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Biomedical subjects

K M Khan

Publications and source records attributed to K M Khan.

At least 19 recordsLinked to original sources
PubMed1991

The histochemical localization of acetylcholinesterase in the rainbow trout saccular macula by electron microscopy.

The hair cells of the teleost saccular macula are morphologically similar to type II vestibular hair cells of higher vertebrates. The two types of nerve endings at the base of the saccular hair cells are the non-vesiculated endings, thought to be afferent, and the vesiculated terminals, presumed to be efferent. The vesicles in the presumptive efferent endings are predominantly round and clear, and a few are dense cored. The morphological characteristics of the vesiculated endings resemble those of presumptive efferent cholinergic endings present in the inner ear of higher vertebrates. In the present study, vesiculated nerve endings were examined histochemically for acetylcholinesterase. The reaction product was observed along the plasma membranes of the vesiculated nerve endings synapsing both with the hair cells and afferent endings, but was not seen at non-vesiculated endings on hair cells. No staining was observed in control specimens incubated in the presence of eserine sulfate, an inhibitor of acetylcholinesterase. These results suggest that the vesiculated nerve endings in the trout saccular macula contain cholinergic elements.

Acetylcholinesterase↗
PubMed1991

Carbohydrates associated with the cell coat surrounding cells of the rainbow trout saccular macula as revealed by lectin probes.

The luminal surface of the saccular macula in the rainbow trout is covered with a glycoconjugate-rich cell coat. The aim of this study was to identify specific carbohydrate moieties present in this coat, using biotinylated lectins as probes. Saccular tissues were fixed in Karnovsky's fixative for 2 h at 1-2 degrees C, followed by incubation with biotinylated lectins for 12-16 h at 25 degrees C. Lectin binding was visualized by performing avidin-biotin-peroxidase reactions. As controls, specimens were reacted with solutions of lectins preincubated with their specific inhibitory sugars. Staining was observed that was consistent with the presence of glucose, galactose, fucose, mannose, N-acetylglucosamine, N-acetylneuraminic acid, and N-acetylgalactosamine in the cell coat. The variability in the intensity of staining associated with the lectin-carbohydrate complexes suggests quantitative differences among the various carbohydrate moieties detected. The presence of these carbohydrates in the cell coat of the trout saccular macula also suggests biochemical similarities between cell coats in teleost and mammalian inner ear structures.

Animals↗
PubMed1990

Proteins of the gelatinous layer of the trout saccular otolithic membrane.

Although the otolithic membrane is thought to play an important role in the stimulation of vestibular hair cells, little is known about its chemical composition. We analyzed proteins of the gelatinous layer of this structure from the trout saccule, a probable organ of hearing in fish, by SDS-polyacrylamide gel electrophoresis. A relatively small number of major proteins were detected in homogenates of the 'membrane' layer, with apparent molecular weights ranging from 35 to greater than 300 kDa. Six bands, with molecular weights of 35, 43, 65, 94, 100, and 160 kDa, were particularly prominent. Periodic acid-Schiff (PAS) staining indicated that the 43, 94, 100, and 160 kDa bands were glycoproteins. Lectin binding on nitrocellulose blots confirmed the PAS results, and further suggested that the 35 and 65 kDa bands may be glycoproteins. Incubation of blots with human anti-collagen type II antibodies suggested that the 94 kDa band was a component of collagen type II or a related protein.

Animals↗
PubMed1990

The cell coat of the sensory and supporting cells of the rainbow trout saccular macula as demonstrated by reaction with ruthenium red and tannic acid.

The surface of most cells is covered by glycoconjugates. The composition and thickness of the surface coat varies among different cell types. The purpose of the present study was to demonstrate the presence of and to characterize the cell coat surrounding the cells in the saccular macula of the rainbow trout. Tissues were fixed in Karnovsky's fixative containing either ruthenium red (0.5, 1, or 2%) or tannic acid (1, 2, or 4%). The apical surface of the sensory and supporting cells reacted with both agents. Varying the concentration of the compounds within a certain range did not significantly affect the degree of tissue staining. Whereas ruthenium red staining was distributed evenly along the luminal surface of the epithelium and along the length of the stereocilia, tannic acid formed electron-dense clumps on the luminal surface of sensory and non-sensory cells and in the basal region of the macular epithelium. The stereocilia of the sensory cells also exhibited tannic acid-positive, electrondense precipitate, particularly near the distal ends of these processes, while uniform staining of the plasma membrane was seen along their lengths. The results of this study suggest that the trout saccular macula is provided with extracellular microenvironments which may be necessary for functional integrity.

