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D M Shasby

Publications and source records attributed to D M Shasby.

At least 37 records · Page 2Linked to original sources
PubMed1992

Staphylococcus aureus alpha-toxin permeabilizes the basolateral membrane of a Cl(-)-secreting epithelium.

Apical membrane ion channels control the rate of transepithelial electrolyte transport in many epithelia. One way to study such channels in their native location, the apical membrane, is to eliminate the resistance of the basolateral membrane to ion flow. Then the opening and closing of apical channels can be measured as a transepithelial current, free from the influence of basolateral membrane transport processes. To develop a method that would permeabilize an epithelial basolateral membrane to ions and nucleotides, we examined the effect of Staphylococcus aureus alpha-toxin on the Cl(-)-secreting T84 epithelial cell line. alpha-Toxin permeabilized the basolateral, but not the apical membrane to Cl-, adenosine 3',5'-cyclic monophosphate (cAMP), and GTP. However, the integrity of signal-transduction pathways, the regulation of apical membrane Cl- channels, and the transepithelial resistance remained intact. In the course of examining the effect of ATP, we found that the basolateral membrane contained purinergic receptors that both stimulated Cl- secretion on their own and, at high concentrations, inhibited cAMP-induced Cl- secretion. These effects of extracellular ATP were eliminated after prolonged exposure to ATP, suggesting receptor downregulation. In addition, depletion of intracellular ATP following permeabilization prevented cAMP-dependent regulation of apical Cl- channels. We conclude that alpha-toxin may prove to be a useful tool for studying the regulation and properties of apical membrane ion channels.

Adenosine Triphosphate↗
PubMed1992

Histamine, actin-gelsolin binding, and polyphosphoinositides in human umbilical vein endothelial cells.

Histamine activates inositol phospholipid metabolism, increases calcium, and causes a change in shape of human umbilical vein endothelial (HUVE) cells. Changes in endothelial cell shape are determined, in part, by changes in the actin cytoskeleton. Gelsolin is an actin-binding protein with the potential to alter the actin cytoskeleton in response to changes in cell calcium and/or changes in polyphosphoinositides. Therefore, we examined the interactions of actin and gelsolin in HUVE cells in which inositol phospholipid metabolism was activated with histamine. In HUVE cells exposed to histamine we estimated actin-gelsolin binding by quantitating actin and gelsolin, immunoprecipitated with anti-gelsolin Sepharose. We estimated the relative amount of filamentous actin in the histamine-exposed HUVE cells by quantitating the amount of actin that was Triton soluble. We also measured the amount of phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2) in the HUVE cells before and after exposure to histamine. We found that histamine decreased the amount of actin that was immunoprecipitated with gelsolin, decreased the fraction of cell actin that was Triton soluble, and increased PIP and PIP2. These results demonstrate that histamine promotes actin filament formation in HUVE cells and that histamine-mediated changes in actin-gelsolin binding in these cells are better predicted by changes in polyphosphoinositides than by increases in cell calcium.

Actins↗
PubMed1992

Mastoparan activates apical chloride and potassium conductances, decreases cell volume, and increases permeability of cultured epithelial cell monolayers.

Mastoparan is a tetradecapeptide. Mastoparan added to the apical surface of monolayers of Madin-Darby canine kidney (MDCK) epithelial cells, cultured on micropore filters, activated ion transport and increased the permeability of the paracellular pathway across the monolayers. In monolayers of similar MDCK cells in which the basolateral membrane was permeabilized with Staphylococcus aureus alpha toxin (Staph. alpha toxin), the effects of mastoparan on apical membrane ion conductances were dependent on the presence of guanosine triphosphate (GTP). Mastoparan and GTP increased apical membrane chloride conductance more than potassium conductance, with very little change in sodium conductance. In intact monolayers, addition of barium to the apical bath prevented mastoparan activation of ion transport and the increase in paracellular permeability. Increasing bath potassium to 130 mM also reduced ion transport and prevented the increase in paracellular permeability. We hypothesized that these observations could be linked by mastoparan activation of apical chloride and potassium conductances, with consequent decreases in cell volume and resultant increases in paracellular permeability. Addition of 270 mM mannitol to isosmotic media to decrease cell volume decreased MDCK monolayer transepithelial resistance. Addition of mastoparan to monolayers of MDCK cells grown on micropore filters decreased cell volume to the same extent as addition of 270 mM mannitol to isosmotic media. Addition of the potassium channel inhibitor, barium, prevented the decrease in cell volume in response to mastoparan. Mastoparan activates apical membrane chloride and potassium conductances in MDCK cells. The loss of these ions from the cells decreases cell volume, and the decrease in cell volume increases the permeability of the paracellular pathway.

