[Downregulation of gap junctional intercellular communication induced by silicon dioxide in the pulmonary alveolar epithelial cell]

To explore the effect of silica dioxide(SiO2) on proliferation and downregulation of gap junctional intercellular communication (GJIC) in pulmonary alveolar epithelial cells (CCL-64 cells).

The pulmonary alveolar macrophages(PAMs) were incubated in the serum-free RPMI 1640 containing the various concentration of SiO2 for 24 hours. The supernatants were prepared and added 5% (V/V) into 2% (V/V) NBS RPMI 1640 to stimulate the proliferation of CCL-64 cells for 24 hours. A set of "blank control", run in parallel, contained RPMI 1640 + 2% (V/V) NBS alone. The proliferation of CCL-64 cells was detected using MTT assay(to show as the absorbency, A570nm). GJIC function was measured using the fluorescence redistribution after photobleaching(FRAP) assay [to express as the transfer rate of the fluorescence, K (x 10(-3)/s)], with a laser scanning confocal microscope(LSCM, Leica TCS SP).

The silica-exposed PAM supernatants could induce both the proliferation(F = 9.679, P < 0.01) and downregulation of GJIC(F = 20.587, P < 0.01) of CCL-64 cells. In the range of 50-500 micrograms/ml SiO2 concentrations, the proliferation (A570nm values) and GJIC(the transfer rate, K) were fitted well in a dose-dependent manner(proliferation: r = 0.891, P < 0.05; GJIC: r = -0.943, P < 0.05).

By way of stimulating the PAM, SiO2 could inhibit GJIC function in lung alveolar epithelial cells, and induce epithelial cell proliferation. In the pathogenesis of silicosis, the downregulation of GJIC of the pulmonary epithelial cells may play an important role in silica-mediated alveolar epithelial cell injury.