Focal but reversible diastolic sheet dysfunction reflects regional calcium mishandling in dystrophic mdx mouse hearts.

Abstract

Cardiac dysfunction is a primary cause of patient mortality in Duchenne muscular dystrophy, potentially related to elevated cytosolic calcium. However, the regional versus global functional consequences of cellular calcium mishandling have not been defined in the whole heart. Here we sought for the first time to elucidate potential regional dependencies between calcium mishandling and myocardial fiber/sheet function as a manifestation of dystrophin-deficient (mdx) cardiomyopathy. Isolated-perfused hearts from 16-mo-old mdx (N = 10) and wild-type (WT; N = 10) were arrested sequentially in diastole and systole for diffusion tensor MRI quantification of myocardial sheet architecture and function. When compared with WT hearts, mdx hearts exhibited normal systolic sheet architecture but a lower diastolic sheet angle magnitude (|β|) in the basal region. The regional diastolic sheet dysfunction was normalized by reducing perfusate calcium concentrations. Optical mapping of calcium transients in isolated hearts (3 mdx and 4 WT) revealed a stretch-inducible regional defect of intracellular calcium reuptake, reflected by a 25% increase of decay times (T(50)) and decay constants, at the base of mdx hearts. The basal region of mdx hearts also exhibited greater fibrosis than did the apex, which matched the regional sheet dysfunction. We conclude that myocardial diastolic sheet dysfunction is observed initially in basal segments along with calcium mishandling, ultimately culminating in increased fibrosis. The preservation of relatively normal calcium reuptake and diastolic/systolic sheet mechanics throughout the rest of the heart, together with the rapid reversibility of functional defects by reducing cytosolic calcium, points to the significance of regional mechanical factors in the progression of the disease.

• Authors: Ya-Jian Cheng, Di Lang, Shelton D Caruthers, Igor R Efimov, Junjie Chen, Samuel A Wickline
• Journal: American journal of physiology. Heart and circulatory physiology (Am J Physiol Heart Circ Physiol) Vol. 303 Issue 5 Pg. H559-68 (Sep 01 2012) ISSN: 1522-1539 [Electronic] United States
• PMID: 22777417 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Topics

• Action Potentials
• Animals
• Biomechanical Phenomena
• Calcium Signaling
• Diffusion Tensor Imaging
• Disease Models, Animal
• Disease Progression
• Excitation Contraction Coupling
• Fibrosis
• Heart Failure (etiology, metabolism, pathology, physiopathology)
• Male
• Mice
• Mice, Inbred mdx
• Muscular Dystrophy, Animal (complications, genetics, metabolism)
• Muscular Dystrophy, Duchenne (complications, genetics, metabolism)
• Myocardial Contraction
• Myocardium (metabolism, pathology)
• Perfusion
• Recovery of Function
• Time Factors
• Ventricular Dysfunction (etiology, metabolism, pathology, physiopathology)
• Ventricular Function
• Voltage-Sensitive Dye Imaging