Palatý V
Department of Anatomy, University of British Columbia, Vancouver, Canada.
Naunyn Schmiedebergs Arch Pharmacol. 1992 Jan;345(1):21-4. doi: 10.1007/BF00175464.
The working hypothesis was that the cocaine-insensitive component of non-exocytotic efflux of noradrenaline represents diffusion of the unprotonated amine across the axonal membrane. It was tested by examination of the effect of changing axoplasmic pH--and thus the fraction of extravesicular noradrenaline in the unprotonated form--on the overflows of endogenous noradrenaline and 3,4-dihydroxyphenylethylene glycol from rat tail arteries. The catechols were assayed by liquid chromatography with amperometric detection. To dissipate the H+ gradient across the axonal membrane, the tissues were incubated in media of different pH, in which Na+ was completely replaced with K+ and which were HCO3(-)-(and Ca(2+)-)free. Exposure of the tissues to these media produced substantial, but reversible increases in the overflow of noradrenaline. Subsequently, the overflows of both noradrenaline and the glycol kept rising, but their ratio did not change. Cocaine (0.1 mmol/l) lowered the (noradrenaline overflow: glycol overflow) ratio significantly. The ratio observed in its presence increased steeply with decreasing external and, presumably, axoplasmic pH. Addition of valinomycin and carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone (1 mumol/l each) to the cocaine-containing media more than doubled the overflows without altering significantly the ratio. Under identical conditions, the overflow of noradrenaline from preparations with inactive neuronal monoamine oxidase did not decrease with decreasing pH. Since, in the presence of cocaine, the overflow ratio increased--rather than decreased--with decreasing pH, and because the overflow or noradrenaline from preparations with inactive monoamine oxidase did not decline with pH, the cocaine-insensitive component of noradrenaline efflux does not seem proportional to the axoplasmic concentration of the unprotonated amine.(ABSTRACT TRUNCATED AT 250 WORDS)
工作假设是去甲肾上腺素非胞吐性外流中对可卡因不敏感的成分代表未质子化胺穿过轴突膜的扩散。通过检测改变轴浆pH值（从而改变未质子化形式的囊泡外去甲肾上腺素比例）对大鼠尾动脉内源性去甲肾上腺素和3,4 - 二羟基苯乙二醇溢出的影响来进行测试。儿茶酚通过液相色谱 - 安培检测法进行测定。为了消除跨轴突膜的H⁺梯度，将组织置于不同pH值的培养基中孵育，其中Na⁺完全被K⁺取代且不含HCO₃⁻（和Ca²⁺）。将组织暴露于这些培养基中会使去甲肾上腺素的溢出量显著但可逆地增加。随后，去甲肾上腺素和二醇的溢出量持续上升，但它们的比例不变。可卡因（0.1 mmol/l）显著降低了（去甲肾上腺素溢出量：二醇溢出量）的比例。在其存在下观察到的比例随着外部pH值降低以及可能的轴浆pH值降低而急剧增加。向含可卡因的培养基中添加缬氨霉素和羰基氰化物对 -（三氟甲氧基）苯腙（各1 μmol/l）使溢出量增加了一倍多，而比例没有显著改变。在相同条件下，具有无活性神经元单胺氧化酶的制剂中去甲肾上腺素的溢出量不会随pH值降低而减少。由于在可卡因存在下，溢出比例随着pH值降低而增加而非降低，并且由于具有无活性单胺氧化酶的制剂中去甲肾上腺素的溢出量不会随pH值下降，去甲肾上腺素外流中对可卡因不敏感的成分似乎与未质子化胺的轴浆浓度不成比例。（摘要截断于250字）