Animals↗
PubMed1992

Interaction of the Pseudomonas aeruginosa secretory products pyocyanin and pyochelin generates hydroxyl radical and causes synergistic damage to endothelial cells. Implications for Pseudomonas-associated tissue injury.

Pyocyanin, a secretory product of Pseudomonas aeruginosa, has the capacity to undergo redox cycling under aerobic conditions with resulting generation of superoxide and hydrogen peroxide. By using spin trapping techniques in conjunction with electron paramagnetic resonance spectrometry (EPR), superoxide was detected during the aerobic reduction of pyocyanin by NADH or porcine endothelial cells. No evidence of hydroxyl radical formation was detected. Chromium oxalate eliminated the EPR spectrum of the superoxide-derived spin adduct resulting from endothelial cell exposure to pyocyanin, suggesting superoxide formation close to the endothelial cell plasma membrane. We have previously reported that iron bound to the P. aeruginosa siderophore pyochelin (ferripyochelin) catalyzes the formation of hydroxyl free radical from superoxide and hydrogen peroxide via the Haber-Weiss reaction. In the present study, spin trap evidence of hydroxyl radical formation was detected when NADH and pyocyanin were allowed to react in the presence of ferripyochelin. Similarly, endothelial cell exposure to pyocyanin and ferripyochelin also resulted in hydroxyl radical production which appeared to occur in close proximity to the cell surface. As assessed by 51Cr release, endothelial cells which were treated with pyocyanin or ferripyochelin alone demonstrated minimal injury. However, endothelial cell exposure to the combination of pyochelin and pyocyanin resulted in 55% specific 51Cr release. Injury was not observed with the substitution of iron-free pyochelin and was diminished by the presence of catalase or dimethyl thiourea. These data suggest the possibility that the P. aeruginosa secretory products pyocyanin and pyochelin may act synergistically via the generation of hydroxyl radical to damage local tissues at sites of pseudomonas infection.

Animals↗
PubMed1991

Synergistic effects of a calcium ionophore and activators of protein kinase C on epithelial paracellular permeability.

Oxidants reversibly increase the paracellular permeability of Madin Darby canine kidney (MDCK) epithelial cell monolayers, and the decrease in resistance occurs within 10 to 15 min of initiating oxidant exposure. Oxidants also initiate hydrolysis of phosphatidylinositol in MDCK cells, with resultant increases in diacylglycerol and inositol phosphates. Phorbol esters and synthetic diacylglycerols increase the paracellular permeability of MDCK monolayers with a time course similar to the oxidants. In contrast, calcium ionophores increase MDCK monolayer paracellular permeability only after 2 to 3 h of exposure. Because the products of the oxidant-initiated phospholipid hydrolysis would be likely to both activate protein kinase C and increase cell calcium, we asked if ionomycin, a calcium ionophore, and phorbol esters or diacylglycerols, activators of protein kinase C, might not act in concert to alter MDCK monolayer paracellular permeability. When ionomycin was added alone to MDCK monolayers, there was an increase in cell calcium, activation of a lumen negative current, a limited transitory decrease in transepithelial resistance, but no increase in mannitol flux across the monolayers. When phorbol dibutyrate (PDBU) or oleyl acetyl glycerol (OAG) were added to MDCK monolayers, there was no current activated, there was a progressive decrease in transepithelial resistance, and there was an increase in mannitol flux across the monolayers which was evident within 20 to 40 min of adding the agent. When 1 microM ionomycin was added to the monolayers along with PDBU or OAG, there was a synergistic increase in paracellular permeability of the monolayers when compared to addition of ionomycin, PDBU, or OAG alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗
PubMed1990

Oxidants, ATP depletion, and endothelial permeability to macromolecules.

Oxidants can reversibly increase the permeability of endothelium to ions and macromolecules. Oxidants also deplete ATP in cultured endothelial cells. We asked if oxidant-mediated ATP depletion, alone, accounted for the effects of oxidants on endothelial permeability to macromolecules. When porcine pulmonary artery endothelial cells were exposed to 2.5 mmol/LH2O2, ATP was depleted to 31.7% +/- 1.8% of control within 15 minutes and was reduced to 23.1% +/- 2.0% of control after 30 minutes. To determine if this magnitude of ATP depletion could account for the oxidant-induced increase in endothelial permeability to macromolecules, we measured ATP in endothelial cells exposed to metabolic inhibitors of ATP production. We then measured the effects of these metabolic inhibitors on endothelial monolayer permeability to macromolecules. ATP levels were reduced to 44% +/- 4% of control by 12 mmol/L deoxyglucose (DOG) in the absence of glucose and to 2% +/- 1.3% of control by DOG with 25 nmol/L antimycin A in the absence of glucose. Reduction of endothelial cell ATP to these levels with the metabolic inhibitors did not alter the flux of albumin or dextran across the endothelial monolayers. Thus ATP depletion, by itself, does not explain oxidant-induced changes in endothelial permeability to macromolecules.

