Background In cardiomyocytes, phosphodiesterases (PDEs) type 3 and 4 are the predominant enzymes that degrade cAMP generated by β-adrenergic receptors (β-ARs), impacting notably the regulation of the L-type Ca²⁺ current (I_Ca,L). Cardiac hypertrophy (CH) is accompanied by a reduction in PDE3 and PDE4, however, whether this affects the dynamic regulation of cytosolic cAMP and I_Ca,L is not known.

Methods and Results CH was induced in rats by thoracic aortic banding over a time period of five weeks and was confirmed by anatomical measurements. Left ventricular myocytes (LVMs) were isolated from CH and sham-operated (SHAM) rats and transduced with an adenovirus encoding a Förster resonance energy transfer (FRET)-based cAMP biosensor or subjected to the whole-cell configuration of the patch-clamp technique to measure I_Ca,L. Aortic stenosis resulted in a 46% increase in heart weight to body weight ratio in CH compared to SHAM. In SHAM and CH LVMs, a short isoprenaline stimulation (Iso, 100 nM, 15 s) elicited a similar transient increase in cAMP with a half decay time (t_1/2off) of ~50 s. In both groups, PDE4 inhibition with Ro-201,724 (10 μM) markedly potentiated the amplitude and slowed the decline of the cAMP transient, this latter effect being more pronounced in SHAM (t_1/2off ~ 250 s) than in CH (t_1/2off ~ 150 s, P < 0.01). In contrast, PDE3 inhibition with cilostamide (1 μM) had no effect on the amplitude of the cAMP transient and a minimal effect on its recovery in SHAM, whereas it potentiated the amplitude and slowed the decay in CH (t_1/2off ~ 80 s). Iso pulse stimulation also elicited a similar transient increase in I_Ca,L in SHAM and CH, although the duration of the rising phase was delayed in CH. Inhibition of PDE3 or PDE4 potentiated I_Ca,L amplitude in SHAM but not in CH. Besides, while only PDE4 inhibition slowed down the decline of I_Ca,L in SHAM, both PDE3 and PDE4 contributed in CH.

Conclusion These results identify selective alterations in cytosolic cAMP and I_Ca,L regulation by PDE3 and PDE4 in CH, and show that the balance between PDE3 and PDE4 for the regulation of β-AR responses is shifted toward PDE3 during CH.

背景在心肌细胞中，3 型和 4 型磷酸二酯酶 (PDE) 是降解 β-肾上腺素能受体 (β-AR) 产生的 cAMP 的主要酶，显着影响 L 型 Ca ²⁺电流 ( I _Ca,L )的调节. 心脏肥大 (CH) 伴随着 PDE3 和 PDE4 的减少，然而，这是否影响胞质 cAMP 和I _Ca,L的动态调节尚不清楚。

方法和结果在大鼠中通过胸主动脉束带在五周的时间内诱导 CH，并通过解剖测量证实。从 CH 和假手术 (SHAM) 大鼠中分离出左心室肌细胞 (LVM)，并用编码基于 Förster 共振能量转移 (FRET) 的 cAMP 生物传感器的腺病毒进行转导或进行膜片钳技术的全细胞配置测量I _Ca,L。与 SHAM 相比，主动脉瓣狭窄导致 CH 中心脏重量与体重之比增加 46%。在 SHAM 和 CH LVM 中，短暂的异丙肾上腺素刺激（Iso，100 nM，15 s）引起 cAMP 类似的瞬时增加，半衰期时间（t _1/2off) 约 50 秒。在两组中，PDE4 用 Ro-201,724 (10 μM) 抑制显着增强了振幅并减缓了 cAMP 瞬变的下降，后一种效应在 SHAM (t _1/2off  ~ 250 s) 中比 CH (t _{1 /2off}  ~ 150 秒，P  < 0.01）。相比之下，西洛他胺 (1 μM) 抑制 PDE3 对 cAMP 瞬变的幅度没有影响，对其在 SHAM 中的恢复影响很小，而它增强了幅度并减缓了 CH 的衰减 (t _1/2off  ~ 80 s ）。Iso 脉冲刺激也引起了类似的瞬态I _{Ca, L}在 SHAM 和 CH 中的增加，尽管上升阶段的持续时间在 CH 中被延迟。PDE3 或 PDE4 的抑制增强了I假手术中的_Ca,L振幅但 CH 中没有。此外，虽然只有 PDE4 抑制减缓了SHAM中I _Ca,L的下降，但 PDE3 和 PDE4 都对 CH 有贡献。

结论这些结果确定了 CH 中 PDE3 和 PDE4对细胞溶质 cAMP 和I _Ca,L调节的选择性改变，并表明 PDE3 和 PDE4 之间用于调节 β-AR 反应的平衡在 CH 期间向 PDE3 转移。