摘要:

Age-related cataract formation in man can be documented with slit and retroillumination photographs. With digitization and image analysis of such photographs a cataract may be characterized by a frequency distribution of picture elements over a 255 step gray scale spectrum. Transition from a clear to a cataractous lens may be manifested as a change from a unimodal, Gaussian to a multimodal, non Gaussian frequency distribution respectively. How should one compare and contrast these two distributions, so to accurately describe the extent and significance of a change in lens opacification?The in vitro system of cold cataract formation in the rabbit lens was used as a model of the much slower process of age-related cataract formation in man. As in the human lens undergoing progressive opacification, the frequency distribution (number of pixels vs. intensity of gray) for a digitized image of a clear lens at 26°C is unimodal and Gaussian; that of a fully developed cold cataract at 10°C is multimodal and non-gaussian. In spite of the increasing multimodality of the frequency distribution as the temperature dropped and the cataract grew in density and size, the mean gray density proved to be a valid and useful measure to characterize the distribution and to compare different unaligned images. The Wilcoxon Rank Sum Test proved to be useless in comparing the frequency distributions from cataract images because it proved to be too sensitive to subtle changes in the degree of opacification. Anomalous behavior of the opacification process-i.e. clarification as well as opacification of the lens during cold cataract formation caused all pairs to appear statistically significantly different when in appearance there was no difference. The mean of the frequency distribution is less sensitive to this anomalous behavior and is useful as a comparative index. The method of calculating the threshold of significant change in the mean density of a cataract image is presented.

ISSN:0271-3683    

DOI:10.3109/02713688809047027

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

The microenvironments of tryptophan residues in bovineα-,βH-,βIs. andγ-crystallins have been examined using acrylamide and KI quenching of fluorescence. From a consideration of the differential effects of the two quenchers, the quenching efficiencies and spectral changes, it was possible to distinguish tryptophans in different environments and to assign these to specific residues in the sequence.Two classes of tryptophan were identified inγ-crystallin, one buried and one moderately accessible. The buried class contained tryptophans 42A and 125 which lie in the angles of the wedge-shaped domains of the protein. These residues, which had emission maxima at 326 nm, were not accessible to quenching by iodide. The more accessible residues, emitting at 334 nm, corresponded to tryptophans 64 and 148 which are in the widest part of the wedge-shaped subunit and close to the surface of the protein.The twoβ-crystallins were virtually indistinguishable. They contained two buried tryptophans, probably residues 58 and 150, and three close to the surface, residues 81, 84 and 166. The quenching efficiencies for these two classes were lower than those observed withγ-crystallin. Since the three-dimensional structures of theβ- andγ-crystallins are probably very similar, this suggests that the polymeric nature of theβ-crystallins is responsible for the decreased accessibility of the tryptophans to the quenchers.α-crystallin demonstrated unusually high static quenching which made it difficult to distinguish different classes of tryptophan. Nevertheless, it is probable that the tryptophan found in position 60 of the B chain is in a different microenvironment from that in position 9 of both chains.The results presented differ from other observations in the literature. Possible reasons for this are discussed.

ISSN:0271-3683    

DOI:10.3109/02713688809047028

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

Adult albino mice received tritiated thymidine either injected subcutaneously (333μCi) every 6 hours for up to 36 hours, or administered in their drinking water for up to 74 days (about 45μCi/day). Tissue sections were examined with autoradiography to determine the distribution of the label. Animals receiving subcutaneous injections showed no labeled cells in the choroid plexus epithelium and only one cell of 6600 cells counted in the ciliary epithelium was labeled. Animals exposed to the isotope in their drinking water for 74 days showed considerable uptake of label in hepatocytes (15%) and cortical kidney tubules (17%), whereas ciliary and choroid epithelia showed very low uptake at 0.25% and 0.01%, respectively. The data show that the ciliary and choroid epithelia have a very slow turnover rate compared to other slow renewing tissues, and, under normal conditions, these tissues are not renewed in the animal's adult life span.

ISSN:0271-3683    

DOI:10.3109/02713688809047029

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

This study confirms the feasibility of monitoring corneal metabolism of an amino acid using high resolution NMR spectroscopy. Alanine metabolism to lactate was detected in intact, freshly isolated rabbit corneas. Progressively decreasing aianine resonances were noted after 4–5 hours of incubation while increasing amounts of lactate were detected. No similar signal was noted in de-epithelialized tissue.This study demonstrates the ability of corneal epithelium to utilise aianine as a metabolic substrate. This technique may be useful to determine the essential amino acids and their optimal concentrations necessary to maintain corneal viability during storage.

ISSN:0271-3683    

DOI:10.3109/02713688809047030

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

Photodamage to lens hexokinase has been investigated by exposing the lenses of rat, rabbit and calf eyes to 300 nm irradiation. Hexokinase activity was diminished by 15.9%±5.4 and 23.4%±5.0 upon irradiation of the isolated rat lens for 1 and 2 hours respectively. Irradiation of the whole eye for 2 hours resulted in hexokinase deactivation of 13.6%±5.8 and 19.2%±6,2 for rat and rabbit lens homogenates and 55%±7 for calf lens capsule plus epithelium. Enzyme deactivation was prevented when the isolated lens was irradiated with the vitreous attached. Glucose, catalase or ascorbate added to the medium prior to irradiation, each had a protective effect on hexokinase deactivation. The results are consistent with a mechanism in which photochemical generation of active species of oxygen, via the photosensitizing action of tryptophan photoproducts, plays a significant role in enzyme deactivation.