Adenosine Triphosphate↗
PubMed1990

The conductance of cultured epithelial cell monolayers: oxidants, adenosine triphosphate, and phorbol dibutyrate.

Oxidants are one class of inflammatory molecules that may contribute to an increase in epithelial permeability to water and solutes that commonly occurs during acute inflammation. We and others have observed that oxidants reversibly alter the paracellular conductance of Madin Darby canine kidney epithelial (MDCK) cell monolayers. The mechanism by which oxidants reversibly alter MDCK monolayer conductance is not yet fully understood. Some investigators have suggested that oxidants might alter MDCK monolayer paracellular conductance by depleting adenosine triphosphate (ATP) in the cells. When we exposed MDCK cells to doses of oxidants that increased monolayer paracellular conductance in earlier studies, ATP was depleted within 10 min. However, when ATP was depleted to similar levels with an inhibitor of glycolytic ATP production, 2-deoxy-D-glucose (DOG), monolayer paracellular conductance was not increased. Severe ATP depletion with DOG and the mitochondrial metabolic inhibitor, antimycin A (AA), had very limited, ATP-independent effects on paracellular conductance. As an alternative explanation for the effects of oxidants on MDCK monolayer paracellular conductance, we had reported that oxidants increased production of inositol phosphates and diglycerides in MDCK cells. Synthetic diglyceride and phorbol dibutyrate (PDBU) increased MDCK monolayer conductance to ions and mannitol in earlier studies. When MDCK cell ATP was depleted with DOG (to the level caused by oxidants), the increase in conductance following PDBU was not different from that observed in control cells. More severe ATP depletion, with DOG and AA, prevented the increase in conductance following PDBU.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1989

Neutrophil cathepsin G increases calcium flux and inositol polyphosphate production in cultured endothelial cells.

Exposure of endothelial cells (ENDO) to human neutrophil cathepsin G (CG) increases albumin flux across the endothelial monolayer. Since calcium influences cell shape and barrier function of ENDO monolayers, the current study was designed to determine if CG acted through alterations in Ca2+ homeostasis in ENDO. The role of Ca2+ in the increased permeability of ENDO monolayers to albumin after exposure to CG was studied by using ENDO monolayers cultured on polycarbonate filters. Exposure of ENDO monolayers to CG in the presence of the Ca2+-antagonist lanthanum partially prevented the increase in albumin flux, but exposure in the presence of agents that block voltage-regulated calcium channels did not block the increase in albumin flux. To monitor the effect of CG on Ca2+-flux, ENDO were labeled with 45Ca2+ and changes in Ca2+ flux were monitored by the release of 45Ca2+. From 1 to 15 minutes after exposure of ENDO to CG, there was increased release of 45Ca2+ compared with control cells. Calcium channel blocking agents did not inhibit the increased release of 45Ca2+, but lanthanum partially blocked the increase. The increased release of Ca2+ appeared to be due, at least in part, to activation of phospholipase C because there was an increase both in inositol polyphosphate species and in diglycerides after incubation of ENDO with CG. These studies support the hypothesis that CG increases the flux of calcium in ENDO, that this increase in Ca2+ flux may result from activation of phospholipase C, and that this system may be involved in the decreased barrier properties of the ENDO after CG exposure.

Albumins↗
PubMed1989

Histamine and inositol phosphate accumulation in endothelium: cAMP and a G protein.

Histamine increases microvascular permeability through a calcium-dependent process, and histamine occupancy of the H1-receptor increases calcium in cultured endothelial cells. Agents that increase adenosine 3',5'-cyclic monophosphate (cAMP) in endothelial cells prevent the in vivo increase in microvascular permeability that follows histamine exposure. In the current experiments, histamine occupancy of the H1-receptor increased the flux of albumin across monolayers of cultured human umbilical vein endothelial cells (HUVEC). This was prevented by pretreating the cells with theophylline, forskolin, and 8-bromo-cAMP (BrcAMP), which also decreased the flux of albumin across control monolayers. Exposing the cells to histamine increased inositol phosphate accumulation in the cells, and this was prevented by the H1-antagonist pyrilamine but not by theophylline, forskolin, and BrcAMP. Exposing the cells to histamine increased intracellular calcium measured with fura-2. The increase in cell calcium was prevented by pyrilamine but not by pretreatment with theophylline, forskolin, and BrcAMP. When endogenous cell GTP was depleted by permeabilizing the membranes of the endothelial cells with Staphylococcus aureus alpha-toxin, histamine-stimulated inositol phosphate accumulation was enhanced with addition of GTP but not with addition of GDP to the buffer. Addition of GTP alone to the buffer did not increase inositol phosphate accumulation in alpha-toxin-treated cells. Histamine stimulates inositol phosphate accumulation in HUVEC via a G protein. Inhibition of the edemagenic effects of histamine by cAMP does not occur by interrupting this signal transduction pathway between the binding of histamine to its receptor and the increase in intracellular calcium.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1989

