Tumor Necrosis Factor Alpha Inducing Spatial Interactions between Calcium-Sensing Receptor and L-Type Voltage-Dependent Calcium Channel

Inflammatory cytokines tumour necrosis factor-α and interleukin-8 enhance airway smooth muscle contraction by increasing L-type Ca2+ channel expression

Inflammation elevates intracellular calcium concentrations ([Ca²⁺ ]_i ) in airway smooth muscle (ASM). The L-type Ca²⁺ channel (L-VDCC) plays an important role in regulating Ca²⁺ influx in ASM. However, the role of L-VDCC in the inflammatory cytokine-induced pathology of ASM remains unclear. In the present study, we used calcium imaging and isometric tension measurements to assess the role of L-VDCC in agonist-induced [Ca²⁺ ]_i rise and the associated contractions in mouse ASM, and we used immunoblotting to identify L-VDCC protein expression levels in mouse ASM after exposure to tumour necrosis factor alpha (TNF-α) or interleukin-8 (IL-8). Our results showed that high-K⁺ - or carbachol-induced contractions of mouse ASM were significantly greater after pretreatment with TNF-α or IL-8 for 24 hours. Both verapamil and nifedipine, L-VDCC inhibitors, abolished this increased contraction induced by TNF-α or IL-8 pretreatment. Moreover, TNF-α treatment enhanced carbachol-induced Ca²⁺ influx in ASM cells, and this effect was abrogated by verapamil. Additionally, immunoblotting results showed that preincubation of mouse ASM with TNF-α or IL-8 also enhanced L-VDCC protein expression. On the basis of these findings, we concluded that proinflammatory cytokines, such as TNF-α and IL-8, increase the expression level of L-VDCC, which in turn contributes to augmented agonist-induced ASM contractions. This effect of inflammation on L-VDCC expression in ASM may be associated with airway hyper-responsiveness and involved in the development of asthma.

Inositol 1,4,5-trisphosphate receptor-mediated initial Ca(2+) mobilization constitutes a triggering signal for hydrogen peroxide-induced apoptosis in INS-1 β-cells

Reactive oxygen species, including hydrogen peroxide (H(2)O(2)), are known to induce β-cell apoptosis. The present study investigated the role of Ca(2+) in H(2)O(2)-induced apoptosis of the β-cell line INS-1. Annexin V assay with flow cytometry and DNA ladder assay demonstrated that treatment of INS-1 cells with 100 µM H(2)O(2) for 18 h significantly increased apoptotic cells. A comparable level of apoptosis was also observed after 18 h when the cells were treated with 100 µM H(2)O(2) only for initial 30 min. The H(2)O(2)-induced apoptosis was abolished by 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl)ester (BAPTA/AM), a chelator of intracellular Ca(2+), by 2-aminoethoxydiphenylborate (2-APB), a blocker of inositol 1,4,5-trisphosphate (IP(3)) receptors and cation channels, and by xestospongin D, a blocker of IP(3) receptors, and was partially blocked by SKF-96365, a non-selective cation channel blocker. However, nicardipine, an L-type voltage-dependent Ca(2+) channel blocker, or N-(p-amylcinnamoyl)anthranilic acid (ACA), a TRPM2 blocker, had little effect on the apoptosis. The inhibitory effect of BAPTA/AM or 2-APB on the H(2)O(2)-induced apoptosis was largely attenuated when the drug was added 30 min or 1 h after start of the treatment with H(2)O(2). These results suggest that the initial intracellular Ca(2+) elevation induced by H(2)O(2), which is mediated via IP(3) receptors and store-operated cation channels, plays an obligatory role in the induction of β-cell apoptosis.