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Biomedical subjects

K A Beck

Publications and source records attributed to K A Beck.

At least 19 recordsLinked to original sources
PubMed1998

A spectrin membrane skeleton of the Golgi complex.

The existence of a Golgi-localized membrane cytoskeleton has been revealed by the identification of two major components of the spectrin membrane skeleton, spectrin and ankyrin, that associate with the Golgi complex. Golgi spectrin was identified with an antibody specific for the beta-subunit of the erythroid isoform of spectrin (beta1Sigma1). This antibody recognizes a 220 kDa polypeptide that localizes to discrete regions of the Golgi complex and associates with Golgi membranes in a Brefeldin A sensitive manner. Two isoforms of Golgi ankyrin have been identified: a 119 kDa form (AnkG119) which represents a truncated, alternatively spliced isoform of a recently cloned novel ankyrin of the nervous system AnkG, and a larger 195 kDa ankyrin (Ank195) that cross-reacts with antibodies to erythrocyte ankyrin. A Golgi localized membrane skeleton composed of these unique membrane skeleton isoforms could serve a variety of important functions, including the maintenance of Golgi structural organization and the formation of discrete membrane domains within Golgi compartments.

Animals↗
PubMed1997

Golgi membrane skeleton: identification, localization and oligomerization of a 195 kDa ankyrin isoform associated with the Golgi complex.

To extend our finding of a Golgi-localized form of the membrane skeleton protein spectrin, we have identified an isoform of ankyrin that associates at steady state with the Golgi complex. Immuno-light and -electron microscopy show that this ankyrin isoform localizes to the perinuclear cytoplasm on tubular vesicular structures that co-stain with Golgi marker proteins. An antiserum raised against erythrocyte ankyrin, which was used to identify the Golgi ankyrin, recognized three prominent polypeptides of 220, 213 and 195 kDa in MDCK cells. Affinity purification of this antiserum against each of these MDCK cell ankyrins revealed that only an antibody specific for the 195 kDa form retained the ability to stain the Golgi complex; affinity purified antibody preparations specific for both the 220 and 213 kDa forms stained punctate and reticular cytoplasmic structures distinct from the Golgi complex. Antibody specific for the 195 kDa ankyrin did not recognize a recently identified 119 kDa ankyrin that is also localized to the Golgi. The 195 kDa Golgi ankyrin binds purified erythrocyte spectrin, and rapidly co-sediments with Golgi beta-spectrin during brief, low speed centrifugation of Triton X-100 extracts of MDCK cells. Golgi ankyrin and beta-spectrin are retained on tubular vesicular 'Golgi ghosts' following extraction of cultured cells with Triton X-100. Significantly, Golgi ghost tubules containing ankyrin/spectrin are co-linear with individual microtubules, suggesting a role for both Golgi membrane skeleton and microtubules in spatial localization of the Golgi. Golgi ankyrin dissociates from Golgi membranes during mitosis and in cells treated with brefeldin A, indicating that Golgi ankyrin has a dynamic assembly state similar to that of Golgi spectrin and other Golgi membrane coat proteins.

Animals↗
PubMed1997

Mechanisms for de novo biogenesis of an apical membrane compartment in groups of simple epithelial cells surrounded by extracellular matrix.

