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R J Mason

Publications and source records attributed to R J Mason.

At least 19 recordsLinked to original sources
PubMed1992

Pulmonary surfactant secretion is regulated by the physical state of extracellular phosphatidylcholine.

Pulmonary alveolar type II cells synthesize, secrete, and recycle the components of pulmonary surfactant. In this report we present evidence that dipalmitoylphosphatidylcholine is a potent inhibitor of surfactant lipid secretion by type II cells. Monoenoic and dienoic phosphatidylcholines with fatty acids of 16 or 18 carbons are ineffective as inhibitors of surfactant lipid secretion. In contrast, disaturated phosphatidylcholines, with either symmetric or asymmetric pairs of fatty acids of 14, 16, or 18 carbons, exhibit inhibition of surfactant secretion that correlates extremely well with the phase transition temperature (Tc) of the phospholipid. The inhibitory activity of dipalmitoylphosphatidylcholine is not dependent upon lipid stereochemistry. N-Methylated derivatives of dipalmitoylphosphatidylethanolamine are significantly less effective than phosphatidylcholine as inhibitors. Phosphatidylcholines below their phase transition temperature are inhibitors of surfactant secretion, whereas those above their phase transition temperature are either ineffective or weakly inhibitory. The phase transition dependence of inhibition is observed when type II cells are incubated at 37 degrees C with different species of phosphatidylcholine. In addition, if type II cells are stimulated to secrete at different temperatures the efficacy of a given phospholipid as an inhibitor is dependent on its relationship to Tc (i.e. dipalmitoylphosphatidylcholine with a Tc of 41 degrees C significantly inhibits secretion at 37 degrees C but not at 42 degrees C). Inhibition of surfactant secretion by dipalmitoylphosphatidylcholine is abrogated when it is incorporated into the same liposome with dioleoylphosphatidylcholine as a 50:50 mixture. In contrast, the simultaneous addition of two separate populations of liposomes, one composed of dipalmitoylphosphatidylcholine and the other composed of dioleoylphosphatidylcholine, does not significantly alter the inhibitory activity found with dipalmitoylphosphatidylcholine alone. These data provide compelling evidence that the physical state of phosphatidylcholine can regulate surfactant secretion from alveolar type II cells and suggest a unique mechanism for regulating exocytosis in the alveolus of the lung.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1992

Primary structure of rat pulmonary surfactant protein D. cDNA and deduced amino acid sequence.

Surfactant protein D (SP-D) is a carbohydrate-binding glycoprotein containing a collagen-like domain that is synthesized by alveolar type II epithelial cells. The complete primary structure of rat SP-D has been determined by sequencing of a cloned cDNA. The protein consists of three regions: an NH2-terminal segment of 25 amino acids, a collagen-like domain consisting of 59 Gly-X-Y repeats, and a COOH-terminal carbohydrate recognition domain of 153 amino acids. There are 6 cysteine residues present in rat SP-D: 2 in the NH2-terminal noncollagenous segment and 4 in the COOH-terminal carbohydrate-binding domain. The collagenous domain contains one possible N-glycosylation site. The protein is preceded by a cleaved, NH2-terminal signal peptide. SP-D shares considerable homology with the C-type mammalian lectins. Hybridization analysis demonstrates that rat SP-D is encoded by a 1.3-kilobase mRNA which is abundant in lung and highly enriched in alveolar type II cells. Extensive homology exists between rat SP-D and bovine conglutinin.

Amino Acid Sequence↗
PubMed1992

Alterations in eicosanoid production by rat alveolar type II cells isolated after silica-induced lung injury.

Although alveolar type II cells in primary culture have been shown to produce eicosanoids and exposure of type II cells to silica in vitro alters eicosanoid production, the production of eicosanoids by alveolar type II cells isolated after acute lung injury in vivo has not been evaluated. Therefore, we investigated the production of arachidonic acid (AA) metabolites by alveolar type II cells isolated after silica-induced lung injury. Alveolar type II cells were isolated from rats 14 days after intratracheal silica instillation and from untreated animals. Type II cells were separated into normotrophic and hypertrophic populations by centrifugal elutriation, and secreted eicosanoids were determined under basal and stimulated conditions by enzyme immunoassay on the day of isolation and after 1 day in culture. Under basal conditions, freshly isolated type II cells from silica-treated animals produced more prostaglandin (PG) E2 than 6-keto-PGF1 alpha or thromboxane B2 (TxB2). Production of all three prostanoids increased with increasing cell size. The calcium ionophore A23187 stimulated a less than 2-fold increase in PGE2 and 6-keto-PGF1 alpha production in all groups of cells. In contrast, this calcium ionophore greatly enhanced TxB2 and leukotriene C4 (LTC4) production by normotrophic type II cells from both untreated and silica-treated animals. Incubation with exogenous AA suggested that the increased capability of the hypertrophic cells to synthesize PGE2 and TxB2 was due primarily to an increase in arachidonate availability. The hypertrophic type II cells also appear to have increased prostacyclin synthase activity. There were no differences in the catabolism of PGE2 between the normotrophic and the hypertrophic type II cells.(ABSTRACT TRUNCATED AT 250 WORDS)

6-Ketoprostaglandin F1 alpha↗
PubMed1992

Surfactant protein C is expressed in alveolar type II cells but not in Clara cells of rat lung.

