A permeability barrier surrounds taste buds in lingual epithelia

Abstract

Epithelial tissues are characterized by specialized cell-cell junctions, typically localized to the apical regions of cells. These junctions are formed by interacting membrane proteins and by cytoskeletal and extracellular matrix components. Within the lingual epithelium, tight junctions join the apical tips of the gustatory sensory cells in taste buds. These junctions constitute a selective barrier that limits penetration of chemosensory stimuli into taste buds (Michlig et al. J Comp Neurol 502: 1003–1011, 2007). We tested the ability of chemical compounds to permeate into sensory end organs in the lingual epithelium. Our findings reveal a robust barrier that surrounds the entire body of taste buds, not limited to the apical tight junctions. This barrier prevents penetration of many, but not all, compounds, whether they are applied topically, injected into the parenchyma of the tongue, or circulating in the blood supply, into taste buds. Enzymatic treatments indicate that this barrier likely includes glycosaminoglycans, as it was disrupted by chondroitinase but, less effectively, by proteases. The barrier surrounding taste buds could also be disrupted by brief treatment of lingual tissue samples with DMSO. Brief exposure of lingual slices to DMSO did not affect the ability of taste buds within the slice to respond to chemical stimulation. The existence of a highly impermeable barrier surrounding taste buds and methods to break through this barrier may be relevant to basic research and to clinical treatments of taste.

Postsynaptic P2X3‐containing receptors in gustatory nerve fibres mediate responses to all taste qualities in mice

“…It is possible that the further right‐shifted concentration dependence in vivo may be due in part to a recently discovered permeability barrier between taste buds and the surrounding lingual epithelium (Dando et al . ). This barrier would tend to limit access of AF‐353 to the basal compartment of the taste bud containing the nerve fibres penetrating the taste bud.…”

Taste buds: cells, signals and synapses

“…Taste cells within taste buds are separated from the mucosal surface, blood supply and surrounding epithelium by a selective barrier that includes enzymatic components (extracellular ATPases), physical components (the zonula occludens) and molecular components (claudins, chondroitin sulfate and other glycosaminoglycans) 112, 168–171 . The barrier probably regulates which small molecules (for example, drugs, trophic factors, hormones and neuropeptides) can penetrate into the taste bud from the mucosal, serosal or vascular environments to influence the function of its constituent cells.…”

The K + channel K IR 2.1 functions in tandem with proton influx to mediate sour taste transduction

“…Application of these acids at neutral pH caused a similar degree of intracellular acidification in both TRPM5 and PKD2L1 cells, but only PKD2L1 cells fired action potentials. However, it is worth noting that, in the intact epithelium where taste buds are surrounded by a relatively impenetrable barrier, weak acids may not enter taste cells unimpeded (49). Alternatively, weak acids may be effective sour stimuli because they buffer pH, protecting protons from absorption by salivary proteins.…”