Mouse taste cells with glialike membrane properties

Taste buds are sensory structures made up by tightly packed, specialized ep ithelial cells called taste cells. Taste cells are functionally heterogeneo us, and a large proportion of them fire action potentials during chemotrans duction. In view of the narrow intercellular spaces within the taste bud, i t is expected that the ionic composition of the extracellular fluid surroun ding taste cells may be altered significantly by activity. This considerati on has led to postulate the existence of glialike cells that could control the microenvironment in taste buds. However, the functional identification of such cells has been so far elusive. By using the patch-clamp technique i n voltage-clamp conditions, I identified a new type of cells in the taste b uds of the mouse vallate papilla. These cells represented about 30% of cell s patched in taste buds and were characterized by a large leakage current. Accordingly, I named them "Leaky" cells. The leakage current was carried by K+, and was blocked by Ba2+ but not by tetraethylammonium (TEA). Other tas te cells, such as those possessing voltage-gated Na+ currents and thought t o be chemosensory in function, did not express any sizeable leakage current . Consistent with the presence of a leakage conductance, Leaky cells had a low input resistance (similar to0.25 G Omega). In addition, their zero-curr ent ("resting") potential was close to the equilibrium potential for potass ium ions. The electrophysiological analysis of the membrane currents remain ing after pharmacological block by Ba2+ revealed that Leaky cells also poss essed a Cl- conductance. However, in resting conditions the membrane of the se cells was about 60 times more permeable to K+ than to Cl-. The resting p otassium conductance in Leaky cells could be involved in dissipating rapidl y the increase in extracellular K+ during action potential discharge in che mosensory cells. Thus Leaky cells might represent glialike elements in tast e buds. These findings support a model in which specific cells control the chemical composition of intercellular fluid in taste buds.