The expression of the surfactant-associated proteins in bronchiolar cells remains to be defined. We used in situ hybridization to identify sites of message expression of the surfactant-associated proteins A, B, and C (SP-A, SP-B, and SP-C) in adult and fetal rat lung. The expression of these messages by in situ hybridization was also compared with the localization of SP-A by immunocytochemistry. The localization of SP-A was used to identify type II cells and nonciliated bronchiolar epithelial (Clara) cells in these sections. The cRNA antisense probes for SP-A, SP-B, and SP-C appeared to hybridize over type II cells. Sense probes showed no localization or apparent specific hybridization. Messages for both SP-A and SP-B were also found in nonciliated bronchiolar epithelial (Clara) cells. However, no message for SP-C was observed in these cells. Clara cells from terminal to large bronchioles lacked detectable mRNA for SP-C. Expression of surfactant protein mRNAs was not detectable in type I cells, alveolar macrophages, interstitial cells, or vascular cells. Similarly, in fetal rat lung the messages for SP-A and SP-B but not SP-C were detected in bronchiolar cells. We conclude that rat Clara cells do not express SP-C mRNA, and thus SP-C can be regarded as a specific marker for rat type II cells.

Animals↗
PubMed1991

Temporal segregation of surfactant secretion and lamellar body biogenesis in primary cultures of rat alveolar type II cells.

Pulmonary alveolar type II cells synthesize and secrete the phospholipids of surfactant. However, type II cells isolated from adult rat lungs rapidly lose their characteristic morphology and differentiated functions (such as surfactant-specific phospholipid and protein biosynthesis) when maintained on tissue culture plastic. In this study, phospholipid secretion and its regulation by type II cells grown on tissue culture plastic were examined up to 8 days after isolation. Type II cells were preincubated with [3H]choline for varying 24-h periods during culture prior to examining phosphatidylcholine ([3H]PtdCho) secretion. Type II cells cultured for 4 days and incubated with [3H]choline 24 h before the secretion experiment failed to show significant basal and tetradecanoyl phorbol acetate (TPA, 100 nM)-stimulated [3H]PtdCho secretion (basal, 0.29 +/- 0.01%; TPA, 0.48 +/- 0.04%). In contrast, type II cells incubated with [3H]choline for the first 24 h during culture and then cultured for 3 more days showed significant [3H]PtdCho secretion (basal, 1.27 +/- 0.19%; TPA, 6.24 +/- 0.82%). Subcellular fractionation of type II cells revealed that [3H]choline was incorporated into phosphatidylcholines in a lamellar body-enriched fraction during the first 24 h of culture but that the assimilation of phosphatidylcholine into the lamellar body fraction progressively declined with increasing time in culture. Radiolabel incorporated into the lamellar body fraction labeled during the first 24 h of culture was detectable for up to 8 days in culture. The [3H]PtdCho incorporated into the lamellar body during the first 24 h of culture was lost gradually over 8 days, suggesting the continuous secretion or turnover of the lamellar bodies during culture.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Surface and tissue forces, surfactant protein A, and the phospholipid components of pulmonary surfactant in bleomycin-induced pulmonary fibrosis in the rat.

Administration of bleomycin to animals results in an alteration of the pressure-volume relationship of the lungs with an increased elastic recoil at any given volume. We sought to evaluate the relative importance of surface forces to elastic recoil by comparing the differences between the air and saline pressure-volume curves. The difference in elastic recoil between air- and saline-filled lungs was altered in bleomycin-treated rats when elastic recoil was compared at 35% of predicted TLC or at 80% of observed TLC. This pressure difference was present both during the early phase (Days 4 and 7) of the injury and acute inflammation as well as during the later phase (Days 14 to 28) when there was chronic inflammation and an elevation in the lung hydroxyproline content. The total amount of phospholipids recovered in lavage was decreased at Day 4 and increased more than 2.5-fold over saline-instilled control animals at Days 21 and 28. The percentage of phosphatidylglycerol was reduced and that of phosphatidylinositol increased. There was no consistent change in the percentage of phosphatidylcholine that was disaturated. The amount of surfactant protein A (SP-A) did not change during the course of the experiment and was not a useful independent marker of alveolar injury or changes in pulmonary compliance. The ratio of SP-A to total phospholipid decreased 14 to 28 days after instillation of bleomycin. These results support the hypothesis that individual components of surfactant are independently regulated and indicate that SP-A content in lavage is insensitive to lung injury and repair.

Animals↗
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↗
PubMed1977

Isolation and properties of type II alveolar cells from rat lung.

Type II alveolar cells can be isolated and partially purified from adult rat lung by a series of steps that includes enzymatic digestion of the lung with trypsin and separation of cells on a discontinuous albumin density gradient. The yield of the isolated type II cells depends on the supplier and the housing of the rats used to prepare the cells. With specific pathogen-free rats housed in a laminar flow hood, the yield was 20.3 x 10(6) cells per rat, of which 50 per cent were type II cells. With rats from 2 other suppliers and no special housing, the yields were 8.8 and 8.3 x 10(6) cells per rat, of which 67 and 65 per cent were type II cells. The ultrastructural appearance of the isolated cells was similar to that of cells from intact lung, except for some dilatation of the endoplasmic reticulum and the perinuclear space. Most cells (92 +/- 5 per cent) excluded the vital dye, trypan blue. The cells consumed O2 at the rate of 76 +/- 12 nmole per 10(6) cells per hour and released only 5.7 +/- 2.0 per cent of their lactate dehydrogenase, a cytoplasmic enzyme, into the medium after 1 hour of incubation. The isolated type II cells contained disaturated phosphatidylcholine, a major component of purified surface-active material. The cells, however, had a low glucose utilization compared to their O2 consumption, which may indicate an abnormality in the metabolism of glucose. This population of cells could be further purified to 89 per cent type II cells by unit gravity velocity sedimentation.

Animals↗