Figure 1.

Efsevin Reduces Diastolic Ca²⁺ Waves and Spontaneous Action Potentials in RyR2^R4496C/WT Cardiomyocytes

(A) Confocal line scans across the long axis of freshly isolated cardiomyocytes from wild-type and RyR2^R4496C/WT mice loaded with Fluo-4 AM to measure intracellular Ca²⁺. Images show line scans, and graphs depict fluorescence intensity plots. Cells were stimulated at 0.5 Hz for 30 s to reach steady state conditions (last 5 Ca²⁺ transients are shown) before pulsing was stopped and the diastolic phase was recorded for 90 s to screen for spontaneous diastolic Ca²⁺ waves. (B) While wild-type cells never showed a significant frequency of spontaneous diastolic Ca²⁺ waves, 25 of 68 RyR2^R4496C/WT cardiomyocytes showed waves, which could be significantly reduced to 2 of 45 cells (p < 0.001, Fisher’s exact test) by addition of 15 μM efsevin. (C) Average number of Ca²⁺ waves per minute was significantly enhanced from 0 in vehicle-treated RyR2^R4496C/WT cardiomyocytes to 0.46 ± 0.09 waves/min in cells treated with 1 µM ISO (p < 0.001, Kruskal-Wallis test). Addition of 15 µM efsevin reduced the number of waves/minute to 0.07 ± 0.05 to levels indistinguishable from untreated cells (p = 0.578). (D) Patch clamp recordings from RyR2^R4496C/WT cardiomyocytes showed an increase in spontaneous action potentials after superfusion with ISO, which were eliminated by addition of 15 μM efsevin. (E) Quantitative analysis of patch clamp recordings revealed a significant increase of spontaneous diastolic action potentials (APs) from 1.12 ± 0.62 APs/min under vehicle (Veh.) to 5.76 ± 2.45 APs/min after superfusion with ISO (p = 0.018, Friedman test, n = 15) and a significant reduction to 0.58 ± 0.34 APs/min when simultaneously treated with ISO and efsevin (p = 0.011). ∗∗p < 0.01; ∗∗∗p < 0.001. ISO = isoproterenol.