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Biomedical subjects

R J Mason

Publications and source records attributed to R J Mason.

At least 199 records · Page 11Linked to original sources
PubMed1982

Transepithelial transport by pulmonary alveolar type II cells in primary culture.

Fluid and electrolyte transport by epithelial cells in vitro can be recognized by the ability of cultured cells to form domes and by the electrical properties of monolayer cultures. Pulmonary alveolar epithelial cells are thought to be partially responsible for fluid movement in the fetal lung, but their role in electrolyte transport in the adult lung is not known. We isolated alveolar type II cells from adult rat lung and maintained them on plastic culture dishes alone, on plastic culture dishes coated with an extracellular matrix, and on collagen-coated Millipore filters. Numerous large domes were formed on culture dishes coated with the extracellular matrix; smaller domes were formed on uncoated plastic culture dishes. Sodium butyrate (3 mM) stimulated dome formation. Transmission electron microscopy showed that the epithelial cells had flattened but still retained lamellar inclusions and that the cells were polarized with microvilli on the apical surface facing the culture medium. The electrical properties of the monolayers maintained on collagen-coated Millipore filters were tested in two laboratories. The transepithelial potential differences were 0.7 +/- 0.1 mV (24 filters, seven experiments) and 1.3 +/- 0.1 mV (13 filters, two experiments) apical side negative, and the corresponding resistances were 217 +/- 11 ohm X cm2 and 233 +/- 12 ohm X cm2. Terbutaline (10 microM) produced a biphasic response with a transient decrease and then a sustained increase in potential difference. Amiloride (0.1 mM) completely abolished the potential difference when it was added to the apical side but not when it was added to the basal side, whereas 1 mM ouabain inhibited the potential difference more effectively from the basal side. Thus, type II cells form a polarized epithelium in culture, and these cells actively transport electrolytes in vitro.

Animals↗
PubMed1982

Angiotensin-converting enzyme substrates hydrolyzed by fibroblasts and vascular endothelial cells.

Angiotensin-converting enzyme (ACE, E.C. 3.4.15.1) activity has been documented in eight cultures of fibroblasts with the ACE substrates benzoyl-phe-ala-pro and hippuryl-his-leu. Hydrolysis of these ACE substrates by fibroblasts is inhibited by SQ-14225 and SQ-20881, specific inhibitors of ACE activity, and by EDTA. However, ACE activity in seven of eight cultures of fibroblasts tested is less than ACE activity in two cultures of vascular endothelial cells. The rats of hydrolysis of benzoyl-phe-ala-pro by fibroblasts and by endothelial cells differ at high substrate concentrations; therefore, the ACE activity in fibroblasts may be due to either a different isoenzyme of ACE of a different accessibility to substrate. Production of angiotensin II from angiotensin I is documented in cultures of vascular endothelial cells but not in cultures of fibroblasts, however, angiotensin II is further degraded by fibroblasts and not by endothelial cells.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1982

Abnormalities of chromatic and luminance critical flicker frequency in multiple sclerosis.

Critical flicker frequency (CFF) was measured for stimuli varying in chromaticity only and in luminance only for patients with multiple sclerosis (MS) and for matched normal controls. The two CFF measurements showed different underlying linear interdependencies for the two groups, consistent with a greater loss of temporal luminance function than of temporal chromatic function in MS patients. These results are discussed in relation to the pathophysiology of demyelinated nerve fibers. It is suggested that demyelination affects all types of nerve fiber unselectively; in particular, no support is found for the notion of a special vulnerability of fibers carrying time-varying chromatic information.

Color Perception↗
PubMed1981

Multiple sclerosis. Luminance threshold and measurements of temporal characteristics of vision.

Luminance threshold, perceptual latency, double-flash resolution, and critical flicker frequency were examined in patients with multiple sclerosis (MS) and in normal control subjects. The intensities of the stimuli used to test the temporal properties of vision were equalized with respect to individual luminance thresholds. In eight patients with MS, all the properties tested showed abnormality, double-flash resolution being most commonly affected. Retinal sites were not however, uniformly abnormal according to these measures. We conclude that abnormal temporal properties of vision in patients with MS are not a simple functional consequence of altered luminance thresholds.

