Action potential-dependent ATP release from taste receptor cells : development of real-time micro determination for neurotransmitter release at single ceII level

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Subsets of taste bud cells generate action potentials in response to sapid stimuli. Type II taste cells have many taste transduction molecules but lack well elaborated synapses, which leads to the question in the functional significance of action potentials in these cells. We examined the dependence of adenosine triphosphate (ATP) transmitter release from taste cells upon action potentials. To identify Type TT taste cells we used mice expressing a green fluorescence protein (GFP) transgene from the gustducin promoter. Action potentials were recorded by an electrode basolaterally attached to a. single GFP-positive taste cell. ATP release was monitored from gustducin-expressing taste cells by collecting the electrode solution immediately after tastant-stimulated action potentials and using a. luciferase assay to quantify ATP. Stimulation of gustducin-expressing taste cells with a. sweet, bitter, or umami compound on the apical membrane increased ATP levels in the electrode solution; the amount of ATP depended on the firing rate. Increased spontaneous firing rates also induced ATP release from gustducin-expressing taste cells. ATP release from gustducin-expressing taste cells was depressed by tetrodotoxin and inhibited below the detection limit by carbenoxolone. Our data support the hypothesis that action potentials in Type II taste cells enhance ATP release through hemichannels.