Intracellular influx of calcium induced by quartz particles in alveolar macrophages.
Historical studies report that cellular injury and silicosis are related to cytosolic free calcium (Ca2+). Moreover, reactive oxygen species (ROS) have been linked to cellular injury. However, the detail mechanism of the increase in [Ca2+]i and the relationship between [Ca2+]i and ROS production remains unknown. Quartz particle has been found to increase [Ca2+]i and activate the generation of ROS. Our hypothesis is that [Ca2+]i increase induced by quartz particle is from extracellular Ca2+ through the Ca2+ channel, and [Ca2+]i increase is believed to activate ROS production. In order to examine this hypothesis, we treated rat alveolar macrophages with quartz (SiO2) particles and used laser scanning confocal microscopy to measure [Ca2+]i and the fluorescence intensity of ROS. Time- and dose-dependent increases in [Ca2+]I and ROS in macrophages as well as cell viability were observed. Through chelating extracellular Ca2+ with ethylene glycol tetraacetic acid and releasing intracellular Ca2+ with thapsigargin, we found that 72.7% of the [Ca2+]i increase was due to the influx of Ca2+ from the extracellular environment, via Ca2+ channels in the plasma membrane. By adding mannitol to scavenge hydroxyl radicals (OH(.)), and removing surface iron from the quartz particles to reduce OH(.) generation, we observed a reduced level of ROS generation, whereas the increase in [Ca2+]i was unaffected. When using EGTA to reduce [Ca2+]i, we observed a decrease in ROS production. This study suggests that the [Ca2+]i influx was independent of OH(.) production, and the [Ca2+]i increase resulted in ROS production. These results further indicate that there is a strong relationship between cytosolic free Ca2+ content and cellular injury as well as silica exposure.
Tian
Feng
F
State Key Laboratory for Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China.
Zhu
Tong
T
Shang
Yu
Y
D000818:Animals; D001992:Bronchoalveolar Lavage Fluid; D002118:Calcium / Q000378:metabolism*; D017136:Ion Transport; D016676:Macrophages, Alveolar / Q000378:metabolism*; D008297:Male; D011791:Quartz; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism
D017382:Reactive Oxygen Species; D011791:Quartz; D002118:Calcium