Garland C J, Smirnov S V, Bagher P, Lim C S, Huang C Y, Mitchell R, Stanley C, Pinkney A, Dora K A
Department of Pharmacology, University of Oxford, Oxford, OX1 3QT, UK.
Br J Pharmacol. 2015 Feb;172(4):1114-23. doi: 10.1111/bph.12985. Epub 2014 Dec 23.
Smooth muscle transient receptor potential melastatin 4 (TRPM4) channels play a fundamental role in the development of the myogenic arterial constriction that is necessary for blood flow autoregulation. As TRPM4 channels are present throughout the vasculature, we investigated their potential role in non-myogenic resistance arteries using the TRPM4 inhibitor 9-phenanthrol.
Pressure and wire myography were used to assess the reactivity of rat arteries, the latter in combination with measurements of smooth muscle membrane potential. Immunohistochemistry (IHC) and endothelial cell (EC) calcium changes were assessed in pressurized vessels and patch clamp measurements made in isolated ECs.
The TRPM4 inhibitor 9-phenanthrol reversibly hyperpolarized mesenteric arteries to circa EK and blocked α1 -adrenoceptor-mediated vasoconstriction. Hyperpolarization was abolished and vasoconstriction re-established by damaging the endothelium. In mesenteric and cerebral artery smooth muscle, 9-phenanthrol hyperpolarization was effectively blocked by the KCa 3.1 inhibitor TRAM-34. 9-Phenanthrol did not increase mesenteric EC [Ca(2+)]i , and Na(+) substitution with N-methyl-D-glucamine only increased the muscle resting potential by 10 mV. Immunolabelling for TRPM4 was restricted to the endothelium and perivascular tissue.
These data reveal a previously unrecognized action of the TRPM4 inhibitor 9-phenanthrol - the ability to act as an activator of EC KCa 3.1 channels. They do not indicate a functionally important role for TRPM4 channels in the reactivity of non-myogenic mesenteric arteries.
平滑肌瞬时受体电位香草酸亚型4（TRPM4）通道在肌源性动脉收缩的发生过程中起重要作用，而肌源性动脉收缩是血流自动调节所必需的。由于TRPM4通道存在于整个血管系统中，我们使用TRPM4抑制剂9-菲咯啉研究了它们在非肌源性阻力动脉中的潜在作用。
采用压力和线肌张力描记法评估大鼠动脉的反应性，后者结合平滑肌膜电位测量。在加压血管中评估免疫组织化学（IHC）和内皮细胞（EC）钙变化，并在分离的EC中进行膜片钳测量。
TRPM4抑制剂9-菲咯啉使肠系膜动脉可逆性超极化至约EK，并阻断α1肾上腺素能受体介导的血管收缩。通过损伤内皮消除超极化并重新建立血管收缩。在肠系膜和脑动脉平滑肌中，9-菲咯啉超极化被钙激活钾通道3.1（KCa 3.1）抑制剂TRAM-34有效阻断。9-菲咯啉未增加肠系膜EC的细胞内钙浓度（[Ca(2+)]i），用N-甲基-D-葡糖胺替代钠仅使肌肉静息电位增加10 mV。TRPM4的免疫标记仅限于内皮和血管周围组织。
这些数据揭示了TRPM4抑制剂9-菲咯啉以前未被认识的作用——作为EC KCa 3.1通道激活剂的能力。它们并未表明TRPM4通道在非肌源性肠系膜动脉反应性中具有功能上的重要作用。
