Dualistic actions of cromakalim and new potent 2<i>H</i>
-1,4-benzoxazine derivatives on the native skeletal muscle K<sub>ATP</sub>
channel
作者:Domenico Tricarico、Mariagrazia Barbieri、Laghezza Antonio、Paolo Tortorella、Fulvio Loiodice、Diana Conte Camerino
DOI:10.1038/sj.bjp.0705233
日期:2003.5
New 2H‐1,4‐benzoxazine derivatives were synthesized and tested for their agonist properties on the ATP‐sensitive K+ channels (KATP) of native rat skeletal muscle fibres by using the patch‐clamp technique. The novel modifications involved the introduction at position 2 of the benzoxazine ring of alkyl substituents such as methyl (–CH3), ethyl (–C2H5) or propyl (–C3H7) groups, while maintaining pharmacophore groups critical for conferring agonist properties.
The effects of these molecules were compared with those of cromakalim in the presence or absence of internal ATP (10−4 M). In the presence of internal ATP, all the compounds increased the macropatch KATP currents. The order of potency of the molecules as agonists was −C3H7 (DE50=1.63 × 10−8 M) >−C2H5 (DE50=1.11 × 10−7 M)>–CH3 (DE50=2.81 × 10−7 M)>cromak‐slim (DE50= 1.42 × 10−5 M). Bell‐shaped dose–response curves were observed for these compounds and cromakalim indicating a downturn in response when a certain dose was exceeded.
In contrast, in the absence of internal ATP, all molecules including cromakalim inhibited the KATP currents. The order of increasing potency as antagonists was cromakalim (IC50=1.15 × 10−8 M)–CH3 (IC50=2.6 × 10−8 M)>–C2H5 (IC50=4.4 × 10−8 M)>–C3H7 (IC50=1.68 × 10−7 M) derivatives.
These results suggest that the newly synthesized molecules and cromakalim act on muscle KATP channel by binding on two receptor sites that have opposite actions. Alternatively, a more simple explanation is to consider the existence of a single site for potassium channel openers regulated by ATP which favours the transduction of the channel opening. The alkyl chains at position 2 of the 2H‐1,4‐benzoxazine nucleus is pivotal in determining the potency of benzoxazine derivatives as agonists or antagonists.
British Journal of Pharmacology (2003) 139, 255–262. doi:10.1038/sj.bjp.0705233
新的2H-1,4-苯并恶嗪衍生物被合成并测试了它们在原代大鼠骨骼肌纤维中ATP敏感的K+通道(KATP)上的激动剂性质,采用膜片钳技术。新型修饰包括在苯并恶嗪环的2位引入烷基取代基,如甲基(-CH3)、乙基(-C2H5)或丙基(-C3H7)基团,同时保持对激动剂性质至关重要的药效团。
这些分子的作用与克罗卡林在有或无细胞内ATP(10-4 M)的存在下进行了比较。在存在细胞内ATP的情况下,所有化合物增加了大孔膜片KATP电流。作为激动剂,分子效力的顺序为−C3H7(DE50=1.63 × 10-8 M)>−C2H5(DE50=1.11 × 10-7 M)>–CH3(DE50=2.81 × 10-7 M)>克罗卡林(DE50=1.42 × 10-5 M)。这些化合物和克罗卡林的剂量-反应曲线呈钟形,表明当剂量超过一定阈值时,反应会出现下降。
相反,在不存在细胞内ATP的情况下,所有分子包括克罗卡林都抑制了KATP电流。作为拮抗剂,效力的顺序为克罗卡林(IC50=1.15 × 10-8 M)–CH3(IC50=2.6 × 10-8 M)>–C2H5(IC50=4.4 × 10-8 M)>–C3H7(IC50=1.68 × 10-7 M)衍生物。
这些结果表明,新合成的分子和克罗卡林通过结合到具有相反作用的两个受体位点来作用于肌肉中的KATP通道。一种更简单的解释是考虑ATP调节的钾通道开放的单一受体位点,这有利于通道开放的转导。2位的烷基侧链在决定苯并恶嗪衍生物作为激动剂或拮抗剂的效力中起关键作用。
《英国药理学杂志》(2003)139卷,255–262页。doi:10.1038/sj.bjp.0705233