Mouse taste cells with G protein-coupled taste receptors lack voltage-gated calcium channels and SNAP-25

Depolarization with high K+ resulted in an increase in intracellular Ca2+ in a small subset of non-GFP labeled cells of both transgenic mouse lines. In contrast, no depolarization-evoked Ca2+ responses were observed in GFP-expressing taste cells of either genotype, but GFP-labeled cells responded to the PLC activator m-3M3FBS, suggesting that these cells were viable. Whole cell recording indicated that the GFP-labeled cells of both genotypes had small voltage-dependent Na+ and K+ currents, but no evidence of Ca2+ currents. A subset of non-GFP labeled taste cells exhibited large voltage-dependent Na+ and K+ currents and a high threshold voltage-gated Ca2+ current. Immunocytochemistry indicated that SNAP-25 was expressed in a separate population of taste cells from those expressing T1R3 or TRPM5. These data indicate that G protein-coupled taste receptors and conventional synaptic signaling mechanisms are expressed in separate populations of taste cells.The taste receptor cells responsible for the transduction of bitter, sweet, and umami stimuli are unlikely to communicate with nerve fibers by using conventional chemical synapses.Taste buds, the transducing elements of gustatory sensation, contain a heterogeneous population of 50 to 100 elongate taste receptor cells, which extend from the basal lamina to the surface of the epithelium. Taste stimuli interact with receptors on the apical membrane, while the basolateral membranes of some taste cells associate with gustatory nerve fibers to transmit taste information to the brain.Several types of taste cells have been identified morphologically. Type I cells, also known as "dark" cells, generally comprise about half of the taste bud. These cells are not believed to have a receptive function, but to play a more glial-like role in the taste bud [1,2]. About 35% of the cells are Type II cells, which are also known as "light" cells due to the electron lucent nature of their cytoplasm. Type II cells express T1R and T2R taste re