Proteinase-activated receptor-2-mediated matrix metalloproteinase-9 release from airway epithelial cells

BACKGROUND

Matrix metalloproteinases (MMPs) digest extracellular matrix components and might be important mediators of tissue remodeling. Proteinase activated receptor-2 (PAR-2) is expressed in a variety of cell types including epithelial cells. PAR-2 receptors are activated by serine proteases such as trypsin and mast cell tryptase and have been implicated in inflammation.

OBJECTIVE

To study the effects of PAR-2-mediated airway epithelial cell activation on the production of MMP-9.

METHODS

A specific PAR-2-activating peptide and trypsin were used to activate the human airway epithelial cell line A549 as well as primary cultures of small airway epithelial cells (SAEC). MMP-2 and MMP-9 messenger RNA and enzymatic activity were evaluated by RT-PCR and gelatin zymography, respectively.

RESULTS

PAR-2-activating peptides upregulated MMP-9 mRNA expression and release of MMP-9 enzymatic activity from airway epithelial cells but had no effect on MMP-2 production. Dexamethasone and budesonide (10(-6) to 10(-10) mmol) inhibited PAR-2-mediated MMP-9 release. Pretreatment with indomethacin indicated that MMP-9 release was not prostaglandin dependent. Inhibitors of the MAP kinase MEK- 1, and NFkappaB showed that both pathways are important for PAR-2-mediated MMP-9 release. Trypsin, a physiologic PAR-2 activator, upregulated MMP-9 but also MMP-2 release from airway epithelial cells.

CONCLUSION

PAR-2 receptors appear to play an important role in the regulation of MMP-9 release from airway epithelial cells. As such, these receptors may be critical elements in tissue remodeling in asthma and other inflammatory conditions in the airways.

Human eosinophils release matrix metalloproteinase-9 on stimulation with TNF-alpha

BACKGROUND

The eosinophil is a prominent cell in allergic lung inflammation and is exposed to a range of cytokines, including TNF-alpha, at the site of allergen challenge. Matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinases (TIMPs) produced by inflammatory cells are thought to play a crucial role in interstitial matrix turnover and tissue remodeling in acute and chronic lung diseases. In addition, protein kinase C is known to be important in MMP-9 expression and secretion.

OBJECTIVE

We investigated the regulation of eosinophil-derived MMP-9 and TIMP proteins by TNF-alpha.

METHODS

Using RT-PCR and gelatin zymography, we investigated the ability of human eosinophils to produce and secrete active MMP-9 on stimulation with TNF-alpha. We also studied the production of TIMP-1 and TIMP-2 in eosinophils by using Western blotting.

RESULTS

The gelatinolytic activity of MMP-9 in unstimulated eosinophils was low, but it increased by 95% after TNF-alpha stimulation. This increase was regulated at both the transcriptional and translational levels. The transcription inhibitor actinomycin D, the nuclear factor kappaB (NFkappaB) inhibitor N-CBZ-Leu-Leu-Leu-AL, the protein synthesis inhibitor cycloheximide, and the protein kinase C inhibitor H7 significantly decreased MMP-9 activity in TNF-alpha-treated cells. TIMP-1 and TIMP-2 gene expression and protein production varied significantly among different cell donors.

CONCLUSION

Eosinophils, on stimulation with TNF-alpha, may play a major role in asthmatic airway remodeling through increased MMP-9 production at the inflammatory site.

Cell poking: quantitative analysis of indentation of thick viscoelastic layers

A recently introduced device, the cell poker, measures the force required to indent the exposed surface of a cell adherent to a rigid substratum. The cell poker has provided phenomenological information about the viscoelastic properties of several different types of cells, about mechanical changes triggered by external stimuli, and about the role of the cytoskeleton in these mechanical functions. Except in special cases, however, it has not been possible to extract quantitative estimates of viscosity and elasticity moduli from cell poker measurements. This paper presents cell poker measurements of well characterized viscoelastic polymeric materials, polydimethylsiloxanes of different degrees of polymerization, in a simple shape, a flat, thick layer, which for our purposes can be treated as a half space. Analysis of the measurements in terms of a linear viscoelasticity theory yields viscosity values for three polymer samples in agreement with those determined by measurements on a macroscopic scale. Theoretical analysis further indicates that the measured limiting static elasticity of the layers may result from the tension generated at the interface between the polymer and water. This work demonstrates the possibility of obtaining quantitative viscoelastic material properties from cell poker measurements and represents the first step in extending these quantitative studies to more complicated structures including cells.

