Inhibition of macrophage spreading by antagonists of cellular calcium

Nitric oxide-induced endoplasmic reticulum stress activates the expression of cargo receptor proteins and alters the glycoprotein transport to the Golgi complex

The endoplasmic reticulum Golgi intermediate compartment 53 protein recycles continuously between the endoplasmic reticulum and the Golgi complex and ensures the anterograde transport of specific glycoproteins with the assistance of the Multiple Clotting Factor Deficiency adaptor protein. Therefore, to analyze the effect of the endoplasmic reticulum stress on the secretory pathway beyond the endoplasmic reticulum, we analyzed the expression of both proteins in J774 macrophages incubated with the nitric oxide donor DETA NONOate or with thapsigargin. Both proteins accumulated progressively, by a transcriptional mechanism, in response to these inducers. Nitric oxide also induced a higher level of calreticulin and glucose regulated 78 protein, two endoplasmic reticulum proteins controlled by the unfolded protein response. Interestingly, nitric oxide induced the processing of the activating transcription factor 6alpha of the unfolded protein response, while thapsigargin also induced the activation of the transcription factor X-box Binding Protein 1. In addition, we showed that the accumulation of both transporters occurred simultaneously with the activation of endoplasmic reticulum-stress-dependent apoptosis, suggesting that these proteins may participate in the events that will eventually decide the fate of the cell. Induction of endoplasmic reticulum stress affected the rate of anterograde transport of a reporter glycoprotein, indicating that the endoplasmic reticulum to Golgi transport is remarkably impaired. Our results indicate that increased levels of cargo receptor proteins might have a function either in the quality control of protein folding in the endoplasmic reticulum or in the homeostasis of the intermediate compartment and Golgi complex during cell stress.

Lipopolysaccharide, muramyl dipeptide and polyinosinic: polycytidylic acid induce the accumulation of inositol phosphates in blood monocytes and lymphocytes

Rabbit macrophages (Mø) and lymphocytes (Ly) incubated with three structurally dissimilar immunomodulators, lipopolysaccharide (bacterial endotoxin, LPS), polyinosinic: polycytidylic acid (poly-I:C) and muramyl dipeptide (MDP), were found to accumulate inositol phosphates (IPs) in a concentration- and time-dependent manner. The threshold concentration of LPS necessary for an increase in IPs in both cell types was less than 1 ng/ml and a maximum effect was observed between 1 and 10 micrograms/ml. The threshold concentrations for poly-I:C and MDP were between 0.1 and 1 microgram/ml for both cell types. Significant increases in the concentration of inositol phosphates occurred between 30 and 60 min after challenge of either cell type with any of the three agents studied. In addition, all three immunomodulators produced a greater accumulation of IPs in macrophages than in mixed lymphocytes and after 2 h appeared to approach a maximum in macrophages, whereas the IPs level in lymphocytes appeared to be still rising after 2 h. In Mø and Ly the IPs level was increased within 10 min of incubation in the presence of either PGE2 or medium previously obtained from cells incubated with LPS. In addition, anisomycin (a protein synthesis inhibitor) and ketoprofen (a cyclo-oxygenase inhibitor) inhibited the LPS-stimulated increase of IPs accumulation in both cell types. These two observations suggest that the LPS-stimulated increase in IPs in macrophages and lymphocytes is mediated by a protein intermediate and possibly a prostanoid.

Effects of TMB-8, a calcium antagonist, on transport properties of the isolated canine tracheal epithelium

The effects of the putative intracellular Ca2+ antagonist, TMB-8 (8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate), on the canine tracheal epithelium were examined. Luminal addition reduced rapidly, but reversibly, the transmucosal potential difference and increased the resistance across the open-circuited epithelium. Under short-circuit conditions, the drug reduced stimulation by prostaglandin E2, forskolin, 8-bromo cyclic AMP, prostaglandin F2 alpha and A23187. Inhibition of prostaglandin E2 responses were accompanied by reversal of net Cl- fluxes produced by the agonist. The effects of TMB-8 were unaffected by increasing Ca2+ in the bathing solutions, and were not mimicked by procaine, nitrendipine, calmidazolium, compound 48/80 or trifluoperazine. W7 did, to a limited extent, produce similar responses, though the drug was more toxic, and the effects were irreversible.

The secretory action of barium chloride in rat colon

BaCl2, applied serosally, caused a rise in the p.d. and short-circuit current (s.c.c), and a decrease in tissue resistance in stripped sheets of rat colon. This response was dose dependent. Mucosal application of BaCl2 was without effect. The BaCl2-induced rise in s.c.c. was inhibited by reducing the serosal Na+ concentration to 25 mM. Lowering the mucosal Na+ concentration was without effect. Ouabain (10(-3) M in serosal fluid) and furosemide (10(-3) M in serosal fluid) both reduced the rise in s.c.c. induced by BaCl2. Flux determinations indicated that BaCl2 inhibited Na+ absorption and stimulated Cl- secretion by the colon. In vivo, BaCl2 increased fluid accumulation within the colonic lumen, an effect that was associated with a rise in the transcolonic p.d. Increasing the serosal K+ concentration to 20 mM reduced the responses to BaCl2, acetylcholine and theophylline, and this could not be entirely accounted for by the concomitant reduction in the serosal Na+ concentration. As high serosal K+ did not mimic the secretory response it would appear that BaCl2 does not act by blocking K+ channels. The rise in s.c.c. induced by BaCl2 was not reduced by Ca2+-free conditions, but it was inhibited by 8-(N,N-diethylamino)-octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB-8) and trifluoperazine. BaCl2 did not alter cyclic AMP production by colonic scrapes. It is concluded that BaCl2 induces colonic secretion by the release of intracellular Ca2+, which then combines with calmodulin to activate the secretory process.