Effects of chlorinated amines on endothelial and epithelial barriers in vitro and ex vivo.

Chlorinated amines are long-lived oxidants released from inflammatory cells. They have been observed to alter the function of important inflammatory molecules. Whether they can contribute directly to the inflammatory alteration of cellular barriers is not known. Monolayers of cultured porcine pulmonary artery endothelial cells, monolayers of cultured dog kidney tubular epithelial cells (MDCK), and the vascular surface of an isolated perfused rabbit lung were exposed to taurine chloramine. Taurine chloramine increased albumin flux across the endothelium, decreased the electrical resistance across the epithelium, and increased the hydraulic conductivity of the rabbit lung vasculature. These alterations in barrier function appeared to occur in the absence of cytolysis of the cells making up the barriers. These results suggest that chlorinated amines, long-lived oxidants released from inflammatory cells, may contribute directly to alteration of cellular barriers.

Albumins↗
PubMed1988

Oxidants and conductance of cultured epithelial cell monolayers: inositol phospholipid hydrolysis.

Reactive oxidants contribute to the alterations in endothelial and epithelial permeability that characterize the inflammatory response. We previously noted that noncytolytic doses of oxidants reversibly decreased the electrical resistance across cultured monolayers of Madin-Darby canine kidney (MDCK) cells (J. Clin. Invest. 76: 1155-1168, 1985). In this investigation, we have found that similar doses of oxidants initiate inositol phospholipid hydrolysis by a phospholipase C in cultured MDCK cells, with resultant increases in inositol polyphosphates, phosphatidic acid, and 1,2 diglycerides. Activation of this pathway is linked to activation of protein kinase C in many cells. The addition of phorbol 12,13-dibutyrate (PDBU) and 1-oleoyl-2-acetyl-sn-glycerol, activators of protein kinase C, decreased the electrical resistance across MDCK monolayers cultured on micropore filters similar to the effects of hydrogen peroxide. In contrast, the addition of 4 alpha-phorbol 12,13-didecanoate, a chemically similar compound that does not activate protein kinase C, did not decrease the electrical resistance. When MDCK monolayers were exposed to PDBU, fixed, and stained with rhodamine phallicidin, the peripheral band of actin in the cells showed a loss of staining density and continuity similar to the changes in phallicidin staining we previously noted in cells exposed to hydrogen peroxide. These data are consistent with the hypothesis that some of the reversible effects of oxidants on epithelial barriers are mediated through phospholipase C hydrolysis of inositol phospholipids with consequent activation of protein kinase C.

Animals↗
PubMed1988

Activated endothelial cells in culture suppress baroreceptors in the carotid sinus of dog.

Vascular stretch increases the activity of arterial baroreceptors along with the production and release of substances from the endothelium. We hypothesized that endothelial factors modulate the sensitivity of baroreceptors during increases in arterial pressure. Baroreceptor activity was recorded from single fibers innervating the isolated carotid sinus of dogs anesthetized with chloralose after removal of the endothelium (balloon denudation) and after replacing into the denuded sinus bovine aortic endothelial cells cultured on microcarrier beads. The endothelial cells were activated with either the calcium ionophore A23187 (2 microM) or bradykinin (10 microM). The threshold pressure (n = 7) determined with a slow ramp increase in static pressure averaged 73 +/- 7 (SEM) mm Hg during exposure to naked beads and was increased significantly (96 +/- 18 mm Hg; p less than 0.05) during exposure to endothelial cell cultures. During stepwise increases in pressure, activity (n = 6) averaged 14 +/- 5, 40 +/- 8, and 54 +/- 8 spikes/sec at 75, 125, and 175 mm Hg during exposure to naked beads and decreased significantly to 2 +/- 2, 30 +/- 11, and 35 +/- 12 spikes/sec at equivalent pressures during exposure to the cell cultures. The activity was restored after replacement of the cell cultures with naked beads. The suppressed activity was not caused by changes in carotid sinus diameter or strain (sonomicrometers) or by the chemical activators that were also added to the naked beads. The results indicate that chemically activated endothelial cells release an inhibitory factor that suppresses baroreceptor activity.

