Serial block face scanning electron microscopy reveals region-dependent remodelling of transverse tubules post-myocardial infarction

Figures

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  Figure 1.. Reduction in LVEF from baseline to eight weeks post-MI. Mean LVEF eight weeks post-MI (52 ± 2%) is reduced by 16 ± 4% when compared with baseline mean LVEF (68 ± 2%). Paired t-test, p = 0.029, GraphPad Prism 8.4.3.

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  Figure 2.. SBF-SEM images and 3D reconstructions of the t-tubular network in healthy sheep cardiac myocytes. (a,b), SBF-SEM images illustrating key features in control cardiac myocytes, cut in transverse (a) and longitudinal (b) sections. t-Tubules are indicated by white arrows. M: mitochondria; mf: myofilaments. (c) 3D reconstruction of the t-tubular network in a control cardiac myocyte in transverse view, where t-tubules (white) adopt a radial orientation extending from the sarcolemma (green) to the cell centre. (d) 3D reconstruction of the t-tubular network in a healthy cardiac myocyte in longitudinal view, displaying an ordered arrangement of t-tubules (white) arranged perpendicular to the sarcolemma (horizontal green regions at the top and bottom) and regularly along z-lines. Vertical green lines are present to delimit the region. (e) Focus on a single t-tubule showing dilations and narrowings along its length. (f) Focus on a pair of t-tubules showing a longitudinal arrangement (blue dashed lines) at the crossover between z-lines (red dashed lines). (g) Focus on twin tubules projecting from the same region on either sides of the z-line (red dashed line). (a–d) scale bars: 2 µm; (e–g)…

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  Figure 3.. Comparison of t-tubule morphology between control, MI remote and border groups. (a–h) Comparison of t-tubule morphological features between control (green), MI remote (yellow) and border (orange) regions, illustrating: (a) increment of t-tubule diameter in border region compared with control; (b) increment of t-tubule length as a fraction of the cell in border region compared with control; (c) changes to the t-tubule volume in the border region compared with control and remote region; (d) volume occupied by t-tubules in the three different regions as a fraction of the cell volume; (e) the depletion of t-tubules in border region compared with control; (f) increment of fragments in border region compared with control; (g) increment in mean fragment volume in border region compared with remote region; (h) increment of fragment volume as a fraction of cell volume in border region compared with control and remote region. p-values demonstrating significant differences (p < 0.05) between groups are indicated.

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  Figure 4.. SBF-SEM images and 3D reconstructions of the t-tubular network in sheep border MI. (a) SBF-SEM image illustrating key features in a border region cell, in transverse section. t-Tubules are indicated by white arrows, and fragments by red arrows. M: mitochondria. (b) 3D reconstruction of the t-tubular network (white) in a border region cell in longitudinal view, displaying disorganization of t-tubules, t-tubule fragmentation (red) and regional t-tubule loss, indicated by a green ellipse. (c) 3D reconstruction of the t-tubular network (white) in a border region cell, in transverse view, illustrating extensive fragmentation (red). (d) 3D reconstruction of the border region cell shown in (c), with its fragments removed, displaying the underlying t-tubule network (white). Green ellipses indicate regions of t-tubule loss. (e) t-Tubules in light grey lined by the basement membrane indicated by black arrows. (f) Fragment in light grey preserving the basement membrane indicated by black arrow. (a–d) Scale bars: 2 µm; (e,f) scale bars: 1 µm.

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  Figure 5.. Regional involution of the tubular system from control to remote to border region MI region. (a) Control t-tubules (white) are regularly aligned along the z-lines (red dashed lines). (b) Remote region t-tubules (white) are aligned along the z-lines (red dashed lines) and present some longitudinal elements (green arrows). (c) Border region t-tubules (white) are irregularly aligned along the z-lines (red dashed lines) and are sparse and fragmented. (a–c) Scale bars: 2 µm.