Molecular mechanisms of transduction of gustatory stimuli in human and mammalian tatse cells.

青蛙味觉细胞的接受膜上有正离子通道和阴离子通道。NaCl的Na^+和Cl^-刺激分别通过阳离子通道和阴离子通道。由于Cl^-渗透性较低，味觉细胞出现去极化现象。我们在青蛙味觉细胞膜上发现了80个pS和40个pS的K^+通道。80ps K^+通道依赖于电压和Ca^<2+>，但40ps K^+通道不依赖于电压和Ca^<2+>。40个pS K^+通道的关闭与cAMP和蛋白激酶a有关，这两种类型的K^+通道都密集地存在于受体膜和树突膜上。将阿米洛利应用于小鼠味蕾内味觉细胞的接受膜产生向外电流，但应用于基底外膜则没有。这表明对氨氮敏感的Na^+通道主要存在于受体膜中。沙鼠味觉细胞对甜味刺激有两条传导途径。糖的味觉转导与第二信使cAMP有关，而非糖如氨基酸的味觉转导与IP_3有关。在味觉刺激过程中，我们测量了人味蕾真菌状乳头内Ca^<2+>的浓度。不同的味觉刺激引起味蕾中不同味觉细胞Ca^<2+>浓度的变化，说明每个味觉细胞具有不同的化学敏感性。

There are cation and anion channels on the receptive membrane of frog taste cells. Na^+ and Cl^- of NaCl stimuli pass through the cation channel and the anion channel, respectively. Since the Cl^- permeability is lower, a depolarization appears in the taste cell.We found 80 pS and 40 pS K^+ channels in the frog taste cell membranes. 80 pS K^+ channel in dependent on voltage and Ca^<2+>, but 40 pS K^+ channel is not. Closure of 40 pS K^+ channels is related to cAMP and protein kinase A.Both types of the K^+ channels exist densily on the receptive and dendritic membranes.Application of amiloride to the receptive membrane of a mouse taste cell within the taste bud produced an outward current, but application of it to the basolateral membrane did not. This suggests that amoloride-sensitive Na^+ channels exist mostly in the receptive membrane.There are two transduction pathways for sweet stimuli in gerbil taste cells. The gustatory transduction for sugars is concerned with a second messenger cAMP,but that for non-sugars like amino acids is concerned with IP_3.We have measured internal Ca^<2+> concentration in human taste buds of the fungiform papillae during taste stimulation. Different taste stimuli caused a change in Ca^<2+> concentration of different taste cells in the taste bud, indicating that each taste cell has differential chemical sensitivity.