Abstract
Taste buds consist of different cell types such as type II and III cells. Type II cells have taste receptor molecules for sweet, bitter, and umami substances, but have no synaptic contact with taste nerves. By contrast, type III cells have none of such taste receptor molecules, but have synaptic contacts with taste nerves. Recent studies thus considered the interactions among these taste bud cells via neurotransmitters. We investigated the expression of neurotransmitter receptors by in-situ Ca2+ imaging. The application of 10 μM ACh and ATP to the basolateral membrane of taste bud cells increased intracellular Ca2+ concentration, but that of 100 μM glutamate, 5HT, and noradrenalin had no effect. All taste buds examined responded to ATP, and all cells in these taste buds were apparently ATP-sensitive. The Ca2+ response to ACh occurred in ∼15% of taste buds examined, and the number of responsive cells in these taste buds was ∼2.4 cells per taste bud. The application of 100 nM atropine completely inhibited the Ca2+ response, but 10 μM d-tubocurarine had no effect, showing that expressed ACh receptors are muscarinic. RT-PCR studies suggested the expression of muscarinic ACh receptor subtypes, M1, M3, M4 and M5. These results suggest that purinergic receptors and muscarinic ACh receptors are involved in the interaction among taste bud cells. Supported by a COE program (center #J19) granted to Kyushu Institute of Technology by MEXT of Japan. [J Physiol Sci. 2008;58 Suppl:S169]
