Initial events in stimulation of taste and smell receptor cells

Analysis of the initial interactions of chemicals with olfactory and taste receptor cells is complicated by problems in controlling stimulus presentation. These interactions arise from chemicals diffusing through an unstirred layer to reach the cell surfaces and, in the case of olfaction, partitioning into mucus from air. In many instances, the odorants are metabolized to products that may be stimulants. In such cases, the analysis is further complicated by uncertainty about which chemical species actually stimulate. Stimulation of chemoreceptors can be thought of as originating from specific and nonspecific interactions of stimuli with the cells. Specific interactions involve receptor proteins in or on the cell membranes. These interactions are probably important in initiating sweet taste but not in detecting salty or sour stimuli. There are many reported preparations including putative olfactory receptor proteins, and evidence exists that the proteins comprise a structurally similar class. In some, the proteins are demonstrated to have olfactory function, but blocking their interaction with odorants only partially inhibits olfactory responses. The remainder of the responses presumably occur by general irritant effects of odorants and their metabolites.