Figure 7. Slow Ca²⁺ sparks promote slow, desynchronized Ca²⁺ transients in HF.

(A) Representative confocal linescan images of Ca²⁺ transients in field-stimulated cells (stimulus illustrated as a horizontal line). The overall Ca²⁺ transient was slowed in HF compared to Sham, as indicated by plots of spatially-averaged Ca²⁺ transients ((A), right panel), and measurements of half rise time (TTF₅₀, (B)) and time to peak (C). Slowed Ca²⁺ transient kinetics included de-synchronization of Ca²⁺ release across HF cells, as indicated by profiles of local TTF₅₀ (lower panels in A). The standard deviation of these values, defined as the dyssynchrony index (Louch et al., 2006), showed a right-shifted distribution in HF compared to Sham (D). To examine the relationship between slowed Ca²⁺ spark kinetics and de-synchronized Ca²⁺ transients in HF, local Ca²⁺ transients were examined within 2 µm regions of the linescan centered at the location of recorded sparks. Paired representative recordings of sparks and local Ca²⁺ transients are shown in (E and F), respectively, corresponding to indicated positions in A) (vertical arrows). Local Ca²⁺ release at ‘slow’ spark locations (rise time > 13 ms) was protracted during the action potential, in comparison with local transients with ‘fast’ sparks in both HF and Sham (F). This association is demonstrated by clustering of locations with slow Ca²⁺ spark and local transient kinetics in ‘heat maps’ (G), and links slowing of Ca²⁺ release kinetics at the level of the single CRU and whole cell. (Ca²⁺ transients: n_cells = 43 in Sham, 57 in HF; n_{fast sparks}= 18 in Sham, 19 in HF; n_{slow sparks}= 18 in HF; *=P < 0.05 vs Sham).

Figure 7—figure supplement 1. T-tubule structure is disrupted during HF.

Isolated cardiomyocytes were stained with di-8-ANEPPS and examined by confocal microscopy (A). Zoomed regions enlarged in (B). In agreement with previous work employing the same post-infarction rat model (Frisk et al., 2016), we observed marked remodeling of t-tubular structure in HF. Skeletonized images (C, D) indicate that this reorganization included a loss of transverse t-tubule elements (colored white) and the appearance of additional longitudinal tubules running in the axial, perpendicular orientation (colored red). Scale bar = 5 µm.