Glutamyl-gamma-boronate inhibitors of bacterial Glu-tRNA(Gln) amidotransferase

Analogues of glutamyl-gamma-boronate (1) were synthesized as mechanism-based inhibitors of bacterial Glu-tRNA(Gln) amidotransferase (Glu-AdT) and were designed to engage a putative catalytic serine nucleophile required for the glutaminase activity of the enzyme. Although 1 provides potent enzyme inhibition, structure-activity studies revealed a narrow range of tolerated chemical changes that maintained activity. Nonetheless, growth inhibition of organisms that require Glu-AdT by the most potent enzyme inhibitors appears to validate mechanism-based inhibitor design of Glu-AdT as an approach to antimicrobial development.

Design, synthesis, and structure-activity relationships of macrocyclic hydroxamic acids that inhibit tumor necrosis factor alpha release in vitro and in vivo

To search for TNF-alpha (tumor necrosis factor alpha) converting enzyme (TACE) inhibitors, we designed a new class of macrocyclic hydroxamic acids by linking the P1 and P2' residues of acyclic anti-succinate-based hydroxamic acids. A variety of residues including amide, carbamate, alkyl, sulfonamido, Boc-amino, and amino were found to be suitable P1-P2' linkers. With an N-methylamide at P3', the 13-16-membered macrocycles prepared exhibited low micromolar activities in the inhibition of TNF-alpha release from LPS-stimulated human whole blood. Further elaboration in the P3'-P4' area using the cyclophane and cyclic carbamate templates led to the identification of a number of potent analogues with IC(50) values of </=0.2 microM in whole blood assay (WBA). Although the P3' area can accommodate a broad array of structurally diversified functional groups including polar residues, hydrophobic residues, and amino and carboxylic acid moieties, in both the cyclophane series and the cyclic carbamate series, a glycine residue at P3' was identified as a critical structural component to achieve both good in vitro potency and good oral activity. With a glycine residue at P3', an N-methylamide at P4' provided the best cyclophane analogue, SL422 (WBA IC(50) = 0.22 microM, LPS-mouse ED(50) = 15 mg/kg, po), whereas a morpholinylamide at P4' afforded the most potent and most orally active cyclic carbamate analogue, SP057 (WBA IC(50) = 0.067 microM, LPS-mouse ED(50) = 2.3 mg/kg, po). Further profiling for SL422 and SP057 showed that these macrocyclic compounds are potent TACE inhibitors, with K(i) values of 12 and 4.2 nM in the porcine TACE assay, and are broad-spectrum MMP inhibitors. Pharmacokinetic studies in beagle dogs revealed that SL422 and SP057 are orally bioavailable, with oral bioavailabilities of 11% and 23%, respectively.

Regulation of human CLC-3 channels by multifunctional Ca2+/calmodulin-dependent protein kinase

The multifunctional calcium/calmodulin-dependent protein kinase II, CaMKII, has been shown to regulate chloride movement and cellular function in both excitable and non-excitable cells. We show that the plasma membrane expression of a member of the ClC family of Cl(-) channels, human CLC-3 (hCLC-3), a 90-kDa protein, is regulated by CaMKII. We cloned the full-length hCLC-3 gene from the human colonic tumor cell line T84, previously shown to express a CaMKII-activated Cl(-) conductance (I(Cl,CaMKII)), and transfected this gene into the mammalian epithelial cell line tsA, which lacks endogenous expression of I(Cl,CaMKII). Biotinylation experiments demonstrated plasma membrane expression of hCLC-3 in the stably transfected cells. In whole cell patch clamp experiments, autonomously active CaMKII was introduced into tsA cells stably transfected with hCLC-3 via the patch pipette. Cells transfected with the hCLC-3 gene showed a 22-fold increase in current density over cells expressing the vector alone. Kinase-dependent current expression was abolished in the presence of the autocamtide-2-related inhibitory peptide, a specific inhibitor of CaMKII. A mutation of glycine 280 to glutamic acid in the conserved motif in the putative pore region of the channel changed anion selectivity from I(-) > Cl(-) to Cl(-) > I(-). These results indicate that hCLC-3 encodes a Cl(-) channel that is regulated by CaMKII-dependent phosphorylation.

Priming of insulin granules for exocytosis by granular Cl− uptake and acidification

ATP-dependent priming of the secretory granules precedes Ca2+-regulated neuroendocrine secretion, but the exact nature of this reaction is not fully established in all secretory cell types. We have further investigated this reaction in the insulin-secreting pancreatic B-cell and demonstrate that granular acidification driven by a V-type H+-ATPase in the granular membrane is a decisive step in priming. This requires simultaneous Cl− uptake through granular ClC-3 Cl− channels. Accordingly, granule acidification and priming are inhibited by agents that prevent transgranular Cl− fluxes, such as 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS) and an antibody against the ClC-3 channels, but accelerated by increases in the intracellular ATP:ADP ratio or addition of hypoglycemic sulfonylureas. We suggest that this might represent an important mechanism for metabolic regulation of Ca2+-dependent exocytosis that is also likely to be operational in other secretory cell types.

Tumor progression despite efficient tumor antigen cross-presentation and effective "arming" of tumor antigen-specific CTL

To determine whether APC function or "arming" of CTL for lytic function are the points at which Ags from a nonimmunogenic tumor fail to induce an effective immune response, we established a murine tumor model that expressed intracellular OVA and selected a clone (cOVA-9) that remained susceptible to lysis by specific CD8(+) T cells throughout tumor growth. Viable cOVA-9 tumor cells grew in normal mice at a rate similar to the parental tumor, and vaccination with irradiated cOVA-9 cells did not induce protection against itself or the parental line, confirming its nonimmunogenic status. In vivo evaluation during tumor growth demonstrated persisting tumor Ag cross-presentation accompanied by the generation of potent, specific CTL which were detectable when tumors were barely palpable. Despite the presence of highly active CTL in the tumor-draining lymph nodes, there was no apparent lysis of tumor-associated APC. These data show that tumor-draining APC are not dysfunctional with regard to two crucial processes, in vivo tumor Ag cross-presentation and specific CTL arming, and that failure to prevent tumor growth is not in the induction phase, but in the effector phase and occurs within the tumor itself before the tumor matrix is established.

Correlation of ionization potentials and HOMO energies versus relative reactivities of Cl2, of Br2, and of I2 with representative acyclic alkenes. comparison with other additions to alkenes

Plots of log k(rel) versus IP or versus HOMO for the title reactions are presented; similarities and differences among the reactions are discussed. The Cl2 and Br2 data each show a single line of correlation with positive slope for all alkenes regardless of the steric requirements; increasing substitution at the double bond increases the reaction rate, indicating an electrophilic reaction. Each plot of the I2 data calculated for adsorption exhibits a natural separation into groups of similarly substituted alkenes, in which increased substitution reduces the rate. Within each group, a good-to-excellent correlation is observed, with a lower IP generally corresponding to a higher relative rate. The results indicate that the relative magnitude of the steric requirements about the double bond is similar to that of the electronic effects in iodination. Plot shapes for iodination are compared to those of other reactions, such as hydroboration, oxymercuration, complexation with Ag+, and complexation with MeHg+.

