayed in the in vivo repair of rectal mucosa are shared with migrating epithelia cultured in vitro. Goblet cells appeared not to be active in resurfacing the lesions. They disappeared from the surface epithelium, but were evident again by 18 and 24 h. The method of producing these lesions can also be used to study the cells that are removed.

Measurement of centripetal migration of normal corneal epithelial cells in the mouse.

Fine punctate marks were made in normal corneas of mice using a needle rotating in a mixture of India ink and thorium dioxide. After 7 days, the marker was visible in the stroma and also in epithelial cells which had moved away from the stromal marks and towards the center of the cornea. The mean distance between these labels at the end of 7 days was 94 microns +/- 14 (SEM). The median distance migrated was about 17 microns per day. This figure represents the distance through which superficial and wing cells had migrated; the distance migrated by basal cells was not determined.

Ultrastructural characteristics associated with the anchoring of corneal epithelium in several classes of vertebrates.

The electron microscopic examination of the basal cells of corneal epithelium certain species of Mammalia, Avia, Reptilia, Amphibia and Pisces was directed particularly towards the hemidesmosomes. Sections cut normal to the basal lamina and sections cut parallel to it were studied in order to establish the number, shape and distribution of the hemidesmosomes. Four basic types of hemidesmosome distribution were recognised among a limited representation of the classes studied. (1) Linear chains of hemidesmosomes (Mammalia, Rana, Bufo). (2) Rosette arrangement of hemidesmosomes surrounding pockets of basal plasma membrane (Avia, Anolis, Xenopus). (3) Punctate hemidesmosomes with no arrangement (Thamnophis). (4) Absence of hemidesmosomes (Carassius). All animals showed a basal lamina, basal pinocytotic vesicles, anchoring filaments, tonofilaments, and interdigitating foot-processes. It is suggested that anchoring filaments deserve to be studied more thoroughly in certain other types of epithelia which do not have focal hemidesmosomes, but require firm anchorage to a basal lamina.

Behavior of vascular smooth muscle cells during repeated stretching of the substratum in vitro.

Smooth muscle cells derived from rat aortic media were established in subcultures and seeded from suspensions on smooth silicone rubber substrata in tissue culture flasks. Each flask contained two substrata, one stationary and one that was stretched and allowed to recoil at 15-s intervals. After 48 h or longer, the cells were fixed and their pattern on the 2 substrata examined by light or scanning electron microscopy. All stretched substrata showed 75% or more of cells lying within 45 degrees of a line drawn at right angles to the direction of stretch and recoil. Cells on the stationary substrata showed a random orientation. The results suggest that stretching of the internal elastic lamina by arterial pulsation may be a factor in creating the characteristic longitudinal orientation of smooth muscle cells that appear in the subendothelial space after injury, diffuse intimal thickening or atherosclerosis.

The influence of contact guidance on the orientation of colonies of subcultured vascular smooth muscle cells.

Subcultures of smooth muscle cells derived from rat thoracic aorta were grown on plane plastic substrata and on plastic substrata having ridges molded in them by a heated, ruled template. The cells were found to have a very high degree of contact guidance when distributed sparsely on the ridged substrata. When the cell density increased multilayered, elongated colonies formed. On plane substrata these were irregular, curved, and disposed in all directions. On the ridged substrata, however, the colonies were straight, evenly spaced, and positioned at right angles to the ridges.

Hemidesmosomes of normal and regenerating mouse corneal epithelium.

Hemidesmosomes of normal mouse corneal epithelium observed in tangential thin sections, occupy 14% of the basal plasma membrane. They consist of linear chains of densities with an orientation that is not random with respect to the radial axis of the cornea, tending to parallel it. During the repair of a small epithelial defect, cells of the corneal epithelium peripheral to the defect show chains of hemidesmosomes arranged parallel to the direction of migration of the epithelial sheet. This is parallel to the radius, like the orientation of the normal chains. Cells of the area that was denuded of epithelium, and is being resurfaced, show no hemidesmosomes. During repair of a large defect of the corneal epithelium hemidesmosomes are present on the cells covering the denuded area but they are small, few in number compared to the normal, and many are not arranged in chains. These small hemidesmosomes appear to be points of attachment of very fine basal filaments, possibly actin.

Comparison of the degree of contact guidance between tumor cells and normal cells in vitro.

A comparison was made between the degree of contact guidance produced by grooved or ridged substrata in cultures of normal mouse embryonic fibroblasts and in fibrosarcoma EMT6 cells or cells of a dibenzanthracene-induced fibrosarcoma. Normal mouse mammary epithelial cells were also compared with cells of C3HBA mammary tumor. All types of cell showed a highly significant orientation in the direction of the grooves or ridges, but there were significantly lower proportions of aligned tumor cells than of their normal counterparts. Fibroblasts showed more alignment than did normal mammary epithelial cells, and the sarcoma cells showed more alignment than did the C3HBA tumor cells. Scanning electron microscopy of cells growing on ridged substrata revealed that all types of cells adhere to the ridges rather than to flat areas between ridges. The difference between normal and malignant cells appears to indicate a real difference in a behavioral characteristic, namely, that tumor cells are less responsive to the topographical features of the substratum that are their normal counterparts. The local infiltration of tissues by tumor cells is due to factors other than contact guidance, for it occurs in spite of their lower contact guidance compared to that of normal cells.