Concentration dependence of protein permeability across the canine visceral pleura

Water and protein movement across the pulmonary endothelial-visceral pleural membrane of spontaneously breathing anesthetized dogs was analyzed to determine if the protein concentration at the microvascular membrane (Cpro) influences microvascular permeability. The left lung was enclosed in a water-impermeable membrane, creating a visceral pleural space (VPS); fluid and solute fluxes were determined as the filtration or reabsorption of water and protein in the VPS. The plasma protein concentration was experimentally varied by plasmapheresis with saline replacement while the pleural fluid protein concentration was varied by introducing different concentrations of plasma mixed with saline into the VPS. Hydrostatic pressures were maintained within a physiologic range (pulmonary capillary pressure 12.1-16.1 mm Hg). The plasma protein concentration fell as low as 1.98 g/dl, and Cpro, calculated as the mean of the plasma and pleural fluid protein concentrations, ranged from 1.73 to 6.23 g/dl. The relationship between Cpro and the apparent homoporous diffusional permeability for protein (Phs), Phs(cm/sec X 10(-6] = 0.95 Cpro (g/dl) + 2.28, was highly significant (r = 0.87, P less than 0.01). In contrast, the hydraulic conductivity was not affected by a reduction in Cpro to this level (r = 0.21, P greater than 0.4). Although the solute concentration at the endothelial membrane should be considered when evaluating changes in protein permeability, under most experimental conditions the magnitude of this effect will be small.     

Transport of water and solutes across sheep visceral pleura

The fluid and solute transport properties of pleural tissue were studied using specimens of intact visceral pleura from adult sheep lungs. After thoracotomy, a shallow incision through the pleural surface permitted 10-cm2 by 10-micrometer pieces of visceral pleura free of lung parenchyma to be peeled off the lung surface. The pleura was then mounted as a planar sheet separating 2 reservoirs of Krebs-Ringer solution. Electrical potential and resistance, hydraulic water permeability, and diffusional permeability to water and several hydrophilic solutes were measured. The results showed that (1) no spontaneous voltage difference was present across the pleura; (2) electrical resistance (27.1 omega/cm2) was very low; (3) hydraulic water permeability was extremely high (1.64 X 10(-8) ml/dyne-s); and (4) diffusional permeability was high, varying from 5.24 X 10(-4) cm/s for water to 4 X 10(-5) cm/s for hemoglobin. Blue dextran (molecular weight, 2 X 10(6) daltons) did not cross the pleura in measurable quantities. We concluded that the isolated visceral pleura of the adult sheep is an extremely "leaky" tissue that probably does not actively transport salt and water. These findings are consistent with a passive model of pleural fluid formation and reabsorption, and suggest that the transport properties of normal pleural tissue are unlikely to be responsible for any differences in composition between interstitial and pleural fluids.     

Drugs and the pleura.

PURPOSE: To identify the drugs associated with pleural disease and to review the clinical, radiographic, and pleural fluid findings that occur, the natural history of the pleural reaction, and the response to therapy. DATA SOURCES: English-language articles published from January 1966 through April 1998 were identified through searches of the MEDLINE database, selective bibliographies, and personal files. DATA EXTRACTION: Case reports, letters, and review articles were assessed for relevancy. Reports of drug-associated pleural effusion, pleuritis, and/or pleural thickening were analyzed. Drug effect was believed to be causal when exposure induced pleural disease, when the pleural response remitted on discontinuation of the drug, and when the pleural disease recurred with reexposure. Drug association was inferred when the pleural disease occurred following drug exposure and remitted after drug discontinuation. The incidence, clinical presentation, dose and duration of drug therapy, chest radiographic findings, pleural fluid analysis, and response to therapy were recorded. CONCLUSIONS: A relatively small number of drugs were found to induce pleural disease when compared to the number of drugs implicated in causing disease of the lung parenchyma. Treatment of drug-induced pleural disease consists of drug therapy withdrawal and corticosteroids for refractory cases. Knowledge of the potential of drug-induced pleural disease will provide a clinical advantage to the physician and should lead to decreased morbidity and economic burden for the patient by avoidance of further diagnostic testing.     