Lack of ignorance to tumor antigens: evaluation using nominal antigen transfection and T-cell receptor transgenic lymphocytes in Lyons-Parish analysis--implications for tumor tolerance

A substantial body of literature has described weak antitumor CTL responses in tumor-bearing hosts, and a number of authors have suggested that tumor tissue in some way sequesters antigen from the immune system, a failure of the tumor-specific immune response largely attributable to "ignorance." To evaluate this in a tumor model, we stably transfected murine tumor cell lines with genes coding for the nominal antigens influenza hemagglutinin (HA) or ovalbumin (OVA) and adoptively transferred HA- or OVA-specific T-cell receptor-transgenic, CD8-positive T cells into mice-bearing these tumors. Tumor antigen cross-presentation within draining lymph nodes (LNs) was then examined using Lyons-Parish analysis, detection of a proliferative response of 5,6-carboxyfluorescein diacetate succinimidyl ester-labeled CD8 T cells from T-cell receptor mice using flow cytometric analysis. Our studies demonstrate clearly that tumor antigens are constitutively presented in LNs draining tumors and can stimulate a T-cell proliferative response. This lack of ignorance was not simply attributable to the model chosen, because it was seen with three different cell lines, two different antigens, and two different mouse strains. Furthermore, it occurred regardless of whether these tumor antigens were expressed as cytoplasmic, transmembrane, or secreted proteins. When tumor antigens were present in low concentrations, antigen cross-presentation was not absent but simply delayed. Interestingly, tumor antigen cross-presentation remained localized to the LNs draining the tumor throughout the period of tumor growth. Curiously, in animals where tumors failed to grow, evidence of continued cross-presentation of the tumor antigen was seen up to 6 months after tumor inoculation. These data suggest that ignorance is not an explanation for the failure of the host immune system to respond to tumor antigens.

Correlation of relative rates of PdCl(2) oxidation of functionalized acyclic alkenes versus alkene ionization potentials, HOMOs, and LUMOs

Investigations of the title reaction, carried out by plotting logs of the relative reaction rates vs IPs, vs HOMOs, and vs LUMOs, reveal multiple nearly parallel lines of correlation with small negative slopes in each. Overall, the natural grouping into monosubstituted and disubstituted alkenes gives better correlations than that obtained by using all alkenes. Comparison with analogous plots for other reactions indicates that the mechanism for this reaction has similarities to that for hydroboration, the major difference being that the lines in the plots for hydroboration have positive slopes, indicating an electrophilic rate-determining step involving the pi electrons, while those for the title reaction have small negative slopes, indicating a nucleophilic rate-determining step. Of the two reaction mechanisms proposed for the title reaction, only one has a nucleophilic attack at the complexed alkene as the rate-determining step, and therefore, this work supports that reaction mechanism.

Molecular dynamics study of Ca(2+) binding loop variants of parvalbumin with modifications at the "gateway" position

The helix-loop-helix (i.e. EF-hand) Ca(2+) ion binding motif is characteristic of a large family of high-affinity Ca(2+) ion binding proteins, including the parvalbumins and calmodulins. In this paper we describe a set of molecular dynamics computations on the major parvalbumin from the silver hake (SHPV-B). In all variants examined, both whole protein and fragments thereof, the ninth loop residue in the Ca(2+) binding coordination site in the CD helix-loop-helix region (the so-called "gateway" residue) has been mutated. The three gateway mutations examined are arginine, which has never been found at the gateway position of any EF-hand protein, cysteine, which is the residue observed least in natural EF-hand sites, and serine, which is the most common (by far) non-acidic residue substitution at this position in EF-hand proteins in general, but never in parvalbumins. Results of the molecular dynamics simulations indicate that all three modifications are disruptive to the integrity of the mutated Ca(2+) binding site in the whole parvalbumin protein. In contrast, only the arginine and cysteine mutations are disruptive to the integrity of the mutated Ca(2+) binding site in the CD fragment of the parvalbumin protein. Surprisingly, the serine variant of the CD helix-loop-helix fragment exhibited remarkable stability during the entire molecular dynamics simulation, with retention of the Ca(2+) binding site. These results indicate that there are no inherent problems (for Ca(2+) ion binding) associated with the sequence of the CD helix-loop-helix fragment that precludes the incorporation of serine at the gateway position. Since the CD site is totally disrupted in the whole protein serine variant, this indicates that the Ca(2+) ion binding deficiencies are most likely related to the unique interaction that exists between the paired EF-hands in the whole protein. Our theoretical results correlate well with previous studies on engineered EF-hand proteins and with all of our experimental evidence on the silver hake parvalbumin.

Oxidants potentiate Ca(2+)- and cAMP-stimulated Cl(-) secretion in intestinal epithelial T84 cells

BACKGROUND & AIMS

Diarrhea is one of the major complications of inflammatory bowel disease. The role of oxidants in promoting net intestinal secretion is important, but the cellular mechanisms underlying their effects are unclear. We examined the effects and defined the cellular actions of the oxidant monochloramine (NH(2)Cl) on anion secretion in human colonic T84 cells.

METHODS

Effects of NH(2)Cl on basal and agonist-stimulated short-circuit current (Isc) of T84 monolayers were determined. Apical Cl(-) and basolateral K(+) conductances were measured by efflux of (125)I(-) and (86)Rb(+), respectively.

RESULTS

NH(2)Cl alone had little effect on Isc and (125)I(-) efflux. However, pretreatment with NH(2)Cl led to a concentration-dependent potentiation of the Ca(2+)-mediated Isc and of submaximal cAMP-mediated responses. These effects were associated with increased basolateral K(+) channel conductance and were blocked by increasing cellular Ca(2+) buffering capacity with Quin-2. Whole-cell voltage clamp experiments showed that NH(2)Cl potentiated Ca(2+) activation of basolateral K(+) channel conductance.

CONCLUSIONS

Oxidants potentiate both Ca(2+)- and cAMP-stimulated Cl(-) secretion by a direct effect on calcium-activated basolateral K(+) channel conductance, lowering its Ca(2+) activation threshold. This effect may play an important role in amplifying and prolonging the secretory response of inflamed intestinal mucosa and enhancing the severity of diarrhea.

Surface modification of diaspirin cross-linked hemoglobin (DCLHb) with chondroitin-4-sulfate derivatives. Part 1

Synthetic methodology was developed for the preparation of chondrotin-4-sulfate reagents that could be specifically attached to the surface of diaspirin cross-linked hemoglobin (DCLHb), a chemically stabilized human hemoglobin. The surface-modified hemoglobin solutions had a significantly higher colloidal osmotic pressures (COP) than DCLHb. The P(50) of the modified DCLHb was dependent upon the reactive end group of the chondrotin-4-sulfate reagents that was used for the protein modification. Modification of DCLHb with the chondroitin-4-sulfate derivatives containing the maleimide end group 23 provided a hemoglobin with a P(50) value of 23 mmHg, while the P(50) of hemoglobins prepared from chondroitin-4-sulfate derivatives containing the aldehyde end group 13 and 18 remained unchanged from that of DCLHb.

Impermeability of the GIRK2 weaver channel to divalent cations

A single amino acid mutation (G156S) in the putative pore-forming region of the G protein-sensitive, inwardly rectifying K(+) channel subunit, GIRK2, renders the conductance constitutively active and nonselective for monovalent cations. The mutant channel subunit (GIRK2wv) causes the pleiotropic weaver disease in mice, which is characterized by the selective vulnerability of cerebellar granule cells and Purkinje cells, as well as dopaminergic neurons in the mesencephalon, to cell death. It has been proposed that divalent cation permeability through constitutively active GIRK2wv channels contributes to a rise in internal calcium in the GIRK2wv-expressing neurons, eventually leading to cell death. We carried out comparative studies of recombinant GIRK2wv channels expressed in Xenopus oocytes and COS-7 cells to determine the magnitude and relative permeability of the GIRK2wv conductance to Ca(2+). Data from these studies demonstrate that the properties of the expressed current differ in the two systems and that when recombinant GIRK2wv is expressed in mammalian cells it is impermeable to Ca(2+).

