Bauer V
Br J Pharmacol. 1985 May;85(1):171-7. doi: 10.1111/j.1476-5381.1985.tb08844.x.
The effects of potassium channel blockers, 3,4-diaminopyridine (DAP) and tetraethylammonium (TEA) were studied on the pre- and post-junctional alpha 2-adrenoceptor mediated effects of noradrenaline in the guinea-pig proximal ileum. Both DAP (4 to 500 mumol l-1) and TEA (0.3 to 3 mmol l-1) transiently increased the basal tension of the ileum. However, DAP also increased the amplitude of the smooth muscle twitches evoked by transmural nerve stimulation, whereas TEA marginally depressed them. Atropine (2 mumol l-1) antagonized the contractions induced by DAP but did not affect the similar effects of TEA. On the other hand, DAP restored the smooth muscle twitches depressed by atropine, while TEA did not. DAP, in a concentration-dependent manner, reduced or abolished the prejunctional inhibitory alpha 2-adrenoceptor mediated effect of noradrenaline, whereas TEA (up to 3 mmol l-1) was almost ineffective. The postjunctional inhibitory alpha 2-adrenoceptor mediated effect of noradrenaline was attenuated even at the smallest TEA concentration used (0.3 mmol l-1) and its postjunctional stimulatory alpha 1-adrenoceptor mediated effect was unmasked. However, DAP, was only marginally effective, even at the highest concentrations used (100 and 500 mumol l-1). From these results it would appear that in both the pre- and post-junctional inhibitory alpha 2-adrenoceptor mediated actions of noradrenaline in the guinea-pig ileum the primary step might be an increased potassium conductance. However, the potassium channels on the neuronal and the smooth muscle membrane have different sensitivities to DAP and TEA.
研究了钾通道阻滞剂3,4-二氨基吡啶（DAP）和四乙铵（TEA）对豚鼠近端回肠中去甲肾上腺素在节前和节后α2-肾上腺素能受体介导作用的影响。DAP（4至500μmol l-1）和TEA（0.3至3mmol l-1）均能短暂增加回肠的基础张力。然而，DAP还能增加经壁神经刺激诱发的平滑肌收缩幅度，而TEA则使其略有降低。阿托品（2μmol l-1）能拮抗DAP诱导的收缩，但不影响TEA的类似作用。另一方面，DAP能恢复被阿托品抑制的平滑肌收缩，而TEA则不能。DAP以浓度依赖的方式降低或消除了去甲肾上腺素节前抑制性α2-肾上腺素能受体介导的作用，而TEA（高达3mmol l-1）几乎无效。即使在所用的最小TEA浓度（0.3mmol l-1）下，去甲肾上腺素节后抑制性α2-肾上腺素能受体介导的作用也会减弱，其节后刺激性α1-肾上腺素能受体介导的作用则会显现出来。然而，即使在所用的最高浓度（100和500μmol l-1）下，DAP也只是略有效果。从这些结果看来，在豚鼠回肠中去甲肾上腺素节前和节后抑制性α2-肾上腺素能受体介导的作用中，主要步骤可能是钾电导增加。然而，神经元和平滑肌膜上的钾通道对DAP和TEA的敏感性不同。