Ins(3,4,5,6)P4 specifically inhibits a receptor-mediated Ca2+-dependent Cl- current in CFPAC-1 cells

We have examined the role of inositol 3,4,5,6-tetrakisphosphate [Ins(3,4,5,6)P4] in the control of Cl- current in CFPAC-1 cells. Intracellular Ins(3,4,5,6)P4 had no effect on basal current, but it produced a five- to sevenfold reduction in the Cl- current stimulated by either 2 microM extracellular ATP or by 1 microM extracellular thapsigargin. The half-maximally effective dose of Ins(3,4,5,6)P4 was 2.9 microM, and 4 microM blocked >80% of the ATP-activated current. In contrast, 10 microM Ins(1,4,5,6)P4, Ins(1,3,4,5)P4, or Ins(1,3,4,6)P4 enhanced rather than inhibited the ATP-activated Cl- current, although Ins(1,4,5,6)P4 only acted transiently. These stimulatory effects were Ca2+ dependent and largely inhibited by coapplication of equimolar Ins(3,4,5,6)P4. Inositol 1,3,4,5,6-pentakisphosphate, the precursor of Ins(3,4,5,6)P4, did not affect Cl- current. These data consolidate and extend the hypothesis that Ins(3,4,5,6)P4 is an important intracellular regulator of Cl- current in epithelial cells.

Polystyrene nanoparticles activate ion transport in human airway epithelial cells

BACKGROUND

Over the last decade, nanotechnology has provided researchers with new nanometer materials, such as nanoparticles, which have the potential to provide new therapies for many lung diseases. In this study, we investigated the acute effects of polystyrene nanoparticles on epithelial ion channel function.

METHODS

Human submucosal Calu-3 cells that express cystic fibrosis transmembrane conductance regulator (CFTR) and baby hamster kidney cells engineered to express the wild-type CFTR gene were used to investigate the actions of negatively charged 20 nm polystyrene nanoparticles on short-circuit current in Calu-3 cells by Ussing chamber and single CFTR Clchannels alone and in the presence of known CFTR channel activators by using baby hamster kidney cell patches.

RESULTS

Polystyrene nanoparticles caused sustained, repeatable, and concentration-dependent increases in short-circuit current. In turn, these short-circuit current responses were found to be biphasic in nature, ie, an initial peak followed by a plateau. EC(50) values for peak and plateau short-circuit current responses were 1457 and 315.5 ng/mL, respectively. Short-circuit current was inhibited by diphenylamine-2-carboxylate, a CFTR Cl(-) channel blocker. Polystyrene nanoparticles activated basolateral K(+) channels and affected Cl(-) and HCO(3) (-) secretion. The mechanism of short-circuit current activation by polystyrene nanoparticles was found to be largely dependent on calcium-dependent and cyclic nucleotide-dependent phosphorylation of CFTR Cl(-) channels. Recordings from isolated inside-out patches using baby hamster kidney cells confirmed the direct activation of CFTR Cl(-) channels by the nanoparticles.

CONCLUSION

This is the first study to identify the activation of ion channels in airway cells after exposure to polystyrene-based nanomaterials. Thus, polystyrene nanoparticles cannot be considered as a simple neutral vehicle for drug delivery for the treatment of lung diseases, due to the fact that they may have the ability to affect epithelial cell function and physiological processes on their own.