Syntaxin 1A is expressed in airway epithelial cells, where it modulates CFTR Cl(-) currents

The CFTR Cl(-) channel controls salt and water transport across epithelial tissues. Previously, we showed that CFTR-mediated Cl(-) currents in the Xenopus oocyte expression system are inhibited by syntaxin 1A, a component of the membrane trafficking machinery. This negative modulation of CFTR function can be reversed by soluble syntaxin 1A peptides and by the syntaxin 1A binding protein, Munc-18. In the present study, we determined whether syntaxin 1A is expressed in native epithelial tissues that normally express CFTR and whether it modulates CFTR currents in these tissues. Using immunoblotting and immunofluorescence, we observed syntaxin 1A in native gut and airway epithelial tissues and showed that epithelial cells from these tissues express syntaxin 1A at >10-fold molar excess over CFTR. Syntaxin 1A is seen near the apical cell surfaces of human bronchial airway epithelium. Reagents that disrupt the CFTR-syntaxin 1A interaction, including soluble syntaxin 1A cytosolic domain and recombinant Munc-18, augmented cAMP-dependent CFTR Cl(-) currents by more than 2- to 4-fold in mouse tracheal epithelial cells and cells derived from human nasal polyps, but these reagents did not affect CaMK II-activated Cl(-) currents in these cells.

X-Ray crystal structure and molecular dynamics simulations of silver hake parvalbumin (Isoform B)

Parvalbumins constitute a class of calcium-binding proteins characterized by the presence of several helix-loop-helix (EF-hand) motifs. In a previous study (Revett SP, King G, Shabanowitz J, Hunt DF, Hartman KL, Laue TM, Nelson DJ, 1997, Protein Sci 7:2397-2408), we presented the sequence of the major parvalbumin isoform from the silver hake (Merluccius bilinearis) and presented spectroscopic and structural information on the excised "EF-hand" portion of the protein. In this study, the X-ray crystal structure of the silver hake major parvalbumin has been determined to high resolution, in the frozen state, using the molecular replacement method with the carp parvalbumin structure as a starting model. The crystals are orthorhombic, space group C2221, with a = 75.7 A, b = 80.7 A, and c = 42.1 A. Data were collected from a single crystal grown in 15% glycerol, which served as a cryoprotectant for flash freezing at -188 degrees C. The structure refined to a conventional R-value of 21% (free R 25%) for observed reflections in the range 8 to 1.65 A [1 > 2sigma(I)]. The refined model includes an acetylated amino terminus, 108 residues (characteristic of a beta parvalbumin lineage), 2 calcium ions, and 114 water molecules per protein molecule. The resulting structure was used in molecular dynamics (MD) simulations focused primarily on the dynamics of the ligands coordinating the Ca2+ ions in the CD and EF sites. MD simulations were performed on both the fully Ca2+ loaded protein and on a Ca2+ deficient variant, with Ca2+ only in the CD site. There was substantial agreement between the MD and X-ray results in addressing the issue of mobility of key residues in the calcium-binding sites, especially with regard to the side chain of Ser55 in the CD site and Asp92 in the EF site.

Cross-presentation of tumour antigens: evaluation of threshold, duration, distribution and regulation

The development of technology to measure antigen presentation in the secondary lymphoid system has provided the opportunity of analysing components of the host antitumour immune response that have, until now, been unavailable for study. In particular, this technology has enabled us to evaluate threshold levels of tumour antigen required for cross-presentation in draining lymph nodes, the duration of this antigen presentation and processes that regulate tumour antigen presentation. Thus, we have been able to dissect out the relationship between antigen presentation and the resultant development of effector function in class I-restricted T cells, as well as the role of regulatory CD4 cells. We have also used this technology to evaluate the effects of antitumour therapy on local antigen cross-presentation.

Polymerization of diaspirin cross-linked hemoglobin (DCLHb) with water-soluble, nonimmunogenic polyamide cross-linking agents

Diaspirin cross-linked hemoglobin (DCLHb), a human hemoglobin that is intramolecularly cross-linked between the alpha chains (lysine 99(alpha)(1)-lysine 99(alpha)(2)), was polymerized with a number of water-soluble, nonimmunogenic polyamide cross-linking agents. The degree of polymerization and the oxygen-carrying capacity depended upon the polyamide reagent, the starting concentration of DCLHb, the molar ratio of the polyamide reagent to DCLHb used, the reaction pH, and whether oxy- or deoxy-DCLHb was used in the polymerization reaction.

The inwardly rectifying K(+) channel subunit GIRK1 rescues the GIRK2 weaver phenotype

The weaver (wv) gene has been identified as a glycine to serine substitution at residue 156 in the H5 region of inwardly rectifying K(+) channel, GIRK2. The mutation is permissive for the expression of homotetrameric channels that are nonselective for cations and G-protein-independent. Coexpression of GIRK2wv with GIRK1, GIRK2, or GIRK3 in Xenopus oocytes along with expression of subunit combinations linked as dimers and tetramers was used to investigate the effects of the pore mutation on channel selectivity and gating as a function of relative subunit position and number within a heterotetrameric complex. GIRK1 formed functional, K(+) selective channels with GIRK2 and GIRK3. Coexpression of GIRK2wv with GIRK1 gave rise to a component of K(+)-selective, G-protein-dependent current. Currents resulting from coexpression of GIRK2wv with GIRK2 or GIRK3 were weaver-like. Current from dimers of GIRK1-GIRK2wv, GIRK2-GIRK2wv, and GIRK3-GIRK2wv was phenotypically similar to that obtained from coexpression of monomers. Linked tetramers containing GIRK1 and GIRK2wv in an alternating array gave rise to wild-type, K(+)-selective currents. When two mutant subunits were arranged adjacently in a tetramer, currents were weaver-like. These results support the hypothesis that in specific channel stoichiometries, GIRK1 rescues the weaver phenotype and suggests a basis for the selective neuronal vulnerability that is observed in the weaver mouse.

Alternative splicing of sur2 Exon 17 regulates nucleotide sensitivity of the ATP-sensitive potassium channel

ATP-sensitive potassium channels (KATP) are implicated in a diverse array of physiological functions. Previous work has shown that alternative usage of exons 14, 39, and 40 of the muscle-specific KATP channel regulatory subunit, sur2, occurs in tissue-specific patterns. Here, we show that exon 17 of the first nucleotide binding fold of sur2 is also alternatively spliced. RNase protection demonstrates that SUR2(Delta17) predominates in skeletal muscle and gut and is also expressed in bladder, fat, heart, lung, liver, and kidney. Polymerase chain reaction and restriction digest analysis of sur2 cDNA demonstrate the existence of at least five sur2 splice variants as follows: SUR2(39), SUR2(40), SUR2(Delta17/39), SUR2(Delta17/40), and SUR2(Delta14/39). Electrophysiological recordings of excised, inside-out patches from COS cells cotransfected with Kir6.2 and the sur2 variants demonstrated that exon 17 splicing alters KATP sensitivity to ATP block by 2-fold from approximately 40 to approximately 90 microM for exon 17 and Delta17, respectively. Single channel kinetic analysis of SUR2(39) and SUR2(Delta17/39) demonstrated that both exhibited characteristic KATP kinetics but that SUR2(Delta17/39) exhibited longer mean burst durations and shorter mean interburst dwell times. In sum, alternative splicing of sur2 enhances the observed diversity of KATP and may contribute to tissue-specific modulation of ATP sensitivity.