In open monolayers of epithelial cells grown in vitro, the apical membrane domain forms on the free cell surface that faces the culture medium. However, in vivo, the apical lumenal compartment arises within groups of cells that do not have a free cell surface. We designed in vitro culture conditions, using small colonies of MDCK cells overlaid with collagen, in which formation of the apical membrane must occur de novo by remodeling existing membrane domains that are contacted by other cells or extracellular matrix. Within 12 hours of collagen overlay, the apical membrane glycoprotein gp135 is removed from the free cell surface, while lateral membrane proteins (e.g. Na+,K+-ATPase) remain at sites of cell-cell contacts. Subsequently, lumenal structures, containing gp135 and the apically secreted protein gp81, formed within these cell-cell contacts. Na+,K+-ATPase, adherens junction (E-cadherin, alpha- and beta-catenins) and tight junction (ZO-1) proteins were localized on the lateral membrane adjacent to, but excluded from the gp135-positive lumenal compartment. Therefore, each lumen represents a newly formed apical compartment on the lateral membrane. The Golgi complex (alpha-mannosidase II and Golgi beta-spectrin), centrosomes (gamma-tubulin) and microtubules reorient to a cytoplasmic position adjacent to the newly-forming apical lumenal compartments. Significantly, addition of colchicine, nocodazole or brefeldin A inhibits apical lumen formation. These results demonstrate that simple epithelial cells form an apical lumenal compartment de novo through initial intermixing, and then sorting of apical and basal-lateral membrane proteins at sites of cell-cell contacts. In addition, apical lumen formation requires an intact microtubule network, microtubule-dependent reorientation of the Golgi complex and secretory apparatus, and fully functional protein delivery from the Golgi complex to the forming apical cell surface.

Animals↗
PubMed1996

The spectrin-based membrane skeleton as a membrane protein-sorting machine.

Normal cell function is dependent on the existence of membrane compartments that have unique populations of membrane proteins. Sorting of membrane proteins forms the basis for the biogenesis of distinct membrane compartments. There are many examples of membrane protein-sorting events in cells, but the molecular machinery involved is poorly understood. We discuss characteristics of a putative membrane protein-sorting machine and show that the spectrin-based membrane skeleton conforms to these characteristics. The spectrin-based membrane skeleton is a submembranous, spatially limited, two-dimensional lattice that binds a subset of membrane proteins. These properties allow the membrane skeleton to facilitate the formation of distinct membrane domains and thus reveal its potential as a membrane protein-sorting machine.

Animals↗
PubMed1995

Automobile-induced obstruction of the intrathoracic caudal vena cava in a dog.

A two-year-old labrador retriever was examined after a year's history of persistent ascites and exercise intolerance that began shortly after the dog was struck by an automobile. Contrast venography showed tortuosity of the intrathoracic caudal vena cava with partial obstruction caused by kinking of the vessel. Surgical resection of a fibrous connective band that was found to be tethering the intrathoracic vena cava ventrally, creating a partial obstruction, was performed. A hypothesis of the aetiology of this phenomenon is presented.

Accidents, Traffic↗
PubMed1994

Organization and function of the cytoskeleton in polarized epithelial cells: a component of the protein sorting machinery.

Development and maintenance of cell-surface polarity in epithelial cells requires specialized localization of proteins to functionally and structurally distinct plasma membrane domains. The organization of these domains is dependent upon targeted delivery of transport vesicles between different membrane compartments, and upon protein sorting in the membranes of the Golgi complex and cell surface. Increasing evidence has been gathered in recent years that cytoskeletal components facilitate these processes.

Actin Cytoskeleton↗
PubMed1994

Golgi spectrin: identification of an erythroid beta-spectrin homolog associated with the Golgi complex.

Spectrin is a major component of a membrane-associated cytoskeleton involved in the maintenance of membrane structural integrity and the generation of functionally distinct membrane protein domains. Here, we show that a homolog of erythrocyte beta-spectrin (beta I sigma*) co-localizes with markers of the Golgi complex in a variety of cell types, and that microinjected beta-spectrin codistributes with elements of the Golgi complex. Significantly, we show a dynamic relationship between beta-spectrin and the structural and functional organization of the Golgi complex. Disruption of both Golgi structure and function, either in mitotic cells or following addition of brefeldin A, is accompanied by loss of beta-spectrin from Golgi membranes and dispersal in the cytoplasm. In contrast, perturbation of Golgi structure without a loss of function, by the addition of nocodazole, results in retention of beta-spectrin with the dispersed Golgi elements. These results indicate that the association of beta-spectrin with Golgi membranes is coupled to Golgi organization and function.

