Contraction and Intracellular Ca 2+ Handling in Isolated Skeletal Muscle of Rats With Congestive Heart Failure

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Abstract
—A decreased exercise tolerance is a common symptom in patients with congestive heart failure (CHF). This decrease has been suggested to be partly due to altered skeletal muscle function. Therefore, we have studied contractile function and cytoplasmic free Ca2+ concentration ([Ca2+]i, measured with the fluorescent dye indo 1) in isolated muscles from rats in which CHF was induced by ligation of the left coronary artery. The results show no major changes of the contractile function and [Ca2+]i handling in unfatigued intact fast-twitch fibers isolated from flexor digitorum brevis muscles of CHF rats, but these fibers were markedly more susceptible to damage during microdissection. Furthermore, CHF fibers displayed a marked increase of baseline [Ca2+]i during fatigue. Isolated slow-twitch soleus muscles of CHF rats displayed slower twitch contraction and tetanic relaxation than did muscles from sham-operated rats; the slowing of relaxation became more pronounced during fatigue in CHF muscles. Immunoblot analyses of sarcoplasmic reticulum proteins and sarcolemma Na+,K+-ATPase showed no difference in flexor digitorum brevis muscles of sham-operated versus CHF rats. In conclusion, functional impairments can be observed in limb muscle isolated from rats with CHF. These impairments seem to mainly involve structures surrounding the muscle cells and sarcoplasmic reticulum Ca2+ pumps, the dysfunction of which becomes obvious during fatigue.