Functional expression of ionotropic purinergic receptors on mouse taste bud cells

Neurotransmitter receptors on taste bud cells (TBCs) and taste nerve fibres are likely to contribute to taste transduction by mediating the interaction among TBCs and that between TBCs and taste nerve fibres. We investigated the functional expression of P2 receptor subtypes on TBCs of mouse fungiform papillae. Electrophysiological studies showed that 100 μ m ATP applied to their basolateral membranes either depolarized or hyperpolarized a few cells per taste bud. Ca 2+ imaging showed that similarly applied 1 μ m ATP, 30 μ m BzATP (a P2X 7 agonist), or 1 μ m 2MeSATP (a P2Y 1 and P2Y 11 agonist) increased intracellular Ca 2+ concentration, but 100 μ m UTP (a P2Y 2 and P2Y 4 agonist) and α,β‐meATP (a P2X agonist except for P2X 2 , P2X 4 and P2X 7 ) did not. RT‐PCR suggested the expression of P2X 2 , P2X 4 , P2X 7 , P2Y 1 , P2Y 13 and P2Y 14 among the seven P2X subtypes and seven P2Y subtypes examined. Immunohistostaining confirmed the expression of P2X 2 . The exposure of the basolateral membranes to 3 m m ATP for 30 min caused the uptake of Lucifer Yellow CH in a few TBCs per taste bud. This was antagonized by 100 μ m PPADS (a non‐selective P2 blocker) and 1 μ m KN‐62 (a P2X 7 blocker). These results showed for the first time the functional expression of P2X 2 and P2X 7 on TBCs. The roles of P2 receptor subtypes in the taste transduction, and the renewal of TBCs, are discussed.