TIGHT JUNCTIONS IN TASTE-BUDS - POSSIBLE ROLE IN PERCEPTION OF INTRAVASCULAR GUSTATORY STIMULI

Exogenous chemicals having low taste thresholds elicit particular tastes when injected into the bloodstream. This phenomenon is called intravascular taste. To explore the origins of intravascular taste we investigated the permeability properties of the paracellular pathways (tight junctions) between taste cells and between epithelial cells in canine fungiform papillae. This was achieved by showing that the transepithelial resistance (TER), which is a measure of the paracellular pathway resistance, increases upon the addition of LaCl3. Thin-section electron microscopy of the same epithelia used for the TER measurements showed that lanthanum deposits are found exclusively in the extracellular spaces. In the epithelium, LaCl3 added to either the mucosal or serosal solutions did not diffuse past the tight junctions at the interface between the strata cornea and granulosa. The blockage of epithelial tight junctions by lanthanum is responsible for the increase in TER. LaCl3 added to the serosal solution was observed throughout the extracellular spaces between taste cells including the extracellular space beyond the tight junctions in the taste pore. Thus, tight junctions of taste cells and epithelial cells differ in their permeability to LaCl3. From these observations we conclude that the tight junctions between taste cells are more permeable to molecules of small molecular weight than are the tight junctions between epithelial cells. Therefore, small molecules that leave the bloodstream can diffuse into the taste pore and interact with receptors in the microvilli of taste cells resulting in intravascular taste.