Regulation of K(+) current in human airway epithelial cells by exogenous and autocrine adenosine

The regulatory actions of adenosine on ion channel function are mediated by four distinct membrane receptors. The concentration of adenosine in the vicinity of these receptors is controlled, in part, by inwardly directed nucleoside transport. The purpose of this study was to characterize the effects of adenosine on ion channels in A549 cells and the role of nucleoside transporters in this regulation. Ion replacement and pharmacological studies showed that adenosine and an inhibitor of human equilibrative nucleoside transporter (hENT)-1, nitrobenzylthioinosine, activated K(+) channels, most likely Ca(2+)-dependent intermediate-conductance K(+) (I(K)) channels. A(1) but not A(2) receptor antagonists blocked the effects of adenosine. RT-PCR studies showed that A549 cells expressed mRNA for I(K)-1 channels as well as A(1), A(2A), and A(2B) but not A(3) receptors. Similarly, mRNA for equilibrative (hENT1 and hENT2) but not concentrative (hCNT1, hCNT2, and hCNT3) nucleoside transporters was detected, a result confirmed in functional uptake studies. These studies showed that adenosine controls the function of K(+) channels in A549 cells and that hENTs play a crucial role in this process.

Cystic fibrosis affects chloride and sodium channels in human airway epithelia

Abnormalities of epithelial function in cystic fibrosis (CF) have been linked to defects in cell membrane permeability to chloride or sodium ions. Recently, a class of chloride channels in airway epithelial cells have been reported to lack their usual sensitivity to phosphorylation via cAMP-dependent protein kinase, suggesting that CF could be due to a single genetic defect in these channels. We have examined single chloride and sodium channels in control and CF human nasal epithelia using the patch-clamp technique. The most common chloride channel was not the one previously associated with CF, but it was also abnormal in CF cells. In addition, the number of sodium channels was unusually high in CF. These findings suggest a wider disturbance of ion channel properties in CF than would be produced by a defect in a single type of channel.

Nitric oxide activates chloride currents in human lung epithelial cells

Epithelial Cl- channels are regulated by various physiological factors, including guanosine 3',5'-cyclic monophosphate (cGMP). Because cGMP mediates many of the physiological actions of nitric oxide (NO), we have studied both the presence of endogenous NO and the effects of exogenous NO on Cl- currents in A549 human lung epithelial cells. We have detected Ca(2+)-dependent NO synthase activity in A549 cells. Using the perforated patch-clamp technique, we have shown that inhibition of this enzyme by NG-monomethyl-L-arginine decreased Cl- current, an effect that was reversed by the NO donor S-nitrosoglutathione (GSNO). In addition, the NO donors GSNO and S-nitroso-N-acetyl-D,L-penicillamine increased whole-cell Cl- currents in A549 cells. This stimulatory effect of the NO donors was sensitive to inhibition by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, suggesting that channels other than the cystic fibrosis transmembrane conductance regulator (CFTR) are involved in the action of NO on A549 cells. In addition, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, a selective inhibitor of soluble guanylyl cyclase, decreased NO-mediated stimulation of Cl- currents. Our results suggest that, in lung epithelial cells, NO regulates a non-CFTR Cl- conductance acting via a cGMP-dependent mechanism.

The 20-pS chloride channel of the human airway epithelium

The single-channel inside-out patch clamp technique was used to characterize chloride channels in the apical membranes of human airway epithelial cells maintained in primary culture. Patches were obtained from single isolated cells or from cells at the edges of confluent groups. The channel seen most often, in 24% of all patches, had a conductance of approximately 20 pS and had a linear current-voltage relationship in symmetric chloride solutions. The anion selectivity sequence for the channel was NO3- greater than Cl- greater than HCO3-, and it was impermeable to gluconate ions, indicating that the channel diameter lies between 4.7 and 5.5 A. Current through the channel saturated at high chloride concentrations, and the relationship between channel current and chloride concentration could be approximated by the Michaelis-Menten equation. Analysis of the channel's anion permeability and its current vs. concentration relationship indicates that it can be described by the one-ion channel theory, with a relatively weak binding site inside the channel. Histograms of channel open and closed durations were constructed using the log binning technique and could be well fitted by triple exponential distributions, suggesting that the channel has at least three open and three closed states.

