Figure 4. Sarcoplasmic reticular (SR) Ca²⁺ uptake activity in cardiomyocyte homogenates after amiR155-PLBr- and shPLBr-mediated PLB silencing.

(A) Ca²⁺ dependence of the cell homogenate oxalate-supported SR Ca²⁺ uptake rate at day 14 after transduction with either scAAV6-amiR155-PLBr (amiR155-PLBr) or scAAV6-amiR155-Con (amiR155-Con) vectors. Reticular Ca²⁺ transport was measured as oxalate-facilitated Ca²⁺ uptake. Rate values are means of two different transduction experiments with primary cultured CM (50x10³ vg/c). Respective rate values were obtained by linear regression analysis of Ca²⁺ uptake data obtained 1, 2, and 3 min after initiation of the reaction. (B) SR Ca²⁺ uptake rates as a function of time after transduction with 25−50×10³ vg/c of either scAAV6-amiR155-PLBr (amiR155-PLBr) or scAAV6-amiR155-Con (amiR155-Con) vectors. (C) SR Ca²⁺ uptake rates as a function of time after transduction with 25−50×10³ vg/c of either scAAV6-shPLBr (shPLBr) or scAAV6-shCon (shCon). For B and C, cells were harvested at indicated time points post transduction and initial oxalate-facilitated Ca²⁺ uptake rates were determined at both submicromolar (0.34 μM) and saturating (3.68 μM) free Ca²⁺ concentrations. The shown relative rate values at submicromolar Ca²⁺ in B and C were obtained by normalization of the rate value at 0.34 μM Ca²⁺ to the respective maximum uptake rate values measured at a saturating Ca²⁺ concentration of 3.68 μM. Values in B and C are means ± SEM for 2 to 6 different cell experiments as indicated in parenthesis, *p<0.05 vs. respective control vector. The column labeled no add contains nontransduced cells.