McNeish Alister J, Sandow Shaun L, Neylon Craig B, Chen Mark X, Dora Kim A, Garland Christopher J
Department of Pharmacy and Pharmacology, University of Bath, Bath, UK.
Stroke. 2006 May;37(5):1277-82. doi: 10.1161/01.STR.0000217307.71231.43. Epub 2006 Mar 23.
Endothelium-derived hyperpolarizing factor responses in the rat middle cerebral artery are blocked by inhibiting IKCa channels alone, contrasting with peripheral vessels where block of both IKCa and SKCa is required. As the contribution of IKCa and SKCa to endothelium-dependent hyperpolarization differs in peripheral arteries, depending on the level of arterial constriction, we investigated the possibility that SKCa might contribute to equivalent hyperpolarization in cerebral arteries under certain conditions.
Rat middle cerebral arteries (approximately 175 microm) were mounted in a wire myograph. The effect of KCa channel blockers on endothelium-dependent responses to the protease-activated receptor 2 agonist, SLIGRL (20 micromol/L), were then assessed as simultaneous changes in tension and membrane potential. These data were correlated with the distribution of arterial KCa channels revealed with immunohistochemistry.
SLIGRL hyperpolarized and relaxed cerebral arteries undergoing variable levels of stretch-induced tone. The relaxation was unaffected by specific inhibitors of IKCa (TRAM-34, 1 micromol/L) or SKCa (apamin, 50 nmol/L) alone or in combination. In contrast, the associated smooth-muscle hyperpolarization was inhibited, but only with these blockers in combination. Blocking nitric oxide synthase (NOS) or guanylyl cyclase evoked smooth-muscle depolarization and constriction, with both hyperpolarization and relaxation to SLIGRL being abolished by TRAM-34 alone, whereas apamin had no effect. Immunolabeling showed SKCa and IKCa within the endothelium.
In the absence of NO, IKCa underpins endothelium-dependent hyperpolarization and relaxation in cerebral arteries. However, when NOS is active SKCa contributes to hyperpolarization, whatever the extent of background contraction. These changes may have relevance in vascular disease states where NO release is compromised and when the levels of SKCa expression may be altered.
在大鼠大脑中动脉中，仅抑制IKCa通道就能阻断内皮衍生超极化因子反应，这与外周血管不同，在外周血管中需要同时阻断IKCa和SKCa通道。由于IKCa和SKCa对外周动脉内皮依赖性超极化的贡献因动脉收缩程度而异，我们研究了在某些条件下SKCa可能对脑动脉中同等超极化起作用的可能性。
将大鼠大脑中动脉（约175微米）安装在钢丝肌动描记器上。然后评估钾通道阻滞剂对蛋白酶激活受体2激动剂SLIGRL（20微摩尔/升）的内皮依赖性反应的影响，以张力和膜电位的同时变化来衡量。这些数据与免疫组织化学显示的动脉钾通道分布相关。
SLIGRL使处于不同程度拉伸诱导张力状态的脑动脉超极化并舒张。单独或联合使用IKCa特异性抑制剂（TRAM-34，1微摩尔/升）或SKCa特异性抑制剂（蜂毒明肽，50纳摩尔/升）时，舒张不受影响。相反，相关的平滑肌超极化受到抑制，但仅在这些阻滞剂联合使用时才会出现。阻断一氧化氮合酶（NOS）或鸟苷酸环化酶会引起平滑肌去极化和收缩，单独使用TRAM-34可消除对SLIGRL的超极化和舒张反应，而蜂毒明肽则无作用。免疫标记显示内皮中有SKCa和IKCa。
在没有一氧化氮的情况下，IKCa是脑动脉内皮依赖性超极化和舒张的基础。然而，当NOS活跃时，无论背景收缩程度如何，SKCa都有助于超极化。这些变化可能与一氧化氮释放受损且SKCa表达水平可能改变的血管疾病状态有关。