Altered responses to potassium in cerebellar neurons from weaver heterozygote mice

The pleiotropic weaver disease is caused by the mutation of a single amino acid in the G-protein-linked inwardly rectifying K+ channel, GIRK2. In homozygous (wv/wv) animals, the disease is characterized by loss of cerebellar and dopaminergic mesencephalic neurons as well as testicular cells, which produce ataxia, fine tremors, and sterility, respectively. Heterozygous (wv/+) animals show no obvious motor impairments, although some loss of both cerebellar and dopaminergic neurons is observed and wv/+ males become sterile at 3.5 months of age. Abnormal influxes of Na+ and Ca2+ have been linked to cerebellar cell death in wv/wv animals, but it's not clear whether similar changes are observed in wv/+ animals. To discover whether changes in K+-channel function or intracellular Ca2+ concentrations ([Ca2+]i) play a role in the augmented cell loss observed in wv/+ animals when compared with +/+ animals, we studied cultured cerebellar granule cells prepared from either wv/+ or +/+ animals. Resting [Ca2+]i was elevated in wv/+ relative to +/+ animals. Further, depolarizations of cells with elevated K+ solutions elicited much smaller changes in [Ca2+]i in wv/+ animals than in +/+ animals, presumably due to altered GIRK2 channel function. Both wv/+ and +/+ cells showed similar changes in [Ca2+]i when cells were depolarized by glutamate (1 mM), suggesting that both glutamate receptors and Ca2+ channels were unchanged in wv/ + animals. In summary, our results suggest that wv/+ cerebellar granule cells exhibit elevated resting [Ca2+]i levels and altered K+-channel function, which may contribute to the developmental abnormalities and increased cell death observed.

Synthesis of water-soluble, nonimmunogenic polyamide cross-linking agents

Novel polyamides were developed that can be used as cross-linking agents for proteins such as hemoglobin. Water-soluble, nonimmunogenic polyamides containing oxygen and sulfur atoms in the backbone were prepared by the polycondensation of the diacids bis(carboxymethyloxyacetyl)-1,4-diaminobutane (1a) or 3, 3'-thiodipropionic acid (1b) with diethylene glycol bis(3-aminopropyl) ether (2). The resulting alpha,omega-diacids were converted to the corresponding activated esters using any of a variety of carboxylic acid activating reagents including the novel reagent diphenyl(1-methylimidazol-2-thiyl)phosphonate (9). The resulting polyamides could be activated with a broad spectrum of groups that allow for the cross-linking and surface modification of proteins.

Membrane capacitance changes associated with particle uptake during phagocytosis in macrophages

We report the use of capacitance measurements to monitor particle uptake after cellular exposure to phagocytic stimuli. In these studies, human monocyte-derived macrophages (HMDMs) and cells from the murine macrophage-like cell line J774.1 were exposed to immune complexes or sized latex particles (0.8 or 3.2 micron in diameter). An average decrease in cell capacitance of 8 pF was seen after exposure of the cells to immune complexes. Cells in which particle uptake was inhibited by cytochalasin B treatment before exposure to immune complexes showed an average increase of 0.5 pF. The decrease in membrane capacitance after exposure of cells to particulate stimuli was absent with the soluble stimulus, platelet-activating factor, further confirming that decreases in membrane capacitance were due to particle uptake. Exposure of cells to sized latex particles resulted in a graded, stepwise decrease in membrane capacitance. The average step size for 0.8-micron particles was 250 fF, and the average step change for the larger 3.2-micron particles was 480 fF, as calculated from Gaussian fits to the step size amplitude histograms. The predicted step size for the individual particles based upon the minimum amount of membrane required to enclose a particle and a specific capacitance of 10 fF/micron2 was 20 and 320 fF, respectively. The step size for the smaller particles deviates significantly from the predicted size distribution, indicating either a possible lower limit to the size of the phagocytic vacuole or multiple particles taken up within a single phagosome. Dynamic interaction between phagocytosis and exocytosis was observed in a number of cells as a biphasic response consisting of an initial rapid increase in capacitance, consistent with cellular exocytosis, followed by stepwise decreases in capacitance.

Syntaxin 1A inhibits CFTR chloride channels by means of domain-specific protein-protein interactions

Previously we showed that the functional activity of the epithelial chloride channel that is encoded by the cystic fibrosis gene (CFTR) is reciprocally modulated by two components of the vesicle fusion machinery, syntaxin 1A and Munc-18. Here we report that syntaxin 1A inhibits CFTR chloride channels by means of direct and domain-specific protein-protein interactions. Syntaxin 1A stoichiometrically binds to the N-terminal cytoplasmic tail of CFTR, and this binding is blocked by Munc-18. The modulation of CFTR currents by syntaxin 1A is eliminated either by deletion of this tail or by injecting this tail as a blocking peptide into coexpressing Xenopus oocytes. The CFTR binding site on syntaxin 1A maps to the third predicted helical domain (H3) of this membrane protein. Moreover, CFTR Cl- currents are effectively inhibited by a minimal syntaxin 1A construct (i.e., the membrane-anchored H3 domain) that cannot fully substitute for wild-type syntaxin 1A in membrane fusion reactions. We also show that syntaxin 1A binds to and inhibits the activities of disease-associated mutants of CFTR, and that the chloride current activity of recombinant DeltaF508 CFTR (i.e., the most common cystic fibrosis mutant) can be potentiated by disrupting its interaction with syntaxin 1A in cultured epithelial cells. Our results provide evidence for a direct physical interaction between CFTR and syntaxin 1A that limits the functional activities of normal and disease-associated forms of this chloride channel.

Regulation of Ca2+-dependent Cl- conductance in a human colonic epithelial cell line (T84): cross-talk between Ins(3,4,5,6)P4 and protein phosphatases

1. We have studied the regulation of whole-cell chloride current in T84 colonic epithelial cells by inositol 3,4,5,6-tetrakisphosphate (Ins(3,4,5,6)P4). New information was obtained using (a) microcystin and okadaic acid to inhibit serine/threonine protein phosphatases, and (b) a novel functional tetrakisphosphate analogue, 1, 2-bisdeoxy-1,2-bisfluoro-Ins(3,4,5,6)P4 (i.e. F2-Ins(3,4,5,6)P4). 2. Calmodulin-dependent protein kinase II (CaMKII) increased chloride current 20-fold. This current (ICl,CaMK) continued for 7 +/- 1.2 min before its deactivation, or running down, by approximately 60 %. This run-down was prevented by okadaic acid, whereupon ICl,CaMK remained near its maximum value for >= 14.3 +/- 0.6 min. 3. F2-Ins(3, 4,5,6)P4 inhibited ICl,CaMK (IC50 = 100 microM) stereo-specifically, since its enantiomer, F2-Ins(1,4,5,6)P4 had no effect at >= 500 microM. Dose-response data (Hill coefficient = 1.3) showed that F2-Ins(3,4,5,6)P4 imitated only the non-co-operative phase of inhibition by Ins(3,4,5,6)P4, and not the co-operative phase. 4. Ins(3,4,5,6)P4 was prevented from blocking ICl,CaMK by okadaic acid (IC50 = 1.5 nM) and microcystin (IC50 = 0.15 nM); these data lead to the novel conclusion that, in situ, protein phosphatase activity is essential for Ins(3,4,5,6)P4 to function. The IC50 values indicate that more than one species of phosphatase was required. One of these may be PP1, since F2-Ins(3,4,5,6)P4-dependent current blocking was inhibited by okadaic acid and microcystin with IC50 values of 70 nM and 0.15 nM, respectively.

