Role of cyclic adenosine-3′,5′-monophosphate in olfactory reception

Abstract

The action of cyclic adenosine-3′,5′-monophosphate (3′,5′-AMP) and of substances modifying the rate of its breakdown (inhibitors and activators of phosphodiesterase) on the olfactory epithelium was investigated in frogs. The slow electrical response of the olfactory epithelium to stimulation by solutions of various substances was recorded. Cyclic 3′,5′-AMP and its dibutyryl derivative were found to excite the olfactory receptors effectively. Responses to these substances developed after an appreciably longer delay than responses to stimulation by solutions of odiferous substances. It is postulated that the depolarizing action of 3′,5′-AMP and dibutyryl 3′,5′-AMP is manifested only after they have penetrated inside the receptor cell through its membrane. Both 5′-AMP and cyclic 2′,3′-AMP were ineffective. In the next series of experiments the integral receptor potential was recorded in response to short stimulation by the vapor of an odiferous substance. The duration of this potential was increased after treatment of the olfactory epithelium with phosphodiesterase inhibitors: methylxanthines or papaverine. Conversely, the negative wave of the integral receptor potential was shortened under the influence of the phosphodiesterase activator imidazole. Cyclic 3′,5′-AMP is considered to play the role of mediator in the mechanism of excitation of the olfactory receptor; during interaction between an odiferous substance and the receptor, adenyl cyclase is activated and the concentration of 3′,5′-AMP increases; this, in turn, causes depolarization of the receptor cell membrane.