Adult↗
PubMed1981

HLA and renal transplantation: yet another approach.

Renal allografts obtained from living related donors have considerably better chances of success than allografts from cadavers. The genetic factors that influence graft survival are linked to the HLA gene complex. Although results of cadaver transplants have not improved significantly when donor and recipient are matched for HLA-A and -B antigens, accumulating data suggest that matching for the more recently recognised HLA-DR antigens may produce increased graft survival.

Graft Survival↗
PubMed1980

Metabolic properties and ultrastructure of alveolar type II cells isolated with elastase.

We used porcine pancreatic elastase to isolate type II cells from the lungs of rats; the yield and purity of the type II cells was better than that obtained by methods using trypsin. In 102 experiments we obtained 82 +/- 23 . 10(6) cells/rat, 68 +/- 11% (mean +/- S.D.) of which type II cells. This preparation of cells, when centrifuged over a discontinuous density gradient, yielded 25 +/- 10 . 10(6) cells/rat, 80 +/- 13% of which were type II cells (n = 102). The cells, after density gradient centrifugation, could be futher purified by centrifugal elutriation (94 +/- 3% type II cells, n = 22) or adherence in primary culture (94 +/- 2% type II cells, n = 34). Type II cells isolated with elastase are similar morphologically and biochemically to type II cells isolated from rats with trypsin. The preparations of cells appeared healthy by several different criteria: ultrastructure, exclusion of vital dye, lack of stimulation of oxygen consumption by exogenous sodium succinate, and linear rates of oxidation of [1-14C]palmitic acid and of incorporation of [1-14C]acetate into fatty acids. Type II cells consumed 75 +/- 20 nmol O2/10(6) cell per h, oxidized [1-14C]palmitic acid at a rate of 0.4 nmol/10(6) cells per h, and incorporated [1-14C]acetate into fatty acids at a rate of 7.5 nmol/10(6) cells per h.

Acetates↗
PubMed1980

Synthesis of phosphatidylcholine and phosphatidylglycerol by alveolar type II cells in primary culture.

Saturated phosphatidylcholine and phosphatidylglycerol are important components of pulmonary surface active material. We studied the synthesis of these two phospholipid classes by alveolar type II cells in primary culture. During a 20-h incubation, type II cells incorporated a high percentage of glycerol, acetate, and palmitate into phosphatidylcholine (61.2, 76.4, and 76.8% of lipid radioactivity, respectively) and into phosphatidylglycerol (16.7, 5.8, and 6.6%). Acetate was incorporated principally by de novo synthesis of fatty acids rather than by chain elongation. We studied the pathways for synthesis of saturated phosphatidylcholine and phosphatidylglycerol with type II cells that had been in culture for 1 day. Palmitate was incorporated nearly equally into positions 1 and 2 of saturated phosphatidylglycerol, but predominantly (72%) into position 2 of saturated phosphatidylcholine. These data imply that saturated phosphatidylcholine is synthesized at least in part by acylation of 1-acyl-2-lysophosphatidylcholine. Alveolar type II cells also incorporated a mixture of saturated 1-[9,10-3H]palmitoyl-2-lysophosphatidylcholine and 1-acyl-2-lysophosphatidyl-[1,2-14C]choline from the medium by direct acylation rather than by transacylation. As the duration of culture increased beyond 1 day, type II cells incorporated a lower percentage of palmitate into phosphatidylglycerol and saturated phosphatidylcholine.

Acetates↗
PubMed1980

Phospholipid composition and ultrastructure of A549 cells and other cultured pulmonary epithelial cells of presumed type II cell origin.

In order to assess the usefulness of A549, L-2, and AK-D cell lines as model systems for alveolar type II cells, we compared their phospholipid composition to that of fibroblasts grown under similar conditions. The percentage of disaturated phosphatidylcholine and phosphatidylglycerol, key phospholipids of purified surface-active material, was the same in epithelial cells and fibroblasts. When A549 cells were maintained in serum-free media for two days, ultrastructural examination showed an increase in cytoplasmic lamellar inclusions but there was no change in the percentage of disaturated phosphatidylcholine or phosphatidylglycerol. Because the lipid content of these cultured cells was very different from that of freshly isolated rat type II cells, we conclude that their suitability as model cell systems for type II cells is questionable.