Inhibition of matrix metalloproteinase MMP-2 activates chloride current in human airway epithelial cells

Matrix metalloproteinases (MMPs) are involved in the remodeling and degradation of the extracellular matrix. Recently, it has been found that MMPs also contribute to processes not directly related to tissue remodeling, such as platelet aggregation or degranulation of airway gland cells. Since mucus secretion is closely related to ion channel function, we investigated whether MMPs could also be involved in the regulation of ion channels. We used human airway submucosal cell line Calu-3 to study the effects of MMPs on whole-cell current and transepithelial short-circuit current (Isc). Phenanthroline, a specific inhibitor of MMPs, increased whole-cell current with the half-maximally effective dose of 5.2 µM, and reversibly activated Isc in transepithelial measurements. Current stimulated by phenanthroline displayed linear current-voltage relationships and had inhibitor pharmacology and ion selectivity consistent with cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel activity. Zymography and Western blot showed significant expression of MMP-2 in Calu-3 cells. Moreover, anti-MMP-2 antibodies (1 µg/mL) increased whole-cell current and Isc, whereas human recombinant MMP-2 (10 ng/mL) reduced it. We also studied the expression of MMPs and the effects of phenanthroline on whole-cell current in A549 cells, which are derived from airway surface epithelium and do not express CFTR Cl- channels. While these cells also showed significant expression of MMP-2, inhibition of this enzyme with phenanthroline exerted no significant effect on whole-cell current. It is concluded that MMP-2 is involved in the regulation of CFTR Cl- channels in human airways.Key words: matrix metalloproteinases, Cl- current, Calu-3 cells, zymography, phenanthroline.

4-Chloro-benzo[F]isoquinoline (CBIQ) activates CFTR chloride channels and KCNN4 potassium channels in Calu-3 human airway epithelial cells

1 Calu-3 cells have been used to investigate the actions of 4-chloro-benzo[F]isoquinoline (CBIQ) on short-circuit current (SCC) in monolayers, whole-cell recording from single cells and by patch clamping. 2 CBIQ caused a sustained, reversible and repeatable increase in SCC in Calu-3 monolayers with an EC50 of 4.0 microm. Simultaneous measurements of SCC and isotopic fluxes of 36Cl- showed that CBIQ caused electrogenic chloride secretion. 3 Apical membrane permeabilisation to allow recording of basolateral membrane conductance in the presence of a K+ gradient suggested that CBIQ activated the intermediate-conductance calcium-sensitive K(+)-channel (KCNN4). Permeabilisation of the basolateral membranes of epithelial monolayers in the presence of a Cl- gradient suggested that CBIQ activated the Cl(-)-channel CFTR in the apical membrane. 4 Whole-cell recording in the absence of ATP/GTP of Calu-3 cells showed that CBIQ generated an inwardly rectifying current sensitive to clotrimazole. In the presence of the nucleotides, a more complex I/V relation was found that was partially sensitive to glibenclamide. The data are consistent with the presence of both KCNN4 and CFTR in Calu-3. 5 Isolated inside-out patches from Calu-3 cells revealed clotrimazole-sensitive channels with a conductance of 12 pS at positive potentials after activation with CBIQ and demonstrating inwardly rectifying properties, consistent with the known properties of KCNN4. Cell-attached patches showed single channel events with a conductance of 7 pS and a linear I/V relation that were further activated by CBIQ by an increase in open state probability, consistent with known properties of CFTR. It is concluded that CBIQ activates CFTR and KCNN4 ion channels in Calu-3 cells.

Regulation of anion secretion by nitric oxide in human airway epithelial cells

Nitric oxide (NO) is continuously produced and released in human airways, but the biological significance of this process is unknown. In this study, we have used Calu-3 cells to investigate the effects of NO on transepithelial anion secretion. An inhibitor of NO synthase, NG-nitro-L-arginine methyl ester, reduced short- circuit current (I(sc)), whereas an NO donor, S-nitrosoglutathione (GSNO), increased I(sc), with an EC50 approximately 1.2 microM. The NO-activated current was inhibited by diphenylamine-2-carboxylate, clotrimazole, and charybdotoxin. Selective permeabilization of cell membranes indicated that NO activated both apical anion channels and basolateral potassium channels. An inhibitor of soluble guanylate cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, prevented activation of I(sc) by NO but not by 8-bromo-cGMP, suggesting that NO acts via a cGMP-dependent pathway. Sequential treatment of cells with forskolin and GSNO or 1-ethyl-2-benzimidazolinone and GSNO showed additive effects of these chemicals on I(sc). Interestingly, GSNO elevated intracellular Ca2+ concentration ([Ca2+]i) but had no effect on I(sc) activated by thapsigargin. These results show that NO activates transepithelial anion secretion via a cGMP-dependent pathway that involves cross talk between NO and [Ca2+]i.

