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

采用膜片钳和Ca^<2+>技术研究味觉细胞对盐味的接收机制。从牛蛙（Rana catesbeiana）味觉盘垂直切片的味觉细胞中记录了膜电流。记录细胞的生理特性后，在移液管中用路西法黄染色鉴定细胞类型。得到了以下结果：1. lb型和II型细胞表现出ttx敏感的电压门控Na^+电流。III型细胞显示耐ttx电压门控Na^+电流。本文首次报道了味觉细胞中耐ttx的电压门控Na~电流。2. 只有III型细胞具有电压门控的Ca^<2+>通道。3. III型细胞电压门控向内Na^+电流失活部分的时间常数远大于lb型和II型细胞。因此，向内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。在本研究中，Ni^<2+>在1 mM时延长了三种类型细胞内Na^+电流的失活。III型细胞表现出较强的Ni^<2+>效应。5. 除了几种制剂外，我们不能将钙指示剂装入味觉细胞。需要进一步的研究来阐明在盐味剂刺激下味觉细胞内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.