摘要:

Chick lens fiber cell gap junctions were isolated to homogeneity by the urea-deoxycholate method, characterized ultrastructurally and biochemically, and their lipid composition determined by quantitative thin layer chromatography (TLC). The junctions were estimated to comprise about 52% of the lens fiber plasma membrane. Unlike the junctions of other organs, the lens gap junctions were found to contain sphingomyelin. The cholesterol/phospholipid molar ratio was 2.1 for total fiber membranes but 3.1 for the fiber gap junctions. The levels of major phospholipids in decreasing order were SPH, PC, PE, PI for fiber junctions and PE, SPH, PC, PI for total fiber membranes. The gap junctions were found to contain about 57% of the total fiber cholesterol and 53% of the total fiber sphingomyelin. The high cholesterol and sphingomyelin content suggests that lens fiber gap junctions constitute highly rigid membrane regions conferring significant constraints to the movement of their intramem-brane particles (connexons) in the plane of the membrane. The findings help to explain the resistance to the crystallization of their conne-xens, observed so far only in lens gap junctions.

ISSN:0271-3683    

DOI:10.3109/02713688208996357

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

Cytoskeletal and membrane proteins were isolated from respectively the urea-soluble and urea-insoluble fractions of the squid lens. The main cytoskeletal polypeptide has a molecular weight (63000) and an amino acid composition similar to those of vertebrate intermediate filament proteins, including mammalian lens vimentins. Intermediate filaments, and bundles thereof, were regenerated from the squid lens urea-soluble fraction upon removal of urea. The main membrane polypeptide of 140000 Mrhas an amino acid composition entirely different from that of the main intrinsic membrane protein of 26000 Mrwhich is found in all vertebrates. Although non-EDTA-extractable, the 140000 Mrsquid membrane polypeptide is best classified as extrinsic, since it has a high polarity (mainly acidic residues) and can be degraded completely upon trypsin treatment of squid lens membranes.

ISSN:0271-3683    

DOI:10.3109/02713688208996358

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

The study was designed to investigate the formation of mixed disulfides (PSSG) of protein and glutathione (GSH) in the lens. The possibility that oxidized GSH reacts with lens protein sulfhydryls was examined by incubating tritiated glutathione disulfide ([3H] GSSG) with a solution of dialyzed water-soluble bovine lens crystallins. Gel chromatography on a Sephacryl S-200 column showed that all crystallins have become labeled. The ratios of radioactivity incorporated into each cry stall in relative to the protein concentration (cpm/O.D. ratios) were 0.5, 6, 12 and 11 forα,βH,βL andγ-crystallins, respectively. When [3H] GSSG was covalently linked to and immobilized on derivatized agarose beads (Affi-Gel 10) and then treated with dialyzed lens crystallins part of the radioactivity was released from the gel. Most of the released radioactivity was associated with the protein and was not dialyzable but susceptible to removal by dithiothreitol or glutathione, indicating that it is linked to the protein as PSSG. Dialysis of [3h] PSSG against increasing concentrations of unlabeled GSSG or GSH showed that only GSH could effectively cause the release of radioactivity into the dialysis medium due to the formation of GSSG. It can be concluded that GSSG rather than GSH is involved in the formation of protein-glutathione disulfide and that such a reaction may retard or prevent protein aggregation due to the protein-protein disulfide bond formation that leads to lens opacification.

ISSN:0271-3683    

DOI:10.3109/02713688208996359

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

Lipid peroxidation has been shown to be involved in the pathogenesis of some types of cataract. The possibility of such a mechanism was investigated in Emory mouse cataract. Malondi aldehyde, a breakdown product of lipid peroxides, increased 4-fold in advanced cataract. Studies on cation transport revealed that in early cataract there was no alteration in permeability and active transport of cations. However, these functions were significantly altered in advanced cataract as evidenced by about 300% increase in cellular influx of22Na+(140 mM) and 50% fall in cellular uptake of86Rb+(5 mM). At this stage of cataract, the ouabain- inhibitable component of uptake of Rb+was drastically decreased, whereas the ouabain-resistant component was unchanged. The mannitol-space increased markedly with progression of cataract. Altered transport of cations in cataract was indicative of damaged membranes which may be due to peroxidation of unsaturated fatty acids in the lipid bilayers concomitant with oxidation of sulfhydryl groups of proteins of the plasma membrane. Superoxide dismutase, catalase and glutathione peroxidase, the defensive enzymes against reactive species of oxygen, were decreased 54%, 57% and 62% respectively in cataract, exposing the lens to oxidants such as O2−, H2O2, OH and1ΔgO2, which can initiate lipid peroxidation and/or oxidation of protein.

