Extended Data Fig. 4. The effect of MARK4 deficiency on sarcomere length, peak shortening, velocity, and calcium transients in cardiomyocytes before and after myocardial infarction.

a-f, Contractility assay of single primary cardiomyocytes (CMs) isolated at baseline (BL) or at day 3 post-myocardial infarction (MI) from the following groups: Mark4 ^+/+ BL (n=4 mice / n=45 CMs examined over 4 independent experiments), Mark4 ^-/- BL (n=3 mice / n=45 CMs examined over 3 independent experiments), Mark4 ^+/+ MI (n=5 mice / n=54 CMs examined over 5 independent experiments), and Mark4 ^-/- MI (n=6 independent mice / n=57 CMs examined over 6 independent experiments). Colour denotation of samples (a). Resting sarcomere length (SL) (b). Average sarcomere shortening traces were compared (c-d). Average velocity traces (dSL/dT) (e-f). g-m, Calcium influx assay on single CMs isolated from Mark4 ^-/- or control mice at baseline or at day 3 post- MI in the following groups: Mark4 ^+/+ BL group (n=2 mice / n=34 CMs examined over 2 independent experiments), Mark4 ^-/- BL groups (n=2 mice / n=33 CMs examined over 2 independent experiments), Mark4 ^+/+ MI group (n=4 mice / n=65 CMs examined over 4 independent experiments), Mark4 ^-/- MI groups (n=3 mice / n=58 CMs examined over 3 independent experiments). Basal Ca²⁺ level (g). Amplitude level of Ca²⁺ transient (h). Ca²⁺ release speed during contraction (i). Ca²⁺ reuptake speed during contraction (j). Ca²⁺ elevation time (k). Ca²⁺ reuptake time (l). Traces of Ca²⁺ kinetic curves (m). The box bounds represent the 25^th and 75^th percentiles, the middle line shows the median, and the whiskers show the minimum and maximum (b, g-l). Mean ± s.e.m.; two-way ANOVA with Bonferroni post-hoc correction for multiple comparisons (b, g-l). P values are indicated on the graphs.