A large conductance, Ca2+-activated K+ channel in a human lung epithelial cell line (A549)

A large conductance, Ca2+-activated K+ channel in a human lung epithelial cell line (A549) was identified using the single channel patch clamp technique. Channel conductance was 242 +/- 33 pS (n = 67) in symmetrical KCl (140 mM). The channel was activated by membrane depolarization and increased cytosolic Ca2+. High selectivity was observed for K+ over Rb+(0.49) > Cs+(0.14) > Na+(0.09). Open probability was significantly decreased by Ba2+ (5 mM) and quinidine (5 mM) to either surface, but TEA (5 mM) was only effective when added to the external surface. All effects were reversible. Increasing cytosolic Ca2+ concentration from 10(-7) to 10(-6) M caused an increase in open probability from near zero to fully activated. ATP decreased open probability at approximately 2 mM, but the effect was variable. The channel was almost always observed together with a smaller conductance channel, although they could both be seen individually. We conclude that A549 cells contain large conductance Ca2+-activated K+ channels which could explain a major fraction of the K+ conductance in human alveolar epithelial membranes.

Coupling of CFTR-mediated anion secretion to nucleoside transporters and adenosine homeostasis in Calu-3 cells

The purpose of this study was to characterize the role of adenosine-dependent regulation of anion secretion in Calu-3 cells. RT-PCR studies showed that Calu-3 cells expressed mRNA for A2A and A2B but not A1 or A3 receptors, and for hENT1, hENT2 and hCNT3 but not hCNT1 or hCNT2 nucleoside transporters. Short-circuit current measurements indicated that A2B receptors were present in both apical and basolateral membranes, whereas A2A receptors were detected only in basolateral membranes. Uptake studies demonstrated that the majority of adenosine transport was mediated by hENT1, which was localized to both apical and basolateral membranes, with a smaller hENT2-mediated component in basolateral membranes. Whole-cell current measurements showed that application of extracellular nitrobenzylmercaptopurine ribonucleoside (NBMPR), a selective inhibitor of hENT1-mediated transport, had similar effects on whole-cell currents as the application of exogenous adenosine. Inhibitors of adenosine kinase and 5'-nucleotidase increased and decreased, respectively, whole-cell currents, whereas inhibition of adenosine deaminase had no effect. Single-channel studies showed that NBMPR and adenosine kinase inhibitors activated CFTR Cl- channels. These results suggested that the equilibrative nucleoside transporters (hENT1, hENT2) together with adenosine kinase and 5'-nucleotidase play a crucial role in the regulation of CFTR through an adenosine-dependent pathway in human airway epithelia.

CFTR and lysozyme secretion in human airway epithelial cells

Lysozyme is secreted in large quantities in human airways (10-20 mg/day), where it helps to defend against bacterial and fungal infection. Lysozyme expression is restricted to the serous cells of the submucosal glands, which also express high levels of cystic fibrosis transmembrane conductance regulator (CFTR) chloride channels. It is often assumed that mucus secretion in human airways is coupled to anion secretion through CFTR Cl(-) channels located in the apical membrane. Therefore, a defect in CFTR function could cause abnormal mucus secretion leading to persistent bacterial infection and inflammation of the airways. In this study we measured simultaneous secretion of lysozyme and Cl(-) from human airway epithelial serous cells. Secretion of lysozyme was measured by a turbidimetric assay that relies on the ability of lysozyme to disrupt the wall of the bacterium Micrococcus lysodeikticus, thus causing a fall in the optical density of the sample. Secretion of Cl(-) was measured as short-circuit current in a modified Ussing chamber. Activation of Cl(-) secretion by stimulation of cAMP- or Ca(2+)-dependent pathways caused comparable increases in lysozyme secretion. Similarly, blockers of Cl(-) secretion, such as diphenylamine-2-carboxylate (DPC), also reduced lysozyme secretion. However, while treatment of airway submucosal gland cells with antisense oligonucleotides directed against CFTR reduced Cl(-) secretion, it had no significant effect on the total amount of lysozyme secretion. These results suggest a role for functional CFTR in regulation of lysozyme secretion in human airways.

