Constitutive phosphodiesterase activity restricts spontaneous beating rate of cardiac pacemaker cells by suppressing local Ca2+ releases
Constitutive phosphodiesterase activity restricts spontaneous beating rate of cardiac pacemaker cells by suppressing local Ca2+ releases
复制标题
DOI：
10.1161/circresaha.107.161679
复制
发表时间：
2008-04-11
影响因子：
20.1
通讯作者：
Lakatta, Edward G.
中科院分区：
文献类型：
--
作者：
Vinogradova, Tatiana M.;Sirenko, Syevda;Lakatta, Edward G.
兔窦房结细胞（SANC）的自发性搏动受cAMP介导的蛋白激酶A依赖的局部肌膜下兰尼碱受体（LCRs）的Ca ~（2+）释放控制。LCR激活了内向Na+/Ca 2+交换电流，增加了舒张末期去极化率，因此，增加了自发SANC搏动率。SANC中的基础cAMP升高，表明磷酸二酯酶（PDE）对cAMP的降解可能较低。令人惊讶的是，用广谱PDE抑制剂3 '-异丁基甲基黄嘌呤（IBMX）完全抑制PDE活性，使cAMP水平增加9倍，使cAMP介导的蛋白激酶A依赖性受磷蛋白磷酸化加倍，并使SANC放电速率增加约55%，表明SANC中PDE的高基础活性。特异性PDE 1与PDE 5抑制剂的比较显示，特异性PDE 3抑制剂米力农使自发放电加速约47%（其他抑制剂的影响较小），并使L型钙电流（I-Ca，I-L）的振幅增加约46%，表明PDE 3是基础状态下主要的组成性活性PDE。PDE依赖性控制SANC自发放电主要依赖于肌膜下LCR，即PDE抑制可增加LCR幅度和大小，缩短LCR周期，导致LCR Ca 2+释放、Na+/Ca 2+交换电流和放电率增加。当Ryanodine受体被Ryanodine抑制时，IBMX和米力农都不能放大LCR，加速舒张期去极化速率，或增加SANC放电速率，尽管保留了PDE抑制诱导的I-Ca，I-L振幅的增加。因此，基础组成型PDE激活提供了一种新的和强大的机制，以减少cAMP，限制cAMP介导的，蛋白激酶A依赖性增加舒张期兰尼碱受体Ca 2+释放，并限制自发SANC搏动率。
Spontaneous beating of rabbit sinoatrial node cells (SANCs) is controlled by cAMP-mediated, protein kinase A-dependent local subsarcolemmal ryanodine receptor Ca2+ releases (LCRs). LCRs activated an inward Na+/Ca2+ exchange current that increases the terminal diastolic depolarization rate and, therefore, the spontaneous SANC beating rate. Basal cAMP in SANCs is elevated, suggesting that cAMP degradation by phosphodiesterases (PDEs) may be low. Surprisingly, total suppression of PDE activity with a broad-spectrum PDE inhibitor, 3'-isobutylmethylxanthine (IBMX), produced a 9-fold increase in the cAMP level, doubled cAMP-mediated, protein kinase A-dependent phospholamban phosphorylation, and increased SANC firing rate by approximate to 55%, indicating a high basal activity of PDEs in SANCs. A comparison of specific PDE1 to -5 inhibitors revealed that the specific PDE3 inhibitor, milrinone, accelerated spontaneous firing by approximate to 47% (effects of others were minor) and increased amplitude of L-type Ca2+ current (I-Ca,I-L) by approximate to 46%, indicating that PDE3 was the major constitutively active PDE in the basal state. PDE-dependent control of the spontaneous SANC firing was critically dependent on subsarcolemmal LCRs, ie, PDE inhibition increased LCR amplitude and size and decreased LCR period, leading to earlier and augmented LCR Ca2+ release, Na+/Ca2+ exchange current, and an increase in the firing rate. When ryanodine receptors were disabled by ryanodine, neither IBMX nor milrinone was able to amplify LCRs, accelerate diastolic depolarization rate, or increase the SANC firing rate, despite preserved PDE inhibition-induced augmentation of I-Ca,I-L amplitude. Thus, basal constitutive PDE activation provides a novel and powerful mechanism to decrease cAMP, limit cAMP-mediated, protein kinase A-dependent increase of diastolic ryanodine receptor Ca2+ release, and restrict the spontaneous SANC beating rate.