Evidence for peptide transport across microsomal membranes.

Antigenic peptides bound to class I molecules of the major histocompatibility complex (MHC) are recognized by T-cell receptors during development of an antiviral immune response. T cells respond to peptides derived from cytoplasmic viral proteins as well as viral membrane proteins, indicating that a pathway exists for the transport of proteins or peptides from the cytosol into the compartment(s) where the MHC class I molecules assemble. To investigate this pathway, we have developed an in vitro assay for the transport of peptides into microsomal vesicles. This assay provides evidence for the transport of chemically synthesized peptides (13-21 amino acids) containing N-linked glycosylation acceptor sequences, which serve as glycosylation substrates. Their transport results in depletion of the pool of available dolichol high-mannose oligosaccharides in the lumen of the microsomal vesicles. We have observed transport of peptides derived from antigenic human immunodeficiency virus gag and influenza B nucleoprotein sequences, but transport of a third randomly selected peptide was not detected, suggesting specificity of the transport process. We were not able to demonstrate ATP dependence of this peptide transport process by using apyrase and an ATPase inhibitor. This result was unexpected in light of the recent identification of MHC-linked genes with homology to ATP-binding cassette transporters, which have been proposed to mediate peptide transport.     

Hypertonic saline alters ion transport across the human airway epithelium.

Aerosolized hypertonic saline is currently being investigated as a new agent for the treatment of impaired mucociliary clearance which occurs in many respiratory diseases. Mannitol aerosols, in particular dry powder inhalers, have been proposed as an alternative treatment to saline, offering the same osmotic load with other benefits. However, the effects of these hypertonic aerosols on airway epithelial ion transport processes have not been tested in human subjects in vivo. This report examines the effect of these solutions on airway ion transport using the nasal potential difference (PD) technique. Seven healthy nonsmoking adult volunteers were studied. On different days, a dose-response curve was constructed for the saline added to Krebs N-[2-hydroxyethyl] piperazine-N'-[2-ethanesulphonic acid] (HEPES) diluent. The reversibility of this saline effect was measured, and the response to additional saline (500 mM) and mannitol (1 M) compared. Hypertonic saline decreased nasal PD in a dose-related manner, with mean (SEM) decreases in PD (less negative) of 6.6 (1.5), 7.6 (1.6), 10.0 (2.0), 13.1 (2.9) and 14.8 (3.2) mV (n =4) for addition of 150 mM, 250 mM, 500 mM, 1,200 mM and 2,000 mM NaCl to the Krebs HEPES diluent, respectively. The effect of hypertonic saline was fully reversible with washout for 3 min (presaline 15.9 (0.5) mV, postwashout 15.8 (1.1) mV, (n=4)). The hypertonic saline response was rapid in onset, sustained for at least 4 min, and decreased PD from 13.7 (1.7) mV to 5.1 (1.3) mV (n = 7, p < 0.001). In contrast, addition of mannitol to the perfusate did not significantly alter nasal PD, with a nonsignificant trend towards an increase (more negative) in the PD, (premannitol 13.9 (1.6) mV, postmannitol 15.3 (2.0) mV, n=7). As the osmotic stimulus of the 1 M mannitol is similar to that of the 500 mM sodium chloride, the divergent nasal potential difference responses suggest that the response to the saline was specific to the sodium chloride itself and not the simultaneous change in osmolarity. This demonstrates that the human airway epithelium in vivo can respond to topical hypertonic saline independent of the altered osmolarity.     

Method for studying kinetics of light-induced transport across membranes.