Animals↗
PubMed1989

Protein associated with the sensory cell layer of the rainbow trout saccular macula.

A protein has been detected that is associated with the saccular hair cell layer of the rainbow trout, Salmo gairdnerii R. By one- and two-dimensional SDS polyacrylamide gel electrophoresis, the molecular weight and isoelectric point of this protein are estimated to be 13.6 and 8.8 kDa, respectively. The 13.6 kDa protein cannot be detected electrophoretically in brain, gill, liver, and fractions containing the basal lamina, non-sensory epithelium, and saccular nerve. This protein does not bind antibodies to bovine myelin basic protein, while trout myelin basic proteins in the same molecular weight range do. In addition, the protein does not bind concanavalin A or react with the periodic acid-Schiff reagent. The 13.6 kDa band represents about 1% of the total protein in saccular sensory epithelium, and may be a marker protein for the hair cell layer.

Animals↗
PubMed1989

Sequestration and degradation of alpha 2u-globulin in rat kidney lysosomes.

alpha 2u-Globulin (M.W. = 18,709) is the major protein synthesized in the liver of adult male rats. alpha 2u-Globulin, secreted from the liver, is filtered by the kidneys where about a half of the protein is reabsorbed and the remainder is excreted in the urine. Highly purified lysosomes from rat kidneys were subjected to immunoblot analysis using antiserum against alpha 2u-globulin. A major immuno-reactive band was observed at the position about 1 k dalton smaller than that of the authentic alpha 2u-globulin. The immuno-reactive band in SDS-polyacrylamide gel was excised and the protein, eluted from the gel, was subjected to amino acid sequence analysis by micro Edman method. The N-terminal amino acid sequence of the intralysosomal alpha 2u-globulin was found to be leu-asp-val-ala-lys-leu-asn-gly-... which exactly corresponded to the sequence from the 10th leucine residue of the authentic urinary alpha 2u-globulin. This result suggests that alpha 2u-globulin, sequestered into the kidney lysosomes, is cleaved intralysosomally between the 9th asparagine and the 10th leucine, and the degradative intermediate, thus produced, is accumulated in the lysosomes. The immuno-blot assay gave the value of 210 +/- 70 mg alpha 2u-globulin/g kidney lysosomal proteins. The molecular basis for the resistance of the degradative intermediate of alpha 2u-globulin against further degradation in the kidney lysosomes was discussed in the light of the computer-predicted secondary structure of alpha 2u-globulin.

Alpha-Globulins↗
PubMed1988

Degradation of aspartate aminotransferase in rat liver lysosomes.

Highly purified lysosomes from the normal and leupeptin-treated rat livers were subjected to immunoblot analysis using antibodies against cytosolic and mitochondrial isozymes of aspartate aminotransferase (cAspAT and mAspAT). In the case of cAspAT (subunit M.W. = 46K), the leupeptin-treated lysosomes showed a major band of 46K and a minor band of 36K while normal lysosomes showed a major band of 36K and a minor band of 41K. In the case of mAspAT (subunit M.W. = 44K), the leupeptin-treated lysosomes showed a 44K band and the normal lysosomes showed a 40K band. These observations suggest that both cAspAT and mAspAT are sequestered into lysosomes with the original subunit molecular weights and are degraded in the lysosomes by way of sequential formation of relatively stable intermediates with distinct molecular weights.

Animals↗
PubMed1978

Detection of H2-b and Thy-1.2 surface antigens on the differentiating murine otocyst using Nomarski optics.

The 12th postcoital day otocyst appears as a hollow cellular ball of pseudostratified columnar epithelium that has entered into its inital stages of differentiation and organogenesis. H-2b antigen was demonstrated on the ectodermally derived epithelial cells of the otocysts and on the mesodermally derived cells of the surrounding mesenchyme. Thy-1.2 antigen was detected in the mesenchymal cells, but not on the epithelial cells of the otocyst. The use of Nomarski optics as a new method for detecting cell surface staining that would otherwise be undetected by bright field optics was demonstrated.

Animals↗
PubMed1976

The role of cellular degeneration in the normal development of (rat) otocyst.

From day 12 to 16 of gestation a highly circumscribed zone of cellular degeneration has been observed in the otocyst of more than 50 normal rats. This zone appears to be produced by selective or programmed cell death, and results in the elimination of unneeded cellular elements. That cells in this zone are also selectively destroying subcellular organelles as a first step in specialization is also discussed. Programmed cellular death has long been known in other systems and is often an obligatory companion to cellular specialization. The ear now joins the long list of organs which demonstrate this phenomenon.

