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

为了探讨味觉细胞对盐味的感受机制，我们采用膜片钳和Ca^<2+>技术。在牛蛙（Rana catesbeiana）味觉盘的垂直切片中记录味觉细胞的膜电流。在记录细胞的生理特性后，通过在移液管中用荧光黄染色来鉴定细胞类型。获得了以下结果。1. Ib型和II型细胞表现出对河豚毒素敏感的电压门控Na^+电流。III型细胞显示出TTX抗性的电压门控Na^+电流。本文首次报道了味觉细胞中TTX抗性的电压门控Na~+电流。2.只有III型细胞具有电压门控性Ca^2+通道。3. III型细胞电压门控内向Na^+电流失活部分的时间常数远大于Ib型和II型细胞。因此，内向Na^+电流的缓慢失活是III型细胞的特征。4.据报道，Ni^<2+>可增强蛙舌咽神经的反应。在这项研究中，1 mM的Ni^2+延长了三种细胞内向Na^+电流的失活。III型细胞表现出比其他类型细胞更强的Ni^<2+>效应。5.除了几种制剂外，我们不能将钙指示剂加载到味细胞中。需要进一步研究来阐明在盐促味剂刺激期间味觉细胞中细胞内Ca^<2+>的变化。在这项研究中，我们发现了III型细胞是盐味觉受体细胞的可能性。

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.