A technique based on phase spectrophotometry is described for studying the rates of elementary processes associated with the light-driven transport of ions and molecules across membranes. The light-induced pumping of protons by bacteriorhodopsin reconstituted into phospholipid vesicles and by chloroplast thylakoids has been studied to illustrate the potential of this technique. The exciting light is modulated by a mechanical chopper over the frequency range 5 Hz to 2 kHz. The internal pH of the membrane vesicles is modulated at the same frequency as the exciting light but differs in phase because of the finite rate of proton pumping. Measurement of this phase difference or of the frequency dispersion of the amplitude of the internal pH modulation is accomplished by use of a lock-in amplifier. The results can be interpreted in terms of relaxation times characterizing the chemical steps in proton pumping. The shortest relaxation time that can be measured is about 50 microseconds, although the time resolution could be easily extended by use of faster light chopping techniques. At pH 8.0, two relaxation processes are associated with proton pumping by bacteriorhodopsin reconstituted into phospholipid vesicles; the relaxation times are 2 and 28 msec. Two relaxation processes also were found with chloroplast thylakoids at pH 7.8, with relaxation times of 2 and 16 msec. The former can be associated with photosystem II and the latter, with photosystem I.     

Macromolecule transport across the pulmonary microvessel walls

In summary, it has been difficult to assess the permeability properties of the pulmonary capillary membrane. However, new mathematical and experimental techniques have recently been developed which are of sufficient sensitivity and specificity to begin to evaluate the complex mechanisms responsible for many forms of lung pathology. While future work will undoubtedly need to address problems associated with heterogeneity of pulmonary blood flow, and with an equally heterogeneous population of vascular permeability and fluid formation sites, we currently need to focus on using the correct experimental approaches for assessing vascular permeability. The appropriate techniques are described in the text and indicate that the measurements of reflection coefficients using lymph obtained at high vascular pressures, filtration coefficients obtained from both isolated and intact lungs, and two-pore models are useful in assessing vascular permeability.     

Magnesium transport across colon ascendens of the rat

Concentration and voltage dependence of unidirectional Mg fluxes across the rat colon ascendens were measured in a modified Ussing chamber. Mucosa (M) to serosa (S) Mg flux exhibits a cellular component, whereas SM flux is totally diffusive. At all the concentrations between 0.125 and 8 mmol/liter MS Mg transport is higher than the flux in the opposite direction, resulting in Mg absorption. In contrast to Mg, in Ca transport a cellular component is involved in both directions across the tissue, 1 alpha, 25-Dihydroxyvitamin D3 has no influence on the Mg transport. Mg (5 mmol/liter) remarkably decreases MS Ca flux and reduces Ca absorption by 70%. The parallel decrease in MS Ca flux with that of the simultaneously measured paracellular marker mannitol and the voltage clamp experiments reveal that Mg has no influence on cellular Ca transport but only reduces diffusive MS Ca flux, possibly by decreasing transepithelial fluid absorption. The experiments demonstrate that the colon ascendens of the rat is capable of absorbing Mg at rates comparable to that found for Ca. There is evidence that Mg and Ca are transported by separate cellular mechanisms. Diffusive movement across the paracellular route plays an important role on net transport of both earth alkali ions.     

Selective and asymmetric molecular transport across electroporated cell membranes.

Transport of a divalent cation (Ca2+) and three DNA indicators [ethidium bromide (EB), propidium iodide (PI), and ethidium homodimer (EthD-1)] across electroporated membranes of several mammalian cell lines was found to be selective and asymmetrical. In low salt medium, Ca2+ and EB were preferentially transported across the anodefacing cell membrane while PI and EthD-1 predominately entered at the site facing the cathode. In high salt medium, the entry site for Ca2+ and EB was reversed to the cathode-facing hemisphere while it remained unchanged for PI and EthD-1. In all these experiments, the observed transport patterns remained unaffected whether the dyes (or ion) were present during or added after the electroporating pulse. The data suggest that asymmetric pores are created on both sides of the membrane facing the electrodes, with smaller pore size (but greater in number) on the anode side and larger pores (with a lower population) on the cathode side. Furthermore, the rate of resealing of the membrane pores is significantly enhanced in high ionic strength medium, thus affecting the entry site. The asymmetric transport pattern is neither caused by electrophoresis induced by the externally applied electric field nor due to one-sided membrane breakdown as previously believed.