Serotonin Modulates Voltage-Dependent Calcium Current inNecturusTaste Cells

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Abstract
Delay, Rona J., Sue C. Kinnamon, and Stephen D. Roper. Serotonin modulates voltage-dependent calcium current in Necturus taste cells. J. Neurophysiol. 77: 2515–2524, 1997. Necturus taste buds contain two primary cell types: taste receptor cells and basal cells. Merkel-like basal cells are a subset of basal cells that form chemical synapses with taste receptor cells and with innervating nerve fibers. Although Merkel-like basal cells cannot interact directly with taste stimuli, recent studies have shown that Merkel-like basal cells contain serotonin (5-HT), which may be released onto taste receptor cells in response to taste stimulation. With the use of whole cell voltage clamp, we examined whether focal applications of 5-HT to isolated taste receptor cells affected voltage-activated calcium current ( ICa). Two different effects were observed. 5-HT at 100 μM increased ICain 33% of taste receptor cells, whereas it decreased ICain 67%. Both responses used a 5-HT receptor subtype with a pharmacological profile similar to that of the 5-HT1Areceptor, but the potentiation and inhibition of ICaby 5-HT were mediated by two different second-messenger cascades. The results indicate that functional subtypes of taste receptor cells, earlier defined only by their sensitivity to taste stimuli, may also be defined by their response to the neurotransmitter 5-HT and suggest that 5-HT released by Merkel-like basal cells could modulate taste receptor function.