Evaluation of stinging-inducing chemicals using cultured neuronal cells: an electrophysiological approach

The effects of various cosmetic ingredients, including preservatives, humectants, ultraviolet absorbents and solvents, on the electrical properties of neuronal cells were investigated using rat phaeochromocytoma PC12 cells and cultured rat dorsal root ganglion (DRG) neurons. When membrane current was measured under whole-cell voltage-clamp, all nine test compounds inhibited voltage-activated K(+) current in PC12 cells. With the five compounds selected for further experiments with DRG neurons, two types of current responses were observed, namely inhibition of K(+) current by methyl or butyl p-hydroxybenzoate (MPHB or BPHB) and resorcinol, and induction of a cationic inward current by MPHB, BPHB, ethanol and dipropylene glycol. The order of potency of these chemicals to inhibit the K(+) current in PC12 cells was similar to that of their cytotoxicity, which was determined by MTT assay. Capsaicin, BPHB, MPHB and resorcinol, however, inhibited the K(+) current at concentrations lower than those required for cytotoxicity. These results suggest that these cosmetic ingredients exert significant effects on the electrical properties of cultured neuronal cells. This electrophysiological method may be useful in prescreening test systems to detect stinging, and also to clarify mechanisms underlying the irritation induced by a variety of compounds.