Role of endoplasmic reticulum, an intracellular Ca2+ store, in histamine release from rat peritoneal mast cell

Flunarizine inhibits osteoclastogenesis by regulating calcium signaling and promotes osteogenesis

Many bone diseases such as osteoporosis and periodontitis are caused by hyperactivation of osteoclasts. Calcium (Ca²⁺ ) signals are crucial for osteoclast differentiation and function. Thus, the blockade of Ca²⁺ signaling may be a strategy for regulating osteoclast activity and has clinical implications. Flunarizine (FN) is a Ca²⁺ channel antagonist that has been used for reducing migraines. However, the role of FN in osteoclast differentiation and function remains unknown. Here, we investigated whether FN regulates osteoclastogenesis and elucidated the molecular mechanism. FN inhibited osteoclast differentiation along with decreased expression of nuclear factor of activated T cells, cytoplasmic 1 (NFATc1), and attenuated osteoclast maturation and bone resorption. FN inhibition of osteoclast differentiation was restored by ectopic expression of constitutively active NFATc1. FN reduced calcium oscillations and its inhibition of osteoclast differentiation and resorption function was reversed by ionomycin, an ionophore that binds Ca²⁺ . FN also inhibited Ca²⁺ /calmodulin-dependent protein kinase IV (CaMKIV) and calcineurin leading to a decrease in the cAMP-responsive element-binding protein-dependent cFos and peroxisome proliferator-activated receptor-γ coactivator 1β expression, and NFATc1 nuclear translocation. These results indicate that FN inhibits osteoclastogenesis via regulating CaMKIV and calcineurin as a Ca²⁺ channel blocker. In addition, FN-induced apoptosis in osteoclasts and promoted osteogenesis. Furthermore, FN protected lipopolysaccharide- and ovariectomy-induced bone destruction in mouse models, suggesting that it has therapeutic potential for treating inflammatory bone diseases and postmenopausal osteoporosis.

Inhibition of influenza virus replication by targeting broad host cell pathways

Antivirals that are currently used to treat influenza virus infections target components of the virus which can mutate rapidly. Consequently, there has been an increase in the number of resistant strains to one or many antivirals in recent years. Here we compared the antiviral effects of lysosomotropic alkalinizing agents (LAAs) and calcium modulators (CMs), which interfere with crucial events in the influenza virus replication cycle, against avian, swine, and human viruses of different subtypes in MDCK cells. We observed that treatment with LAAs, CMs, or a combination of both, significantly inhibited viral replication. Moreover, the drugs were effective even when they were administered 8 h after infection. Finally, analysis of the expression of viral acidic polymerase (PA) revealed that both drugs classes interfered with early events in the viral replication cycle. This study demonstrates that targeting broad host cellular pathways can be an efficient strategy to inhibit influenza replication. Furthermore, it provides an interesting avenue for drug development where resistance by the virus might be reduced since the virus is not targeted directly.

Amperometric characterization of exocytotic events from single mast cells: dependence on external and internal Ca++ sources

Mast cells exocytotically release histamine/serotonin in response to different secretagogues. We have used substance P and compound 48/80 to study the Ca++ dependency of serotonin exocytosis from peritoneal mast cells using carbon fiber amperometric techniques. The exocytotic release pattern consists of a burst of events superimposed on a slow, transient, amperometric current baseline increase. Cellular re lease parameters (number, frequency and total charge of amperometric events) and individual event characteristics (charge integral, half width and peak amplitude) were similar for the two secretagogues used. Zero Ca++ conditions greatly reduced, without completely abolishing,cellular release parameters. Cyclopiazonic acid, an inhibitor of the endoplasmatic Ca++ ATPase, reduced the cellular exocytotic capacity and diminished the amplitude of individual exocytotic events more effectively than the 0 Ca++ condition. The cyclopiazonic acid effects occurred in the presence of external Ca++, indicating that this condition is not sufficient for maintaining full exocytotic capacity. The results confirm the importance of intracellular Ca++ for exocytotic activation. For the first time evidence is presented that the integrity of intracellular Ca++ pools determines the amplitude and frequency of individual exocytotic events. Saponin, a non-specific detergent, also induced quantal release similar to that obtained with substance P and compound 48/80. This release was not dependent on extracellular Ca++, but cyclopiazonic acid significantly reduced individual exocytotic release.

