Selective changes in cytosolic β-adrenergic cAMP signals and L-type Calcium Channel regulation by Phosphodiesterases during cardiac hypertrophy

Background In cardiomyocytes, phosphodiesterases (PDEs) type 3 and 4 are the predominant enzymes that degrade cAMP generated by beta-adrenergic receptors (beta-ARs), impacting notably the regulation of the L-type Ca2+ current (I-Ca,I-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,I-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 Forster resonance energy transfer (FRET)-based cAMP biosensor or subjected to the whole-cell configuration of the patch-clamp technique to measure I-Ca,I-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 similar to 50 s. In both groups, PDE4 inhibition with Ro 20-1724 (10 mu M) markedly potentiated the amplitude and slowed the decline of the cAMP transient, this latter effect being more pronounced in SHAM (t(1/)(2off )similar to 250 s) than in CH (t(1/)(2off )similar to 150 s, P < 0.01). In contrast, PDE3 inhibition with cilostamide (1 mu M) 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) similar to 80 s). Iso pulse stimulation also elicited a similar transient increase in I-Ca,I-L in SHAM and CH, although the duration of the rising phase was delayed in CH. Inhibition of PDE3 or PDE4 potentiated I-Ca,I-L amplitude in SHAM but not in CH. Besides, while only PDE4 inhibition slowed down the decline of I-Ca,I-L in SHAM, both PDE3 and PDE4 contributed in CH. Conclusion These results identify selective alterations in cytosolic cAMP and I-Ca,I-L regulation by PDE3 and PDE4 in CH, and show that the balance between PDE3 and PDE4 for the regulation of beta-AR responses is shifted toward PDE3 during CH.

Automated summary

In cardiomyocytes, PDE3 and PDE4 are the main enzymes that degrade cAMP generated by beta-ARs, affecting the regulation of I-Ca,I-L. Cardiac hypertrophy is associated with reduced PDE3 and PDE4, leading to selective alterations in the regulation of cAMP and I-Ca,I-L. The balance between PDE3 and PDE4 for beta-AR responses shifts towards PDE3 in CH.