Chemoreception: Paramecium as a Receptor Cell

Abstract

In the sensory modalities of taste, smell and common chemical sense, there are receptor cells that make contact with the external environment and detect the presence of external chemical stimuli. The receptor cell is the site of stimulus recognition, which is thought to be mediated through binding of the stimulus to specific surface receptors and then transduction of this binding into “useful” electrical information. Information in this new form is passed on to higher order neurons and eventually is translated into a response. In order to study receptor cell function, it seems straightforward to isolate these receptor cells, identify the receptors among the membrane proteins and determine the ionic basis of receptor binding by conventional electrophysiology. However, there are limitations inherent in many of the chemosensory systems traditionally used to study chemoreception. Relatively small amounts of olfactory or taste epithelium limit the binding studies and biochemical studies necessary to identify receptor proteins; tissue is often of a mixed cell type, even when avaiable in quantity, making it difficult to be sure of the origins of putative receptor proteins (Price, 1981; Mooser, 1981; Cagan, 1981). Hence, indirect methods (e.g. treating the tissue with n-ethyl-maleimide to disrupt protein sulfhydryl bonds, and hence disrupting the chemoresponse, or demonstrating specificity and saturability of a response) are used to demonstrate that the receptor site is a protein.