Animals↗
PubMed1993

Use of fenbendazole for treatment of Crenosoma vulpis infection in a dog.

An 8-month-old Labrador Retriever was examined because of a 1-month history of productive coughing unresponsive to ampicillin treatment. Larvae of Crenosoma vulpis were found in fecal samples examined by zinc sulfate centrifugation and Baermann technique. Physical examination abnormalities or larvae in fecal samples were not detected 6 weeks after treatment with prednisone (1 mg/kg, PO, q 24 h, for 7 days, then 0.5 mg/kg, PO, q 48 h, for 8 days) and fenbendazole granules (50 mg/kg, PO, q 24 h, for 3 days). This report suggests that fenbendazole may be effective for treating Crenosoma vulpis infection in dogs.

Animals↗
PubMed1993

Recognition of Pneumocystis carinii in foals with respiratory distress.

Five 3-month-old foals presenting with fever and respiratory disease were found to have pulmonary abscesses with patchy to diffuse alveolar and interstitial pneumonia on post-mortem examination. All affected foals had evidence of Rhodococcus equi infection and had few to abundant Pneumocystis carinii cysts in the sections of affected lung. Of the 5 foals examined radiographically, 3 had a distinct reticulonodular (miliary) pattern which may aid in the ante-mortem diagnosis of P. carinii pneumonia (PCP). Leukocyte counts of foals with PCP were significantly greater than in the control group of foals with uncomplicated bacterial pneumonia. Foals with PCP tended to be more tachypnoeic than the control foals and 4 of the 5 PCP+ foals appeared dyspnoeic before death. The ante-mortem recognition of PCP may be expedited by bronchoalveolar lavage and successful treatment of foals with PCP may require the administration of adequate levels of potentiated sulphonamides.

Actinomycetales Infections↗
PubMed1993

Examination of frozen cross sections of cervical spinal intersegments in nine horses with cervical vertebral malformation: lesions associated with spinal cord compression.

Nine horses with clinical and radiographic findings of cervical vertebral malformation that were necropsied and examined using frozen cervical spinal cord cross sections were reviewed. Only cases with actual distortion of the spinal cord due to compression were selected. The goal of the study was to determine the morphologic features responsible for narrowing of the spinal canal and compression of the spinal cord. In individual cases, bony changes are associated with osteochondrosis and osteomyelitis of the dorsal articular facets and osteosclerosis of the dorsal cervical lamina. Soft tissue pathology associated with spinal cord compression included ligamentum flavum hypertrophy, joint capsule swelling and hypertrophy, and synovial cysts. In most cases, a combination of abnormalities was found in horses with spinal cord compression.

Animals↗
PubMed1993

Joint laxity and its association with hip dysplasia in Labrador retrievers.

A study was done to determine whether radiographic-distraction measurement of coxofemoral joint (hip) laxity at 4 and 8 months of age can serve as a predictor of hip dysplasia in older Labrador Retrievers. The method of Smith, Biery, and Gregor was used for radiologic examination of hips and for evaluation of radiographs. Mean (+/- SEM) distraction laxity (ie, distraction index) for 10 adult disease-free dogs was 0.29 +/- 0.05, whereas a group of 8 dogs with dysplastic hips had mean distraction index of 0.60 +/- 0.10 (P < 0.05). Mean distraction index at 4 months of age for 11 pups of 4 litters from matings between dogs with normal hips was 0.39 +/- 0.07, and was 0.54 +/- 0.04 for 31 pups of 7 litters from matings between dogs with hip dysplasia. The distraction index and, thus, joint laxity at that age was significantly (P = 0.0351) different for the 2 groups. The distraction index at 4 months correlated positively with the distraction index at a later age at necropsy (r = 0.43; P = 0.0289). Distraction index < 0.4 at 4 months of age predicted normal hips in 88% of cases and distraction index > or = 0.4 predicted hip dysplasia in 57% of the dogs. Logistic regression modeling indicated that the odds of a hip being normal decreased with increasing distraction index, and thus, with increasing joint laxity. The logistic regression models provided a reasonable mathematical description of the data. Based on the logistic model of the data, distraction indexes between 0.4 and 0.7 at either 4 or 8 months of age were not associated strongly enough with evidence of disease to be clinically reliable in predicting, on an individual basis, the outcome for dysplastic hip conformation when dogs were older. Index > 0.7 was associated with high probability for developing dysplastic joints and distraction index < 0.4 predicted normal hips with high probability.

