Gap junctions among taste bud cells in mouse fungiform papillae.

Introduction Mouse taste buds in fungiform papillae consist of ∼50 cells (TBCs; unpublished data), but only a few of them have synaptic contacts with taste nerves (Kinnamon et al., 1993; Seta and Toyoshima, 1995). Neither chemical nor electrical synapses/gap junctions have been confirmed in mammalian taste buds, though a subpopulation of TBCs expressed a variety of neurotransmitter receptors (Kumazawa et al., 2001; Hayato et al., 2002). Non-innervated TBCs thus have been assumed to be supportive. However, we considered their roles in taste transduction. We tested this hypothesis under in situ whole-cell patch clamp and optical recording conditions (Ohtubo et al., 2001). Patch clamp studies showed that a part of TBCs generated depolarizing or hyperpolarizing receptor potentials in response to taste substances. Optical recordings with a voltage-sensitive dye showed that such chemosensitive TBCs tended to form colonies by the polarity of their receptor potentials, suggesting the existence of any interactions among TBCs. In the present study, we show the diffusion of probe dyes from injected TBCs to their neighbors (dye-couplings), which evidences the existence of intercellular corridor between TBCs. These results suggest that there are TBC networks within mammalian taste buds, and that taste buds are miniature processing units rather than the aggregation of chemosensitive cells.