Salom Juan B, Castelló-Ruiz María, Burguete María C, Guzmán Carla, Jover-Mengual Teresa, Torregrosa Germán, Jover Ramiro, Lizasoain Ignacio, Alborch Enrique
Centro de Investigación, Hospital Universitario La Fe, Valencia, Spain.
Eur J Pharmacol. 2008 Feb 26;581(1-2):138-47. doi: 10.1016/j.ejphar.2007.11.032. Epub 2007 Nov 28.
The aim of this study was to assess the role of K(+) and Ca(2+) fluxes in the cerebroarterial vasoactive effects of the phosphodiesterase-5 inhibitor sildenafil. We used isolated rabbit basilar arteries to assess the effects of extracellular K(+) raising on sildenafil-induced vasodilatation, and studied the pharmacological interaction of sildenafil with selective modulators of membrane K(+) and Ca(2+) channels. Expression of Kv1 subunits of K(+) channels was assessed at messenger and protein levels. Parallel experiments were carried out with zaprinast for comparison. Sildenafil (10 nM-0.1 mM) induced concentration-dependent relaxation of endothelin-1 (10 nM)-precontracted arteries, which was partially inhibited by depolarization with KCl (50 mM), 3 mM tetraethylammonium (non-selective K(+) channel blocker) or 1 mM aminopyridine (inhibitor of K(v) channels), but not by 1 microM glibenclamide (inhibitor of K(ATP) channels) or 50 nM iberiotoxin (inhibitor of K(Ca) channels). Arterial smooth muscle expressed messengers for Kv1.2, Kv1.3, Kv1.4, Kv1.5 and Kv1.6, and proteins of Kv1.1, Kv1.2 and Kv1.4. CaCl(2) (10 microM- 10 mM) induced concentration-dependent contraction in Ca(2+)-free, depolarizing (50 mM KCl) medium. Sildenafil (0.1-100 microM) produced reversible concentration-dependent inhibition of the response to CaCl(2), which was completely abolished by the highest sildenafil concentration. By contrast, only 100 microM zaprinast inhibited the response to CaCl(2). The L-type Ca(2+) channel activator Bay K 8644 (0.1 nM-1 microM) induced concentration-dependent potentiation of the response to CaCl(2) inhibited by 100 microM sildenafil. Moreover, Bay K 8644 (0.1 nM-1 microM) induced concentration-dependent contraction in slightly depolarizing (15 mM) medium, which was inhibited to the same extent and in a concentration-dependent way by sildenafil (0.1-100 microM) and zaprinast (1 or 100 microM). These results show that sildenafil relaxes the rabbit basilar artery by increasing K(+) efflux through K(v) channels, which in turn may affect Ca(2+) signalling. Expression of Kv1 subunits involved in this pharmacological effect occurs at the messenger and, in some cases, at the protein level. In addition to this phosphodiesterase-5-related effect, sildenafil and zaprinast inhibit cerebroarterial vasoconstriction at least in part by directly blocking L-type Ca(2+) channels, although a decrease in the sensitivity of the contractile apparatus to Ca(2+) can not be discarded.
本研究旨在评估钾离子（K⁺）和钙离子（Ca²⁺）通量在磷酸二酯酶-5抑制剂西地那非对脑动脉血管活性作用中的角色。我们使用离体兔基底动脉来评估细胞外钾离子浓度升高对西地那非诱导的血管舒张的影响，并研究西地那非与膜钾离子和钙离子通道选择性调节剂之间的药理相互作用。在信使核糖核酸和蛋白质水平评估钾离子通道Kv1亚基的表达。使用扎普司特进行平行实验以作比较。西地那非（10 nM - 0.1 mM）可诱导内皮素-1（10 nM）预收缩动脉产生浓度依赖性舒张，该舒张作用被氯化钾（50 mM）去极化、3 mM四乙铵（非选择性钾离子通道阻滞剂）或1 mM氨基吡啶（Kv通道抑制剂）部分抑制，但不受1 μM格列本脲（KATP通道抑制剂）或50 nM艾替通毒素（KCa通道抑制剂）抑制。动脉平滑肌表达Kv1.2、Kv1.3、Kv1.4、Kv1.5和Kv1.6的信使核糖核酸以及Kv1.1、Kv1.2和Kv1.4的蛋白质。氯化钙（10 μM - 10 mM）在无钙、去极化（50 mM氯化钾）培养基中诱导浓度依赖性收缩。西地那非（0.1 - 100 μM）对氯化钙反应产生可逆的浓度依赖性抑制，在最高西地那非浓度时完全消除该反应。相比之下，仅100 μM扎普司特抑制对氯化钙的反应。L型钙离子通道激活剂Bay K 8644（0.1 nM - 1 μM）诱导对氯化钙反应的浓度依赖性增强，该反应被100 μM西地那非抑制。此外，Bay K 8644（0.1 nM - 1 μM）在轻度去极化（15 mM）培养基中诱导浓度依赖性收缩，该收缩被西地那非（0.1 - 100 μM）和扎普司特（1或100 μM）以相同程度且浓度依赖性方式抑制。这些结果表明，西地那非通过增加钾离子经Kv通道外流使兔基底动脉舒张，这反过来可能影响钙离子信号传导。参与此药理作用的Kv1亚基在信使核糖核酸水平表达，在某些情况下也在蛋白质水平表达。除了这种与磷酸二酯酶-5相关的作用外，西地那非和扎普司特至少部分通过直接阻断L型钙离子通道抑制脑动脉血管收缩，尽管不能排除收缩装置对钙离子敏感性降低的可能性。
