Molecular mechanisms of ion channels and second messengers in gustatory transduction of taste cells.

1. 通过对nacl刺激诱导的蕈状乳头味觉细胞内电流的分析，发现小鼠的味觉细胞根据其顶端感受膜中是否存在或几乎不存在amiloridable上皮Na^+通道（ENaC）可分为两种类型。当由NaCi刺激引起的大向内电流被阿米洛利阻断时，ENaC的亚基可能由α、β和γ组成。然而，当向内电流没有被阿米洛利完全或几乎完全阻断时，味觉细胞的顶膜很可能缺乏enac2的整个亚基或β和γ。小鼠体内由酸刺激引起的向内电流完全不被阿米洛利阻断。因此，小鼠味觉细胞的酸反应不会通过可阻断的ENaC引起。我们最近的发现表明，酸反应的产生有两种途径。一种是顶端膜上质子与离子型受体的级联结合和阳离子通过阳离子通道流入。另一个途径是g蛋白和效应分子的级联激活，第二信使的产生，以及通过蛋白激酶关闭基底侧膜中的C1^-通道。沙鼠味觉细胞对两种甜味剂产生甜反应有两条途径。糖刺激的一个途径是g蛋白和腺苷酸环化酶的级联激活，cAMP的产生以及通过蛋白激酶关闭K^+通道。非糖甜味剂的另一途径是g蛋白和PLC的级联激活、1P3的产生和细胞内Ca^2^+储存的Ca^2^+的释放。

1. When inward currents in the fungiform papilla taste cells induced by NaCi stimuli were analysed, it was found that the taste cells in the mouse were divided into two types according to the presence and absence or almost absence of amiloride-blockable epithelial Na^+ channels (ENaC) in the apical receptive membrane. When large inward currents elicited by NaCi stimuli were blocked by amiloride, the subunits of ENaC may be composed of alpha, beta and gamma. However,when the inward currents were not blocked completely or almost completely by amiloride, it is likely that the apical membrane of a taste cell lacks the whole subunits or beta and gamma of ENaC.2. The inward current in the mouse induced by an acid stimulus was not blocked at all by amiloride. Therefore, the acid response of mouse taste cells is not evoked via the amiloride-blockable ENaC.Our recent finding suggests that there are two pathways for generation of acid responses. One is a cascade of binding of proton to ionotoropic receptor in the apical membrane and inflow of cations through the cation channels. The other pathway is a cascade of activation of G-protein and effector molecule, production of a second messenger and closure of C1^- channels in the basolateral membrane via a protein kinase.3. Two pathways are concerned with generation of sweet responses in gerbil taste cells for two types of sweeteners. One pathway for sugar stimuli is a cascade of activation of G-protein and adenylate cyclase, production of cAMP and closure of K^+ channels via a protein kinase. The other pathway for non-sugar sweeteners is a cascade of activation of G-protein and PLC, production of 1P3 and release of Ca^2^+ from the intracellular Ca^2^+ store.