T‐tubule disorganization and reduced synchrony of Ca²⁺ release in murine cardiomyocytes following myocardial infarction

Abstract

In cardiac myocytes, initiation of excitation-contraction coupling is highly localized near the T-tubule network. Myocytes with a dense T-tubule network exhibit rapid and homogeneous sarcoplasmic reticulum (SR) Ca2+ release throughout the cell. We examined whether progressive changes in T-tubule organization and Ca 2+ release synchrony occur in a murine model of congestive heart failure (CHF). Myocardial infarction (MI) was induced by ligation of the left coronary artery, and CHF was diagnosed by echocardiography (left atrial diameter >2.0 mm). CHF mice were killed at 1 or 3 weeks following MI (1-week CHF, 3-week CHF) and cardiomyocytes were isolated from viable regions of the septum, excluding the MI border zone. Septal myocytes from SHAM-operated mice served as controls. T-tubules were visualized by confocal microscopy in cells stained with di-8-ANEPPS. SHAM cells exhibited a regular striated T-tubule pattern. However, 1-week CHF cells showed slightly disorganized T-tubule structure, and more profound disorganization occurred in 3-week CHF with irregular gaps between adjacent T-tubules. The authors are indebted to Dr Gregory R. Ferrier who contributed immeasurably to the inception of this project during his sabbatical in Oslo. Sadly, he passed away before its completion. This manuscript is dedicated to his memory. channels (ryanodine receptors) are in close proximity (Flucher & Franzini-Armstrong, 1996). Thus, initiation of excitation-contraction coupling is highly localized near the T-tubule network (Shacklock et al. 1995).In myocytes with a high density of T-tubules, such as in rats and mice, SR Ca 2+ release occurs almost simultaneously throughout the cell (Berlin, 1995; Shacklock et al. 1995;Heinzel et al. 2002). However, myocytes with less-dense T-tubule networks exhibit less synchronous Ca 2+ transients, with regions of delayed Ca 2+ release occurring where T-tubules are not present (Heinzel et al. 2002) sarcolemma, but more slowly in the cell interior following propagation of Ca 2+ (Berlin, 1995;Cordeiro et al. 2001). Experimentally promoting loss of T-tubules by cell culture or de-tubulation techniques has also been shown to reduce the synchrony of Ca 2+ transients, which results in slower spatially averaged Ca 2+ release (Lipp et al. 1996;Yang et al. 2002;Louch et al. 2004). Thus, there is considerable evidence to suggest that a dense and intact T-tubular network is required for rapid and homogeneous SR Ca 2+ release.Several reports have suggested that the T-tubular network may be altered in heart failure. A marked loss of T-tubules has been observed in failing canine ventricular myocytes (He et al. 2001;Balijepalli et al. 2003), although it is unclear whether such changes occur in human heart failure (Kaprielian et al. 2000;Wong et al. 2001;Ohler et al. 2001). However, the structural organization of T-tubules may be altered in failing human cardiomyocytes (Kostin et al. 1998;Kaprielian et al. 2000;Wong et al. 2001;Louch et al. 2004). It is not known how such disorganization may influence excitation-...

Extreme sarcoplasmic reticulum volume loss and compensatory T-tubule remodeling after Serca2 knockout

“…The increased frequency of LTTs in KO mimics the disposition during early differentiation, when tubules are essentially longitudinal (9). Although KO animals exhibit heart failure symptoms (3,4), there are significant differences between the increased presence of LTTs observed here and T-tubule remodeling normally reported during heart failure development (10)(11)(12)(13)(14)(15). First, whereas the transverse component of the network and its association with dyads are disarranged in classic heart failure models (16), KO cardiomyocytes exhibit a maintained transverse and unaltered dyadic architecture.…”

Human cardiomyocyte calcium handling and transverse tubules in mid‐stage of post‐myocardial‐infarction heart failure

“…Disrupted T‐tubule density has previously been demonstrated in explanted end‐stage HF human hearts from different aetiologies, also including ischaemic heart disease 2, 45, 46, 47, 48, 49. Data from both larger animal models like pig and dogs49, 50 and smaller animal models like mice and rats report disrupted T‐tubule density also in earlier stages of the disease 51. Data from the present study confirm therefore that T‐tubule disorganization and loss are present also at earlier, not terminal, stages of human post‐MI HF.…”

Size Matters: Ryanodine Receptor Cluster Size Affects Arrhythmogenic Sarcoplasmic Reticulum Calcium Release

“…However, pathological conditions such as heart failure with altered RyR sensitization1 and structure cluster and T‐tubule–SR organization35, 36, 37, 38, 39, 40 could undermine these intrinsically beneficial effects and contribute to cardiac dysfunction and arrhythmogenesis.…”