Danson E J F, Zhang Y H, Sears C E, Edwards A R, Casadei B, Paterson D J
University Laboratory of Physiology, Parks Road, Oxford, OX1 3PT, UK.
Cardiovasc Res. 2005 Sep 1;67(4):613-23. doi: 10.1016/j.cardiores.2005.04.034.
Cardiac parasympathetic nerve activity is reduced in most cardiovascular disease states, and this may contribute to enhanced cardiac sympathetic responsiveness. Disruption of inhibitory G-proteins (Gi) ablates the cholinergic pathway and increases cardiac endothelial nitric oxide (NO) synthase (eNOS) expression, suggesting that NO may offset the impaired attenuation of beta-adrenergic regulation of supraventricular excitability. To test this, we investigated the role of endogenous NO production on beta-adrenergic regulation of rate (HR), contraction (CR) and calcium (Ca2+) handling in atria following blockade of Gi-coupled muscarinic receptors.
Mice were administered pertussis toxin (PTx, n=105) or saline (C, n=100) intraperitoneally. After 3 days, we measured CR, HR, and NOS protein levels in isolated atria. Intracellular calcium (Ca2+) transients and Ca2+ current density (I(Ca)) were also measured in atrial myocytes.
PTx treatment increased atrial myocyte eNOS protein levels compared to C (P<0.05). This did not affect basal atrial function but was associated with a significant reduction in the CR and HR response to isoprenaline (ISO) compared with C. NOS inhibition normalized responses in PTx atria with respect to responses in C atria (P<0.05), which were unaffected. Furthermore, PTx did not affect ISO-stimulated HR and CR in eNOS gene knockout mice (n=40). In agreement with these findings, the ISO-mediated increase in Ca2+ transient was suppressed in PTx-treated myocytes (P<0.05), whereas I(Ca) did not differ between groups.
eNOS-derived NO inhibits beta-adrenergic responses following disruption of Gi signaling. This suggests that increased eNOS expression may be a compensatory mechanism which reduces beta-adrenergic regulation of heart rate when cardiac parasympathetic control is impaired.
在大多数心血管疾病状态下，心脏副交感神经活动会降低，这可能会导致心脏交感反应性增强。抑制性G蛋白（Gi）的破坏会消除胆碱能途径并增加心脏内皮一氧化氮（NO）合酶（eNOS）的表达，这表明NO可能会抵消β-肾上腺素能对室上性兴奋性调节的减弱。为了验证这一点，我们研究了内源性NO生成在Gi偶联的毒蕈碱受体被阻断后对心房率（HR）、收缩（CR）和钙（Ca2+）处理的β-肾上腺素能调节中的作用。
给小鼠腹腔注射百日咳毒素（PTx，n = 105）或生理盐水（C，n = 100）。3天后，我们测量了分离心房中的CR、HR和NOS蛋白水平。还测量了心房肌细胞内的钙（Ca2+）瞬变和Ca2+电流密度（I(Ca)）。
与C组相比，PTx处理增加了心房肌细胞eNOS蛋白水平（P<0.05）。这并未影响基础心房功能，但与C组相比，对异丙肾上腺素（ISO）的CR和HR反应显著降低有关。NOS抑制使PTx心房中的反应相对于C心房中的反应恢复正常（P<0.05），而C心房中的反应未受影响。此外，PTx对eNOS基因敲除小鼠（n = 40）的ISO刺激的HR和CR没有影响。与这些发现一致，PTx处理的心肌细胞中ISO介导的Ca2+瞬变增加受到抑制（P<0.05），而各组之间的I(Ca)没有差异。
eNOS衍生的NO在Gi信号破坏后抑制β-肾上腺素能反应。这表明eNOS表达增加可能是一种补偿机制，当心脏副交感神经控制受损时，可减少β-肾上腺素能对心率的调节。
