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Biomedical subjects

W K Lo

Publications and source records attributed to W K Lo.

At least 91 records · Page 5Linked to original sources
PubMed1990

Sclerosing peritonitis complicating continuous ambulatory peritoneal dialysis with the use of chlorhexidine in alcohol.

Sclerosing peritonitis (SP) is an uncommon but serious complication of CAPD with various suggested etiology. We have documented 14 cases of SP in 18 CAPD patients using chlorhexidine in alcohol (ChA) in the connection procedure; 13 died. Nine of the 14 patients had been transferred to haemodialysis or renal transplantation, yet all still developed symptoms of SP within a few months after transfer even though 5 of them were originally asymptomatic. The main symptoms of SP were peritoneal ultrafiltration failure, exudative bloody ascites and intestinal obstruction. They present at around 5 years (30-80 months) after commencement of CAPD. Four other patients with a comparable duration of ChA exposure were continued on CAPD with a Travenol Spike System (TSS) without further exposure to ChA. They were all asymptomatic of SP after 9-12 months. Comparing the 2 groups of asymptomatic patients at 9 months after transfer, those transferred to TSS have a much better outcome than those transferred to HD or renal transplantation (P = 0.0476). We concluded that ChA is the main cause of SP in our patients and continuing CAPD without further exposure to ChA is a better alternative than stopping CAPD in preventing the progression of SP.

Adult↗
PubMed1989

Visualization of crystallin droplets associated with cold cataract formation in young intact rat lens.

The structure, distribution, and nature of scattering elements associated with cold cataract formation in the young rat lens were studied in situ using light and electron microscopy and ImmunoGold electron microscopy. A large accumulation of spherical droplets, ranging from approximately 1.5 microns to 10 microns in diameter, were found in the lens nucleus in cold cataracts induced at 22 degrees C or 4 degrees C in TC-199 culture medium. Many droplets of all sizes were associated with the cell membranes. A cooled and then rewarmed lens was found to lose its opacity and subsequently no droplets were observed, indicating that there was a good correlation between the onset of opacification and the formation of droplets. Electron microscopy showed that droplets were composed of homogeneous electron-dense aggregates without limiting membranes. ImmunoGold study revealed that alpha-, beta-, and gamma-crystallins were all present within each droplet. This study demonstrates that extensive accumulation of the crystallin droplets in the lens nucleus is the contributing factor for the light scattering and opacification of the cold cataract in the young intact rat lens.

Animals↗
PubMed1989

Endocytosis of macromolecules in the lenses of guinea pig and rabbit.

Endocytosis in lenses of rabbit and guinea pig was studied using freeze-fracture electron microscopy and horseradish peroxidase (HRP) as a macromolecular tracer during various periods of lens organ culture. Thin-section and freeze-fracture TEM show that endocytosis occurs predominantly in the epithelial cells of both rabbit and guinea pig lenses before incubation in the HRP. Tracer study in the guinea pig lens reveals that vesicular transport of HRP was most active in the epithelium and elongating young fiber cells where the metabolic activity is high. The endocytic vesicles, smooth in surface and about 0.07 microns in size, were frequently found associated with the lateral epithelial membranes. Isolated vesicles were seen to fuse with lysosomes to form multivesicular bodies or secondary lysosomes. The number of endocytic vesicles shows only a slight decrease after a 4-hr incubation, while secondary lysosomes gradually increase their number and reach the peak at the end of the culture period. The results suggest that endocytosis is a continuous physiologic process, and may play an important role in transporting some useful macromolecules from aqueous humor into the lens cells.

Animals↗
PubMed1988

Adherens junctions in the ocular lens of various species: ultrastructural analysis with an improved fixation.

The ultrastructure and distribution of adherens junctions in the intact adult lens of human, chicken, dove, rat, and rainbow trout were studied with thin-section electron microscopy, using an improved fixation containing a mixture of glutaraldehyde, lysine, and tannic acid. The nature of adherens junctions in the fiber-cells of the lens was also verified by immunofluorescence and rhodamine-phalloidin labelings for vinculin and actin. Electron microscopy revealed that adherens junctions of the lens were different ultrastructurally from the desmosomes found only between the lateral epithelial cells of the lens. The adherens junctions had the same structural characteristics as the zonulae adherentes, except that they were macular contacts, not belts. However, cross bridges were evident within the interspace of the junctions. Adherens junctions were located between the fiber-cells, between the epithelial cells and fiber-cells, and between the epithelial cells. They had a characteristic distribution in the "intersections" where three hexagonal fiber-cells met, as seen in cross-sections in all species studied. In addition, adherens junctions and associated actin were found distributed randomly along the entire cell membranes of both wide and narrow sides of cortical fiber-cells in the human, chicken, and dove lenses which have good accomodating capability. However, in the poorly-accomodating lenses of rat and fish, these junctions were seen predominantly on the narrow sides and at the regions of the wide sides that were very close to the "intersections". It is suggested that adherens junctions and associated actin microfilaments are involved in stabilizing the structural integrity of lens cells during accomodation and in preserving a specific lens shape.

