CARDIAC A1-ADENOSINE RECEPTOR RESERVE

描述：（改编自申请人的摘要） 申请人的实验室揭示了腺苷抑制 异丙肾上腺素刺激的L-型钙内向电流（β-ICa，L） 心房肌细胞是12倍高于激活向内整流 K+电流（IKAdo）。 本申请中提出的研究旨在 为了检验以下与以下物质的差异效力有关的假设， 腺苷抑制心房肌细胞中的β-ICa，L并激活IKAdo： 目的#1 -不同的A1受体亚型（A1 a和A1 b）有助于抑制 β-ICa，L和IKAdo的活化;目的#2 -单个受体偶联至 这两种反应，但有一个更大的受体储备抑制 β-ICa，L比IKAdo的激活;目的#3 -不同的A1 β R激动剂 会有不同程度的受体储备。 的重要性 受体储备作为心肌细胞对A1受体反应性的决定因素 激动剂将被解决。 一种新合成的不可逆A1受体 拮抗剂将用于分析受体 保护区 药理学方法将用于定义A1 β R亚型， 以确定两者的受体占据-反应关系， A1受体介导的反应（IKAdo的激活/β-Ica，L的抑制） 心房肌细胞和心房肌细胞的直接缩短 动作电位（MAP）由各种A1受体激动剂引起。 研究将 用豚鼠新鲜分离的心房肌细胞进行， 灌注的心脏 IKAdo的激活和β-ICa，L的抑制 腺苷和A1 β R激动剂将通过使用全细胞记录 膜片钳技术 腺苷引起的心房MAP缩短， 将通过标准电生理学方法定量A1 β R激动剂 方法. 虽然该项目的主要重点是受体储备， 他们还将研究（目标4）是否具有更高的效力和 潜在的抗β-肾上腺素能作用的更大储备可能赋予 内源性腺苷对交感神经激活的紧张性抑制 麻醉豚鼠的心脏。 内生性假说 腺苷对心脏刺激作用产生紧张性抑制， 增加的交感神经活动将通过测量 硝普钠诱导的低血压引起的反射性心动过速的幅度， 在不存在和存在A1 β R拮抗剂和变构剂的情况下， 激动剂结合A1受体的增强剂。 这些研究将对 A1 β R激动剂的设计和使用的临床意义 心脏病的治疗，以及腺苷在调节 心脏功能。 这些研究的长期目标是了解 对A1 β R激动剂的器官和/或反应选择性的机制 可实现的。

DESCRIPTION: (Adapted from the Applicant's Abstract) Recent studies in the applicants' laboratory revealed that the potency of adenosine to inhibit isoproterenol-stimulated L-type calcium inward current (beta-ICa,L) of atrial myocytes is 12-fold higher than to activate the inwardly rectifying K+ current (IKAdo). The studies proposed in this application are designed to test the following hypotheses related to the differential potency of adenosine to inhibit beta-ICa,L and to activate IKAdo in atrial myocytes: Aim #1 - distinct A1 receptor subtypes (A1a and A1b) subserve inhibition of beta-ICa,L and activation of IKAdo; Aim #2 - a single receptor is coupled to both responses, but there is a greater receptor reserve for inhibition of beta-ICa,L than for activation of IKAdo; Aim #3 - different A1AdoR agonists will have different magnitudes of receptor reserve. The importance of receptor reserve as a determinant of cardiomyocyte responsiveness to A1AdoR agonists will be resolved. A newly synthesized irreversible A1AdoR antagonist will be used to inactivate A1AdoRs for the analysis of receptor reserve. Pharmacological methods will be used to define A1AdoR subtypes and to determine the receptor occupancy-response relationships for both A1AdoR-mediated responses (activation of IKAdo/inhibition of beta-Ica,L) in atrial myocytes and for the direct shortening of the atrial monophasic action potential (MAP) caused by various A1AdoR agonists. Studies will be carried out with guinea pig freshly isolated atrial myocytes and isolated perfused hearts. Activation of IKAdo and inhibition of beta-ICa,L by adenosine and A1AdoR agonists will be recorded by use of the whole cell patch-clamp technique. Shortening of the atrial MAP caused by adenosine and by A1AdoR agonists will be quantitated by standard electrophysiological methods. Although the main focus of this project is on receptor reserve, they will also investigate (Aim #4) whether the higher potency and potentially greater reserve for the anti beta-adrenergic action may confer tonic inhibition by endogenous adenosine of sympathetic activation of the heart in the anesthetized guinea pig. The hypothesis that endogenous adenosine exerts tonic inhibition of the cardiostimulatory effects of increased sympathetic neural activity will be tested by measuring the magnitude of reflex tachycardia caused by nitroprusside-induced hypotension, in the absence and presence of A1AdoR antagonists and of an allosteric enhancer of agonist binding to the A1AdoR. The studies will have important clinical implications for the design and use of A1AdoR agonists in the treatment of cardiac disease, and for the role for adenosine in regulation of cardiac function. The long-term goal of the studies is to understand mechanisms by which organ and/or response selectivity to A1AdoR agonists is achievable.