Adenocarcinoma, Bronchiolo-Alveolar↗
PubMed1980

Irrelevance of local position information in visual adaptation to random arrays of small geometric elements.

Experiments were carried out to test whether spatial relationships between local pattern features are important in the production of pattern-specific visual adaptation effects. Evidence was found for sensitivity to the shape of local pattern features, but not to their relative positions. These findings are contrasted with recent results for texture discrminination where the visual system can make use of local position information.

Adaptation, Ocular↗
PubMed1979

Transformation and relational-structure schemes for visual pattern recognition. Two models tested experimentally with rotated random-dot patterns.

Two models for visual pattern recognition are described; the one based on application of internal compensatory transformations to pattern representations, the other based on encoding of patterns in terms of local features and spatial relations between these local features. These transformations and relational-structure models are each endowed with the same experimentally observed invariance properties, which include independence to pattern translation and pattern jitter, and, depending on the particular versions of the models, independence to pattern reflection and inversion (180 degrees rotation). Each model is tested by comparing the predicted recognition performance with experimentally determined recognition performance using as stimuli random-dot patterns that were variously rotated in the plane. The level of visual recognition of such patterns is known to depend strongly on rotation angle. It is shown that the relational-structure model equipped with an invariance to pattern inversion gives responses which are in close agreement with the experimental data over all pattern rotation angles. In contrast, the transformation model equipped with the same invariances gives poor agreement to the experimental data. Some implications of these results are considered.

Field Dependence-Independence↗
PubMed1979

Isolation of alveolar type II cells by centrifugal elutriation.

Centrifugal elutriation (counterflow centrifugation) was used to develop a reproducible method for obtaining a nearly pure population of isolated alveolar type II cells. Lung was dissociated into individual cells with recrystallized trypsin, and the type II cells were partially purified by centrifugation on a discontinuous density gradient. The alveolar type II cells were finally purified by centrifugal elutriation. Cells were collected from the elutriator rotor by stepwise increases in flow rates. Cells obtained at flow rates of 7 and 14 ml per min were lymphocytes, other small cells, a few type II cells and cell debris; cells collected at flow rates of 18 and 22 ml per min were mainly type II cells; and cells collected at flow rates of 28, 34 and 43 ml per min were macrophages, some type II cells, other lung cells and cell aggregates. At flow rates of 18 and 22 ml per min, 1.9 +/- 1.0 x 10(6) cells per rat lung (mean +/- S.D., n=30) were recovered of which 86 +/- 6% were type II cells. At these flow rates, 94% of the cells excluded the vital dye erythrosin B from their cytoplasm. They consumed oxygen at a rate of 101 +/- 21 nmol per hr . 10(6) cells (mean +/- S.D., n=4), and their oxygen consumption increased only 10% after 10 mM sodium succinate was added. The cells incorporated [14C]leucine into protein and lipid for 4 hr. Electron micrographs of the cells collected at flow rates of 18 and 22 ml per min show a high percentage of morphologically intact alveolar type II cells. We conclude that centrifugral elutriation is a reproducible method for obtaining nearly pure, metabolically active alveolar type II cells.

Animals↗
PubMed1979

Pulmonary alveolar type II cells isolated from rats. Release of phosphatidylcholine in response to beta-adrenergic stimulation.

