Control of Cerebral Blood Flow by KCa2 and KCa3

描述(由申请人提供)：在大脑动脉和小动脉中发现了一种新的内皮依赖性扩张器机制。这种扩张器机制被称为内皮衍生超极化因子(EDHF)或内皮依赖性超极化(EDH)，这种机制不涉及一氧化氮(NO)或环氧合酶代谢产物(即前列环素)，需要激活脑血管中和/或小电导钙激活的钾通道(分别为IKCa和SKCa)。利用分离的大脑动脉和小动脉的研究提供了间接证据，表明这种涉及IKCa和SKCa的扩张器机制在调节脑血流量(CBF)方面可能与内皮来源的NO一样重要。这一想法是基于IKCa/SKCa在设定大脑动脉和小动脉的静息内径方面的关键作用，它们对内皮介导的扩张的贡献，以及它们在穿透小动脉方面相对于一氧化氮的相对重要性，小动脉是大脑中主要血管阻力的部位。此外，在缺血/再灌注、创伤性脑损伤和其他病理状态下，当没有生物利用度降低时，通过IKCa/SKCa的扩张会增强。在病理状态下，上调IKCa/SKCa介导的扩张可能是一种重要的保护策略，用于补偿NO的减少，最终限制CBF的减少。尽管具有挑衅性，但必须强调的是，到目前为止，涉及IKCa/SKCa介导的扩张的研究主要使用了分离的脑血管，这些血管被从大脑中取出，并在血管室中进行体外检查。为了充分了解IKCa和SKCa在控制CBF中的重要性，有必要将这些研究扩展到体内的情况，即动脉和小动脉在心血管系统中作为一个协调网络发挥作用。因此，我们建议在体内验证IKCa和/或SKCa通道调节CBF的假设。我们建议证明激活IKCa和SKCa增加脑血流量(特定目标1)。我们将确定IKCa和SKCa对静息CBF的贡献(特定目标2)。最后，我们将确定IKCa和SKCa在由红细胞释放到血浆中的激动剂三磷酸腺苷(ATP)引起的CBF增加中的贡献(特定目标3)。在直接刺激IKCa和SKCa通道或间接通过内皮细胞P2Y2受体激动剂ATP后，将使用激光多普勒血流仪从皮质表面测量CBF的增加。为了达到特定的目的，我们将利用选择性的药物抑制剂来确定IKCa和SKCa在控制CBF中的相对贡献。间接证据表明IKCa/SKCa在调节CBF中起着重要作用，这增强了在体内进行拟议研究的必要性。在NO生物利用度受损的病理条件下，IKCa/SKCa通道可能具有临床意义和治疗靶点。此外，IKCa/SKCa通道可以以类似于NO的方式进入临床实践。 公共卫生相关性：脑血流的控制是中风和创伤性脑损伤等许多病理状态的重要临床考虑因素。中、小电导钾通道只允许钾离子通过细胞膜，似乎是内皮细胞控制脑血流的重要机制。拟议的研究将确定这些中、小电导钾通道在调节脑血流中的作用。

DESCRIPTION (provided by applicant): A novel endothelium-dependent dilator mechanism was identified in cerebral arteries and arterioles. This dilator mechanism has been called endothelium-derived hyperpolarizing factor (EDHF) or endothelium- dependent hyperpolarization (EDH).This mechanism, which does not involve nitric oxide (NO) or cyclooxygenase metabolites (i.e., prostacyclin), requires the activation of intermediate and/or small conductance calcium-activated K+ channels (IKCa and SKCa respectively) in cerebral vessels. Studies utilizing isolated cerebral arteries and arterioles provide circumstantial evidence that this dilator mechanism, involving IKCa and SKCa, may be as important as endothelium-derived NO in regulating cerebral blood flow (CBF). This idea is based on the key role of IKCa/SKCa in setting the resting diameter of cerebral arteries and arterioles, their contribution to endothelium-mediated dilations, and their relative importance compared to NO in penetrating arterioles, a site of major vascular resistance in the brain. In addition, dilations through IKCa/SKCa are enhanced following ischemia/reperfusion, traumatic brain injury, and other pathological states when NO bioavailability is diminished. Upregulation of IKCa/SKCa-mediated dilations may be an important protective strategy serving to compensate for decreased NO and ultimately limit reductions in CBF during pathological states. Although provocative, it is important to emphasize that studies to date involving IKCa/SKCa-mediated dilations have primarily used isolated cerebral vessels, which were removed from the brain and examined ex vivo in a vessel chamber. In order to fully understand the importance of IKCa and SKCa in controlling CBF, it is imperative that these studies are extended to the in vivo situation where arteries and arterioles function as a coordinated network in the cardiovascular system. Therefore, we propose to test the hypothesis that IKCa and/or SKCa channels regulate CBF in vivo. We propose to demonstrate that activation of IKCa and SKCa increase cerebral blood flow (Specific Aim 1). We will determine the contribution of IKCa and SKCa to resting CBF (Specific Aim 2). Finally, we will determine the contribution of IKCa and SKCa to increases in CBF elicited by ATP, an agonist released by red blood cells into the plasma (Specific Aim 3). Increases in CBF will be measured from the cortical surface using laser Doppler flowmetry following direct stimulation of IKCa and SKCa channels or indirectly through ATP, an agonist for endothelial P2Y2 receptors. For the specific aims, we will utilize selective pharmacological inhibitors to determine the relative contribution of IKCa and SKCa in controlling CBF. The need to conduct the proposed studies in vivo is amplified by the circumstantial evidence indicating an important role for IKCa/SKCa in regulating CBF. IKCa/SKCa channels could be of clinical relevance and a therapeutic target during pathological conditions where the bioavailability of NO is compromised. Furthermore, IKCa/SKCa channels could find their way into clinical practice in a manner similar to that of NO. PUBLIC HEALTH RELEVANCE: The control of cerebral blood flow is an important clinical consideration for a number of pathological states such as stroke and traumatic brain injury. Intermediate and small conductance potassium channels, which allow only K+ to pass across the cell membrane, appear to be an important mechanism for endothelial control of cerebral blood flow. The proposed studies will determine the role of these intermediate and small conductance potassium channels in the regulation of cerebral blood flow.