Bay 60-7550, a PDE2 inhibitor, exerts positive inotropic effect of rat heart by increasing PKA-mediated phosphorylation of phospholamban.

This study investigated the hemodynamic effect of Bay 60-7550, a phosphodiesterase type 2 (PDE2) inhibitor, in healthy rat hearts both in vivo and ex vivo and its underlying mechanisms. In vivo rat left ventricular pressure-volume loop, Langendorff isolated rat heart, Ca2+ transient of left ventricular myocyte and Western blot experiments were used in this study. The results demonstrated that Bay 60-7550 (1.5 mg/kg, i. p.) increased the in vivo rat heart contractility by enhancing stroke work, cardiac output, stroke volume, end-diastolic volume, heart rate, and ejection fraction. The simultaneous aortic pressure recording indicated that the systolic blood pressure was increased and diastolic blood pressure was decreased by Bay 60-7550. Also, the arterial elastance which is proportional to the peripheral vessel resistance was significantly decreased. Bay 60-7550 (0.001, 0.01, 0.1, 1 µmol/l) also enhanced the left ventricular development pressure in non-paced and paced modes with a decrease of heart rate in non-paced model. Bay 60-7550 (1 µmol/l) increased SERCA2a activity and SR Ca2+ content and reduced SR Ca2+ leak rate. Furthermore, Bay 60-7550 (0.1 µmol/l) increased the phosphorylation of phospholamban at 16-serine without significantly changing the phosphorylation levels of phospholamban at 17-threonine and RyR2. Bay 60-7550 increased the rat heart contractility and reduced peripheral arterial resistance may be mediated by increasing the phosphorylation of phospholamban and dilating peripheral vessels. PDE2 inhibitors which result in a positive inotropic effect and a decrease in peripheral resistance might serve as a target for developing agents for the treatment of heart failure in clinical settings.

[Positive inotropic effect of phosphodiesterase type 9 inhibitor PF-04449613 in rats and its underlying mechanism].

This study aimed to explore the positive inotropic effect of phosphodiesterase type 9 (PDE9) inhibitor PF-04449613 in ratsand its cellular and molecular mechanisms. The heart pressure-volume loop (P-V loop) analysis was used to detect the effects of PF-04449613 on rat left ventricular pressure-volume relationship, aortic pressures and peripheral vessel resistance in healthy rats. The Langendorff perfusion of isolated rat heart was used to explore the effects of PF-04449613 on heart contractility. The cardiomyocyte sarcoplasmic reticulum (SR) Ca2+ transients induced by field stimulation and caffeine were used to analyze the mechanism underlying the effect of PF-04449613 using Fluo-4 AM as a Ca2+ indicator. The results indicated as follows: (1) PF-04449613 (5.5 mg/kg, ip) significantly increased the stroke work, cardiac output, stroke volume, end-systolic pressure and ejection fraction (P < 0.05), and decreased the end-systolic volume, end-diastolic volume and end-diastolic pressure (P < 0.05). Meanwhile, the systolic blood pressure was increased and diastolic blood pressure and arterial elastance were decreased after PF-04449613 treatment (P < 0.05). (2) PF-04449613 (0.001, 0.01, 0.1, 1 µmol/L) significantly increased the left ventricular developed pressure (LVDP) in a concentration-dependent manner in vitro (P < 0.05). (3) PF-04449613 (5 µmol/L) significantly increased the amplitude of SR Ca2+ transients mediated by facilitating sarcoplasmic reticulum Ca2+-ATPase-2a (SERCA2a) (P < 0.05). (4) PF-04449613 (5 µmol/L) decreased the SR Ca2+ leak rate via ryanodine receptor 2 (RyR2) (P < 0.05). In conclusion, PF-04449613 exerted positive inotropic effect both in vivo and in vitro by enhancing SERCA2a activity.

[Positive inotropic effect of atractylodin in normal rats and its underlying mechanism].

Objective: To explore the positive inotropic effect of atractylodin which is major active component of Rhzoma Atractylodis Lanceae and its underlying mechanism. Methods: For in vivo study, six male SD rats were randomly selected for the heart pressure-volume loop (P-V loop) experiment. The effects of atractylodin (3 mg/kg, intraperitoneal injection) on hemodynamic parameters such as LVDP (left ventricular developed pressure), SW (stroke work), HR (heart rate), CO (cardiac output), SBP (systolic blood pressure) and DBP (diastolic blood pressure) were analyzed. For in vitro study, left ventricular developed pressure (LVDP) from the Langendroff-perfused isolated rat heart was analyzed before as the control and after atractylodin perfusion. For in vitro study, the effects of atractylodin and atractylodin with H89 (PKA inhibitor) or KN-93 (CaMKII inhibitor or Calyculin A (PP1, PP2A inhibitor) on LVDP were analyzed. The experiments were separated into four parts with six isolated hearts for each as follows: (1) Control→0.1→1→10 µmol/L atractylodin; (2) Control→200 nmol/L H89 (PKA inhibitor)→200 nmol/L H89+10 µmol/L atractylodin; (3) Control→500 nmol/L KN-93 (CaMKII inhibitor)→500 nmol/L KN-93+10 µmol/L atractylodin; (4) Control→10 nmol/L Calyculin A (PP1, PP2A inhibitor)→10 nmol/L Calyculin A+10 µmol/L atractylodin. For the study of rat left ventricular myocyte Ca2+ transient induced by field stimulation, the experiment design was the same as in vitro study. The six cells from the different rats were used for each part experiment. Results: ① Atractylodin (3 mg/kg) significantly increased the heart rate, cardiac output and stroke work (P＜0.05) and decreased the diastolic blood pressure (P＜0.05). ② Atractylodin (0.1, 1, 10 µmol/L) significantly increased the LVDP in a concentration dependent manner (P＜0.05). The positive inotropic effect of atractylodin could be blocked by PKA inhibitor H89. ③ Atractylodin (10 µmol/L) significantly increased the amplitude of SR Ca2+ transient amplitude mediated by facilitating sarcoplasmic reticulum SERCA2a. The enhanced amplitude of SR Ca2+ transient could be blocked by PKA inhibitor H89. Conclusion: Atractylodin had positive inotropic effect in rat heart both in vivo and in vitro with decreased diastolic blood pressure and its underlying mechanism was mediated by PKA. Based on the fact that the atractylodin exerted its positive inotropic effect was mediated by PKA, the PKA-SERCA2a signaling pathway might be the mechanism of the atractylodin's positive inotropy.