ISSN:0271-3683    

DOI:10.3109/02713688809047031

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

The temporal frequency components in the steady-state visual evoked response (VEP) depend on the method of stimulus presentation; a first harmonic is generated to“on-off”patterns while a second harmonic occurs to both“on-off”and counterphase patterns. This study examined the VEP response in humans to patterns between these two extremes. In the main experiment, a 1 c/d sinusoidal grating was phase reversed sinusoidally at 8Hz. The DC offset, however, was adjusted such that two different levels of peak contrast occurred during a temporal cycle. Within this context, a counterphase pattern would represent complete contrast symmetry and an“on-off”pattern would represent maximum contrast asymmetry during a temporal cycle. With this manipulation, the a) integrated luminance change; b) local luminance change; and c) total contrast remained constant. Only mean contrast varied. The amplitude of the first harmonic strongly depended on mean contrast. The amplitude and phase of the second harmonic, however, changed little across experimental conditions suggesting a dependence on one or more of the above three listed stimulus attributes which remained constant. In a supplementary experiment, this phase constancy was confirmed using other temporal frequencies.

ISSN:0271-3683    

DOI:10.3109/02713688809047032

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

We studied 8 soft contact lenses from asymptomatic wearers by means of an immuno-cytochemical method, in transmission electron microscopy. In particular, the presence of IgA, IgG, IgE, C1qcomplement fraction within the surface deposits was analyzed.All the lenses were found positive for the immunoglobulins and the C1q, being the tarsal side more heavily coated than the corneal one. IgA was the predominant Ig, followed by IgG, IgE, and C1qin this descending order. New, never worn lenses were found completely negative for any of the proteins under investigation.We conclude that the Igs come from the tear fluid and speculate about the C1qas a possible sign of involvement of the host immuno-defense mechanism against the prosthesis.

ISSN:0271-3683    

DOI:10.3109/02713688809047033

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

Inhibition of ciliary process adenylate cyclase was studied on rabbit membrane preparations. When considered individually, epinephrine, GTP and NaCl did not inhibit adenylate cyclase activity. On the other hand, when present together, epinephrine, GTP (10–5M) and NaCl (200 mM) acted synergistically to cause a 27 % inhibition of basal activity. A similar inhibition was observed with 1-norepinephrine. Clonidine and BHT 920, two alpha2-agents were found to be partial agonists causing 63% and 82% as much inhibition as epinephrine. Phenylephrine, an alpha1-agonist did not inhibit adenylate cyclase activity at concentrations up to 10–4M. Yohimbine and phen-tolamine prevented the inhibition of adenylate cyclase by epinephrine, while prazosin was ineffective. Alpha2-receptor selectivity in rabbit ciliary processes and their negative coupling to an adenylate cyclase via a NaCl-dependent GTP binding protein, Ni, is thus well established.

ISSN:0271-3683    

DOI:10.3109/02713688809047034

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

Extracellular matrix and basement membrane proteins are important in promoting the adhesion and migration of various cell types. Laminin and type IV collagen are found in basement membranes throughout the body while fibronectin is found associated with some basal lamina, in loose connective tissue, and in all body fluids. In the current study fibronectin, laminin, and type IV collagen were assessed to determine their effect on the adhesion and migration of dissociated rabbit epithelial cells. In a kinetic analysis fibronectin was found to be the most effective of the three proteins in promoting cell adhesion. Cell adhesion promoted by fibronectin could be modulated by an arg-gly-asp-ser (RGDS) peptide, a sequence which is found within the fibronectin molecule. In dose-response experiments type IV collagen effectively promoted cell adhesion at concentrations as low as 4×10–16moles per well in 96 well tissue culture plates. Type IV collagen was the most effective protein tested in promoting chemotactic and haptotactic migration.These proteins, proteolytic fragments, and peptides derived from them, could prove useful as therapeutic agents, modifying corneal epithelial phenotypic behavior in wound healing, corneal transplantation and following ocular surgery or trauma.

ISSN:0271-3683    

DOI:10.3109/02713688809047035

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

Tissues maintained in vitro often undergo changes in the pattern of protein synthesis that result in the deposition of macromolecules quantitatively or qualitatively unrelated to those normally synthesized. In these preliminary studies, we modified published techniques to maintain adult and neonate rabbit corneas in vitro for 24 to 48 h. Measurements of corneal wet weight, and histologic and ultrastructural analyses were made to determine the success of maintaining rabbit corneas in culture. The results show that rabbit corneas can maintain normal corneal hydration and tissue structure for at least 48 h when incubated in Coon‘s modification of Ham’s F12, 5% fetal or newborn calf serum, 2 mM glutamine, and 2% chondroitin sulfate or 2% 50 kDa dextran sulfate at 37°C in a 5% CO2/air atmosphere. In addition, we confirmed previous observations that corneal explants must have a 1 to 2 mm rim of limbal sclera, and the organ placed in the culture dish with the epithelial side down to guard against damage and insure endothelial functioning. Normal ultrastructure of neonate rabbit cornea is also maintained when organ-cultured with these procedures. Moreover, neonate corneas continue to synthesize collagen in culture.

ISSN:0271-3683    

DOI:10.3109/02713688809047036

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor