Okada Y, Miyamoto T, Sato T
Department of Physiology, Nagasaki University School of Dentistry, Japan.
J Exp Biol. 1994 Feb;187:19-32. doi: 10.1242/jeb.187.1.19.
The ionic mechanism of the conductance activated by acetic acid was analyzed in isolated bullfrog taste cells under whole-cell voltage-clamp. Bath-application of acetic acid (pH 3.9-4.7) induced an inward current in about 80% of the taste cells. The current occurred in external 80 mmol l-1 Ba2+ and internal 100 mmol l-1 Cs+, which completely blocked the delayed outward K+ current. The concentration-response relationship for the acid-activated current was consistent with that of the gustatory neural response. Prolonged adaptation of the surface of the tongue to HCl prior to taste cell isolation decreased the acid-induced current to about 20% of the control value without decreasing NaCl-induced neural responses and voltage-activated Na+ currents. The results suggest that the transduction mechanism of the acid response might be different from that of the response to salt. The I-V relationship of the acid-induced response was nearly linear at membrane potentials between -80 and 80 mV. The acid-induced conductance was permeable to alkali metal and alkali earth metal ions. The permeability ratios were PCa:PBa:PSr:PNa:PCs = 1.87:1.17:0.73:0.99:1.00. The present study suggests that the acid-induced receptor current in bullfrog taste cells is generated by an increase in a cation conductance in the apical taste membrane.
在全细胞膜片钳条件下，对分离出的牛蛙味觉细胞中由乙酸激活的电导的离子机制进行了分析。将乙酸（pH 3.9 - 4.7）施加于浴液中，在约80%的味觉细胞中诱发了内向电流。该电流在外部80 mmol l-1 Ba2+和内部100 mmol l-1 Cs+存在时出现，这两种离子完全阻断了延迟外向K+电流。酸激活电流的浓度 - 反应关系与味觉神经反应的一致。在分离味觉细胞之前，让舌表面长时间适应HCl，可使酸诱发电流降至对照值的约20%，而不降低NaCl诱发的神经反应和电压激活的Na+电流。结果表明，酸反应的转导机制可能与盐反应的不同。在 - 80至80 mV的膜电位之间，酸诱发反应的电流 - 电压关系近乎线性。酸诱发的电导对碱金属和碱土金属离子通透。通透率之比为PCa:PBa:PSr:PNa:PCs = 1.87:1.17:0.73:0.99:1.00。本研究表明，牛蛙味觉细胞中酸诱发的受体电流是由顶端味觉膜中阳离子电导的增加所产生的。