Cytoskeletal actin gates a Cl- channel in neocortical astrocytes

Increases in astroglial Cl- conductance accompany changes in cell morphology and disassembly of cytoskeletal actin, but Cl- channels underlying these conductance increases have not been described. We characterize an outwardly rectifying Cl- channel in rodent neocortical cultured astrocytes and describe how cell shape and cytoskeletal actin modulate channel gating. In inside-out patch-clamp recordings from cultured astrocytes, outwardly rectifying Cl- channels either were spontaneously active or inducible in quiescent patches by depolarizing voltage steps. Average single-channel conductance was 36 pS between -60 and -80 mV and was 75 pS between 60 and 80 mV in symmetrical (150 mM NaCl) solutions. The permeability ratio (PNa/PCl) was 0.14 at lower ionic strength but increased at higher salt concentrations. Both ATP and 4, 4-diisothiocyanostilbene-2,2'-disulfonic acid produced a flicker block, whereas Zn2+ produced complete inhibition of channel activity. The frequency of observing both spontaneous and inducible Cl- channel activity was markedly higher in stellate than in flat, polygonally shaped astrocytes. In addition, cytoskeletal actin modulated channel open-state probability (PO) and conductance at negative membrane potentials, controlling the degree of outward rectification. Direct application of phalloidin, which stabilizes actin, preserved low PO and promoted lower conductance levels at negative potentials. Lower PO also was induced by direct application of polymerized actin. The actions of phalloidin and actin were reversed by coapplication of gelsolin and cytochalasin D, respectively. These results provide the first report of an outwardly rectifying Cl- channel in neocortical astrocytes and demonstrate how changes in cell shape and cytoskeletal actin may control Cl- conductance in these cells.

Effect of ozone exposure on alveolar macrophage-mediated immunosuppressive activity in rats

Ozone (O3), a major component of photochemical air pollution, is a strong oxidizing agent and highly toxic. Resident alveolar macrophages (AM) play an important immunomodulatory role in the lung via suppression of lymphocyte proliferation, thus limiting the magnitude and duration of local immune responses. Nitric oxide (NO) plays a crucial role in the immunosuppressive activity of AM. However, during immunoinflammatory responses, microenvironmental changes within the alveoli inhibit this AM function, permitting full expression of local T-cell-mediated immune responses. We hypothesize that similar changes in AM function may occur during inflammation induced by exposure to inorganic air pollutants, such as O3. In order to test this hypothesis, in the present study, we investigated (1) whether O3 exposure of rats might affect the immunosuppressive activity and NO production of bronchoalveolar lavage cells (BAL cells) and (2) whether changes in the microenvironment of the alveoli induced by O3 exposure can affect the immunosuppressive activity and NO production of AM. AM-mediated immunosuppressive activity was measured as inhibition of concanavalin A (Con A)-induced proliferation of lymph node cells (LNC). Bronchoalveolar lavage was used to sample the alveolar microenvironment, and the resulting fluid (BALF) was tested for capacity to modulate AM activity in the cultures. BALF and BAL cells from rats exposed to 1 ppm O3 or filtered air for 3 days were used. The present results demonstrate that BAL cells isolated from O3-exposed rats suppressed Con A-induced LNC proliferation and produced NO in the same manner as BAL cells (AM) from air-exposed rats. AM-mediated suppressive activity of LNC proliferation and NO production were markedly inhibited by BALF from O3-exposed but not from air-exposed rats. These results suggested that AM-mediated immunosuppressive activity in vivo may be inhibited by the O3-induced release of soluble factors which inhibit NO production by AM.

Absence of immunogenicity of diaspirin cross-linked hemoglobin in humans

Diaspirin cross-linked hemoglobin (DCLHb) is an intramolecularly cross-linked hemoglobin-based oxygen carrier being developed as a therapy for acute blood loss. We report here the absence of immunogenicity of DCLHb in patients enrolled in phase II and III clinical trials of DCLHb. Two very sensitive immunoassays, an enzyme-linked immunosorbent assay (ELISA) and a Western blot assay, were developed and validated for this assessment. The DCLHb-antibodies used in these assays were raised in monkeys, had similar affinities for DCLHb and native human hemoglobin (SFHb), and showed cross-reactivity for subunits of DCLHb and SFHb on the Western blot, suggesting that these antibodies were elicited as a xenogenic response to the protein. In the ELISA, the optical density of a patient sample exposed to DCLHb-coated wells was compared with that of the patient sample exposed to carbonate buffer-coated wells; an optical density ratio of 1.4 was established for discriminating between a positive (reactive) or negative DCLHb antibody response. To date, all of the more than 300 patient specimens (preinfusion and postinfusion) from clinical trials have exhibited a ratio of less than 1.4, confirming the lack of preexisting antibodies to DCLHb and clearly showing the absence of DCLHb antibodies after exposure to this new biologic entity. There has been no requirement for use of the confirmatory Western blot assay. Taken together, the results from this study indicate DCLHb is not immunogenic in humans at doses evaluated clinically.

Regulation of CFTR chloride channels by syntaxin and Munc18 isoforms

The cystic fibrosis gene encodes a cyclic AMP-gated chloride channel (CFTR) that mediates electrolyte transport across the luminal surfaces of a variety of epithelial cells. The molecular mechanisms that modulate CFTR activity in epithelial tissues are poorly understood. Here we show that CFTR is regulated by an epithelially expressed syntaxin (syntaxin 1A), a membrane protein that also modulates neurosecretion and calcium-channel gating in brain. Syntaxin 1A physically interacts with CFTR chloride channels and regulates CFTR-mediated currents both in Xenopus oocytes and in epithelial cells that normally express these proteins. The physical and functional interactions between syntaxin 1A and CFTR are blocked by a syntaxin-binding protein of the Munc18 protein family (also called n-Secl). Our results indicate that CFTR function in epithelial cells is regulated by an interplay between syntaxin and Munc18 isoforms.

Characterization of a helix-loop-helix (EF hand) motif of silver hake parvalbumin isoform B

Parvalbumins are a class of calcium-binding proteins characterized by the presence of several helix-loop-helix (EF-hand) motifs. It is suspected that these proteins evolved via intragene duplication from a single EF-hand. Silver hake parvalbumin (SHPV) consists of three EF-type helix-loop-helix regions, two of which have the ability to bind calcium. The three helix-loop-helix motifs are designated AB, CD, and EF, respectively. In this study, native silver hake parvalbumin isoform B (SHPV-B) has been sequenced by mass spectrometry. The sequence indicates that this parvalbumin is a beta-lineage parvalbumin. SHPV-B was cleaved into two major fragments, consisting of the ABCD and EF regions of the native protein. The 33-amino acid EF fragment (residues 76-108), containing one of the calcium ion binding sites in native SHPV-B, has been isolated and studied for its structural characteristics, ability to bind divalent and trivalent cations, and for its propensity to undergo metal ion-induced self-association. The presence of Ca2+ does not induce significant secondary structure in the EF fragment. However, NMR and CD results indicate significant secondary structure promotion in the EF fragment in the presence of the higher charge-density trivalent cations. Sedimentation equilibrium analysis results show that the EF fragment exists in a monomer-dimer equilibrium when complexed with La3+.

