Activation of acetylcholine receptor elicits intracellular Ca2+ mobilization, transient cytotoxicity, and induction of RANKL expression

Acetylcholine receptors (AChR) including muscarinic and nicotinic AChR are widely expressed and mediate a variety of physiological cellular responses in neuronal and non-neuronal cells. Notably, a functional cholinergic system exists in oral epithelial cells, and nicotinic AChR (nAChR) mediates cholinergic anti-inflammatory responses. However, the pathophysiological roles of AChR in periodontitis are unclear. Here, we show that activation of AChR elicits increased cytosolic Ca²⁺ ([Ca²⁺]ᵢ), transient cytotoxicity, and induction of receptor activator of nuclear factor kappa-B ligand (RANKL) expression. Intracellular Ca²⁺ mobilization in human gingival fibroblast-1 (hGF-1) cells was measured using the fluorescent Ca²⁺ indicator, fura-2/AM. Cytotoxicity and induction of gene expression were evaluated by measuring the release of glucose-6-phosphate dehydrogenase and RT-PCR. Activation of AChR in hGF-1 cells by carbachol (Cch) induced [Ca²⁺]ᵢ increase in a dose-dependent manner. Treatment with a high concentration of Cch on hGF-1 cells caused transient cytotoxicity. Notably, treatment of hGF-1 cells with Cch resulted in upregulated RANKL expression. The findings may indicate potential roles of AChR in gingival fibroblast cells in bone remodeling.

Effects of C18 Fatty Acids on Intracellular Ca2+ Mobilization and Histamine Release in RBL-2H3 Cells

To investigate the underlying mechanisms of C18 fatty acids (stearic acid, oleic acid, linoleic acid and alpha-linolenic acid) on mast cells, we measured the effect of C18 fatty acids on intracellular Ca2+ mobilization and histamine release in RBL-2H3 mast cells. Stearic acid rapidly increased initial peak of intracellular Ca2+ mobilization, whereas linoleic acid and alpha-linolenic acid gradually increased this mobilization. In the absence of extracellular Ca2+, stearic acid (100 microM) did not cause any increase of intracellular Ca2+ mobilization. Both linoleic acid and alpha-linolenic acid increased intracellular Ca2+ mobilization, but the increase was smaller than that in the presence of extracellular Ca2+. These results suggest that C18 fatty acid-induced intracellular Ca2+ mobilization is mainly dependent on extracellular Ca2+ influx. Verapamil dose-dependently inhibited stearic acid-induced intracellular Ca2+ mobilization, but did not affect both linoleic acid and alpha-linolenic acid-induced intracellular Ca2+ mobilization. These data suggest that the underlying mechanism of stearic acid, linoleic acid and alpha-linolenic acid on intracellular Ca2+ mobilization may differ. Linoleic acid and alpha-linolenic acid significantly increased histamine release. Linoleic acid (C18:2: omega-6)-induced intracellular Ca2+ mobilization and histamine release were more prominent than alpha-linolenic acid (C18:3: omega-3). These data support the view that the intake of more alpha-linolenic acid than linoleic acid is useful in preventing inflammation.

Intracellular Ca2+ Mobilization and Beta-hexosaminidase Release Are Not Influenced by 60 Hz-electromagnetic Fields (EMF) in RBL 2H3 Cells

The effects of extremely low frequency electromagnetic fields (EMF) on intracellular Ca2+ mobilization and cellular function in RBL 2H3 cells were investigated. Exposure to EMF (60 Hz, 0.1 or 1 mT) for 4 or 16 h did not produce any cytotoxic effects in RBL 2H3 cells. Melittin, ionomycin and thapsigargin each dose-dependently increased the intracellular Ca2+ concentration. The increase of intracellular Ca2+ induced by these three agents was not affected by exposure to EMF (60 Hz, 1 mT) for 4 or 16 h in RBL 2H3 cells. To investigate the effect of EMF on exocytosis, we measured beta-hexosaminidase release in RBL 2H3 cells. Basal release of beta-hexosaminidase was 12.3+/-2.3% in RBL 2H3 cells. Exposure to EMF (60 Hz, 0.1 or 1 mT) for 4 or 16 h did not affect the basal or 1 microM melittin-induced beta-hexosaminidase release in RBL 2H3 cells. This study suggests that exposure to EMF (60 Hz, 0.1 or 1 mT), which is the limit of occupational exposure, has no influence on intracellular Ca2+ mobilization and cellular function in RBL 2H3 cells.

Depression of Ca2+ influx in complement C5a-stimulated neutrophils by calmodulin inhibitors

Role of Ca2+/calmodulin complex in intracellular Ca2+ mobilization in neutrophils has not been clearly elucidated. In this study, effects of chlorpromazine, trifluoperazine and imipramine on the intracellular Ca2+ mobilization, including Ca2+ influx, in C5a-activated neutrophils were investigated. Complement C5a-stimulated superoxide production and myeloperoxidase release in neutrophils were inhibited by chlorpromazine, trifluoperazine and imipramine, except no effect of imipramine on myeloperoxidase release. A C5a-elicited elevation of (Ca2+)i in neutrophils was inhibited by chlorpromazine, trifluoperazine, imipramine, staurosporine, genistein, EGTA, and verapamil but not affected by pertussin toxin. The intracellular Ca2+ release in C5a-activated neutrophils was not affected by chlorpromazine and imipramine. Chlorpromazine and imipramine inhibited Mn2+ influx by C5a-activated neutrophils. Thapsigargin-evoked Ca2+ entry was inhibited by chlorpromazine, trifluoperazine, imipramine, genistein, EGTA and verapamil, while in the activation process of neutrophils. The depressive action of calmodulin inhibitors on the elevation of cytosolic Ca2+ level in C5a-activated neutrophils appears to be accomplished by inhibition of Ca2+ influx from the extracellular medium.