Animals↗
PubMed1993

Lack of residual lung damage in horses in which Rhodococcus equi-induced pneumonia had been diagnosed.

The effect of prior Rhodococcus equi-induced pneumonia on pulmonary health was investigated in 5 horses (< 24 months old) using endoscopy, radiography, hematologic and bronchoalveolar lavage analyses, and pulmonary function testing. Rhodococcus equi-induced pneumonia had been diagnosed in principal horses when they were foals. Diagnosis was based on positive results of transtracheal aspiration and thoracic radiography at the time of initial clinical examination. Results of reevaluation of the respiratory system of these horses (R+) were compared with those of 5 age-matched healthy horses (R-) that lacked clinical or historical evidence of foalhood pneumonia. Significant differences in variables between the 2 groups of horses were not evident. In both groups, most horses had radiographic evidence of an accentuated bronchointerstitial pattern, although results of analysis of bronchoalveolar lavage specimens were normal and mononuclear cells predominated. Variability in results of the pulmonary function tests was observed within the between the 2 groups of horses. Only normalized dynamic lung compliance was slightly lower in the previously infected horses, but this difference was not significant. We concluded that horses previously infected with and successfully treated for R equi-induced pneumonia do not have detectable evidence of residual lung damage.

Actinomycetales Infections↗
PubMed1992

Thoracotomy in adult dairy cattle: 14 cases (1979-1991).

Fourteen cows were subjected to thoracotomy as an aid in the treatment of either septic pericarditis (n = 7) or unilateral pleuritis (fibrous or purulent; n = 7). Thoracic lesions were primary in 4 cows, secondary to traumatic reticuloperitonitis in 9 cows, and secondary to extension of a liver abscess in 1 cow. Thoracotomy was performed on 9 cows under local anesthesia. Surgery was performed on 5 cows under general anesthesia; 2 died during anesthesia, and 2 others were euthanatized. Of the 10 cows allowed to recover from surgery, 4 had pericarditis and 6 had pleuritis. Four cows with pleuritis had thoracic abscesses. All but 1 cow with pericarditis died or were euthanatized, and 5 of the 6 cows with pleuritis were discharged from the hospital. A year after surgery, 1 cow was culled because of infertility, and the other 5 cows were returned to production.

Anesthesia, General↗
PubMed1992

Clathrin assembly protein AP-2 induces aggregation of membrane vesicles: a possible role for AP-2 in endosome formation.

