Single taste stimuli elicit either increases or decreases in intracellular calcium in isolated catfish taste cells

Taste cells are specialized epithelial cells that respond to stimulation with release of neurotransmitters onto afferent nerves that innervate taste buds. In analogy to neurotransmitter release in other cells, it is expected that neurotransmitter release in taste cells is dependent on an increase in intracellular Ca²⁺ ([Ca²⁺](i)). We have studied changes in [Ca²⁺], elicited by the taste stimuli Land D-arginine in isolated taste cells from the channel catfish (Ictalurus punctatus). In a sample of 119 cells, we found 15 cells responding to L-arginine, and 12 cells responding to D-arginine with an increase in [Ca²⁺](i(. The response to L-arginine was inhibited by equimolar D-arginine in cells where D-arginine alone did not cause a change in [Ca²⁺], which is consistent with mediation of this response by a previously characterized L-arginine-gated nonspecific cation channel antagonized by D-arginine [31]. However, we also found that these taste stimuli elicited decreases in [Ca²⁺](i), in substantial number of cells (6 for L-Arg, and 2 for D-Arg, n = 119). These observations suggest that stimulation of taste cells with sapid stimuli may result in simultaneous excitation and inhibition of different taste cells within the taste bud, which could be involved in local processing of the taste signal.