Involvement of ion channels in human eosinophil respiratory burst

BACKGROUND

Human eosinophils possess a variety of ion channels that play a crucial role in the regulation of cellular activity. During eosinophil respiratory burst, efflux of H(+) ions through H(+) channels provides an efficient mechanism of H(+) extrusion and charge compensation. Interestingly, recent studies suggest that other ion channels may also be involved in this process.

OBJECTIVE

We sought to investigate the role of ion channels in phorbol 12-myristate 13-acetate-induced superoxide (O(2)(*-)) generation by human eosinophils.

METHODS

O(2)(*-) production was measured by using the superoxide dismutase-inhibitable reduction of cytochrome c. Ion channel expression and function were studied by using RT-PCR and the patch clamp technique, respectively.

RESULTS

O(2)(*-) generation was affected by several ion channel blockers, especially 4,4-diisothio-cyanostilbene-2,2'-disulfonic acid. The involvement of Cl(-) channels in this process was confirmed by replacement of Cl(-) with gluconate or other anions. The halide dependence of O(2)(*-) production could be described by the sequence Cl(-)> or =Br(-)>I(-), which is similar to the selectivity sequence of several members of the chloride channel (ClC) family. RT-PCR studies performed with primers for ClC-2, ClC-3, ClC-4, ClC-5, ClC-6, and the cystic fibrosis transmembrane conductance regulator showed only the expression of ClC-3. The presence of phorbol 12-myristate 13-acetate-sensitive Cl(-) channels in human eosinophils with biophysical properties similar to the ClC-3 channel has been studied.

CONCLUSION

Cl(-) channels play an important role in the regulation of O(2)(*-) production by human eosinophils.

An analytical model of ionic movements in airway epithelial cells

A new mathematical model of ion movements in airway epithelia is presented, which allows predictions of ion fluxes, membrane potentials and ion concentrations. The model includes sodium and chloride channels in the apical membrane, a Na/K pump and a cotransport system for Cl- with stoichiometry Na+:K+:2Cl- in the basolateral membrane. Potassium channels in the basolateral membrane are used to regulate cell volume. Membrane potentials, ion fluxes and intracellular ion concentration are calculated as functions of apical ion permeabilities, the maximum pump current and the cotransport parameters. The major predictions of the model are: (1) Cl- concentration in the cell is determined entirely by the intracellular concentration of negatively charged impermeable ions and the osmotic conditions; (2) changes in intracellular Na+ and K+ concentrations are inversely related; (3) cotransport provides the major driving force for Cl- flux, increases intracellular Na+ concentration, decreases intracellular K+ concentration and hyperpolarizes the cell interior; (4) the maximum rate of the Na/K pump, by contrast, has little effect on Na+ or Cl- transepithelial fluxes and a much less pronounced effect on cell membrane polarization; (5) an increase in apical Na+ permeability causes an increase in intracellular Na+ concentration and a significant increase in Na+ flux; (6) an increase in apical Cl- permeability decreases intracellular Na+ concentration and Na+ flux; (7) assuming Na+ and Cl- permeabilities equal to those measured in human nasal epithelia, the model predicts that under short circuit conditions, Na+ absorption is much higher than Cl- secretion, in agreement with experimental measurements.

