MODULATION OF CA2+ INFLUX BY A MEDIATOR RELEASED FROM HUMAN TRACHEAL EPITHELIAL-CELLS EXPOSED TO OZONE IN-VITRO

Intracellular free Ca2+ ([Ca2+](i)) plays a vital role both in maintaining normal cellular function and in cell killing. Few studies have been published regarding its role in ozone (O-3)-induced health effects. This study investigated the effect and mechanism of O-3 exposure on [Ca2+](i) in human tracheal epithelial (HTE) cells. HTE cells grown on Costar Transwell inserts with a liquid-gas interface were exposed to 0, 0.05, 0.1, 0.2, and 0.4 ppm O-3 at 37 degrees C for 1 h. After exposure, [Ca2+](i) was measured using the fluorescent dye Flue 3. O-3 at 0.4 ppm produced a significant increase in [Ca2+](i), and the increases in [Ca2+](i) were blocked by verapamil and 8-(diethylamino)-octyl-3,4,5,-trimethoxybenzoate (TMB-8). These results suggest that the O-3-induced [Ca2+](i) elevation may involve both Ca2+ release from internal stores and Ca2+ influx across the plasma membrane. Furthermore, both buffer and cell lysate of HTE cells exposed to 0.4 ppm O-3 caused a rapid increase in [Ca2+](i) of THP-1 human phagocytic monocytes, but the buffer and lysate from air exposed cells did not. These results suggest that O-3 exposure causes HTE cells to release a diffusible mediator from the empty Ca2+-storing organelle and may be responsible for the sustained and persistent [Ca2+](i) elevation in HTE cells exposed to 0.4 ppm O-3.