Figure 2.

Polyarginine CPPs inhibit Ca²⁺ uptake in SR vesicles isolated from mouse ventricles. (A) Ca²⁺ homeostasis was examined in untreated mouse ventricular homogenates (Ctr) compared with homogenates incubated with TAT, Arg₉, or Arg₁₁ in the presence or absence of the indicated, scrambled cargo. (B) Oxalate-supported Ca²⁺ uptake was assessed by monitoring the Fura-2 salt fluorescence ratio (340/390) in the test buffer upon addition of Na₄ATP. SR Ca²⁺ leak was measured as the increase in slope upon the addition of thapsigargin (Thapsi). Application of the ryanodine receptor opener CmC was employed to assess SR Ca²⁺ content, i.e., the releasable [Ca²⁺], and these values were used to normalize leak measurements. Representative Ca²⁺ recordings in the absence of cargo are presented in the left panel, with mean measurements presented in the remaining panels. (C) Equivalent data obtained in mouse ventricles incubated with Arg₉-cargo or Arg₁₁-cargo. Data are presented as mean ± SEM. Statistical analyses were performed by one-way ANOVA with Tukey’s post hoc correction. p values are indicated versus Ctr. NS = not statistically significant. n_runs in Ctr, TAT, Arg₉, Arg₁₁ = 69, 14, 23, 24; n_runs in Ctr, Arg₉-cargo, Arg₁₁-cargo = 60, 10, 10 in homogenates from 9 hearts.