Shefner S A, Levy R A
Can J Physiol Pharmacol. 1980 Nov;58(11):1286-94. doi: 10.1139/y80-195.
In view of the possible contribution of both gamma-aminobutyric acid (GABA) and K+ to primary afferent depolarization (PAD) it was of interest to study the way in which depolarizations caused by administration of these agents combine at the primary afferent membrane. GABA (and glutamate) depolarizations of bullfrog afferents were found to be reduced if they were superimposed on ongoing K+-induced depolarizations. The extent of reduction was greater with K+ depolarizations of increasing size. The contribution of GABA to PAD should therefore be greatest when extracellular K+ is low, such as during single volleys or low frequency afferent activity. The effect of temporal order of administration on the summation of amino acid and K+ responses was tested by reversing the order of their application. GABA could not be used in this test because GABA depolarizations rapidly desensitize. However, when K+ depolarization was superimposed on maintained glutamate depolarization, the total depolarization was equal to the sum of depolarizations observed when glutamate and K+ were given alone (linear summation). Therefore, the temporal order of administration of amino acid and K+ affects the size of the total depolarization. No evidence was found for a superadditive effect when amino acid and K+ were applied together.
鉴于γ-氨基丁酸（GABA）和K⁺ 都可能对初级传入纤维去极化（PAD）有影响，研究这些药剂在初级传入纤维膜上引起的去极化如何结合是很有意义的。发现牛蛙传入纤维的GABA（和谷氨酸）去极化如果叠加在持续的K⁺ 诱导的去极化上，就会减弱。K⁺ 去极化幅度越大，减弱程度越大。因此，当细胞外K⁺ 浓度较低时，如在单个冲动或低频传入活动期间，GABA对PAD的作用应该最大。通过颠倒氨基酸和K⁺ 应用顺序来测试给药时间顺序对氨基酸和K⁺ 反应总和的影响。由于GABA去极化会迅速脱敏，所以在这个测试中不能使用GABA。然而，当K⁺ 去极化叠加在持续的谷氨酸去极化上时，总的去极化等于单独给予谷氨酸和K⁺ 时观察到的去极化之和（线性总和）。因此，氨基酸和K⁺ 的给药时间顺序会影响总的去极化大小。没有发现氨基酸和K⁺ 一起应用时有超加性效应的证据。