The role of nitric oxide in the regulation of ion channels in airway epithelium: implications for diseases of the lung

The human respiratory tract is covered with airway surface liquid (ASL) that is essential for lung defense and normal airway function. The quantity and composition of ASL is regulated by active ion transport across the airway epithelium. Abnormal electrolyte transport produces changes in ASL volume and composition, inhibits mucociliary clearance and leads to chronic infection of airway surfaces, as is evident in cystic fibrosis. Agonists that induce intracellular increases in cAMP or Ca2+ are generally associated with electrolyte secretion. While these mechanisms have been studied in detail for many years, modulation of ion channels by nitric oxide (NO) has emerged only recently as a significant determinant of ion channel function. NO is a physiological regulator of transepithelial ion movement and alterations of its generation and action may play an important role in the pathogenesis of lung disorders characterized by hypersecretion of ASL. This review presents the current understanding of regulation of airway epithelial ion channels by NO and attempts to highlight the importance of this regulation for lung defense.

Determination of cell surface charge by photometric titration

A colloid titration method has been frequently used to determine the number of charged residues at the cell surface. Here we present a new version of this technique, based on photometric measurements of a metachromatic shift in the maximum absorption of toluidine blue as it binds to the cell surface. The major improvements are: (1) simplified methodology and (2) increased precision of equivalence point determination. The data are analyzed using Gran's theory, which allows measurements to be taken at regular intervals instead of being concentrated around the equivalence titration point. We used this method to characterize the cell surface charge of three populations of rat mast cells: (1) peritoneal mast cells (PMC), (2) bone marrow-derived mast cells (BMMC) and (3) a rat cultured mast cell line (RCMC). Our results indicate that PMC have (4.23 +/- 0.59) x 10(8), while BMMC (8.58 +/- 0.26) x 10(7) negatively charged residues per cell. The results for RCMC were similar to those for BMMC. Taking into account the size differences between PMC and BMMC, the average charge density of PMC was also significantly higher than that of BMMC. The differences in cell surface charge were analyzed in the light of different sensitivities of mast cells to polycationic secretagogues.

Poiseuille flow method for measuring cell-to-cell adhesion

A theoretical description of the cell aggregation process in the Poisseuille flow is presented, the capture efficiency being used as the measure of cell adhesiveness. The value of this coefficient is determined both for nonspecific and specific (i.e., mediated by molecules) cell-to-cell interactions. Regarding the cell adhesion described by the DLVO theory, it is possible to determine the conditions under which cell adhesion is maximal. The dependence of capture efficiency on parameters such as shear rate, size of cell, surface potential of cell, the Hamaker constant of substances constituting the cell membrane, and composition of the medium is analyzed. In the case of specific cell adhesion during flow, the change of suspension concentration is related to the number of free and occupied receptor sites, the diffusion constant of the receptors in the cell membrane, the force of a single bond, and the conditions of flow. It is possible to determine the diffusion constant from cell aggregation measurement when the force of a single bond and the number of free and occupied receptor sites are known.

Evidence that channels below 1 pS cause the volume-sensitive chloride conductance in T84 cells

The volume-activated chloride current of T84 human colonic cells was studied using the whole-cell patch clamp. The current appeared reliably with a mild osmotic gradient and in the absence of intracellular ATP. It reversed at the chloride equilibrium potential and was blocked by the chloride channel blocker DIDS. Development of the current was accompanied by an increase in the current noise variance, typical of increasing ion channel open probability. Noise variance was always well-fitted by a double Lorentzian relationship with corner frequencies at approximately 1.7 Hz and approximately 60 Hz. The increase in variance during development of the volume-sensitive current was mostly due to an increase in the high frequency component. The relationship between noise variance and membrane current was well-fitted by a relationship with a single channel conductance of approximately 0.2 pS.

Decreased cell surface charge in cystic fibrosis epithelia

A colloid titration technique has been used to determine the surface charge of cystic fibrosis (CF) and corresponding non-CF epithelial cells. We have shown that the negative surface charge of CF epithelial cells is significantly reduced in comparison with non-CF cells. This fact may play an important role in CF, where the increased adherence of microorganisms is known to cause chronic lung infection. Neuraminidase treatment removed approximately the same amount of surface charge in both cell lines, indicating no differences in cell surface sialylation. Similar results were obtained by direct measurements of the amount of N-acetylneuraminic acid released by neuraminidase. Therefore, our results indicate that sialic acid residues are not involved in the reduction of the negative surface charge in CF. This conclusion does not support the hypothesis that undersialylation of cell-membrane molecules occurs in cystic fibrosis.