Structural studies by 1H NMR of a prototypic alpha-helical peptide (LYQELQKLTQTLK) and homologs in trifluoroethanol/water and on sodium dodecyl sulfate micelles

The 1H NMR-determined structure and dynamics of a synthetic, amphiphilic alpha-helical peptide, PH-1.0 (LYQELQKLTQTLK), and several homologs were compared in 50% trifluoroethanol-d2 (TFE-d2)/H20 and in sodium dodecyl-d25 sulfate (SDS-d25) micelles. The peptides were designed to test the influence on secondary structure of placement of favored and disfavored residues relative to a "longitudinal, hydrophobic strip-of-helix" defined by the repeating leucines. PH-1.0 was highly ordered as an alpha-helix in 50% TFE-d2/H20 and in SDS-d25 micelles. Homologs PH-1.1, in which L1 was replaced by T, and PH-1,4, in which L12 was replaced by T. were found to be partially helical in both media. Calculated structures in SDS-d25 revealed that the helix of PH-1.1 was slightly disordered at the N-terminus, but that of PH-1.4 was completely disordered at the C-terminus. Examination of distributions of hydrophobic residues in protein structures revealed that, when [symbol: see text] = LIVFM and [symbol: see text] = nonLIVFM, the pattern [symbol: see text] is favored and [symbol: see text] is disfavored in alpha-helices. Several analogs of PH-1.0 incorporating these patterns were studied. Peptide PH-1.12 (LYQELQKLLQTLK) retained alpha-helical structure in both 50% TFE-d2/H20 and in SDS-d25 micelles. However, although PH-1.13 (LYQELQKLTLTLK) was fully helical in 50% TFE, it was helical only through residue 6 in SDS micelles. Two homologs containing an additional loop of the helix and repeats of favored (PH-5.0, NYLQTLLETLKTLLQK) or suppressed LL patterns (PH-5.11, NYLQTLETLKLTQK) gave similar results, i.e. the latter peptide was helical only through residue 6 in SDS micelles. The degree of local order in these SDS micelle-adsorbed peptides correlates to placement of hydrophobic residues in motifs which are favored or disfavored in proteins in general and in alpha-helices specifically.

The isolation of parvalbumin isoforms from the tail muscle of the American alligator (Alligator mississipiensis)

Multiple parvalbumin isoforms have been detected in the tail (skeletal) muscle of the American alligator (Alligator mississipiensis). One of these isoforms (APV-1) has been highly purified and partially characterized. Protein purification involved mainly gel filtration and anion exchange chromatography, and characterization included gel electrophoresis, amino acid composition analysis, metal ion analysis, MALDI-TOF and ESI mass spectrometry, ultraviolet and fluorescence spectroscopy, and one- and two-dimensional 500 MHz proton NMR spectroscopy. The alligator isoforms are rich in phenylalanine and deficient in the other aromatic residues as is typical for parvalbumins. In fact, the one highly purified isoform that forms the basis of this study has only phenyl-alanine as an aromatic residue. Ion exchange chromatography further indicates that this isoform has a relatively high isoelectric point (pl approximately 5.0), indicating that it is an alpha-lineage parvalbumin. This alligator parvalbumin isoform is unusual in that it has an atypically high Ca2+ content (almost 3.0 mole of Ca2+ per mole of protein) following purification, a fact supported by terbium fluorescence titration experiments. Preliminary comparative analysis of the highly purified alligator parvalbumin isoform (in the Ca2-loaded state) by two-dimensional 1H-NMR (2D 1H TOCSY and 2D 1H NOESY) indicates that there is considerable similarity in structure between the alligator protein and a homologous protein obtained from the silver hake (a saltwater fish species).

Dendritic cells are recruited into the airway epithelium during the inflammatory response to a broad spectrum of stimuli

A key rate-limiting step in the adaptive immune response at peripheral challenge sites is the transmission of antigen signals to T cells in regional lymph nodes. Recent evidence suggests that specialized dendritic cells (DC) fulfill this surveillance function in the resting state, but their relatively slow turnover in most peripheral tissues brings into question their effectiveness in signaling the arrival of highly pathogenic sources of antigen which require immediate mobilization of the full range of host defenses for maintenance of homeostasis. However, the present report demonstrates that recruitment of a wave of DC into the respiratory tract mucosa is a universal feature of the acute cellular response to local challenge with bacterial, viral, and soluble protein antigens. Consistent with this finding, we also demonstrate that freshly isolated respiratory mucosal DC respond in vitro to a variety of CC chemokines as well as complementary cleavage products and N-formyl-methionyl-leucine-phenylalanine. This suggests that rapid amplification of specific antigen surveillance at peripheral challenge sites is an integral feature of the innate immune response at mucosal surfaces, and serves as an "early warning system" to alert the adaptive immune system to incoming pathogens.

Inositol 3,4,5,6-tetrakisphosphate inhibits the calmodulin-dependent protein kinase II-activated chloride conductance in T84 colonic epithelial cells

The mechanism by which inositol 3,4,5,6-tetrakisphosphate (Ins(3,4,5, 6)P4) regulates chloride (Cl-) secretion was evaluated in the colonic epithelial cell line T84 using whole cell voltage clamp techniques. Our studies focused on the calcium-dependent chloride conductance (gClCa) that was activated either by mobilizing intracellular calcium (Cai) stores with thapsigargin or by introduction of the autonomous, autophosphorylated calmodulin-dependent protein kinase II (CaMKII) into the cell via the patch pipette. Basal concentrations of Ins(3,4,5,6)P4 (1 microM) present in the pipette solution had no significant effect on Cl- current; however, as the concentration of the polyphosphate was increased there was a corresponding reduction in anion current, with near complete inhibition at 8-10 microM Ins(3,4,5,6)P4. Corresponding levels are found in cells after sustained receptor-dependent activation of phospholipase C. The Ins(3,4,5, 6)P4-induced inhibition of gClCa was isomer specific; neither Ins(1, 3,4,5)P4, Ins(1,3,4,6)P4, Ins(1,4,5,6)P4, nor Ins(1,3,4,5,6)P5 induced current inhibition at concentrations of up to 100 microM. Annexin IV also plays an inhibitory role in modulating gClCa in T84 cells. When 2 microM annexin IV was present in the pipette solution, a concentration that by itself has no effect on gClCa, the potency of Ins(3,4,5,6)P4 was approximately doubled. The combination of Ins(3,4,5,6)P4 and annexin IV did not alter the in vitro activity of CaMKII. These data demonstrate that Ins(3,4,5,6)P4 is an additional cellular signal that participates in the control of salt and fluid secretion, pH balance, osmoregulation, and other physiological activities that depend upon gClCa activation. Ins(3,4,5,6)P4 metabolism and action should also be taken into account when designing treatment strategies for cystic fibrosis.

N-type inactivation in the mammalian Shaker K+ channel Kv1.4

Mammalian voltage-gated K+ channels are oligomeric proteins, some of which may be composed in vivo of subunits derived from several similar genes. We have studied N-type inactivation in the rapidly inactivating Kv1.4 channel and, in specific, heteromultimers of this gene product with Kv1.5 noninactivating subunits. Heteromultimeric channels were analyzed for the stoichiometry of Kv1.4:Kv1.5 subunits by observing shifts in the midpoints of steady-state availability from that of homomultimeric channels. This analysis was employed to examine inactivation of heteromultimeric channels expressed in Xenopus oocytes using two model systems: by expression of a Kv1. 4-Kv1.5 tandem fusion construct and by coexpression of native Kv1.4 and Kv1.5 channels across a wide relative concentration range of microinjected mRNA. Additionally, inactivation was examined in coexpression experiments of N-terminal deletion mutants of Kv1.4. We found that (i) a single inactivating subunit conferred inactivation in all hetero-multimers studied; (ii) the rate of inactivation could not be distinguished in channels containing two inactivating subunits from those containing one inactivating subunit; and (iii) large deletions in the linker region between the N-terminal inactivation region and the first membrane-spanning domain had no effect on the rate of inactivation. These data confirm the importance of the proximal N-terminal region in the inactivation of mammalian Kv1.4 channels, and suggest that the inactivation particle remains in close proximity to the permeation pathway even when the channel is in the open state.

