Beat to beat Ca2+-dependent regulation of pacemaker cell rate and rhythm

起搏细胞速率和节律的逐搏 Ca2 依赖性调节

• 批准号: 8335874
• 负责人: Edward Lakatta
• 金额: $ 5.8万
• 依托单位: NATIONAL INSTITUTE ON AGING
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/8335874
• 关键词: Action Potentials; Buffers; Cells; Coupled; Egtazic Acid; Generations; Ion Channel; Membrane; Membrane Potentials; Regulation; Sarcoplasmic Reticulum; Sinoatrial Node; Surface; System; Testing; Time; base; flash photolysis; nodal myocyte; voltage

Normal automaticity in sinoatrial node cells (SANC) involves intracellular Ca2+ cycling within a coupled-clock system: periodic local, subsarcolemmal Ca2+ releases (LCRs) from sarcoplasmic reticulum (Ca2+ clock) activate an inward Na+-Ca2+ exchange current that accelerates the diastolic depolarization prompting the ensemble of surface membrane ion channels (membrane clock) to generate the next action potential (AP). Whether intracellular Ca2+ regulates SANC AP firing rate on a beat-to-beat basis is controversial. We loaded single isolated SANC with a caged Ca2+ buffer, NP-EGTA, and simultaneously recorded membrane potential and intracellular Ca2+. Prior to introduction of the caged Ca2+ buffer, spontaneous LCRs during diastolic depolarization (DD) were tightly coupled to rhythmic APs (r2=0.9). The buffer markedly prolonged the decay time (T50) of the AP-induced Ca2+ transient and partially depleted the SR load level, suppressed spontaneous diastolic LCRs and uncoupled them from AP generation, and caused AP firing to become markedly slow and dysrhythmic. When Ca2+ was acutely released from the caged compound by flash photolysis, intracellular Ca2+ dynamics were acutely restored and rhythmic APs resumed immediately at a normal rate. After a few rhythmic cycles, however, these effects of the flash waned as interference with Ca2+ dynamics by the caged buffer was reestablished. Our results directly support the hypothesis that a system of an intracellular Ca2+ clock coupled to a surface membrane voltage clock regulates normal SANC automaticity on a beat-to-beat basis.

窦房结细胞 (SANC) 的正常自动性涉及耦合时钟系统内的细胞内 Ca2+ 循环：肌浆网（Ca2+ 时钟）周期性局部肌膜下 Ca2+ 释放 (LCR) 激活向内的 Na+-Ca2+ 交换电流，加速​​舒张期去极化，促进表面膜离子通道的集合 （膜时钟）产生下一个动作电位（AP）。细胞内 Ca2+ 是否逐次调节 SANC AP 放电率尚存在争议。我们用笼式 Ca2+ 缓冲液 NP-EGTA 加载单个分离的 SANC，并同时记录膜电位和细胞内 Ca2+。在引入笼式 Ca2+ 缓冲液之前，舒张期去极化 (DD) 期间的自发 LCR 与节律性 AP 紧密耦合 (r2=0.9)。该缓冲液显着延长了 AP 诱导的 Ca2+ 瞬变的衰减时间 (T50)，并部分耗尽了 SR 负荷水平，抑制了自发舒张 LCR 并将其与 AP 生成分离，并导致 AP 放电变得明显缓慢且节律失调。当 Ca2+ 通过闪光光解从笼状化合物中急剧释放时，细胞内 Ca2+ 动力学急剧恢复，并且有节律的 AP 立即以正常速率恢复。然而，经过几个有节奏的循环后，随着笼式缓冲液对 Ca2+ 动力学的干扰重新建立，闪光的这些影响减弱了。我们的结果直接支持这样的假设：细胞内 Ca2+ 时钟与表面膜电压时钟耦合的系统在逐次心跳的基础上调节正常的 SANC 自动性。