Effect of toluene diisocyanate on homeostasis of intracellular-free calcium in human neuroblastoma SH-SY5Y Cells

The mechanisms of TDI (2,4-toluene diisocyanate)-induced occupational asthma are not fully established. Previous studies have indicated that TDI induces non-specific bronchial hyperreactivity to methacholine and induces contraction of smooth muscle tissue by activating ‘capsaicin-sensitive’ nerves resulting asthma. Cytosolic-free calcium ion concentrations ([Ca 2+] c) are elevated when either capsaicin acts at vanilloid receptors, or methacholine at muscarinic receptors. This study therefore investigated the effects of TDI on Ca 2+ mobilization in human neuroblastoma SH-SY5Y cells. TDI was found to elevate [Ca 2+] c by releasing Ca 2+ from the intracellular stores and extracellular Ca 2+ influx. 500 μM TDI induced a net [Ca 2+] c increase of 112 ± 8 and 78 ± 6 nM in the presence and absence of extracellular Ca 2+, respectively. In Ca 2+-free buffer, TDI induced Ca 2+ release from internal stores to reduce their Ca 2+ content and this reduction was evidenced by a suppression occurring on the [Ca 2+] c rise induced by thapsigargin, ionomycin, and methacholine after TDI incubation. In the presence of extracellular Ca 2+, simultaneous exposure to TDI and methacholine led a higher level of [Ca 2+] c compared to single methacholine stimulation, that might explain that TDI induces bronchial hyperreactivity to methacholine. We conclude that TDI is capable of interfering the [Ca 2+] c homeostasis including releasing Ca 2+ from internal stores and inducing extracellular Ca 2+ influx. The interaction of this novel character and bronchial hyperreactivity need further investigation.