Influence of the anti-allergic drug oxatomide on the signal transduction mechanism in a mast cell model

In a mast cell model, oxatomide displays inhibition of mediator release which is not related to its histamine H1 receptor antagonistic activity. From a previous study it appeared that especially early steps in the signal transduction leading to exocytosis were influenced by oxatomide. We now studied effects of oxatomide on those early steps in more detail. The antigen- and thapsigargin-mediated exocytosis in rat basophilic leukemia (RBL-2H3) cells were both inhibited by oxatomide. After aggregation of high affinity receptors for immunoglobulin E (Fc epsilon RI), protein tyrosine phosphorylation is induced. Oxatomide caused remarkable changes in the tyrosine phosphorylation pattern in resting cells. Also after antigen and thapsigargin activation, changes in the tyrosine phosphorylation of cellular proteins are observed. In addition, Ca2+ fluxes were studied by means of the net influx of 45Ca2+ and by measuring intracellular free Ca2+ concentrations ([Ca2+]) with the fluorescent probe fura-2. Oxatomide inhibited the 45Ca2+ influx and the increase in [Ca2+]i upon antigen and thapsigargin activation of the cells. Neither the release of Ca2+ from internal stores nor the efflux of Ca2+ over the plasma membrane seems to be affected. The effect of oxatomide on Ca2+ influx was further characterized by studying Ba2+ influx in the absence of extracellular free Ca2+. We conclude that inhibition of mediator release is mainly caused by inhibition of influx of extracellular Ca2+, via plasma membrane Ca2+ channels that are activated by depletion of intracellular Ca2+ stores. The molecular mechanism with which oxatomide might interfere with these channels is discussed.

Two-phase increment of Ca2+ uptake, intracellular Ca2+ concentration, and histamine release following antigen stimulation in mouse bone marrow-derived mast cells (BMMC)

The relationship between the influx of Ca2+ into cells or cytosolic Ca2+ concentration ([Ca2+]i) and the histamine release following antigen stimulation in mouse bone marrow-derived mast cells (BMMC) was examined, and the results were compared with those from human lung mast cells (HLMC) and rat peritoneal mast cells (RPMC) in some experiments. Anaphylactic histamine release from BMMC as well as HLMC, but not that from RPMC, was dependent on the extracellular Ca2+. When BMMC were challenged by antigen following radioactive 45Ca2+ addition, two phases of 45Ca2+ influx into the cells were observed. The first phase, which was initiated and completed within 30 sec and 2 min, respectively, after antigen treatment, appeared to be related to anaphylactic histamine release. The second influx began 30 sec subsequent to the first one and lasted for at least 2 min, and this occurred after the completion of the histamine release; So far, it is not known how this second influx participates in the intracellular event(s). On the other hand, only one sustained elevation of [Ca2+]i occurred that reached its maximum within 2 min after antigen stimulation. Following stimulation of BMMC with antigen in the absence of Ca2+, Ca2+ addition 1 to 5 min later time-dependently enhanced the histamine release, although the release was deteriorated by further extension of Ca2+ addition. In contrast, the releasability of HLMC was rapidly decreased. These results indicate that extracellular Ca2+ not only is prerequisite for anaphylactic histamine release from BMMC, but also may modulate the release and participate in some intracellular event(s) which has yet to be focused upon.

