Tight junctions in taste buds: possible role in perception of intravascular gustatory stimuli

Exogenous chemicals having low taste thresholds elicit particulartastes when injected into the bloodstream. This phenomenon iscalled intravascular taste. To explore the origins of intravasculartaste we investigated the permeability properties of the paracellularpathways (tight junctions) between taste cells and between epithelialcells in canine fungiform papillae. This was achieved by showingthat the transepithelial resistance (TER), which is a measureof the paracellular pathway resistance, increases upon the additionof LaCl₃. Thin-section electron microscopy of the same epitheliaused for the TER measurements showed that lanthanum depositsare found exclusively in the extracellular spaces. In the epithelium,LaCl₃ added to either the mucosal or serosal solutions did notdiffuse past the tight junctions at the interface between thestrata cornea and granulosa. The blockage of epithelial tightjunctions by lanthanum is responsible for the increase in TER.LaCl₃ added to the serosal solution was observed throughoutthe extracellular spaces between taste cells including the extracellularspace beyond the tight junctions in the taste pore. Thus, tightjunctions of taste cells and epithelial cells differ in theirpermeability to LaCl₃. From these observations we conclude thatthe tight junctions between taste cells are more permeable tomolecules of small molecular weight than are the tight junctionsbetween epithelial cells. Therefore, small molecules that leavethe bloodstream can diffuse into the taste pore and interactwith receptors in the microvilli of taste cells resulting inintravascular taste.