Mitochondrial oxidative phosphorylation in hearts subjected to Ca2+ depletion and Ca2+ repletion

• Published in: Canadian journal of physiology and pharmacology 2009-10, Vol.87 (10), p.789-797
• Main Authors: MAKAZAN, Zhanna, SAINI-CHOHAN, Harjot K, DHALLA, Naranjan S
• Format: Article
• Language: English
• Subjects: Animals; Antioxidants - pharmacology; Biological and medical sciences; Ca(2+) Mg(2+)-ATPase - metabolism; Calcium - pharmacology; Calcium - physiology; Calcium Channel Blockers - pharmacology; Coloring Agents; Drug therapy; Fundamental and applied biological sciences. Psychology; Heart; Heart Function Tests; In Vitro Techniques; Kinetics; Male; Mannitol - pharmacology; Mitochondria, Heart - physiology; Oxidative Phosphorylation; Oxidative Stress - drug effects; Oxidative Stress - physiology; Oxygen Consumption - drug effects; Rats; Rats, Sprague-Dawley; Respiration; Ruthenium Red; Studies; Superoxide Dismutase - metabolism; Vertebrates: anatomy and physiology, studies on body, several organs or systems
• ISSN: 0008-4212; 1205-7541
• DOI: 10.1139/Y09-050

Repletion of Ca2+ in the Ca2+-depleted heart has been shown to produce cardiac dysfunction, myocardial cell damage, intracellular Ca2+ overload, and defects in sarcolemmal and sarcoplasmic reticulum function (Ca2+ paradox). Although these alterations in the Ca2+-paradox heart are associated with a depression in the high-energy phosphate stores, little information regarding changes in mitochondrial oxidative phosphorylation is available. Perfusion of rat hearts with Ca2+-free medium for 5 min followed by reperfusion with a medium containing 1.25 mmol/L Ca2+ for 10 min depressed mitochondrial state 3 respiration, respiratory control index, ADP/O ratio, and rate of oxidative phosphorylation without any change in state 4 respiration. These alterations were partially prevented when the reperfusion was carried out with a medium containing low Ca2+ (0.10-0.50 mmol/L). Treatment of heart with inhibitors of sarcolemmal Ca2+ channels (verapamil and diltiazem) or inhibitors of Na+/Ca2+ exchange (KB-R7943) and Na+/H+ exchange (amiloride) failed to modify changes in mitochondrial function due to Ca2+ paradox. Likewise, antioxidants N-acetylcysteine and N-(2-mercaptopropionyl)-glycine and an oxyradical-scavenging mixture of superoxide dismutase and catalase were ineffective in preventing the mitochondrial alterations in the Ca2+-paradox heart. Incubation of mitochondria with various concentrations of Ca2+ inhibited oxidative phosphorylation; this Ca2+-induced change in mitochondrial function was not affected by different oxyradical-scavenging systems. These observations suggest that defects in mitochondrial function in the Ca2+-paradox heart may be due to the occurrence of intracellular Ca2+ overload rather than the development of oxidative stress.