Cell-to-Cell Communication in the Taste Bud: ATP and Acetylcholine as Primary Mediators |
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Authors: | O A Rogachevskaya R A Romanov A A Khokhlov M F Bystrova S S Kolesnikov |
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Institution: | 1.Institute of Cell Biophysics,Russian Academy of Sciences,Pushchino,Russia |
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Abstract: | It was shown that physiological processes in taste buds (peripheral sensory gustatory organs in vertebrates) are realized
with the involvement of several signal systems. In these structures, a number of “classical” neurotransmitters, including
glutamate, serotonin, GABA, ATP, noradrenaline, and others, as well as receptors to these agents, were identified. The physiological
roles of the above systems (separate ones and all as a whole) remain, however, far from final elucidation. We studied purinergic
and cholinergic systems in the taste buds. Based on the data obtained in behavioral experiments using knockout animals, which
indicated that ATP is an afferent neurotransmitter, we found stimulation-induced secretion of ATP by type-II cells. The release
of ATP does not require the entry of external calcium and is mediated by ion channels permeable for ATP. The obtained data
allowed us to explain the fact that classical synaptic structures are absent in the type-II cells. The type-I cells coat other
elements including type-II cells; they provide formation of compartments in the intercellular space of the taste buds (this
limits ATP diffusion). We showed that taste cells of just type I mostly generate calcium signals in response to the action
of ATP and acetylcholine. These cell responses are generated with the involvement of metabotropic purine receptors (isoforms
P2Y1, P2Y2, and P2Y4) and muscarinic receptors (isoforms M1, M3, and M5), respectively. Functioning of these receptors is
combined with a phosphoinositide cascade, mobilization of intracellular Ca2+, and subsequent activation of calcium-activated Cl– channels. It seems probable that purinergic and cholinergic signal systems in type-I cells are elements of negative feedback
in the taste buds, which promote the process of adaptation to the action of gustatory stimuli. |
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