Flunarizine blocks elevation of free cytosolic calcium in synaptosomes following sustained depolarization

Gerbil cerebral cortical synaptosomes loaded with the fluorescent calcium probe FURA-2 were used to study depolarization-induced presynaptic cytosolic free calcium concentration, as an in vitro model of cerebral ischemia. The depolarization-induced increase in intrasynaptosomal cytosolic free calcium concentration is not sodium-dependent or sodium channel-dependent and may be due to an influx of extrasynaptosomal calcium resulting from a cadmium- and omega-conotoxin-sensitive, nickel-, nifedipine-, and nimodipine-insensitive voltage-regulated channel. The depolarization-induced increase in intrasynaptosomal free cytosolic calcium concentration is also inhibited by flunarizine, a calcium antagonist that has protective effects in animal models of cerebral anoxia and ischemia. Our results suggest that presynaptic calcium uptake following depolarization may be mediated in part by an N-type channel. Flunarizine may block presynaptic calcium accumulation, in part, by blocking this N-type channel; this blockade may be just one of several mechanisms by which flunarizine exerts protective effects following cerebral ischemia.

Taurine release evoked by NMDA receptor activation is largely dependent on calcium mobilization from intracellular stores

It is known that the activation of N-methyl-D-aspartate (NMDA) receptors leads to an increase in extracellular taurine concentration in different brain regions. The mechanism that mediates this effect is not totally understood. In this study, rat hippocampal slices were used to determine the dependence of NMDA-induced taurine release on extracellular calcium and/or on calcium mobilization from intracellular stores. NMDA was administered through a microdialysis probe inserted into the slice, at the level of CA1 stratum radiatum, which was also used to collect amino acids from the extracellular space. Field potentials evoked by stimulation of the Schaffer collaterals and recorded in the stratum pyramidale of CA1 were used as a control of NMDA receptor activation. NMDA induced a marked increase in extracellular taurine levels and a decrease in field potential amplitude, and both effects were suppressed in the presence of MK-801, a blocker of the NMDA receptor-linked channel. Dantrolene, an inhibitor of calcium release from intracellular stores, partially inhibited the extracellular taurine increase, while 2-nitro-4-carboxyphenyl-N,N-diphenyl carbamate (NCDC), an inhibitor of phosphatidylinositol-specific phospholipase C activation, had no effect. Removal of extracellular calcium diminished, but did not abolish, the extracellular taurine increase caused by NMDA. The remaining taurine response was totally suppressed by dantrolene, and also by NCDC. These results demonstrate that the release of taurine induced by NMDA receptor activation is triggered by the increase in cytoplasmic calcium concentration. We suggest that, under physiological conditions, calcium influx provides the signal for NMDA-induced taurine release, which is amplified by calcium-dependent calcium mobilization from intracellular stores.(ABSTRACT TRUNCATED AT 250 WORDS)

Thrombin-stimulated phosphorylation of myosin light chain and its possible involvement in endothelin-1 secretion from porcine aortic endothelial cells

Thrombin-stimulated secretion of endothelin-1 (ET-1) from porcine aortic endothelial cells was inhibited in the presence of 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester (TMB-8), trifluoperazine and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7). 1-(5-Chloronaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine (ML-9) also prevented the thrombin-stimulated secretion of ET-1 but it enhanced the accumulation of ET-1 in the endothelial cells. When the endothelial cells were treated with thrombin, the phosphorylation of a 20-kDa protein which was identified as myosin light chain (MLC) was detected. Phosphorylation was augmented in a time-dependent manner. As in the case of ET-1 secretion, MLC phosphorylation was prevented by TMB-8, trifluoperazine, W-7 and ML-9 at the same concentrations which were effective in inhibiting the ET-1 secretion. The site of phosphorylation of MLC was identified as a serine residue. Parallel to the phosphorylation of MLC, thrombin increased the amounts of the 43- and 200-kDa proteins in the Triton-insoluble fraction; these proteins were identified as actin and myosin heavy chain, respectively. These results suggest that the MLC phosphorylation elicited by MLC kinase may facilitate the formation of filamentous myosin and actin which are probably involved in ET-1 secretion, possibly in the transport of ET-1-containing vesicles in thrombin-stimulated endothelial cells.