Okada Y, Fujiyama R, Miyamoto T, Sato T
Department of Physiology, Nagasaki University School of Dentistry, 1-7-1 Sakamoto, Nagasaki 852-8588, Japan.
Eur J Neurosci. 2001 Jan;13(2):308-14.
The transduction mechanism of the conductance activated by saccharin was analysed in isolated bullfrog taste cells under whole-cell voltage-clamp. Bath application of 30 mM saccharin induced an inward current of -34 +/- 12 pA (mean +/- SEM, n = 10) at a membrane potential of -50 mV in 10 (23%) of 44 rod cells. The concentration-response relationship for the saccharin-gated current was consistent with that of the gustatory neural response. The saccharin-induced current was accompanied with a conductance increase under internal low Cl- condition (E(Cl) = -56 mV), suggesting that saccharin activated a cation conductance. The reversal potential of the saccharin-induced current was -17 +/- 2 mV (n = 10). Intracellular dialysis of 0.5 mM guanosine 5'-O-(2-thiodiphosphate) (GDP-beta-S) completely blocked the saccharin-induced response, suggesting the involvement of a G protein in the transduction. The dialysis of heparin (1 mg/mL) also inhibited the response almost completely, but the dialysis of 1 mM 8-Br-cAMP did not affect the response significantly. Intracellular 50 microM inositol 1,4,5-trisphosphate (1,4,5 InsP(3)) also induced the inward current in five (38%) of 13 rod cells, but intracellular Pasteurella multocida toxin (5 microg/mL, G alpha q-coupled PLC activator) did not elicit any response in the cells. The results suggest that saccharin mainly activates a cation conductance in frog taste cells through the mediation of IP3 production.
在全细胞膜片钳条件下，对分离的牛蛙味觉细胞中糖精激活的电导转导机制进行了分析。在44个杆状细胞中的10个（23%）细胞中，当膜电位为-50 mV时，浴槽中施加30 mM糖精可诱导出-34±12 pA（平均值±标准误，n = 10）的内向电流。糖精门控电流的浓度-反应关系与味觉神经反应的一致。在细胞内低Cl-条件下（E(Cl)= -56 mV），糖精诱导的电流伴随着电导增加，这表明糖精激活了阳离子电导。糖精诱导电流的反转电位为-17±2 mV（n = 10）。细胞内透析0.5 mM鸟苷5'-O-(2-硫代二磷酸)(GDP-β-S)可完全阻断糖精诱导的反应，提示转导过程中有G蛋白参与。肝素（1 mg/mL）透析也几乎完全抑制了反应，但1 mM 8-溴-cAMP透析对反应无明显影响。细胞内50 μM肌醇1,4,5-三磷酸（1,4,5 InsP(3)）也在13个杆状细胞中的5个（38%）细胞中诱导出内向电流，但细胞内多杀巴斯德菌毒素（5 μg/mL，Gαq偶联的PLC激活剂）未在细胞中引起任何反应。结果表明，糖精在蛙味觉细胞中主要通过IP3产生的介导激活阳离子电导。
