The mechanism of salt taste reception: patch-clamp and Ca^<2+> studies of taste cells

为了探讨味觉细胞接受盐味的机制，我们采用了膜片钳技术和钙离子技术。在牛蛙(Rana Catesbeiana)味盘的垂直切片上记录了味觉细胞的膜电流。在记录细胞的生理特性后，通过在吸管中用荧光黄染色来鉴定细胞类型。得到了以下结果。1.Lb型和II型细胞呈现TTX敏感的电压门控性钠电流。III型细胞呈现TTX抗性电压门控性Na~+电流。本文首次报道了味觉细胞的TTX阻抗型电压门控钠电流。2.只有III型细胞具有电压门控性钙通道。3.III型细胞电压门控内向钠电流失活部分的时间常数明显大于Lb型和II型细胞。因此，内向Na~+电流缓慢失活是III型细胞的特征。4.据报道，Ni^&lt；2+&gt；具有增强蛙舌咽神经反应的作用。在本研究中，1 mM的镍离子延长了三种细胞内向Na+电流的失活时间。III型细胞表现出比其他类型细胞更强的镍离子效应。5.除几种制剂外，未见钙指示剂进入味觉细胞。需要进一步的研究来阐明味觉细胞在盐味剂刺激过程中细胞内钙离子的变化。在本研究中，我们证明了III型细胞是盐味感受器细胞的可能性。

To investigate the mechanism of salt taste reception in taste cells, we used patch-clamp and Ca^<2+> technique. Membrane currents were recorded from taste cells in vertical slices of the bullfrog (Rana catesbeiana) taste disc. Cell types were identified by staining with Lucifer yellow in a pipette after recording their physiological properties. The following results were obtained. 1. Type lb and type II cells exhibited TTX-sensitive voltage-gated Na^+ currents. Type III cells showed TTX-resistant voltage-gated Na^+ currents. TTX-resistant voltage-gated Na~ currents in taste cells are reported for the first time here. 2. Only type III cells possess the voltage-gated Ca^<2+> channels. 3. The time constant for the inactivating portion of the voltage-gated inward Na^+ currents of type III cells was much larger than that of type lb and type II cells. Therefore, slow inactivation of inward Na^+ currents characterizes type III cells. 4. Ni^<2+> has been reported to enhance the response of the frog glossopharyngeal nerve. In this study, Ni^<2+> at 1 mM prolonged inactivation of inward Na^+ currents in three types of cells. The type III cells showed much stronger Ni^<2+> effec than other types of cells. 5. We could not load the calcium indicator into taste cells except several preparations. Further study will be needed to clarify changes in intracellular Ca^<2+> in taste cells during stimulation with salt tastants. In this study, we showed a possibility that type III cells are salt taste receptor cells.