Characteristics of action potentials and their underlying outward currents in rat taste receptor cells
Characteristics of action potentials and their underlying outward currents in rat taste receptor cells
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DOI：
10.1152/jn.1996.75.2.820
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发表时间：
1996-02-01
影响因子：
2.5
通讯作者：
Herness, S
中科院分区：
文献类型：
--
作者：
Chen, YS;Sun, XD;Herness, S
1.味觉感受器细胞产生动作电位，这是当这些细胞被促味剂刺激时发生的转导机制的结果。这些动作电位被认为是将信息传递到中枢神经系统的关键信号事件。采用膜片钳技术，在电压钳和电流钳两种模式下，探讨了大鼠后尾味细胞动作电位的离子基础.通过从-80 mV的保持电位向细胞内注射去极化电流脉冲诱发动作电位。触发动作电位的阈值电位约为-35 mV;这些细胞的输入电阻平均为6.9 G Ω。长去极化脉冲可诱发2 ~ 3个动作电位，峰电位高度逐渐降低。后超极化现象较常见.钠电流和钙电流都有助于动作电位的去极化阶段。在钠通道阻断剂河豚毒素的存在下，动作电位被完全阻断。当复极化钾电流被阻断且钡被用作电荷载体时，钙的贡献可以被可视化为延长的钙平台。钾电流由持续延迟整流电流、瞬时钾电流和钙激活钾电流组成。瞬时和持续钾电流在接近-30 mV时激活，并随着进一步去极化而单调增加。多达一半的外向电流失活，衰减常数为秒级。持续和瞬态电流显示陡峭的电导和失活曲线的电压依赖性。半失活发生在-20 +/- 3.1 mV（平均值+/- SE），每e倍降低11.2 +/- 0.5 mV。半最大电导发生在3.6 +/- 1.8 mV，每e倍增加12.2 +/- 0.6 mV。钙激活钾电流的应用证明了蜂毒肽和使用无钙的沐浴液。在更高的去极化保持电位下，大部分瞬时和持续外向电流失活最为明显.钾电流对动作电位的复极化和后超极化阶段都有贡献。这些电流被四乙基铵的浴涂所阻断，这也大大拓宽了动作电位。应用4-氨基吡啶能够选择性阻断瞬时钾电流而不影响持续电流。这也扩大了动作电位以及消除后超极化.观察到第二种类型的动作电位，其持续时间不同。这些慢动作电位的t（1/2）持续时间为9.6 ms，而快动作电位为1.4 ms。两组的输入电阻是不可区分的。大约四分之一的细胞诱发动作电位的慢型。7.诱发快速动作电位的细胞具有能够产生快速复极化的大外向电流，而具有缓慢动作电位的细胞相比之下具有小外向电流。快细胞的平均值为2，563 pA和1.4 ms，而慢细胞的平均值为373 pA和9.6 ms。电流和持续时间值呈指数相关。内向电流无显著差异。这些结果表明，许多味觉感受器细胞传导动作电位，根据动作电位持续时间和钾电流大小，可以大致分为两组。这些基团可能与细胞更新有关。动作电位的生理作用仍有待阐明，但可能是重要的味蕾内以及传入神经的通信。
1. Taste receptor cells produce action potentials as a result of transduction mechanisms that occur when these cells are stimulated with tastants. These action potentials are thought to be key signaling events in relaying information to the central nervous system. We explored the ionic basis of action potentials from dissociated posterior rat taste cells using the patch-clamp recording technique in both voltage-clamp and current-clamp modes.2. Action potentials were evoked by intracellular injection of depolarizing current pulses from a holding potential of -80 mV. The threshold potential for firing of action potentials was approximately -35 mV; the input resistance of these cells averaged 6.9 G Omega. With long depolarizing pulses, two or three action potentials could be elicited with successive attenuation of the spike height. Afterhyperpolarizations were observed often.3. Both sodium and calcium currents contribute to depolarizing phases of the action potential. Action potentials were blocked completely in the presence of the sodium channel blocker tetrodotoxin. Calcium contributions could be visualized as prolonged calcium plateaus when repolarizing potassium currents were blocked and barium was used as a charge carrier.4. Outward currents were composed of sustained delayed rectifier current, transient potassium current, and calcium-activated potassium current. Transient and sustained potassium currents activated close to -30 mV and increased monotonically with further depolarization. Up to half the outward current inactivated with decay constants on the order of seconds. Sustained and transient currents displayed steep voltage dependence in conductance and inactivation curves. Half inactivation occurred at -20 +/- 3.1 mV (mean +/- SE) with a decrease of 11.2 +/- 0.5 mV per e-fold. Half maximal conductance occurred at 3.6 +/- 1.8 mV and increased 12.2 +/- 0.6 mV per e-fold. Calcium-activated potassium current was evidenced by application of apamin and the use of calcium-free bathing solution. It was most obvious at more depolarized holding potentials that inactivated much of the transient and sustained outward currents.5. Potassium currents contribute to both the repolarization and afterhyperpolarization phases of the action potential. These currents were blocked by bath application of tetraethylammonium, which also substantially broadened the action potential. Application of 4-aminopyridine was able to selectively block transient potassium currents without affecting sustained currents. This also broadened the action potential as well as eliminated the afterhyperpolarization.6. A second type of action potential was observed that differed in duration. These slow action potentials had t(1/2) durations of 9.6 ms compared with 1.4 ms for fast action potentials. Input resistances of the two groups were indistinguishable. Approximately one-fourth of the cells eliciting action potentials were of the slow type.7. Cells eliciting fast action potentials had large outward currents capable of producing a quick repolarization, whereas cells with slow action potentials had small outward currents by comparison. The average values of fast cells were 2,563 pA and 1.4 ms compared with 373 pA and 9.6 ms for slow cells. Current and duration values were related exponentially. No significant difference was noted for inward currents.8. These results suggest that many taste receptor cells conduct action potentials, which may be classified broadly into two groups on the basis of action potential duration and potassium current magnitude. These groups may be related to cell turnover. The physiological role of action potentials remains to be elucidated but may be important for communication within the taste bud as well as to the afferent nerve.