Abstract
Mouse taste bud cells (TBCs) expressed various voltage-gated channels, including inward rectifier K+ channels, on their basolateral membranes to generate receptor/generator potentials and action potentials. Although tight junctions among TBCs prevent the free diffusion of taste substances from the receptor membranes to the basolateral membranes of TBCs, a little amount of taste substances may permeate tight junctions and modify taste transduction mechanism. In reverse, changes in ion channel currents test the permeation of taste substances. We investigated the permeability of tight junctions as the changes of inward rectifier K+ channel currents in magnitude (Iir) and in activation potential (Eir) under in-situ whole-cell clamp conditions. Their basolateral membranes were irrigated with a physiological saline containing 5 mM K+. The application of 500 mM KCl to the receptor membrane increased Iir and shifted Eir to the positive direction. Since Eir was equal to the equilibrium potential of K+ on the basolateral membrane, we calculated K+ concentration there by the shift. The increase in K+ concentration on the basolateral membrane thus calculated was 4.3 ± 4.8 mM (mean ± SD, n = 23). KF (500 mM) less effectively increased K+, indicating that gap junctions were less permeable to F− than Cl−. The application of 100 mM CsCl to the receptor membrane decreased Iir without shifting Eir. The estimated Cs+ concentration on the basolateral membrane was ~0.3 mM (n = 2). These results showed that tight junctions were low-conductance, ion-selective barriers. [Jpn J Physiol 54 Suppl:S176 (2004)]
