Fig. 7: Functional characterization of miR-365-based action potential regulation in human myocardium.

a Slices were prepared from human ventricular myocardium with 300 µm thickness, glued to plastic triangles and mounted in biomimetic tissue culture chambers that enable constant measurement of contraction force. The slices were maintained under 1 mN preload and 0.5 Hz electrical pacing for at least two weeks before starting the functional experiments to reach an equilibrium (scheme created using Servier Medical Art). b Confocal microscopy images of 5 µm sections prepared from myocardial slices transfected with Fluorescein amidite (FAM)-labeled oligonucleotides (green) compared to an untreated slice. Wheat germ agglutinin staining (WGA, magenta) defines the area of the cells and DAPI (blue) marks the nuclei (scale bar = 75 µm). c MiR-365 levels in mimic-treated slices as determined by qRT-PCR. Data are presented as mean ± SEM (n = 4 independent samples). d The correlation between the effective refractory period and AP duration in ventricular myocytes (left panel) and the automated electrical stimulation protocol for determining the RP. The point where the myocardial slice reaches refractoriness is marked with a grey dashed frame (right panel). e Experimental scheme representing the timeline for transfection of cardiac slices with synthetic oligonucleotides following by medium exchange after 24 h. RP measurements were performed before and 48 h after miR-365 manipulation. f Representative RP measurement traces from slices treated with mimic-Ctrl (pink) or mimic-365 (blue) 48 h after the transfection. Grey dashed frames in high-resolution traces depict the refractoriness of each slice. g Representative contraction force traces acquired from slices transfected with antimiR-Ctrl (green) or antimiR-365 (brown) 48 h after transfection. The refractoriness of slices is marked with a gray dashed frame. h, i Quantitative analysis of RP recordings upon elevation (h) or inhibition (i) of mimic-365. Measurements were performed on cardiac tissue acquired from 5 independent patients per each condition. Source data and detailed statistical analyses for c, h, and i are provided as a Source Data file.