Figure 1. Na⁺_i overload induces Ca²⁺_i mishandling and ROS generation in adult rabbit cardiomyocytes.

A. Activation of I_NaL by Anemone toxin (ATX-II) in rabbit ventricular myocytes, i) representative recordings of I_NaL in the absance of drug (control) and after superfusion with 5 nM ATX-II. ii) Mean values of I_NaL decay time in control (n=4) and after superfusion with 5 nM ATX-II (n=4). B.) Confocal images of a rabbit ventricular myocyte paced at 1 Hz and loaded with Na⁺ dye Asante NaTRIUM Green AM. Application of ATX-II for 2 min increased cytosolic Na⁺ compared to control (Ctrl), which was reversed by ranolazine (RAN, 10 μM). ii) Cytosolic ROS, measured using DCFDA, was increased in response to ATX-II, and was also reduced by treatment with RAN. iii) Line-scan recordings of Ca²⁺ transients using the dye Fluo-4 AM. ATX-II increased spontaneous Ca²⁺ release and increased diastolic Ca²⁺ level (shown in blue under each Ca²⁺ transient profile). ATX-II effects on Ca²⁺ transients were reversed by RAN. C. Quantification of results for ATX-ll-induced changes in i) cytosolic Na⁺, ii) cytosolic ROS level, and iii) diastolic Ca²⁺ levels in the absence and presence of RAN (10 μM), TTX (1 μM) and GS-967 (1 μM). Data are normalized to F₀ - the baseline fluorescence signal at the beginning of an experiment. N=3-14, * p<0.05 vs control; † P<0.05 vs ATX-II.