Quast U, Bray K M, Andres H, Manley P W, Baumlin Y, Dosogne J
Sandoz Pharma Ltd., Basel, Switzerland.
Mol Pharmacol. 1993 Mar;43(3):474-81.
P1075 [N-cyano-N'-(1,1-dimethylpropyl)-N"-3-pyridylguanidine], an analogue of the K+ channel opener pinacidil, was shown to be a K+ channel opener in rat aorta, based on (i) its ability to stimulate 86Rb+ efflux, (ii) its ability to relax contractions in response to noradrenaline under normal conditions (5 mM KCl) but not under depolarized conditions (55 mM KCl), and (iii) the sensitivity of these effects to inhibition by the sulfonylurea glibenclamide. In these assays, P1075 was approximately 20 times more potent than cromakalim. Using a tritiated derivative, [3H] P1075, specific binding could not be detected in microsomal preparations from various tissues. However, in rat aortic strips specific binding of [3H]P1075 has been observed and was reduced by lowering the temperature or by decreasing intracellular ATP levels via metabolic inhibition. Specific [3H]P1075 binding was influenced neither by depolarization (55 mM KCl) nor by lowering the pH from 7.4 to 6.0. Binding was inhibited by representatives from all major families of K+ channel openers, with potencies that correlated well with the potencies obtained in 86Rb+ efflux and relaxation studies. However, stimulation of 86Rb+ efflux occurred at 40 times higher concentrations than did binding (and vasorelaxation). Of the various inhibitors of the K+ channel openers tested, only the sulfonylureas inhibited [3H] P1075 binding with the same rank order of potencies as that required for inhibition of P1075-induced 86Rb+ efflux, although at higher concentrations. The results show that binding of [3H] P1075 is independent of membrane potential but decreases concomitantly with the intracellular ATP level. The excellent correlation between the potencies of the openers and sulfonylurea blockers in binding assays and functional studies suggests that the 'drug receptor' labeled by [3H]P1075 in rat isolated aorta is of functional relevance. However, the fact that binding of the openers occurred at concentrations considerably lower than those required for K+ channel opening and that binding of the sulfonylureas was only reflected at concentrations higher than those needed to block the channel requires complex models to link binding and effect, possibly involving two agonist binding sites coupled by negative cooperativity.
P1075 [N-氰基-N'-(1,1-二甲基丙基)-N"-3-吡啶基胍]，一种钾通道开放剂吡那地尔的类似物，基于以下几点被证明是大鼠主动脉中的钾通道开放剂：(i) 其刺激86Rb+外流的能力；(ii) 其在正常条件下（5 mM氯化钾）而非去极化条件下（55 mM氯化钾）松弛去甲肾上腺素引起的收缩的能力；(iii) 这些效应对磺酰脲类格列本脲抑制作用的敏感性。在这些实验中，P1075的效力约为克罗卡林的20倍。使用氚标记的衍生物[3H]P1075，在来自各种组织的微粒体制剂中未检测到特异性结合。然而，在大鼠主动脉条中观察到了[3H]P1075的特异性结合，并且通过降低温度或通过代谢抑制降低细胞内ATP水平可使其减少。特异性[3H]P1075结合不受去极化（55 mM氯化钾）影响，也不受将pH从7.4降至6.0的影响。所有主要钾通道开放剂家族的代表物均抑制结合，其效力与在86Rb+外流和舒张研究中获得的效力密切相关。然而，刺激86Rb+外流所需的浓度比结合（和血管舒张）所需的浓度高40倍。在所测试的各种钾通道开放剂抑制剂中，只有磺酰脲类以与抑制P1075诱导的86Rb+外流所需效力相同的顺序抑制[3H]P1075结合，尽管所需浓度更高。结果表明，[3H]P1075的结合与膜电位无关，但随细胞内ATP水平的降低而降低。在结合实验和功能研究中，开放剂和磺酰脲类阻滞剂效力之间的良好相关性表明，在大鼠离体主动脉中被[3H]P1075标记的“药物受体”具有功能相关性。然而，开放剂的结合发生在比钾通道开放所需浓度低得多的浓度下，并且磺酰脲类的结合仅在高于阻断通道所需浓度时才得以体现，这一事实需要复杂的模型来将结合与效应联系起来，可能涉及通过负协同作用耦合的两个激动剂结合位点。
