Decreased passive stiffness of cardiac myocytes and cardiac tissue from copper-deficient rat hearts

Passive stiffness characteristics of isolated cardiac myocytes, papillary m uscles, and aortic strips from male Holtzman rats fed a copper-deficient di et for similar to 5 wk were compared with those of rats fed a copper-adequa te diet to determine whether alterations in these characteristics might acc ompany the well-documented cardiac hypertrophy and high incidence of ventri cular rupture characteristic of copper deficiency. Stiffness of isolated ca rdiac myocytes was assessed from measurements of cellular dimensional chang es to varied osmotic conditions. Stiffness of papillary muscles and aortic strips was determined from resting length-tension analyses and included ste ady-state characteristics, dynamic viscoelastic stiffness properties, and m aximum tensile strength. The primary findings were that copper deficiency r esulted in cardiac hypertrophy with increased cardiac myocyte size and frag ility, decreased cardiac myocyte stiffness, and decreased papillary muscle passive stiffness, dynamic stiffness, and tensile strength and no alteratio n in aortic connective tissue passive stiffness or tensile strength. These findings suggest that a reduction of cardiac myocyte stiffness and increase d cellular fragility could contribute to the reduced overall cardiac tissue stiffness and the high incidence of ventricular aneurysm observed in coppe r-deficient rats.