The involvement of calcium in the intestinal response to secretagogues in the rat

The involvement of Ca2+ in the regulation of intestinal secretion was investigated in stripped sheets of rat mid-intestine. Removal of serosal Ca2+ together with the addition of EGTA at concentrations of 0.5 and 1 mM inhibited the rise in short-circuit current (s.c.c.) induced by both acetylcholine and theophylline, a similar degree of inhibition being observed with both secretagogues. Ca2+-free serosal fluid with 0.5 mM-EGTA added reduced significantly the rises in s.c.c. induced by A23187, acetylcholine, 5-hydroxytryptamine, theophylline, dibutyryl cyclic AMP and prostaglandin E2, but not the increased s.c.c. associated with glucose absorption. The Ca2+ channel blocker verapamil produced similar results. The calmodulin antagonist trifluoperazine inhibited secretagogue action while its sulphoxide derivative was without effect at the same concentration. The intracellular Ca2+ antagonist TMB-8 reduced the increased s.c.c. observed with acetylcholine and dibutyryl cyclic AMP. The net Cl- secretion, but not the decreased mucosal-to-serosal Na+ flux, induced by acetylcholine was abolished in Ca2+-free conditions. There was no consistent effect on the reduction in the residual ion flux caused by acetylcholine. Absence of Ca2+ converted the stimulation of Cl- secretion induced by dibutyryl cyclic AMP observed under control conditions to an enhancement of net Na+ and Cl- absorption. It is concluded that intestinal secretagogues, whether they act through cyclic AMP or not, require both internal and external sources of Ca2+ if they are to produce their full effects. Moreover, it appears that the nature of the response to dibutyryl cyclic AMP depends on the prevailing Ca2+ concentration.

Adenosine triphosphate-dependent calcium pump in the plasma membrane of guinea pig and human neutrophils

Changes in cytosolic free Ca may function as a second messenger in neutrophils. Since the plasma membrane seems to be a major regulator of intracellular Ca in many cells, we characterized an energy-dependent Ca transport system in plasma membrane-enriched fractions ("podosomes") from phorbol myristate acetate-stimulated guinea pig and human neutrophils. The active Ca transport system in guinea pig podosomes exhibited a high affinity for Ca (Michaelis constant [Km]Ca 280 +/- 120 nM) and a maximum velocity of 0.83 nmol Ca/mg protein per min. Uptake showed an absolute requirement for Mg ATP (Km ATP 67 microM), whereas other trinucleotides were inactive. Ca uptake was optimal at pH 7, was azide insensitive and temperature dependent. Vanadium, an inhibitor of the Ca/Mg ATPase of heart sarcolemma, inhibited Ca pump activity by 50% at 1 microM. Ca transport was not affected in a NaCl-containing medium, an observation arguing against the presence of a Na/Ca exchange system. Calmodulin at 0.5-10 micrograms/ml stimulated the Ca pumping activity of EGTA-washed podosomes. Calmodulin depletion decreased the affinity of the Ca pump for Ca (Km Ca 2.07 microM) and its readdition restored it (Km Ca 0.55 microM). ATP-dependent Ca transport by podosomes and phagocytic vesicles was inactivated by exposure to trypsin or to the nonpenetrating sulfhydryl reagent rho-chloromercuribenzene sulfonate. Human podosomes had a Ca uptake system with properties similar to those of the guinea pig. These findings demonstrate the presence of a Ca pump in the neutrophil plasma membrane, which is active at physiological concentrations of free cytosolic Ca. By changing Ca concentrations at the cell periphery, this pump could control various motile functions of the neutrophil, such as locomotion or degranulation.

An improved macrophage spreading assay--a simple and effective measure of activation

The development of a quantitative spreading assay of macrophage activation is described. The assay involved incubation of macrophages on glass coverslips for 1 hour and assessment of cell size using a microscope attached to a microcomputer-assisted digitising system which allowed the diameter of 200 cells to be assessed within 10 minutes. Mouse peritoneal macrophages were used in the development of the assay. Internal consistency of the assay was shown by minimal inter-observer, intra-observer and inter-animal variation. Validation of the assay as a measure of macrophage activation was confirmed by the use of in vivo and in vitro activating agents. Once validated the assay was used to detect activation in alveolar macrophages from rats exposed to airborne asbestos. The macrophage spreading assay described here is quick, reliable, consistent and easy to perform and has a potentially wide application in studies of macrophage function and dysfunction.

The effect of barium chloride on intestinal secretion in the rat

The addition of BaCl2 to the serosal solution, at concentrations from 0 X 25 mM to 10 mM, caused increases in potential difference, short-circuit current and resistance across stripped sheets of rat mid-intestine, although mucosal application had little effect. The response to BaCl2 was significantly greater than that obtained with the same concentration of CaCl2. An increase in net Cl- secretion entirely accounted for the rise in short-circuit current induced by BaCl2. BaCl2 inhibited net fluid uptake by everted sacs. It also enhanced the accumulation of fluid by intestinal loops in vivo and this was associated with an increased potential difference. The response to BaCl2 in vitro was not reduced in the absence of serosal Ca2+ ions. The effect of BaCl2 was abolished by trifluoperazine and also by TMB-8 (8-(N,N-diethylamino)-octyl-3,4,5-trimethoxybenzoate hydrochloride). BaCl2 did not alter cyclic AMP production by isolated enterocytes. It is concluded that BaCl2 induces intestinal secretion by releasing Ca2+ from intracellular stores which then combines with calmodulin to stimulate the secretory process.