Evidence for non-receptor odor discrimination using neuroblastoma cells as a model for olfactory cells.

The mouse neuroblastoma cell (N-18 clone), which is independent of an olfactory cell, was depolarized by 20 odorants examined, suggesting that specific proteins are not required for reception of odorants. The mechanism of non-receptor-mediated odor discrimination was examined using the N-18 cell. Changes in the membrane fluidity of the cell induced by adsorption of odorants were measured with various fluorescence probes, which monitor the fluidity at the different depth and in the different phase of the membrane. The profiles of the membrane fluidity changes monitored with these dyes were different from one species of odorants to another, suggesting that odorants having different odors are adsorbed at different sites in the membranes. The alteration of the lipid composition of the cell membrane brought about by exogenous application of stearic acid and cholesterol led to modification of the responses (magnitude of depolarization) to various odorants. The extent and direction (increase or decrease) of changes in the responses greatly varied among species of odorants. The following mechanism on odor discrimination was proposed. A membrane composition of each olfactory cell is postulated to be different from cell to cell. Different combinations of lipids and proteins in the membranes provide different adsorption sites for odorants. Relative amounts of the membrane potential changes in many olfactory cells in response to an odorant are characteristic of the species of the odorant. The response profiles at the cell level determine the quality of the odor.