Figure 3.

PDE8 co-localizes with LTCC. (A) Co-immunoprecipitation (Co-IP) assay followed by immunoblotting (IB) confirmed that with L-type Ca²⁺ channel (Cav1.2) binds to PDE8B, PKA_RII and PKA_C in human atria from patients with persistent (chronic) atrial fibrillation (cAF). NSB, non-specific binding. (B) Top, representative Co-IP and IB of Cav1.2 binding to PDE8B in human atrial samples from patients in sinus rhythm (SR), paroxysmal AF (pAF) and cAF. Bottom, mean data of PDE8B binding to Cav1.2 for all groups (n = 6 SR, n = 4 pAF, and 5 cAF patients). Lys, Lysate. Vertical white lines separate non-adjacent lanes on the same blot. (C) Representative western blot (left) and quantification (right, mean ± SEM) of relative steady-state LTCC phosphorylation (pSer1928/total Ca_v1.2) in atrial tissue homogenates from 6 SR and 6 cAF patients, at baseline and after 5 min stimulation with the selective PDE8 inhibitor PF-04957325 (30 nM) or the β-adrenoceptor agonist isoprenaline (ISO, 100 nM). GAPDH was used as loading control. *P < 0.05 based on ANOVA with a Kruskal–Wallis test.