Vinyl acetate is a synthetic organic
ester that has been shown to produce nasal
tumors in rats following exposure to 600 ppm in air. The proposed mechanism of action involves the metabolism of
vinyl acetate by
carboxylesterases and the production of
protons leading to cellular acidification. While
vinyl acetate-induced decreases in intracellular pH (pHi) have been demonstrated in rat hepatocytes, comparable data from nasal epithelial cells do not exist. Using an in vitro assay system, we have determined the effects of
vinyl acetate exposure on pHi in respiratory and olfactory nasal epithelial cells from rats. The respiratory and olfactory epithelial cells were isolated from dissected maxillo- and ethmoturbinates by
enzyme digestion. The cells were plated; loaded with the pH-sensitive
dye, carboxyseminaphthorhodafluor-1 (SNARF-1); and observed using confocal microscopy. Individual cellular analysis demonstrated that both respiratory and olfactory epithelial cells responded to
vinyl acetate exposures with a dose-dependent decrease in pHi. Changes occurred at 100 microM but reached a plateau above 250 microM. Maximal decreases in pHi were 0.3 pH unit in respiratory epithelial cells. While pHi values were normally distributed for the respiratory epithelial cells, the olfactory epithelial cells demonstrated a bimodal distribution, indicating at least two populations of cells, with only one population of cells responding to
vinyl acetate. Acidification in these cells did not plateau but continued to increase at 1000 microM.
Bis(p-nitrophenyl)phosphate (BNPP), a
carboxylesterase inhibitor, was able to attenuate the
vinyl acetate-induced decrease in pHi. Data obtained from the isolated cells were validated using tissue explants. These results are consistent with the proposed mode of action for
vinyl acetate and supply further data for developing appropriate risk assessments for
vinyl acetate exposure.