The mechanism of taste reception of morphological indentified cells in the frog taste disc

为了探讨味觉细胞味觉感受的机制，我们采用膜片钳技术和Ca^<2+>成像技术。在牛蛙（Rana catesbeiana）味觉盘的垂直切片中，通过在移液管中用Alexa Fluor染色来鉴定细胞类型。还将钙绿色-1葡聚糖（CaGD）（一种荧光Ca^2+指示剂）加入到贴片移液管中。用扫描共聚焦显微镜对含有CaDG标记的味细胞的舌片进行成像。将局部化学刺激施加到味觉盘的顶端。局灶性苦味（奎宁）刺激诱导Ib型和II型细胞膜电流增加和细胞内Ca^2+增加。在无Ca^2+浴溶液中，观察到Ib型和II型细胞中苦味刺激诱导的细胞内Ca^2+增加。这表明，局灶性苦味刺激诱导钙离子从内部储存中释放。局灶性Ca^2+（或Na^+）刺激也可诱导膜电流增加和胞内Ca^2+增加，但仅在III型细胞中。高K^+外溶液去极化仅在III型细胞中诱导细胞内Ca^<2+>增加。因此，III型细胞内Ca^<2+>的增加可能是由于外部Ca^<2+>通过电压门控Ca^<2 +>通道所致.本研究结果表明，Ib型和II型细胞是味觉感受细胞，III型细胞是咸味感受细胞。

To investigate the mechanism of taste reception in taste cells, we used patch-clamp and Ca^<2+> imaging technique. In vertical slices of the bullfrog (Rana catesbeiana) taste disc, cell types were identified by staining with Alexa Fluor in a pipette. Calcium Green-1 Dextran (CaGD), a fluorescent Ca^<2+> indicator, was also added to the patch pipette. Lingual slices containing CaDG-labeled taste cells were imaged with a scanning confocal microscoe. Focal chemical stimulation was applied to the apical end of the taste disc. Focal bitter (quinine) stimulation induced an increase in membrane current and an increase in intracellular Ca^<2+> in type Ib and type II cells. In Ca^<2+> free bath solution, an increase in intracellular Ca^<2+> induced by bitter stimulation was observed in type Ib and type II cells. This suggests that focal bitter stimulation induce release of Ca^<2+> from internal stores. Focal Ca^<2+> (or Na^+) stimulation also induced an increase in membrane current and an increase in intracellular Ca^<2+> only in type III cells. Depolarization with high K^+ external solution induced an increase in intracellular Ca^<2+> only in type III cells. Therefore, an increase in intracellular Ca^<2+> in type III cells may be due to external Ca^<2+> via voltage- gated Ca^<2+> channels. The present results suggest that type Ib and type II cells are bitter-taste receptor cells and that type III cells are salt-taste receptor cells.