Fig. 2.

Tbx5 modulates SERCA2 expression. (A) Western blots showing decreased levels of SERCA2 protein in Tbx5^del/+ and Tbx5^Vdel/+ ventricular extracts. Normal levels of Ncx1, RyR2, and PLN were found in all genotypes. (B) Quantitative RT-PCR demonstrating decreased Tbx5 and Atp2a2 mRNA levels in Tbx5^del/+ and Tbx5^Vdel/+ ventricular extracts (n = 6 for each genotype; means ± SEMs are shown). *, P < 0.05; **, P < 0.01. (C) Ca²⁺ uptake in ventricular tissues demonstrating impaired Ca²⁺ uptake in Tbx5^del/+ and Tbx5^Vdel/+ mice and restoration to WT levels in Tbx5^Vdel/+;PLN^−/− mice. (D) Intracellular Ca²⁺ transients. (Upper) Representative Ca²⁺ transient recordings obtained from control and Tbx5^Vdel/+ cardiomyocytes under field stimulation at 1 Hz (35.5 ± 0.5°C) and loaded with indo 1-AM. ΔR stands forΔR_405/495, the ratio of the intensity of fluorescence emitted at 405 nm to that at 495 nm, which is used as an index of intracellular Ca²⁺ concentrations in this study. (Lower) Mean data of Ca²⁺-transient amplitude (ΔR_405/495) and time constant (τ) of Ca²⁺ transient decay (in milliseconds) obtained from myocytes isolated from control (n = 41 cells) and Tbx5^Vdel/+ (n = 43 cells) mice. (E) Luciferase reporter assay shows dosage-dependent activation of Atp2a2-luciferase. Expression vectors: +, 100 ng; ++, 250 ng; +++, 500 ng.