Animals↗
PubMedDate not supplied

Lack of Alzheimer pathology after beta-amyloid protein injections in rat brain.

In order to establish a direct relationship between beta-amyloid protein (beta AP) and in vivo neurotoxicity, we made intraparenchymal injections and Alzet pump infusions of beta AP into the hippocampus and cortex of adult rats. We tested a number of synthetic beta AP peptides (beta AP 1-40, 1-38, and 25-35) and peptide controls (scrambled and reversed 1-40, and scrambled and reversed 25-35) over a wide range of concentrations and in a variety of vehicles. The rats were sacrificed from 2-35 days following the implant, and the brains examined by standard immunohistochemical and histological methods used to evaluate the pathologies associated with Alzheimer's disease. We report the lack of Alzheimer related pathology and no significant morphological differences between the beta AP peptide and the peptide and vehicle control injections. These observations indicate that the simple intraparenchymal injection of beta AP in the rat brain is not an appropriate model of Alzheimer-related neurotoxicity.

Alzheimer Disease↗
PubMedDate not supplied

An improved method for processing early rat otocysts for the electron microscope.

Various methods of dissection, fixation, osmication, sectioning and staining were tested in order to develop an acceptable technique for preparing 9, 10, 11, and 12-day-old rat otocysts for electron microscopic study. The general problems associated with embryonic tissue-difficult handling, high water content and poor stainability are discussed, and concrete methods of preparation which significantly decrease these difficulties are proposed. The specific fixation and sectioning requirements of rat otocyst are also described in the elaboration of a method which will be used in subsequent studies of the organogenesis of rodent ear.

Animals↗
PubMedDate not supplied

Ultrastructural development of the early rat otocyst.

The ultrastructural development and differentiation of cells forming the rat otocyst were studied from the 9th to the 13th postcoital day (PCD). The earliest stage investigated was a simple ovoid structure with a connecting stalk to the surface ectoderm. A process of programmed cellular death involving surface ectoderm, connecting stalk, and lateral otocyst wall rapidly detached the otocyst. The cells forming the otocyst were roughly columnar, the organelles were polarized; mitochondria occurred in greatest number basally and in the supranuclear area; Golgi membranes when present were supranuclear. Luminal cells had many microvilli and cilia of various lengths were detected. The shorter, incompletely formed cilia terminated in small knob-like blebs. With each day the otocysts became more complicated and the endolymphatic duct made its appearance as an evagination of the otocyst. Many more cells were seen to have cilia in various stages of development, and by the 12th PCD possibly each cell of the main otocystic cavity had a kinocilium. Growth of the otocyst due to mitosis occurred to a great extent from a single ventromedial center. Cells in mitosis, although seen at other sites, were in greatest abundance in this area; cellular involution apparently was a related function. Together the process of over-production and programmed cellular involution of supranumerary cells not lost to other causes (e.g., environmental) may represent an evolutionary advantage.

Animals↗
PubMedDate not supplied

Scanning electron microscopic appearance of rat otocyst of the twelfth postcoital day: elaboration of a method.

A method for removal, fixation, microdissection, and drying of early rat otocyst for examination by the scanning electron microscope is elaborated. Tissues were dissected, fixed as for conventional transmission electron microscopy and dried by critical point evaporation using amylacetate as the transitional fluid and carbon dioxide as the pressure head. Otocysts were either dissected at the time of initial fixation, or subsequent to drying. The otocyst of the 12th postcoital day was used as a model system in this preliminary report. Critical point drying retained the overall configuration and the fine ultrastructural detail of the otocyst. The interior otocystic surface was visualized and cilia bearing cells of the luminal surface were identified. Most if not all of these cells had a comspicuous, but short kinocillum which terminated in an ovoid bulb. The scanning electron microscopic appearance was correlated to the transmission electron microscopic image seen in the second paper in this Supplement.

Animals↗
PubMedDate not supplied

Intercellular junctions in the differentiating rat otocyst.

Intercellular junctions between cells of the rat otocyst on the 12th day of gestation were studied using lanthanum tracer and freeze-fracture techniques. At the luminal surface, the intercellular space is closed by a series of tight junctions. Gap junctions are also present between cells both within and below the luminal junctional complex. The presence of tight and gap junctions at this early stage in the differentiating otocyst is probably essential for the development of a normally functioning adult ear.

Animals↗