TOLUENE DISRUPTS OUTER HAIR CELL MORPHOMETRY AND INTRACELLULAR CALCIUM HOMEOSTASIS IN COCHLEAR CELLS OF GUINEA-PIGS

The aromatic hydrocarbon, toluene, has been demonstrated to disrupt au ditory system function both in occupational epidemiological and in lab oratory animal investigations. This agent, along with several other or ganic solvents, impairs hearing preferentially at middle frequencies-a finding that distinguishes these agents from the traditional high-fre quency impairment observed with ototoxic drugs such as aminoglycoside antibiotics and cisplatin. Prior investigations have identified the ou ter hair cell as a probable target for toluene exposure, although stud ies designed to evaluate spiral ganglion cell impairment have not been reported. The purpose of this investigation was to determine directly whether outer hair cells isolated from the guinea pig cochlea show mo rphological alterations consistent with a toxic response to toluene ex posure. Since slow adjustments of outer hair cell length can result fr om alteration in free intracellular calcium concentration, the effect of toluene on calcium homeostasis was monitored in both outer hair cel ls and spiral ganglion cells. A dose-response relationship was observe d in the extent of outer hair cell shortening produced by toluene with a significant shortening observed at concentrations of 100 mu M and h igher. By contrast, the nonototoxic solvent, benzene, produced little shortening at 100 mu M to 1 mM concentrations. Studies of calcium home ostasis conducted using the fluorescent probe, Fura-2, showed that tol uene enhanced free intracellular calcium levels of both outer hair cel ls and spiral ganglion cells within 5 min of exposure at concentration s of 30 mu M and higher. Intracellular calcium levels were elevated on ly slightly following benzene administration at 1 mM, but not at lower concentrations. Cells cultured in artificial perilymph nominally cont aining no calcium and those to which EGTA was added still showed a max imal increase in intracellular calcium level when treated with toluene . These data indicate that the elevation in free intracellular calcium levels produced by toluene results from release of calcium from intra cellular stores. (C) 1997 Academic Press.