The Effects of SEA0400 on Ca2+ Transient Amplitude and Proarrhythmia Depend on the Na+/Ca2+ Exchanger Expression Level in Murine Models

Figures

• 

  Figure 1. SEA0400 mediated NCX forward mode inhibition in caffeine application experiments. Representative tracings of caffeine-induced Ca2+ transients illustrate the different decay rates in OE (A), hetKO (C) and respective WTs as a direct measure of NCX-mediated Ca2+ removal under basal conditions and during NCX inhibition by SEA0400. Quantification of time to 50% decay (T50) of caffeine-induced Ca2+ transients confirmed increased NCX forward mode function in OE (B) and decreased in hetKO (D), and verified NCX forward mode inhibition by SEA0400 in all investigated groups but to different levels. *p < 0.05 vs. basal; +p < 0.05 OE/hetKO vs. WTOE/WThetKO basal; ANOVA on ranks test.

• 

  Figure 2. Relative effect of increasing SEA0400 concentrations on the amplitude of field stimulated Ca2+ transients as a measure for inotropy. SEA0400 mediated a significant relative increase of the Ca2+ transient amplitude vs. basal in WTOE (A), WThetKO and hetKO (B), but not in OE (A). Thus, the effect of SEA0400 on the Ca2+ transient amplitude seems to depend on the respective NCX expression level. *p < 0.05 vs. basal; two-way repeated measures ANOVA test.

• 

  Figure 3. Quantification of spontaneous Ca2+ releases (sCR) as a measure for proarrhythmia. (A) Representative tracings illustrate the occurrence of numerous sCR (arrows below respective tracings) between field-stimulated Ca2+ transients (stim, arrows above respective tracings) in OE but not in hetKO in absence of SEA0400. (B) Quantification of sCR/cell under basal conditions and during exposure with 1 μM SEA0400. (C) Number of sCR-positive cardiomyocytes under basal conditions and during exposure with 1 μM SEA0400. SEA0400 significantly reduced the occurrence of sCR/cell in OE. Conversely, in hetKO SEA0400 increased the occurrence of sCR. Hence, the effect of SEA0400 on the occurrence of proarrhythmic spontaneous Ca2+ transients again depends on the NCX expression level. *p < 0.05 vs. basal; +p < 0.05 vs. corresponding WT basal; two-way repeated measures ANOVA test; z-test.

• 

  Figure 4. Quantification of Ca2+ hypercontractions as a measure for proarrhythmia. In a fraction of cardiomyocytes application of 1 μM SEA0400 caused a sudden increase of the diastolic Ca2+ level with highly frequent contractions and subsequent cell death (“Ca2+ hypercontraction”) (B) as illustrated by the representative tracing in (A). The proportion of cells with Ca2+ hypercontractions was significantly increased only in the hetKO group. *p < 0.05 vs. basal; +p < 0.05 vs. WT; Fisher's exact test with R.