Chemical‐Modification Studies on Rat Olfactory Mucosa using a Thiol‐Specific Reagent and Enzymatic Iodination

Abstract

A rat olfactory preparation, suitable for biochemical in vitro on olfactory mechanisms, is described. The effects of the impermeant chemical modification reagents mersalyl (a thiol reagent) and enzymatic iodination, on the amplitude of the electroolfactogram (EOG) responses elicited from rat olfactory mucosa by pulses of odorant vapors was studied using 12 odorants differing widely in odor quality and molecular structure: amyl acetate, carvone, decanal, butylamine, cineole, citronellol, cresol, diacetyl, dimethylethylpyrazine, naphthalene, octanethiol and valeric acid. Both reagents irreversibly reduced the EOG amplitude to all odorants to an extent dependent on the reagent concentration. Two subpopulations of animal preparations could be distinguished on the basis of the extent to which they survived the iodination whereas mersalyl appeared to sample a single population of preparations. Small but statistically significant differences were observed between the responses of each odorant with each reagent but no simple correlation between either the molecular structure or odor quality of the odorants and the reagent effect is apparent for the case of mersalyl. With iodination the responses from the 3 flexible-aliphatic-chain odorants were reduced to a greater extent than the other odorants, all of which had a dissimilar molecular structure. The ability of 3 odorants, amyl acetate, carvone and decanal, to protect the receptors for the odorants against chemical modification was investigated. The protecting odorants were applied directly to the mucosa as a dilute solution in Ringer''s medium. No specific odorant protection effects were observed. The results are discussed in relation to a model of the olfactory mechanism involving relatively non-specific receptor proteins. Each receptor type is envisaged as interacting weakly with a number of odorants and each odorant interacts with a number of receptors.