Hydroxyl Radical-Induced Acute Diastolic Dysfunction Is Due to Calcium Overload via Reverse-Mode Na ⁺ -Ca ²⁺ Exchange

Abstract

Abstract-Hydroxyl radicals (OH) are involved in the development of reperfusion injury and myocardial failure. In the acute phase of the OH-mediated diastolic dysfunction, increased intracellular Ca 2ϩ levels and alterations of myofilaments may play a role, but the relative contribution of these systems to myocardial dysfunction is unknown. Intact contracting cardiac trabeculae from rabbits were exposed to OH, resulting in an increase in diastolic force (F dia ) by 540%. Skinned fiber experiments revealed that OH-exposed preparations were sensitized for Ca 2ϩ (EC 50 : 3.27Ϯ0.24ϫ10Ϫ6 versus 2.69Ϯ0.15ϫ10 Ϫ6 mol/L; PϽ0.05), whereas maximal force development was unaltered. Western blots showed a proteolytic degradation of troponin T (TnT) with intact troponin I (TnI). Blocking of calpain I by MDL-28.170 inhibited both TnT-proteolysis and Ca 2ϩ sensitization, but failed to prevent the acute diastolic dysfunction in the intact preparation. The OH-induced diastolic dysfunction was similar in preparations with intact (540Ϯ93%) and pharmacologically blocked sarcoplasmic reticulum (539Ϯ77%), and was also similar in presence of the L-type Ca 2ϩ -channel antagonist verapamil. In sharp contrast, inhibition of the reverse-mode sodium-calcium exchange by KB-R7943 preserved diastolic function completely. Additional experiments were performed in rat myocardium; the rise in diastolic force was comparable to rabbit myocardium, but Ca 2ϩ sensitivity was unchanged and maximal force development was reduced. This was associated with a degradation of TnI, but not TnT. Electron microscopic analysis revealed that OH did not cause irreversible membrane damage. We conclude that OH-induced acute diastolic dysfunction is caused by Ca 2ϩ influx via reverse mode of the sodium-calcium exchanger. Degradation of troponins appears to be species-dependent but does not contribute to the acute diastolic dysfunction.

Iron overload thalassemic cardiomyopathy: Iron status assessment and mechanisms of mechanical and electrical disturbance due to iron toxicity

“…Other than the effects of membrane lipid peroxidation causing cellular environmental changes, the membrane-embedding enzymes, such as Na + -K + ATPase, Ca 2+ ATPase and 5′-nucleotidase, may be attacked directly by oxygen radicals (59,69,70). It has been shown that modification of the sulfhydryl groups of these enzymes by an oxygen radical reduces their activity (70).…”

“…Oxygen free radicals also have a direct effect on decreased cardiac SR Ca 2+ ATPase activity (72), which may be responsible for diastolic failure. In the in vitro study by Zeitz et al (69), hydroxyl radical-exposed rabbit heart muscle was demonstrated to have calcium overload (via Na + -Ca 2+ exchange), with an acute diastolic dysfunction. These mechanisms may explain the pathophysiology of early cardiac dysfunction in iron overload cardiomyopathy.…”

Myofilament proteins: From cardiac disorders to proteomic changes

“…More interestingly, several groups have reported degradation products of TnI in serum of patients after acute myocardial infarction (AMI) [35][36][37]. Degradation products of TnT were also found both in animal models of ischemia/reperfusion injury [38,39] and in serum of patients with AMI [40,41]. In 2000, TnI and TnT have been approved as the biomarkers for AMI diagnosis [42], and several kits have been commercially developed and used in clinical studies [43][44][45].…”

“…Protein degradation often involves significant molecular weight (MW) reduction, which can be readily detected by 1-D-gel separation followed by Western blot analysis [31,32,[34][35][36][37][38][39][40][41]. Comparative 2-DE was also used to study proteomic changes on a broader scale, and PMF can be employed to identify changed proteins [46].…”

Efeitos da associação entre treinamento físico e tratamento farmacológico com -bloqueadores sobre a cardiomiopatia induzida por hiperatividade simpática em camundongos

“…O aumento do estresse oxidativo, presente na insuficiência cardíaca, pode proporcionar um aumento da tensão diastólica, proteólise de miofilamentos e diminuição da contratilidade (78). Estes efeitos estão associados à sobrecarga de cálcio que é resultado, dentre outros fatores, de danos ao retículo sarcoplasmático.…”