Actins↗
PubMed1987

In vivo and in vitro observations on permeability and diffusion pathways of tracers in rat and frog lenses.

Two tracers [horseradish peroxidase (HRP) and lanthanum] with different properties were injected separately into eyes of the rat and frog to determine the diffusion pathways of tracers in the lens. HRP can diffuse rapidly into lens tissue and can also be washed out, whereas lanthanum has opposite properties. In a short (2-5 min) in vivo intravitreal injection of HRP into the rat eye using an automated micro syringe, tracer reached the entire intercellular space between lens epithelium and fiber cells, and between epithelial cells primarily at the peripheral region; however, it reached the central zone in a longer period (10-20 min) of injection, as examined with light microscope and transmission electron microscope. HRP in epithelial intercellular spaces basal to the tight junctions was washed away upon 5-15 min washing with TC-199, but was retained in the spaces apical to the junctions and between epithelium and fiber cells. Lanthanum studies in both rat and frog lenses showed that within 3-4-hr incubation, tracer was seen in epithelial intercellular spaces only basal to the tight junctions at the central epithelium. At the peripheral zone, however, tracer was visualized in the entire intercellular spaces between epithelial cells, and between epithelium and fiber cells. These studies strongly suggest that both tracers seen in the intercellular space between epithelium and fiber cells are derived from the most equatorial region of the lens, and they may not leak out to the anterior lens surface through tight junctions between epithelial cells in the rat and frog. This leads us to conclude that the equatorial region of the lens is the major site of efflux and influx of substances for the anterior lens region.

Animals↗
PubMed1987

Alterations in fiber cell membranes of Emory mouse cataract: a morphologic study.

Morphologic alterations in cortical fiber cell membranes of the developing Emory mouse cataract were studied with scanning, transmission and freeze-fracture electron microscopy. Scanning electron microscopy revealed the extensive formation of prominent ridges on the surfaces of normal-appearing fibers, greatly enlarged degenerating fibers and globular structures in the relatively superficial cortical regions of the cataractous lenses where such a surface pattern was not found in the normal controls. Transmission electron microscopy showed undulating 13 nm pentalamellar structures, which were thinner than 17 nm heptalamellar (or pentalamellar) structures of gap junctions, were distributed within the cell membranes having ridge patterns. Some globular structures were encircled by repeated undulating 13 nm pentalamellar structures and multilamallar membranes. Freeze-fracture studies demonstrated that 13 nm pentalamellar structures consisted of square crystalline arrays of 6 nm intramembrane particles whereas 17 nm heptalamellar profiles showed randomly-packed 9 nm intramembrane particles of typical lens fiber gap junctions. It is suggested that the extensive formation of ridges in the relatively superficial cortical regions of the Emory mouse lenses may be associated with a degenerative process of lens fiber cell membranes during cataractogenesis.

Animals↗
PubMed1986

Structure and distribution of gap junctions in lens epithelium and fiber cells.

We report a comparative study of gap junctions in lens epithelia of frog, rabbit, rat and human, using a "double mounting" method for freeze-fracture electron microscopy. The gap junctions on the narrow sides of hexagonal cortical fiber cells of various species were also studied with the same technique. Gap junctions were commonly present between epithelial cells of the entire undifferentiated epithelium, between fiber cells on both wide and narrow sides, and between epithelial cells and fiber cells. Structural diversity of gap junctions, based on connexon arrangements, was evident in lens epithelia among the four species studied. Gap junctions with random arrays of connexons were found predominantly in frog lens epithelium, while the crystalline and striated configurations were mainly observed in the epithelia of human and rat, and of rabbit, respectively. On the other hand, there was no structural variation of gap junctions observed on either wide or narrow sides of lens fiber cells from any species studied. Only the random-type gap junction was found. However, the distribution of gap junctions was unique on the narrow sides. There was a single row of junctional plaques along the middle of the narrow sides, whereas the wide sides showed an uneven distribution pattern. The gap junctions between epithelial cells and fiber cells had a random packing of connexons.

Adolescent↗
PubMed1984

Square arrays and their role in ridge formation in human lens fibers.

