Vinogradova Tatiana M, Lakatta Edward G
Laboratory of Cardiovascular Science, Gerontology Research Center, NIA, NIH, 5600 Nathan Shock Drive, Baltimore, MD 21224-6825, USA.
J Mol Cell Cardiol. 2009 Oct;47(4):456-74. doi: 10.1016/j.yjmcc.2009.06.014. Epub 2009 Jun 30.
Decades of intensive research of primary cardiac pacemaker, the sinoatrial node, have established potential roles of specific membrane channels in the generation of the diastolic depolarization, the major mechanism allowing sinoatrial node cells to generate spontaneous beating. During the last three decades, multiple studies made either in the isolated sinoatrial node or sinoatrial node cells have demonstrated a pivotal role of Ca(2+) and, specifically Ca(2+) release from sarcoplasmic reticulum, for spontaneous beating of cardiac pacemaker. Recently, spontaneous, rhythmic local subsarcolemmal Ca(2+) releases from ryanodine receptors during late half of the diastolic depolarization have been implicated as a vital factor in the generation of sinoatrial node cell spontaneous firing. Local Ca(2+) releases are driven by a unique combination of high basal cAMP production by adenylyl cyclases, high basal cAMP degradation by phosphodiesterases and a high level of cAMP-mediated PKA-dependent phosphorylation. These local Ca(2+) releases activate an inward Na(+)-Ca(2+) exchange current which accelerates the terminal diastolic depolarization rate and, thus, controls the spontaneous pacemaker firing. Both the basal primary pacemaker beating rate and its modulation via beta-adrenergic receptor stimulation appear to be critically dependent upon intact RyR function and local subsarcolemmal sarcoplasmic reticulum generated Ca(2+) releases. This review aspires to integrate the traditional viewpoint that has emphasized the supremacy of the ensemble of surface membrane ion channels in spontaneous firing of the primary cardiac pacemaker, and these novel perspectives of cAMP-mediated PKA-dependent Ca(2+) cycling in regulation of the heart pacemaker clock, both in the basal state and during beta-adrenergic receptor stimulation.
几十年来,针对心脏的主要起搏器——窦房结展开的深入研究,已确定了特定膜通道在舒张期去极化产生过程中的潜在作用,舒张期去极化是窦房结细胞产生自发搏动的主要机制。在过去三十年里,对分离的窦房结或窦房结细胞进行的多项研究表明,Ca(2+),特别是肌浆网释放的Ca(2+),对心脏起搏器的自发搏动起着关键作用。最近,在舒张期去极化后半段,来自兰尼碱受体的自发、有节律的局部肌膜下Ca(2+)释放,被认为是窦房结细胞自发放电产生的一个重要因素。局部Ca(2+)释放由腺苷酸环化酶产生的高基础cAMP、磷酸二酯酶对cAMP的高基础降解以及高水平的cAMP介导的PKA依赖性磷酸化的独特组合驱动。这些局部Ca(2+)释放激活内向Na(+)-Ca(2+)交换电流,加速终末舒张期去极化速率,从而控制自发起搏器放电。基础的主要起搏器搏动率及其通过β-肾上腺素能受体刺激的调节,似乎都严重依赖于完整的兰尼碱受体功能和局部肌膜下肌浆网产生的Ca(2+)释放。这篇综述旨在整合传统观点,即强调表面膜离子通道整体在心脏主要起搏器自发放电中的主导地位,以及cAMP介导的PKA依赖性Ca(2+)循环在基础状态和β-肾上腺素能受体刺激期间对心脏起搏器时钟调节的这些新观点。