The spontaneous rhythmic action potentials generated by the sinoatrial node (SAN), the primary pacemaker in the heart, dictate the regular and optimal cardiac contractions that pump blood around the body. Although the heart rate of humans is substantially slower than that of smaller experimental animals, current perspectives on the biophysical mechanisms underlying the automaticity of sinoatrial nodal pacemaker cells (SANCs) have been gleaned largely from studies of animal hearts. Using human SANCs, we demonstrated that spontaneous rhythmic local Ca²⁺ releases generated by a Ca²⁺ clock were coupled to electrogenic surface membrane molecules (the M clock) to trigger rhythmic action potentials, and that Ca²⁺–cAMP–protein kinase A (PKA) signaling regulated clock coupling. When these clocks became uncoupled, SANCs failed to generate spontaneous action potentials, showing a depolarized membrane potential and disorganized local Ca²⁺ releases that failed to activate the M clock. β-Adrenergic receptor (β-AR) stimulation, which increases cAMP concentrations and clock coupling in other species, restored spontaneous, rhythmic action potentials in some nonbeating “arrested” human SANCs by increasing intracellular Ca²⁺ concentrations and synchronizing diastolic local Ca²⁺ releases. When β-AR stimulation was withdrawn, the clocks again became uncoupled, and SANCs reverted to a nonbeating arrested state. Thus, automaticity of human pacemaker cells is driven by a coupled-clock system driven by Ca²⁺-cAMP-PKA signaling. Extreme clock uncoupling led to failure of spontaneous action potential generation, which was restored by recoupling of the clocks. Clock coupling and action potential firing in some of these arrested cells can be restored by β-AR stimulation–induced augmentation of Ca²⁺-cAMP-PKA signaling.

心脏的主要起搏器窦房结（SAN）产生的自发性节律性动作电位决定了将血液泵送到身体周围的规则和最佳的心脏收缩。尽管人的心率实质上比较小的实验动物慢，但目前对动物窦房结起搏器细胞（SANC）自动化的生物物理机制的看法已从动物心脏研究中大体上收集到。使用人类SANC，我们证明了由Ca ²⁺时钟产生的自发有节奏的局部Ca ²⁺释放与电表面膜分子（M时钟）耦合以触发有节奏的动作电位，并且Ca ²⁺–cAMP–蛋白激酶A（PKA）信号调节时钟耦合。当这些时钟断开耦合时，SANC无法产生自发的动作电位，显示出去极化的膜电位和混乱的局部Ca ²⁺释放，从而无法激活M时钟。β-肾上腺素能受体（β-AR）刺激增加了其他物种的cAMP浓度和时钟耦合，通过增加细胞内Ca ²⁺浓度并同步舒张局部Ca ²⁺，恢复了一些不搏动的“被捕”人SANC的自发性，节律性动作电位。发布。撤消β-AR刺激后，时钟再次断开，SANC恢复为无跳动的停滞状态。因此，人类起搏器细胞的自动化是由Ca ²⁺ -cAMP-PKA信号驱动的耦合时钟系统驱动的。极端的时钟解耦导致自发动作电位生成失败，通过重新耦合时钟将其恢复。通过β-AR刺激引起的Ca ²⁺ -cAMP-PKA信号增强，可以恢复其中一些停滞细胞的时钟耦合和动作电位激发。