Johns Hopkins Medical Institutions, Baltimore, MD 21287, USA.
Anesth Analg. 2010 Oct;111(4):870-7. doi: 10.1213/ANE.0b013e3181ee8312. Epub 2010 Aug 12.
Emerging evidence suggests that phosphoinositide 3-kinase (PI3K) may modulate cardiac inotropy; however, the underlying mechanism remains elusive. We hypothesized that β(2)-adrenergic receptor (AR)-coupled PI3K constrains increases in cardiac inotropy through cyclic adenosine monophosphate (cAMP)-dependent phosphodiesterase (PDE) activation.
We tested the effects of PI3K and PDE4 inhibition on myocardial contractility by using isolated murine cardiac myocytes to study physiologic functions (sarcomere shortening [SS] and intracellular Ca(+) transients), as well as cAMP and PDE activity.
PI3K inhibition with the reversible inhibitor LY294002 (LY) resulted in a significant increase in SS and Ca(2+) handling, indicating enhanced contractility. This response depended on G(iα) protein activity, because incubation with pertussis toxin (an irreversible G(iα) inhibitor) abolished the LY-induced hypercontractility. In addition, PI3K inhibition had no greater effect on SS than both a PDE3,4 inhibitor (milrinone) and LY combined. Furthermore, LY decreased PDE4 activity in a concentration-dependent manner (58.0% of PDE4 activity at LY concentrations of 10 μM). Notably, PI3K(γ) coimmunoprecipitated with PDE4D. The β(2)-AR inverse agonist, ICI 118,551 (ICI), abolished induced increases in contractility.
PI3K modulates myocardial contractility by a cAMP-dependent mechanism through the regulation of the catalytic activity of PDE4. Furthermore, basal agonist-independent activity of the β(2)-AR and its resultant cAMP production and enhancement of the catalytic activity of PDE4 through PI3K represents an example of integrative cellular signaling, which controls cAMP dynamics and thereby contractility in the cardiac myocyte. These results help to explain the mechanism by which milrinone is able to increase myocardial contractility in the absence of direct β-adrenergic stimulation and why it can further augment contractility in the presence of maximal β-adrenergic stimulation.
新出现的证据表明，磷酸肌醇 3-激酶（PI3K）可能调节心肌变力性；然而，其潜在的机制仍不清楚。我们假设β（2）-肾上腺素能受体（AR）偶联的 PI3K 通过环腺苷单磷酸（cAMP）依赖性磷酸二酯酶（PDE）的激活来限制心肌变力性的增加。
我们使用分离的鼠心肌细胞研究生理功能（肌节缩短[SS]和细胞内 Ca（2+）瞬变）以及 cAMP 和 PDE 活性，来检测 PI3K 和 PDE4 抑制对心肌收缩力的影响。
可逆抑制剂 LY294002（LY）抑制 PI3K 导致 SS 和 Ca（2+）处理显著增加，表明收缩力增强。该反应取决于 G（iα）蛋白的活性，因为用百日咳毒素（一种不可逆的 G（iα）抑制剂）孵育消除了 LY 诱导的超收缩力。此外，PI3K 抑制对 SS 的作用并不比 PDE3、4 抑制剂（米力农）和 LY 的组合更强。此外，LY 以浓度依赖性方式降低 PDE4 活性（LY 浓度为 10 μM 时 PDE4 活性为 58.0％）。值得注意的是，PI3K（γ）与 PDE4D 共免疫沉淀。β（2）-AR 反向激动剂 ICI 118,551（ICI）消除了诱导的收缩力增加。
PI3K 通过调节 PDE4 的催化活性通过 cAMP 依赖性机制调节心肌收缩力。此外，β（2）-AR 的基础激动剂非依赖性活性及其随后通过 PI3K 产生的 cAMP 产生和增强 PDE4 的催化活性代表了一种整合细胞信号传导的范例，其控制 cAMP 动力学，从而控制心肌细胞的收缩力。这些结果有助于解释米力农能够在没有直接β-肾上腺素能刺激的情况下增加心肌收缩力的机制，以及为什么它在存在最大β-肾上腺素能刺激的情况下能够进一步增强收缩力。