We have examined the in vitro behavior of clathrin-coated vesicles that have been stripped of their surface coats such that the majority of the clathrin is removed but substantial amounts of clathrin assembly proteins (AP) remain membrane-associated. Aggregation of these stripped coated vesicles (s-CV) is observed when they are placed under conditions that approximate the pH and ionic strength of the cell interior (pH 7.2, approximately 100 mM salt). This s-CV aggregation reaction is rapid (t1/2 < or = 0.5 min), independent of temperature within a range of 4-37 degrees C, and unaffected by ATP, guanosine-5'-O-(3-thiophosphate), and in particular EGTA, distinguishing it from Ca(2+)-dependent membrane aggregation reactions. The process is driven by the action of membrane-associated AP molecules since partial proteolysis results in a full loss of activity and since aggregation is abolished by pretreatment of the s-CVs with a monoclonal antibody that reacts with the alpha subunit of AP-2. However, vesicle aggregation is not inhibited by PPPi, indicating that the previously characterized polyphosphate-sensitive AP-2 self-association is not responsible for the reaction. The vesicle aggregation reaction can be reconstituted: liposomes of phospholipid composition approximating that found on the cytoplasmic surfaces of the plasma membrane and of coated vesicles (70% L-alpha-phosphatidylethanolamine (type I-A), 15% L-alpha-phosphatidyl-L-serine, and 15% L-alpha-phosphatidylinositol) aggregated after addition of AP-2, but not of AP-1, AP-3 (AP180), or pure clathrin triskelions. Aggregation of liposomes is abolished by limited proteolysis of AP-2 with trypsin. In addition, a highly purified AP-2 alpha preparation devoid of beta causes liposome aggregation, whereas pure beta subunit does not, consistent with results obtained in the s-CV assay which also indicate the involvement of the alpha subunit. Using a fluorescence energy transfer assay we show that AP-2 does not cause fusion of liposomes under physiological solution conditions. However, since the fusion of membranes necessarily requires the close opposition of the two participating bilayers, the AP-2-dependent vesicle aggregation events that we have identified may represent an initial step in the formation and fusion of endosomes that occur subsequent to endocytosis and clathrin uncoating in vivo.

Adaptor Proteins, Vesicular Transport↗
PubMed1992

Effects of intramuscular administration of glycosaminoglycan polysulfates on signs of incipient hip dysplasia in growing pups.

We tested the hypothesis that treatment of growing, susceptible (to hip dysplasia) pups by IM administration of glycosaminoglycan polysulfates would mitigate the signs of incipient hip dysplasia. In 1 experiment, 7 pups, selected at random from 2 litters, were administered glycosaminoglycan polysulfates (2.5 mg/kg of body weight, IM) twice weekly, and 7 control pups from the same litters were given sterile buffered 0.9% saline solution from the age of 6 weeks to 8 months. Hip joints were examined by radiography, with pups in the standard, limbs-extended position. At 8 months of age, all pups in this experiment did not manifest femoral head subluxation radiographically. The Norberg angle, a measure of coxofemoral congruity, improved from a mean +/- SEM value of 102 degrees +/- 1 degrees in controls to 106 degrees +/- 1 degrees in treated pups (P = 0.008). Pups were not subjected to necropsy. In the second experiment, 8 pups were selected at random from 2 litters and were administered 5 mg of glycosaminoglycan polysulfates/kg, IM, twice weekly from 6 weeks to 8 months of age. Similarly, 8 control pups were administered saline solution. At 8 months of age, hip joints were examined by radiography with pups in the standard position; at necropsy, intra-articular tissues were evaluated macroscopically and biochemically. Of 8 treated pups, none had subluxation radiographically, whereas 4 of 8 control dogs had femoral head subluxation. Mean Norberg angle on the radiographs was 109.7 degrees +/- 1.6 degrees for the treated group and was 101.5 degrees +/- 1.6 degrees for controls, representing a mean improvement in coxofemoral congruity of 8.2 degrees in the treated pups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Caudocranial horizontal beam radiographic projection for evaluation of femoral fracture and osteotomy repair in dogs and cats.

A new radiographic projection of the femur was evaluated for use in the assessment of fracture or osteotomy repair in small animals. The view is obtained by directing the x-ray beam horizontally through the hind limb, from caudad to craniad, with the animal positioned in lateral recumbency, the hip flexed, and the stifle extended. Views obtained, using the new projection, were compared with the standard ventrodorsal views of the pelvis, with hind limbs extended. Osteotomy lines in the femoral shaft were significantly (P less than 0.01) more visible on the horizontal beam view. Significant difference was not evident in visibility of fracture lines between the 2 radiographic projections. The horizontal beam view was easily obtained, and equivalent to the standard ventrodorsal view for radiographic evaluation of femoral fracture and osteotomy repair.

Animals↗