Neuregulin-1β Partially Improves Cardiac Function in Volume-Overload Heart Failure Through Regulation of Abnormal Calcium Handling

Figure 1. Schematic depiction of the animal study. Volume-overload heart failure (HF) was established in rats by aorta-caval fistula surgery. Sham-operated rats (SO group) received the same operation without the fistula. HF rats were confirmed at 8 weeks after surgery by echocardiographic measurement. HF rats were injected with NRG-1β (10 μg/kg·d) by intravenous injection via the tail vein for 7 days as previously reported. The rats in the HF group and the SO group were administered with the same dose of saline. All of the rats were maintained for 12 weeks. Echocardiographic and hemodynamic measurements measured cardiac function. Rats were sacrificed after the last measurement

Figure 2. Effects of NRG-1β on ICa-L in rat ventricular myocytes. (A) Stimulated protocol and original current recording. (B) I–V relationship of ICa-L. For obtaining the current-voltage (I–V) curves and steady-state activation curves, the holding potential was set at −40 mV, and ICa-L was elicited by a single pulse of 300 ms to +70 mV from the holding potential in 5-mV increments at 0.1 Hz. The current amplitude was normalized to the cell capacitance (current density, pA/pF).

Figure 3. Kinetics of ICa-L. (A) Steady-state activation curve of ICa-L. (B) Steady-state inactivation curve. (C) Biexponential recovery from inactivation of ICa-L. The cells were depolarized from −40 to 0 mV over 150 ms, and various interpulse (10–12,800 ms) were applied. NRG-1β did not affect the time dependence of ICa-L recovery from inactivation.

Figure 4. Expressions of calcium handling proteins. The confocal image showed fluorescein isothiocyanate (green)-labeled Cav1.2, SERCA2a, and NCX1 expressed in isolated rat cardiac ventricular myocytes in SO (left panel), HF (middle panel), and NRG group (right panel). Nuclei were stained with DAPI (blue). The scale bar represents 20 μm (n = 5 for each set of staining).

Figure 5. Quantitative analysis of calcium handling proteins expressions. (A) Representative expression of Cav1.2, SERCA2a, and NCX1, β-actin as loading controls. (B) Comparison of Cav1.2 protein expression (n = 3 rats). (C) Comparison of SERCA2a protein expression (n = 4 rats). (D) Comparison of NCX1 protein expression (n = 4 rats). *P < 0.05, **P < 0.01 vs. SO; # P < 0.05, ## P < 0.01 vs. HF.