Poulat P, De Champlain J, D'Orléans-Juste P, Couture R
Department of Physiology, Faculty of Medicine, Université de Montréal, Québec, Canada.
Eur J Pharmacol. 1996 Nov 21;315(3):327-34. doi: 10.1016/s0014-2999(96)00610-3.
In rat spinal cord slices, endothelin-1 and endothelin-3 enhanced [3H]inositol phosphate production between 1 nM and 10 microM (endothelin-1 > endothelin-3) while sarafotoxin 6c and the endothelin ETB receptor agonist IRL-1620 (Suc-[Glu9,Ala11,15]endothelin-1-(8-21)) were almost ineffective. BQ-123 (cyclo(D-Trp,D-Asp,L-Pro,D-Val,L-Leu), a selective endothelin ETA receptor antagonist, reduced the endothelin-1- and endothelin-3-induced [3H]inositol phosphate production, with similar inhibition constants (IC50: 16.7 +/- 3.4 and 8.0 +/- 1.6 microM, respectively). The inhibition of endothelin-1 was enhanced when BQ-123 was preincubated for 30 min instead of 15 min. BQ-788 (N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D -1-methoxy- carbonyltryptophanyl-D-Nle), a selective ETB receptor antagonist, did not modify the endothelin-1-induced [3H]inositol phosphate production. Big endothelin-1 (1 nM to 1 microM) was slightly less potent than endothelin-1 in enhancing [3H]inositol phosphate production. This response was sensitive to phosphoramidon and [Phe22]big endothelin-1-(19-37), two inhibitors of endothelin-converting enzyme. Pretreatment of slices with pertussis toxin, indomethacin or PN 200-110 ((-)-isradipine, a dual inhibitor of L- and R-type Ca2+ channels) did not alter the response to 1 microM endothelin-1 while this response was abolished by tetrodotoxin. Finally, endothelin-1 enhanced [3H]inositol phosphate production with an identical EC50 (2.1 nM) in spinal cord slices of Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) although the maximal response was reduced in SHR. These data indicate that endothelins stimulated [3H]inositol phosphate production in the rat spinal cord through the activation of an endothelin ETA receptor that trigger the release of an unidentified neurotransmitter. This effect does not appear to be associated to activation of a Gi/G(o)-type of G-protein, dihydropyridine-sensitive L-type Ca2+ channels or to the production of prostaglandins. Furthermore, the findings support the presence of a phosphoramidon-sensitive endothelin-converting enzyme in the spinal cord.
在大鼠脊髓切片中，内皮素 -1 和内皮素 -3 在 1 nM 至 10 μM 浓度范围内增强了 [³H] 肌醇磷酸的生成（内皮素 -1 ＞ 内皮素 -3），而 sarafotoxin 6c 和内皮素 ETB 受体激动剂 IRL -1620（Suc -[Glu9,Ala11,15]内皮素 -1-(8 - 21)）几乎无效。选择性内皮素 ETA 受体拮抗剂 BQ -123（环(D - Trp,D - Asp,L - Pro,D - Val,L - Leu)）可降低内皮素 -1 和内皮素 -3 诱导的 [³H] 肌醇磷酸生成，其抑制常数相似（IC50 分别为 16.7 ± 3.4 和 8.0 ± 1.6 μM）。当 BQ -123 预孵育 30 分钟而非 15 分钟时，对内皮素 -1 的抑制作用增强。选择性 ETB 受体拮抗剂 BQ -788（N - 顺式 - 2,6 - 二甲基哌啶羰基 - L - γ - 甲基亮氨酰 - D - 1 - 甲氧基羰基色氨酰 - D - Nle）并未改变内皮素 -1 诱导的 [³H] 肌醇磷酸生成。大内皮素 -1（1 nM 至 1 μM）在增强 [³H] 肌醇磷酸生成方面的效力略低于内皮素 -1。该反应对内皮素转化酶的两种抑制剂磷酰胺素和 [Phe22] 大内皮素 -1-(19 - 37) 敏感。用百日咳毒素、吲哚美辛或 PN 200 - 110（(-)-异搏定，一种 L 型和 R 型 Ca²⁺ 通道的双重抑制剂）预处理切片，并未改变对 1 μM 内皮素 -1 的反应，而河豚毒素可消除该反应。最后，尽管自发性高血压大鼠（SHR）的最大反应降低，但内皮素 -1 在 Wistar - Kyoto 大鼠（WKY）和 SHR 的脊髓切片中以相同的 EC50（2.1 nM）增强了 [³H] 肌醇磷酸生成。这些数据表明，内皮素通过激活内皮素 ETA 受体刺激大鼠脊髓中 [³H] 肌醇磷酸的生成，该受体触发了一种未知神经递质的释放。这种效应似乎与 Gi/G(o) 型 G 蛋白的激活、二氢吡啶敏感的 L 型 Ca²⁺ 通道或前列腺素的产生无关。此外，这些发现支持脊髓中存在对磷酰胺素敏感的内皮素转化酶。