Animals↗
PubMed1988

Exogenous oxidants initiate hydrolysis of endothelial cell inositol phospholipids.

Oxidants released from inflammatory cells contribute to the pathogenesis of acute inflammatory edema in many models. Chemically produced oxidants can reversibly alter the barrier properties of cultured endothelial and epithelial monolayers. This report examines the effects of nonlytic doses of H2O2 on endothelial cell lipids. H2O2 oxidized omega-6 fatty acids in the endothelial cells and initiated hydrolysis of endothelial cell phospholipids. When endothelial cells were exposed to peroxidized linoleic acid, it caused lysis of the cells at doses 1,000-fold lower than effective doses of H2O2. The phospholipid hydrolysis was directed primarily at the inositol phospholipids and consisted of both A and C type phospholipase activity. The phospholipase A hydrolysis resulted in increases in endothelial cell free fatty acids and lysophosphatidylinositol. The phospholipase C hydrolysis resulted in increases in diglycerides, phosphatidic acid, and inositol polyphosphate levels. The phospholipase C hydrolysis of phosphatidylinositol is known to activate protein kinase C in most cells. Stimulation of protein kinase C with phorbol-12,13-dibutyrate increased albumin flux across endothelial monolayers and altered endothelial cell shape, similar to effects of oxidants. These data are consistent with the hypothesis that oxidant-initiated hydrolysis of endothelial cell inositol phospholipids contributes to oxidant-mediated reversible changes in endothelial monolayer barrier function.

Animals↗
PubMed1987

Differential opening of the brain endothelial barrier following neutralization of the endothelial luminal anionic charge in vitro.

This study was undertaken to determine the effect of neutralization of brain endothelial cell luminal membrane anionic charge on endothelial permeability properties. Mouse brain microvessel endothelial cells were grown to confluence on a nitrocellulose filter. The permeability of the endothelium to Evan's blue dye (EBD) (molecular weight 960) and fluoresceinated dextran (FITC-D) (molecular weight 20,000), both polar molecules, was assessed before and after the exposure of the endothelium to cationic ferritin (CF) or native ferritin (NF). The use of CF resulted in a significant increase in permeability of the endothelium to EBD compared to NF. This result indicates that ablation of endothelial surface anionic charge enhances endothelial transport of a small, polar-charged molecule. Cationic ferritin did not increase the permeability of FITC-D compared to NF. This negative result is not surprising because FITC-D differs from EBD in terms of charge and solubility as well as in size. The electrical resistance of the endothelial cell layer after the application of CF was unchanged from baseline values suggesting a transcellular rather than a paracellular route of the EBD leakage.

Animals↗
PubMed1987

Effects of albumin concentration on endothelial albumin transport in vitro.

Albumin transfer across cultured porcine pulmonary artery endothelial cell monolayers was studied at different concentrations of luminal and interstitial albumin. Increased interstitial and luminal albumin concentrations increased the rates of transfer of albumin from interstitium to lumen and lumen to interstitium, respectively. Interstitial-to-luminal albumin clearance reached a maximum rate at 725 microM interstitial albumin. The clearance of dextran from interstitium to lumen also increased when interstitial-to-luminal albumin clearance increased, suggesting that albumin was not transferred alone across the endothelium. The increase in interstitial-to-luminal albumin clearance did not occur in the absence of endothelial cells, at 4 degrees C, or when dextran or dextran sulfate sodium were added to the interstitial compartment. These data demonstrate that albumin concentrations can influence the rates of endothelial albumin transfer and that albumin can be transported across the endothelium by a process mediated by endothelial cells.

Animals↗
PubMed1987

Polarity of arachidonic acid metabolism by bovine aortic endothelial cell monolayers.

Monolayers of bovine aortic endothelial cells cultured on micropore filters were used to determine the polarity of endothelial uptake, release, and transfer of arachidonic acid and some of its metabolites. Uptake and spontaneous release of arachidonic acid were more rapid at the luminal than at the interstitial surface. Transfer of arachidonic acid was more rapid from the luminal to the interstitial compartment than from the interstitial to the luminal compartment. After stimulation with the ionophore A23187, monolayers released arachidonate metabolites, including prostacyclin, to both the luminal and the interstitial compartments. The ability of the endothelium to rapidly take up and release arachidonic acid from the luminal surface and the ability to release biologically active eicosanoids to both the lumen and interstitium could be important for endothelial modulation of vascular events.

Animals↗