ISSN:0271-3683    

DOI:10.3109/02713688208996360

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

Rabbit lenses were incubated in organ culture with14C acetate for 3, 6, 12 and 20 hours and the nonsaponifiable fraction, composed primarily of sterols, was isolated. The incorporation of acetate into the nonnaponifiable fraction was linear for periods of 3 to 20 hours incubation. The nonsaponifiable fraction was subjected to thin-layer chromatography and 6 bands were observed. On the basis of Rfvalues, one band was tentatively identified as squa-lene, another as lanosterol and a third as a coholesterol-desmosterol mixture. The percentage of the radioactivity incorporated into the eholesterol-desmosterol band increased with incubation time. Conversely the percentage of the radioactivity incorporated into the squalene and lanosterol bands decreased with incubation time, indicating a precursor-product relationship.

ISSN:0271-3683    

DOI:10.3109/02713688208996361

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

The corneal epithelium of a fish is in direct contact with the aquatic environment and is a barrier to movement of ions and water into and through the cornea. This tissue layer is thus important in maintenance of corneal transparency. When the epithelium is wounded, its protective function is lost and corneal transparency remains compromised until the epithelial barrier is re-established. This study was undertaken to investigate the healing response of the fish cornea to epithelial abrasion. Wounds were stained with fluorescein and photographed during healing. Wound areas were measured by planimetry. The cornea of the sculpin, a marine teleost, becomes edematous after wounding and heals at 2.54 to 3.42 mm2/hr. Nonswelling corneas of the elasmobranchs—dogfish shark and skate—heal at 1.29 mm2/hr, respectively. The wounded eye of the rainbow trout, a freshwater teleost, is stressed by the low osmolality of the environment. Severe corneal edema and cataracts develop following epithelial wounding, and the cornea heals at 0.64 mm2/hr. Although the healing rates in teleosts differ from those in mammals, histology shows that the corneal healing mechanism is essentially the same in fish and mammals.

ISSN:0271-3683    

DOI:10.3109/02713688208996362

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

Lysophosphatidyl choline (LPC), which has been shown to be toxic to the lens in organ culture, is markedly elevated in uveitic eyes. These findings have led to the suggestion that LPC is an initiator of cataractogenesis in uveitis. We report here that a factor not considered by previous investigators, i.e. the presence of serum proteins, can modulate LPC toxicity in vitro. First, the toxicity of LPC to lens epithelial cells or to whole lens in organ culture was effectively neutralized by addition of serum or serum albumin to the test cultures, thus suggesting that the potential toxicity of the increased LPC in the uveitic eye might be neutralized by the concomitant increase in serum protein. Secondly, the susceptibility to LPC toxicity of lens epithelial cells was no greater than that of lymphocytes which are normally exposed to LPC levels higher than those in the uveitic eye.

ISSN:0271-3683    

DOI:10.3109/02713688208996363

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

Cataracts, inherited in an autosoraal dominant manner in New Zealand Romney sheep were first detected at 1 - 2 months of age as focal anterior and posterior cortical opacities. Within a short time these coalesced to form spoke-like patterns which gradually became more diffuse. Total lens opacity developed by 10 - 11 months of age. Congenital mature cataracts occurred in two lambs believed to be homozygous for the mutant gene and in these animals lens resorption later occurred.Histology showed that new lens fibres formed normally at the equator but then underwent progressive degenerative swelling and lysis. Cytoplasmic vacuolation of anterior epithelial cells was a notable feature and occurred apparently in response to adjacent cortical degeneration. Ultrastructurally these vacuoles were interpreted as dilations of endoplasmic reticulum but there were also a number of smaller vacuoles not lined by membrane. Anterior epithelial cells also underwent metaplasia, hyperplasia, and migration beneath the posterior capsule. Analyses of lenses reflecting different stages of cataracto-genesis showed a progressive increase in water, sodium and calcium ions with cataract development and a concomitant decrease in potassium and magnesium ions.

ISSN:0271-3683    

DOI:10.3109/02713688208996364

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

Although information is available on thein vit-roproperties of lens epithelia of young adult animals from several species, few, if any reports document the conditions required for the initiation and long-term culture of lens epithelium from animals beyond their medium life-span. We report here on the conditions required for the culture of lens cells from an 8 year old rabbit. New Zealand White rabbits have a median life-span of approximately 7 years. Primary culture was initiated in MEM supplemented with 10% rabbit serum. Cells reached confluency within 25 days, responded to serum in a dose dependent manner and had an average doubling time of 23 h during the logarithmic growth phase. Cells increased in number in a dose dependent manner when insulin, insulin growth factor, epidermal growth factor (EGF), or fibroblast growth factor (FGF) was added to the culture medium. Thus, lens epithelia from this very old rabbit retained the ability to respond to highly purified growth factors. Cells exposed to a medium supplemented with insulin, EGF and FGF showed a five-fold increase in number at day 7 of culture, a value exceeding that brought about by the individual growth factors. An examination of chromosomal preparations indicated that the cells were aneuploid. Whether the aneuploidy was acquiredin vitroor is a normal adjunct of aging in the lensin vivois unknown. Proteins extracted from this line contained polypeptides that migrated to the position of and had apparent molecular weights of lens proteins.

ISSN:0271-3683    

DOI:10.3109/02713688208996365

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

ISSN:0271-3683    

DOI:10.3109/02713688208996366

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor