Mechanisms of bitter taste reception

味觉感受器细胞中的味觉传导机制还没有得到很好的描述。一个原因是过去的研究大多是在分离的味觉感受器细胞上进行的，其中的细胞类型和细胞位置无法识别。在本研究中，我们开发了一种从牛蛙乳头制作牛蛙真菌切片的技术。用全细胞膜片钳技术研究了四种形态识别的味觉细胞的电压门控性离子电流及其对奎宁的响应。染料偶联型LA细胞(粘液细胞)不显示电压激活电流。Ib型细胞(翼细胞)、II型细胞(视杆细胞)和III型细胞具有电压门控性钠电流(I&lt；Na&gt；)和钾电流(IK)，并产生动作电位。Ib型和II型细胞的NA值明显大于III型细胞。Ib型和II型细胞对奎宁有反应，而III型细胞不反应。我们还研究了奎宁激活的蛙类味觉感受器细胞的阳离子电流。根据奎宁激活电流的方差/均值比，估算出零胞外钙离子的单通道电导为12pS。在1.8 mM Ca^&lt；2+&gt；存在下，电导降至5ps。电流对奎宁浓度的依赖关系在无细胞外Ca~(2+)的情况下为0.48 mm，在1.8 mm的细胞外Ca~(2+)&gt；时为2.8 mm。奎宁激活电流的频谱功率密度分布可以用两个洛伦兹函数之和来描述，在没有和存在1.8 mm外部钙离子的情况下，拐角频率没有本质上的差异。上述结果支持蛙类味觉感受器细胞对奎宁反应的主要成分来自奎宁直接激活的离子通道的观点。

Mechanisms of taste transduction in gustatory receptor cells are not well described. One reason is that most of the past studies have been carried out on isolated taste receptor cells, in which identification of cell types and the cell location are unidentifiable. In the present study we developed a technique to making a slice preparation of the bullfrog fungi form papilla. Voltage-gated ionic current and the response to quinine were studied on the four types of morphologically identified taste cells by whole-cell patch clamp recording with Lucifer yellow-filled pipette. Dye-coupled type la cells (mucous cells) did not show voltage-activated currents. Type Ib cells (wing cells), type II cells (rod cells) and type III cells had voltage-gated sodium (I_<Na>) and potassium currents (I_K) and generated action potentials. The amplitude of Nawas significantly larger in type Ib and II cells than in type III cells. Type Ib and II cells responded to quinine but Type III cells did not.We also studied the cation current from the frog taste receptor cell activated by quinine. From the variance/mean ratio of the quinine-activated current, the single-channel conductance was estimated to be 12 pS in zero extracellular Ca^<2+>. In the presence of 1.8 mM Ca^<2+>, this conductance decreased to 5 pS. The dependence of the current on quinine concentration had a K_<1/2> of 0.48 mM in the absence of extracellular Ca^<2+>, which increased to 2.8 mM in 1.8 mM external Ca^<2+>. The spectral power density distribution of the quinine-activated current could be described by the sum of two Lorentzian functions, with corner frequencies not substantially different in the absence and presence of 1.8 mM external Ca^<2+>. The above results support the notion that the major component of the response of frog taste receptor cells to quinine comes from an ion channel directly activated by quinine.