Rodríguez R, Sitges M
Depto. de Biología Celular, UNAM, Ciudad Universitaria, México, D.F., México.
Neurochem Res. 1996 Aug;21(8):889-95. doi: 10.1007/BF02532337.
The effect of the putative K+/H+ ionophore, nigericin on the internal Na+ concentration ([Nai]), the internal pH (pHi), the internal Ca2+ concentration ([Cai]) and the baseline release of the neurotransmitter, GABA was investigated in Na+-binding benzofuran isophtalate acetoxymethyl ester (SBFI-AM), 2',7'-bis(carboxyethyl)-5(6) carboxyfluorescein acetoxymethyl ester (BCECF-AM, fura-2 and [3H]GABA loaded synaptosomes, respectively. In the presence of Na+ at a physiological concentration (147 mM), nigericin (0.5 microM) elevates [Nai] from 20 to 50 mM, increases the pHi, 0.16 pH units, elevates four fold the [Cai] at expense of external Ca2+ and markedly increases (more than five fold) the release of [3H]GABA. In the absence of a Na+ concentration gradient (i.e. when the external Na+ concentration equals the [Nai]), the same concentration (0.5 microM) of nigericin causes the opposite effect on the pHi (acidifies the synaptosomal interior), does not modify the [Nai] and is practically unable to elevate the [Cai] or to increase [3H]GABA release. Only with higher concentrations of nigericin than 0.5 microM the ionophore is able to elevate the [Cai] and to increase the release of [3H]GABA under the conditions in which the net Na+ movements are eliminated. These results clearly show that under physiological conditions (147 mM external Na+) nigericin behaves as a Na+/H+ ionophore, and all its effects are triggered by the entrance of Na+ in exchange for H+ through the ionophore itself. Nigericin behaves as a K+/H+ ionophore in synaptosomes just when the net Na+ movements are eliminated (i.e. under conditions in which the external and the internal Na+ concentrations are equal). In summary care must be taken when using the putative K+/H+ ionophore nigericin as an experimental tool in synaptosomes, as under standard conditions (i.e. in the presence of high external Na+) nigericin behaves as a Na+/H+ ionophore.
在分别用钠结合苯并呋喃异邻苯二甲酸酯乙酰氧基甲酯（SBFI - AM）、2',7'-双（羧乙基）-5（6）羧基荧光素乙酰氧基甲酯（BCECF - AM）、fura - 2和[³H]GABA负载的突触体中，研究了假定的K⁺/H⁺离子载体尼日利亚菌素对细胞内Na⁺浓度（[Nai]）、细胞内pH（pHi）、细胞内Ca²⁺浓度（[Cai]）以及神经递质GABA基线释放的影响。在生理浓度（147 mM）的Na⁺存在下，尼日利亚菌素（0.5 μM）使[Nai]从20 mM升高至50 mM，使pHi升高0.16个pH单位，使[Cai]升高四倍，消耗细胞外Ca²⁺，并显著增加（超过五倍）[³H]GABA的释放。在不存在Na⁺浓度梯度时（即当细胞外Na⁺浓度等于[Nai]时），相同浓度（0.5 μM）的尼日利亚菌素对pHi产生相反的作用（使突触体内部酸化），不改变[Nai]，并且实际上无法升高[Cai]或增加[³H]GABA的释放。只有当尼日利亚菌素的浓度高于0.5 μM时，在净Na⁺移动被消除的条件下，该离子载体才能够升高[Cai]并增加[³H]GABA的释放。这些结果清楚地表明，在生理条件下（细胞外Na⁺浓度为147 mM），尼日利亚菌素表现为Na⁺/H⁺离子载体，其所有作用都是由Na⁺通过离子载体本身进入并交换H⁺所触发的。仅当净Na⁺移动被消除时（即在细胞外和细胞内Na⁺浓度相等的条件下），尼日利亚菌素在突触体中才表现为K⁺/H⁺离子载体。总之，在突触体中使用假定的K⁺/H⁺离子载体尼日利亚菌素作为实验工具时必须谨慎，因为在标准条件下（即在高细胞外Na⁺存在时），尼日利亚菌素表现为Na⁺/H⁺离子载体。