It is unclear what factors control the secretion of pulmonary surface active material from alveolar type II cells in vivo. Other workers have suggested that cholinergic stimuli, adrenergic stimuli, and prostaglandins may all stimulate secretion. We isolated type II cells from the lungs of rats by treatment with elastase, discontinuous density centrifugation, and adherence in primary culture. beta-Adrenergic agonists, but not cholinergic agonists, caused an increase in the release of [(14)C]disaturated phosphatidylcholine, the major component of surface-active material, from type II cells in culture. The beta-adrenergic effect was stereo-selective, (-)-isoproterenol being 50 times more potent than (+)-isoproterenol. Terbutaline, 10 muM, a noncatecholamine beta-2 adrenergic agonist, caused a release of 2.0+/-0.5 (mean+/-SD) times the basal release of [(14)C]disaturated phosphatidylcholine in 3 h; the concentration of terbutaline causing half maximal stimulation was 800 nM. The terbutaline effect was blocked by propranolol, a beta-adrenergic antagonist (calculated K(d) = 6 nM), but not by phentolamine, an alpha-adrenergic antagonist. Isobutylmethylxanthine, a phosphodiesterase inhibitor, and 8-Br cyclic AMP, but not 8-Br cyclic guanosine monophosphate, also stimulated release. We conclude that type II cells secrete disaturated phosphatidylcholine in response to treatment with adrenergic stimulation.

Adrenergic alpha-Agonists↗
PubMed1978

Stimulation of secretion of disaturated phosphatidylcholine from isolated alveolar type II cells by 12-O-tetradecanoyl-13-phorbol acetate.

Alveolar type II synthesize and secrete pulmonary surface-active material; the stimuli for secretion in vivo and the mechanisms by which secretion occurs are not well understood. We studied the secretion of disaturated phosphatidylcholine, the principal component of surfactant, from a purified population of type II cells. We isolated type II type from the lungs of adult male rats by treatment with trypsin, centrifugation over discontinuous density gradients, and adherence in primary culture; our preparations were 93 +/- 5 per cent (mean +/- SD; n = 10) type II cells. Basal secretion was 2.9 +/- 1.0 per cent (n = 16) of total cellular carbon-14 [14C]-disaturated phosphatidycholine in 3 hours. We found that 10(-8) M 12-O-tetradecanoyl-13-phorbol-acetate (TPA), a substance that has been shown to stimulate secretion in other cell systems, caused a release of 14C-disaturated phosphatidylcholine that was 8.4 times the basal rate. TPA caused a greater release of disaturated phosphatidylcholine than did any other substance that we have tested. Low temperature (4 degree C) inhibited the basal release by 85 per cent and the TPA-stimulated release by 98 per cent. The effect of TPA was also inhibited 25 per cent by 10(-6) M colchicine and 33 per cent by 10(-5) M vinblastine. Medium from control cells contained 6.3 +/- 1.3 per cent (mean +/- SD; n = 5) of total cellular lactate dehydrogenase (a marker for cell damage) after a 3-hour incubation period; medium from cells treated with TPA contained a similar amount, 6.7 +/- 1.5 per cent (n = 5). We concluded that the TPA-induced secretion of disaturated phosphatidylcholine is an active process probably mediated by microtubules. Because it has a large stimulatory effect on secretion, TPA may be useful for the study of the mechanisms by which surfactant is secreted.

Animals↗
PubMed1978

Glucocorticoid binding by isolated lung cells.

Synthesis of surfactant in the lung of fetal, and perhaps adult, animals responds to glucorticoids, and glucocorticoid receptor activity has been identified in this tissue of several sepecies. To determine whether receptor is present in the alveolar type II cell, which is the site of surfactant production, we studied glucocorticoid binding by various populations of lung cells. Specific binding was demonstrated in freshly isolated populations of rat lung cells containing primarily alveolar type II cells, in organotypic cultures derived from fetal rat lung containing 90% type II cells, in cultured A549, L-2, and F-42 cell lines which apparently originated from type II cells, and in human lung fibroblastic cells. The equilibrium dissociation constants for nuclear binding of dexamethasone by intact cells at 37 C ranged from 5.0--10.8 nM, and the number of binding sites per cell ranged from 5,700--57,000. In cytosol preparations from L-2 and A549 cells, there was equivalent specific binding of both natural and synthetic corticosteroids, and binding activity had the expected specificity for steroids with glucocorticoid activity. These findings indicate that glucocorticoid receptor is present in both fetal and adult pulmonary type II cells and in cell lines which apparently originated from these cells. The presence of receptor in type II cells in consistent with direct action of glucocorticoids on these cells in vivo.

Cell Line↗