Figure 3. Slc26a5^−/− cardiomyocytes show reduced sarcomere shortening.

(A and B) Representative traces for sarcomere shortening and Ca²⁺ transients (CaT) measured using Fura-2 ratio (R_FURA) from WT and Slc26a5^−/− cardiomyocytes. Summary data for percentages of sarcomere shortening and peak CaT from the two groups of animals are shown in the right panels.

(C) Examples of mechanical alternans in Slc26a5^−/−cardiomyocytes. Alternans were not observed in WT cardiomyocytes.

(D) There were no significant differences in the sarcoplasmic reticulum (SR) Ca²⁺ load between WT and Slc26a5^−/− cardiomyocytes.

(E) Representative traces of SR Ca²⁺ load measurement of WT and Slc26a5^−/− ventricular myocytes. The myocytes were first paced to steady state. The pacing was stopped for 15 s, followed by a rapid application of 20 mM of caffeine to induce SR Ca²⁺ release.

(F) A diagram showing quantification of sarcomere shortening during relaxed and contracted states from SHG recordings. Li is the distance between 2 adjacent A-bands within the same sarcomere, while L_a is the distance between the 2 A-bands across the adjacent sarcomeres. The sarcomere length is equal to the sum of L_i and L_a and shortens during cell contraction because of the sliding of the thick filament against the thin filament.

(G) A representative example of SHG recording and the corresponding Ca²⁺ transients from a ventricular myocyte.

(H) Quantification of the rise time (t_rise) and half decay time (t_1/2) from a representative Ca²⁺ transient.

(I–L) Summary data comparing percentages of sarcomere shortening (I), contracting speed (μm/s) (J), CaT rise time (K), and CaT half decay time (L) from WT and Slc26a5^−/− cardiomyocytes. *p < 0.05. The numbers within the bar graphs represent the sample sizes.