Noise analysis and single-channel observations of 4 pS chloride channels in human airway epithelia

Apical membranes of human airway epithelial cells have significant chloride permeability, which is reduced in cystic fibrosis (CF), causing abnormal electrochemistry and impaired mucociliary clearance. At least four types of chloride channels have been identified in these cells, but their relative roles in total permeability and CF are unclear. Noise analysis was used to measure the conductance of chloride channels in human nasal epithelial cells. The data indicate that channels with a mean conductance of 4.5 pS carry most of the chloride current, and that the mean number of such channels per cell is approximately 4,000. Chloride channels in this conductance range were also seen in single-channel recordings.

Characterization and regulation of a chloride channel from bovine tracheal epithelium

1. The patch-clamp technique was used to characterize chloride channels from the apical membranes of bovine tracheal epithelial cells. Application of GTP gamma S or NaF to excised patches revealed the existence of a novel type of Cl- channel regulated by G-proteins in a membrane-delimited manner. 2. The channel had a linear current-voltage relationship, with a conductance of 100-120 pS. Its open probability was independent of voltage. 3. The channel was highly anion selective (permeability ratio, PNa/PCl = 0.06 +/- 0.04) and had the halide permeability sequence: I- > Br- > or = Cl- > F-, corresponding to the Eisenman I sequence. This suggested that neither ionic size nor diffusion rate determined ion permeation through the channel. 4. The mole fraction behaviour was studied using fluoride and chloride ions. Mixtures of ions produced currents that would be expected from the linear combination of the two ions acting independently, indicating relatively simple permeation through the pore and compatible with a single ion binding site. 5. The channel was inhibited by the stilbene disulphonates SITS (4-acetamido-4'-isothiocyanatostilbene-2, 2'-disulphonic acid) and DNDS (4,4'-dinitrostilbene-2,2'-sulphonic acid). SITS introduced voltage dependence to channel gating and indicated the possible involvement of lysine residues in the channel permeation pathway. 6. NaF was unable to activate Cl- channels in the presence of the aluminum chelator, deferoxamine mesylate. This indicates that Al3+ ions play an important role in chloride channel activation by fluoride. NaF activation was not dependent on the presence of calcium ions. 7. The channel was insensitive to alkaline phosphatase and to the specific inhibitors of protein phosphatase types I and 2A, okadaic acid and calyculin A. 8. The channels could be activated by GTP gamma S or by NaF in the presence of the phospholipase A2 inhibitor quinacrine, indicating that this enzyme is not involved in channel regulation.

Halide permeation through three types of epithelial anion channels after reconstitution into giant liposomes

Anion-selective channels from apical membranes of cultured CFPAC-1 cells were isolated and incorporated into giant liposomes for patch clamp recording. Liposomes were formed from L-alpha-lecithin by a dehydration-hydration method. Ion channels were characterized using the excised inside-out patch clamp configuration. The most commonly observed anion channels were similar to those observed in native epithelial tissues. The linear 20 pS Cl- channel had the halide permeability sequence Cl- > I- > or = Br- > F-, and showed anomalous mole-fraction behavior in solutions containing different proportions of Cl- and F- ions. The autwardly rectifying Cl- channel had the halide permeability sequence I- > Br- > Cl- > F-, and also showed anomalous mole-fraction behavior, indicating that both these channels probably contain multi-ion pores. The third, voltage-dependent anion channel showed at least five different substrates, had a conductance of 390 pS in the main state, and showed two types of kinetics, fast (openings and closings < 1 ms), and slow (openings and closings > 1 s). The channel was seen more frequently after reconstitution into giant liposomes than in intact cells. It was not selective amongst the halides, and there was no deviation from a linear dependence of relative current on molar fractions, indicating relatively simple permeation through the pore. Differences in halide permeabilities suggest that different anion channels may be related to different membrane proteins. Comparison with the chloride channel proteins isolated biochemically from epithelial cell membranes is discussed.