FIG. 4.

Ca²⁺ signaling components in VAChT KD^HOM hearts. In panels A to D, the top image is a representative Western blot and the bottom shows an average densitometry graph (n, number of heart samples analyzed). (A) SERCA2 levels in VAChT KD^HOM hearts were observed to be significantly reduced compared to levels in WT hearts. Phosphorylated-PLN levels at the protein kinase A (PKA)-dependent site (Ser-16) were lower in VAChT mutant hearts (B), while phospho-Thr-17-PLN levels were increased in these hearts (C). (D) Phospho-Ser-23/24-troponin I levels were decreased in VAChT mutant hearts relative to WT hearts. Tubulin expression levels were used as a loading control. (E) The SR Ca²⁺ content in ventricular cardiomyocytes from VAChT mutants was significantly reduced compared to that in WT cells. n, number of cells. (F) Ca²⁺ spark frequency showed a tendency to be lower in VAChT KD^HOM cardiomyocytes than in WT mice, but the difference was not statistically different. n, number of cells. *, P < 0.05.