Square arrays in human lens fibers were studied with freeze-fracture and thin-section TEM. In superficial fibers a number of patches of square array particles in the P face and pits in the E face are found in the smooth membrane. In the deeper cortex and the nucleus, fiber cells have undulating membranes and many ridges. Numerous patches of the particles (P face) are distributed in the concave regions, and the pits (E face) in the convex areas of the bumpy membrane. In most ridges, patches of the particles occur at regular intervals in the "valley" portion, while the pits are on the "crest" portion of ridges. Also, continuous square arrays having the same "valley" location as the regularly arranged patches are found in areas with extensive ridge patterns. The overlapping of the outer portions of two adjacent square arrays is found on the sides between the "crest" and the "valley" of the ridges. Structurally, square arrays are located in a nonjunctional part of the membrane; in an orthogonal crystalline arrangement; and with a particle size of about 6 nm and center-center spacing about 6.4 nm. They are structurally different from gap junctions found in the lens fibers. Thin-section studies reveal two types of cellular contacts: thin pentalamellar structures (about 12-13 nm in overall thickness) associated with the ridge patterns are believed to be square arrays; thick heptalamellar structures (about 16-17 nm in overall thickness) with a narrow gap in between the two central laminae are believed to be gap junctions. This study strongly suggests that square arrays are specifically involved in ridge formation in human lens fibers.

Cataract↗
PubMed1983

Tight junctions in the lens epithelia of human and frog: freeze-fracture and protein tracer studies.

For the first time, the existence of zonulae occludentes in the lens epithelia of human and frog has been demonstrated, using a "double mounting" method in freeze-fracture transmission electron microscope (TEM). The physiologic barrier function of zonulae occludentes in frog lens epithelium is determined by a "wash out" procedure in the protein tracer studies. It was found that within various time intervals of washing, horseradish peroxidase (HRP) was consistently restricted to the location of membrane fusions (zonulae occludentes), as seen with thin-section TEM. This corresponds to the location of zonulae occludentes found in the freeze-fracture studies. Thus, these data strongly suggest that there are zonulae occludentes in the frog lens epithelium and that these structures do provide a barrier function for the transepithelial diffusion of HRP with a molecular weight of 40,000 daltons.

Animals↗
PubMed1983

Calcium-containing opacities in the human lens.

Cooperative Cataract Research Group (CCRG) photographic procedures developed by Chylack have made it possible to localize and analyze specific lens opacities for their ultrastructural and chemical characteristics. One group of human lens opacities has been shown to have a high phosphorus/sulfur ratio (as compared to normal lens fiber cells) and an accumulation of unit membranes. The present paper describes another variety of human lens opacity with the following characteristics: (1) high calcium, low sulfur, undetectable phosphorus, as determined by Energy Dispersive X-ray Analysis (EDXA) of bulk specimens in the scanning electron microscope (SEM), or "thick" sections with the transmission mode of the SEM; (2) spheroidal shape; (3) up to approximately 300 microns in size; and (4) birefringence. Microchemical analysis of these opacities shows that the calcium is in the form of calcium oxalate. These calcium-containing opacities, which have been detected in 14 out of 406 human cataractous lenses, have a characteristic morphology, as seen in the CCRG stereo photographs. Therefore, the presence of these calcium opacities, if not obscured by other kinds of opacities, can be detected with a high degree of accuracy in the fresh lens from the CCRG photographs alone.

Calcium↗
PubMed1981

A newly described organ associated with the eye and lateral line system in the marine teleost, Stenotomus chrysops.

A hitherto undescribed type of organ, possibly sensory, is reported. It is in the form of small cylindrical projections primarily concentrated on the surface in the area of the reticular lateral-line complex and around the eye of the scup (Stenotomus chrysops). The projection is composed of a central core cell surrounded by an epithelium. Enveloped within the epithelium and parallel to the core cell are six to eight symmetrically arranged 'bulbs' with cytoplasmic stems extending to cell bodies within the epidermis proper. A circle of 'collar' cells at the base of the cylinder facilitates the observed bending of the projection. Detection of the direction of water movement is hypothesized.

Animals↗
PubMed1980

Polypeptides of the lens fibre cell intracellular matrix.

The cytoskeletal proteins of the vertebrate lens fibre cell comprise polypeptides raging in mol.wt from 43,000 to 250,000 daltons. The main intermediate filament polypeptide of the pickerel, Northern frog, chick, bovine, and human lens has a mol.wt of 54,000 daltons. Peptide analysis revealed that the chick 54,000 dalton protein was more similar to the bovine protein than to the pickerel protein.

Animals↗
PubMedDate not supplied

Reproducibility of the peritoneal equilibration test in CAPD patients.

A study was undertaken to evaluate the short-term reproducibility of peritoneal equilibration test (PET) results. Nine patients with end-stage renal disease undergoing continuous ambulatory peritoneal dialysis underwent PETs under similar conditions on 2 consecutive days. Dialysate samples were obtained at 0 hours, midcycle, and at the end of exchange. There were no significant differences between the mean ratios at 4 hours for creatine, urea nitrogen, potassium and protein, and glucose between PET 1 and PET 2. A standard PET is highly reproducible when repeated under similar conditions. Reproducibility is better for ratios of creatinine, glucose, urea nitrogen, and potassium than for protein.

Aged↗