Schoffelmeer A N, Mulder A H
Eur J Pharmacol. 1984 Oct 1;105(1-2):129-35. doi: 10.1016/0014-2999(84)90656-3.
The inhibitory actions of exogenous noradrenaline (1 microM) and clonidine (1 microM) as well as well as of the opiate receptor agonists morphine (1 microM) and [D-Ala2,D-Leu5]enkephalin (DADLE, 1 microM) on the potassium-induced Ca2+-dependent release of [3H]noradrenaline from superfused rat brain cortex slices were independent of the degree of depolarization when release was effected by 15 or 56 mM K+ for 5 min. The non-depolarization-dependent release of [3H]noradrenaline induced by exposing the slices for 5 min to medium with NaCl replaced by LiCl was only partially Ca2+-dependent and was not inhibited by the Ca2+ antagonist Cd2+ (50 microM). This release was strongly inhibited by morphine, DADLE, exogenous noradrenaline and clonidine at 1 microM concentrations both in the presence and the absence of extracellular Ca2+. Together with other data in the literature these results strongly suggest that opiate receptors and alpha 2-adrenoceptors located on noradrenergic axonal varicosities, unlike those located on cell bodies, do not primarily mediate hyperpolarization of the neuronal membrane. Instead the activation of these presynaptic receptors causes a reduction of Ca2+ availability for, or the utilization of Ca2+ by the secretion process upon invasion of an action potential.
当用15或56 mM K⁺处理5分钟来实现释放时，外源性去甲肾上腺素（1 microM）、可乐定（1 microM）以及阿片受体激动剂吗啡（1 microM）和[D - Ala²，D - Leu⁵]脑啡肽（DADLE，1 microM）对从灌流的大鼠脑皮质切片中钾诱导的Ca²⁺依赖性[³H]去甲肾上腺素释放的抑制作用与去极化程度无关。将切片暴露于用LiCl替代NaCl的培养基中5分钟所诱导的[³H]去甲肾上腺素的非去极化依赖性释放仅部分依赖于Ca²⁺，并且不受Ca²⁺拮抗剂Cd²⁺（50 microM）的抑制。在存在和不存在细胞外Ca²⁺的情况下，这种释放在1 microM浓度下均受到吗啡、DADLE、外源性去甲肾上腺素和可乐定的强烈抑制。与文献中的其他数据一起，这些结果强烈表明，位于去甲肾上腺素能轴突膨体上的阿片受体和α₂ - 肾上腺素能受体，与位于细胞体上的受体不同，并不主要介导神经元膜的超极化。相反，这些突触前受体的激活会导致动作电位侵入时分泌过程中Ca²⁺可用性的降低或Ca²⁺的利用减少。