Shrinkage activates a nonselective conductance: involvement of a Walker-motif protein and PKC

The ability of all cells to maintain their volume during an osmotic challenge is dependent on the regulated movement of salt and water across the plasma membrane. We demonstrate the phosphorylation-dependent gating of a nonselective conductance in Caco-2 cells during cellular shrinkage. Intracellular application of exogenous purified rat brain protein kinase C (PKC) resulted in the activation of a current similar to that activated during shrinkage with a Na(+)-to-Cl- permeability ratio of approximately 1.7:1. To prevent possible PKC- and/or shrinkage-dependent activation of cystic fibrosis transmembrane regulator (CFTR), which is expressed at high levels in Caco-2 cells, a functional anti-peptide antibody, anti-CFTR505-511, was introduced into the cells via the patch pipette. Anti-CFTR505-511, which is directed against the Walker motif in the first nucleotide binding fold of CFTR, prevented the PKC/shrink-age current activation. The peptide CFTR505-511 also induced current inhibition, suggesting the possible involvement of a regulatory element in close proximity to the channel that shares sequence homology with the first nucleotide binding fold of CFTR and whose binding to the channel is required for channel gating.

Defective regional immunity in the respiratory tract of neonates is attributable to hyporesponsiveness of local dendritic cells to activation signals

A variety of studies suggest that the increased susceptibility of neonates to allergic and infectious respiratory diseases is due to delayed postnatal maturation of local mucosal immune function. We have recently demonstrated that the postnatal development of the major resident APC population in the respiratory tract (RT), class II MHC (Ia)-bearing dendritic cells (DC), is delayed relative to that in other tissues, and that both the intensity of Ia expression on these RTDC and their density within respiratory epithelia remain low until after weaning. The present study focuses on the functional capacity of neonatal RTDC and their responses to exogenous stimuli, and demonstrates that 1) infant Ia+ RTDC respond poorly to GM-CSF, under conditions that stimulate high levels of Ia expression and concomitant APC activity in adult cells; 2) both infant and adult RTDC contain a subpopulation of Ia- cells recognized by mAb OX62 that also respond poorly to GM-CSF; 3) inhalation of microbial stimuli or parenteral administration of IFN-gamma triggers rapid recruitment of DC into the airway epithelium and lung parenchyma of adults; this response is markedly attenuated in newborns and does not attain levels of competence until after weaning; and 4) endogenous macrophage-mediated suppression of the RTDC response to GM-CSF, the principal mechanism limiting in situ DC functional maturation in the adult lung, is highly active in the neonates. Taken together with earlier evidence of the relatively rapid postnatal development of T and B cell function in these animals, the present findings suggest that the sluggish performance of respiratory mucosal immune function(s) during infancy is attributable primarily to delayed maturation of local DC populations.

Defective regional immunity in the respiratory tract of neonates is attributable to hyporesponsiveness of local dendritic cells to activation signals

A variety of studies suggest that the increased susceptibility of neonates to allergic and infectious respiratory diseases is due to delayed postnatal maturation of local mucosal immune function. We have recently demonstrated that the postnatal development of the major resident APC population in the respiratory tract (RT), class II MHC (Ia)-bearing dendritic cells (DC), is delayed relative to that in other tissues, and that both the intensity of Ia expression on these RTDC and their density within respiratory epithelia remain low until after weaning. The present study focuses on the functional capacity of neonatal RTDC and their responses to exogenous stimuli, and demonstrates that 1) infant Ia+ RTDC respond poorly to GM-CSF, under conditions that stimulate high levels of Ia expression and concomitant APC activity in adult cells; 2) both infant and adult RTDC contain a subpopulation of Ia- cells recognized by mAb OX62 that also respond poorly to GM-CSF; 3) inhalation of microbial stimuli or parenteral administration of IFN-gamma triggers rapid recruitment of DC into the airway epithelium and lung parenchyma of adults; this response is markedly attenuated in newborns and does not attain levels of competence until after weaning; and 4) endogenous macrophage-mediated suppression of the RTDC response to GM-CSF, the principal mechanism limiting in situ DC functional maturation in the adult lung, is highly active in the neonates. Taken together with earlier evidence of the relatively rapid postnatal development of T and B cell function in these animals, the present findings suggest that the sluggish performance of respiratory mucosal immune function(s) during infancy is attributable primarily to delayed maturation of local DC populations.

The biology of airway dendritic cells

Recent work from our laboratory has identified a network of constitutively class II MHC (Ia) bearing dendritic cells (DC) within the epithelium of the conducting airways of laboratory animal species and in humans. The density of DC within the respiratory tract is highest in those areas exposed to greater amounts of inhaled antigen and further work has identified these DC as being critically important in controlling the induction of immune responses within the airways. The DC population in the airway epithelium is renewed every 48-72 h; this represents a more rapid turnover than DC in other tissues which are exposed to a smaller antigenic load. In addition to these results we will discuss other work which shows that airway DC are a very reactive population, comparable with neutrophils in their response to acute inflammatory stimuli and that their numbers and Ia content can be modulated following exposure to topical and systemic steroids. Finally we will discuss the development of these cells after birth and how this may influence the pathogenesis of immune regulated diseases such as asthma and allergic rhinitis.

Extracellular pH modulates the Ca2+ current activated by depletion of intracellular Ca2+ stores in human macrophages

Intracellular Ca2+ (Ca(i)) signaling following the binding of surface receptors activates a Ca2+ permeable plasma membrane conductance which has been shown to be associated with store depletion in a number of cell types. We examined the activation of this conductance in human monocyte-derived macrophages (HMDMs) using whole-cell voltage-clamp techniques coupled with fura-2 microfluorimetry and characterized the importance of external pH (pHo) as a modulator of current amplitude. Current activation was observed following experimental maneuvers designed to deplete intracellular Ca(2+)-stores including: (i) dialysis of the cell with 100 microM inositol 1,4,5-triphosphate (IP3), (ii) intracellular dialysis with high concentrations of the Ca2+ buffers EGTA and BAPTA, or (iii) exposure of the cell to the Ca(2+)-ATPase inhibitor thapsigargin (1 microM). Currents associated with store depletion were inwardly rectifying with kinetics, inactivation, and selectivity that appeared similar irrespective of the mode of activation. Currents were Ca2+ selective with a selectivity sequence of Ca2+ > Sr2+ >> Mg2+ = Mn2+ = Ni2+. The Ca2+ influx current was modulated by changes in pHo; modulation was not produced as a consequence of changes in internal pH (pHi). External acidification led to a reversible reduction in current amplitude with a pKa at pH 8.2. Changes in pHo alone failed to induce current activation. These observations are consistent with a scheme by which changes in pHo, as would be encountered by macrophages at sites of inflammation, could change the time course and magnitude of the Cai transient associated with receptor activation by regulating the influx of Ca2+ ions.

Calcium signaling in cultured rat oligodendrocytes

The syntax of neuronal-glial or axonal-glial interaction is frequently communicated through transient changes in internal calcium (Cai). We examined mechanisms for Cai signaling and intercellular propagation of Cai responses in cultured oligodendrocytes (OLGs) derived from adult spinal cord (SC), postnatal day 21 (P21) SC, and P21 brain. We found that (1) cultured OLGs exhibited a heterogeneous response to norepinephrine, carbachol, ATP, histamine, and glutamate; (2) receptor-mediated Cai increases were derived from both Ca2+ influx and intracellular Ca2+ release; (3) the percentage of responders to neuroligands varied as a function of cell origin; (4) cultured OLGs exhibited a thapsigargin-sensitive, but not a caffeine-sensitive, intracellular Ca2+ pool; and (5) gap junctional contacts between OLGs permitted limited intercellular propagation of mechanically stimulated Cai responses. Receptor-mediated Cai signaling appears to occur not only in cultured OLGs but also in acutely dissociated OLGs. The heterogeneity in Cai responses as a function of cell origin may reflect the existence of OLG subsets or differences in the maturation stage of OLGs.

