Aluminum as a specific inhibitor of the reactive oxygen species-responsive calcium channels

Abstract

Al plays dual roles as an inducer and an inhibitor of Ca²⁺ influx depending on the concentration. Here, effects of Al on Ca²⁺ signaling were assessed in tobacco BY-2 cells expressing aequorin. Al treatment induced the superoxide generation and Ca²⁺ influx was secondarily induced by superoxide. Al concentrations higher than 3 mM inhibited the Al-stimulated superoxide-mediated Ca²⁺ influx. H₂O₂-induced Ca²⁺ influx was also inhibited by Al (IC₅₀, ca. 0.3 mM), indicating that Ca²⁺ channels responsive to reactive oxygen species (ROS) are blocked. Similarly, known Ca²⁺ channel blockers (lanthanides) inhibited the H₂O₂-induced Ca²⁺ influx. Lanthanides also inhibited hypo-osmotically induced Ca²⁺ influx. However, Al showed no effect against the hypo-osmotic Ca²⁺ influx. Al may be a novel channel blocker specific for ROS-responsive Ca²⁺ channels. Since such a selective channel blocker has not been reported to date, use of Al in addition to lanthanides may provide information on ROS-induced Ca²⁺ signaling.