Fig. 4.

BB improved RV myocyte contraction-frequency relationship. A Representative traces of Ca²⁺ transients at different stimulation frequencies. B Ca²⁺ transient amplitude of RV myocytes field stimulated at 1 Hz was greater in MCT than CON and MCT + BB. C The Ca²⁺ transient amplitude remained stable in CON cells as pacing frequency was increased, whereas it progressively declined in MCT. Ca²⁺ transient amplitude was greater in MCT + BB than MCT at 7 Hz. The number of cells that could be paced at 7 Hz is shown. D Representative traces of unloaded sarcomere shortening in a separate group of cells without Fura-4 at different stimulation frequencies. E Shortening at 1 Hz was not different between groups. F Changes in sarcomere shortening with increased stimulation frequency reflected the changes in Ca²⁺ transient amplitude. Shortening in MCT + BB cells was greater than MCT at 7 Hz. G Example recording of a MCT cell unable to regularly pace at 7 Hz due to the emergence of Ca²⁺ release (upper panel) and sarcomere shortening (lower panel) alternans. H,I Representative Western blots of SERCA2a, PLN and GAPDH. Note difference in group orders between blots (upper panels) and data (lower panels). H There was a reduction in protein expression of SERCA2a in MCT RV that was partially restored by BB. I There was a reduction in protein expression of PLN in the RV of MCT and MCT + BB hearts. N = 6 rats per group. B,E,H,I one-way ANOVA, C,F two-way ANOVA. *P < .05, **P < .01 vs CON, †P < .05 vs MCT + BB.