Simultaneous detection of free radical release and membrane current during phagocytosis

Stimulation of macrophages induces the "respiratory burst" response which is associated with the generation of superoxide (O2-), a drop in cytoplasmic pH, and a pronounced depolarization of the membrane potential. The purpose of the present studies was to determine whether an increase in O2- was temporally related to changes in membrane potential and transmembrane current. Release of O2- at the single cell level was photometrically monitored during phagocytosis of immune complexes while simultaneously measuring whole-cell current. Membrane depolarization and the generation of a non-selective current followed an increase in O2- production with a variable lag time which was correlated with the state of cellular maturation in culture. In the absence of phagocytosis, the exposure of macrophages to O2- generated by a xanthine-xanthine oxidase reaction activated a non-selective current similar to that seen after phagocytosis. These results provide the first demonstration of the relationship between free radical release and the ensuing electrophysiological signaling events which are linked to particle engulfment in phagocytic cells.

1H and 31P NMR study of speciation in systems containing ADP, Al3+, and fluoride

It has been proposed that AlF4- can serve as a tetrahedral pseudophosphate bound to guanosine diphosphate (GDP) [or other nucleoside diphosphates (NDP)] in G-protein systems. In a previous paper [D. J. Nelson and R. B. Martin, J. Inorg. Biochem. 43, 37 (1991)], 19F and 1H NMR were used to analyze the ternary system Al(3+)-NDP-F- in aqueous solutions. Ternary complexes (NDP)AlFx (with x = 1-3) were identified, but no (NDP)AlF4 was found. In this paper, the equilibrium constants for ternary complex formation that were obtained in the previous paper were further tested in a more extensive 1H and 31P NMR study of speciation in systems that contained Al3+, F-, and adenosine 5'-diphosphate (ADP). The results of the study are in general support of previously derived constants for ternary complexes and also provide support for the existence at relatively high ADP concentration (approximately 10 mM) of a base-stacked intermolecular dihydroxy-di-Al3+ bridged ADP dimeric structure at an ADP to Al3+ molar ratio of 1:1. 31P NMR of the dimer reveals that each of the two Al3+ ions is bidentately coordinated to the alpha and beta phosphates of a single (but different) ADP molecule. Evidence is also presented for the existence at relatively low ADP concentration (approximately 0.5 mM) of a monomeric species in which a single Al3+ ion is coordinated to alpha and beta phosphates of a single ADP molecule. 1H NMR of the monomeric species reveals the expected "wrong-way chemical shift" of the adenine C8 proton upon Al3+ ion complexation to the phosphate chain.

Modulation of airway intraepithelial dendritic cells following exposure to steroids

Recent studies from our laboratory have identified a network of constitutively class II major histocompatibility complex (MHC) (Ia)-bearing dendritic cells (DC) within the epithelium of the conducting airways of laboratory animal species and in humans. These studies have also demonstrated that the density of the DC network increases within the airway epithelium in response to inflammatory challenge. In the present report, we demonstrate that exposure of adult rats to inhaled steroids leads to a rapid but readily reversible decrease both in the number of airway intraepithelial DC, and in their surface Ia expression. Similar changes are also seen in response to high doses of systemic dexamethasone. In addition, we demonstrate that steroid inhalation reduces the rate of postnatal expansion of the airway intraepithelial DC network in rat pups, and prevents the rapid expansion of the DC network in adults which occurs during the acute inflammatory response following inhalation of microbial stimuli.

Mechanism of clofilium block of the human Kv1.5 delayed rectifier potassium channel

The effect of clofilium on potassium conductance was studied in excised membrane patches from Chinese hamster ovary cells stably transfected with the Kv1.5/hPCN1 delayed rectifier K+ channel gene. Bath application of clofilium resulted in current inhibition, displaying concentration-dependent acceleration of the apparent channel inactivation in both outside-out and inside-out patches. The steady state half-inhibition concentration in inside-out patches was 140 +/- 80 nM (n = 10), which was less than the half-inhibition concentration of 840 +/- 390 nM (n = 10) observed in outside-out patches. Clofilium accelerated apparent current inactivation but did not influence the kinetics of current activation or deactivation. The rate of onset of channel block induced by clofilium was not voltage dependent. In contrast, the rate of recovery from channel block was slower at more hyperpolarized membrane potentials. Elevation of extracellular K+ levels accelerated recovery from channel block without influencing the rate of onset of block. These data suggest that clofilium may induce channel block by an "activation trap" mechanism. Clofilium may be trapped near the conductivity pore so that permeating K+ ions promote recovery from clofilium-induced block.

Calmodulin regulates fast axonal transport of squid axoplasm organelles

The role of calmodulin (CaM) in organelle motility (fast axonal transport) in the axoplasm of the squid giant axon was evaluated directly using video-enhanced microscopy. Addition of 6 microM CaM to extruded squid axoplasm produced a 2.6-fold increase in the number of organelles moving per minute per unit area of axoplasm. When lower concentrations of CaM, including physiological concentration (2 micrograms/ml), were added to extruded axoplasm, the number of organelles moving was equally increased. CaM had no significant effect on the mean velocity of organelle translocations. The stimulatory effect of CaM was reduced significantly by the CaM inhibitors melittin (36 microM) and trifluoperazine (50 microM). Parvalbumin, a high-affinity calcium binding protein, did not stimulate motile activity. These results suggest that CaM is a positive regulator of fast axonal transport. At the molecular level, this regulation may involve microtubule-and/or actin-based motor proteins. Several possible molecular mechanisms are proposed.

Annexin IV inhibits calmodulin-dependent protein kinase II-activated chloride conductance. A novel mechanism for ion channel regulation

Ca(2+)-activated Cl- current (ICl,Ca) in colonic T84 cells is inhibited by the specific peptide inhibitor of Ca2+/calmodulin-dependent kinase II (CaM KII). Annexin IV, a Ca(2+)-dependent phospholipid binding protein also inhibits Ca(2+)-dependent anion current activation (Kaetzel, M.A., Chan, H.-C., Dubinsky, W.P., Dedman, J.R., and Nelson, D.J. (1994) J. Biol. Chem. 269, 5297-5302). Intracellular injection of antibodies against annexin IV enhances current activation; this activation is inhibited by the peptide inhibitor of CaM KII. Intracellular application of autonomously active CaM KII in the presence of ATP induced a Cl- current similar to that activated by the Ca2+ ionophore A23187. Current activation by the exogenous kinase was completely inhibited in the presence of purified annexin IV. In vitro, annexin IV does not inhibit CaM KII activity nor does it act as a substrate for CaM KII. Thus, it appears that annexin IV inhibits phosphorylation-dependent anion conductance activation by preventing CaM KII-ion channel interaction rather than by direct interaction with the enzyme itself. These findings suggest a novel mechanism by which Ca(2+)-dependent membrane binding proteins, cytoplasmic kinases, and ion channels interact to regulate membrane conductance. The characterization of unique channel regulatory pathways in Cl- transporting epithelia may identify potential avenues of alternate therapy to compensate for the loss of functional Cl- channels in the disease of cystic fibrosis.