Long-chain fatty acids increase basal metabolism and depolarize mitochondria in cardiac muscle cells

Abstract

The effects of long-chain (LC) fatty acids on rate of heat production (heat rate) and mitochondrial membrane potential (⌬⌿) of intact guinea pig cardiac muscle were investigated at 37°C. Heat rate of ventricular trabeculae was measured with microcalorimetry, and ⌬⌿ was monitored in isolated ventricular myocytes with either JC-1 or tetramethylrhodamine ethyl ester (TMRE). Methyl-␤-cyclodextrin was used as fatty acid carrier. Application of 400 M oleate or linoleate increased resting heat rate by ϳ30% and ϳ25%, respectively. When LC fatty acid was supplied as sole metabolic substrate, resting heat rate was decreased by 3-mercaptopropionic acid. In TMRE-loaded myocytes, neither 40-80 M oleate nor 40 M linoleate affected ⌬⌿. At a higher concentration (400 M) both oleate and linoleate increased TMRE fluorescence by ϳ20% of maximum, obtained using 2,4-dinitrophenol (100 M), indicating a depolarization of the inner mitochondrial membrane. We conclude that LC fatty acids, at sufficiently high concentration, increase heat rate and decrease ⌬⌿ in intact cardiac muscle, consistent with a protonophoric uncoupling action. These effects may contribute to the high metabolic rate after reperfusion of postischemic myocardium. mitochondrial membrane potential; microcalorimetry IN CARDIAC MUSCLE, the resting (basal) level of metabolism is extraordinarily high, accounting for 25-30% of the metabolic rate of mechanically active muscle (3,4,9,12,22,29). Although the origin of this high resting metabolic rate is unknown, it has been shown to be sensitive to metabolic substrate (4, 9). This is well illustrated with pyruvate, which has been shown to increase resting rate of heat production (4) and oxygen consumption (9) of isolated cardiac muscle preparations.In isolated mitochondrial preparations, long-chain (LC) fatty acids have been shown convincingly to uncouple oxidative phosphorylation (27,31). Whether this uncoupling action manifests in intact cardiac muscle is not known (14,35). This unresolved issue is important because LC fatty acids are the major metabolic substrates of the heart and, furthermore, they are known to accumulate in high concentrations during ischemia (6, 33). The aims of the present study were to determine the effects of LC fatty acids on both resting heat rate and mitochondrial membrane potential (⌬⌿) of intact cardiac muscle. METHODS Isolation of trabeculae and microcalorimetry.Guinea pigs (200-300 g) were anesthetized with 3-4% isoflurane in oxygen and then decapitated with a guillotine. The heart was rapidly excised and perfused with dissecting solution containing (mM) 105 NaCl, 15 KCl, 2 CaCl 2, 1 MgCl2, 1 NaH2PO4, 24 NaHCO3, 20 2,3-butanedione monoxime, and 10 glucose. The solution was equilibrated with 95% O2-5% CO2, and the pH was 7.4. The right ventricle was opened, and free running trabeculae (diameter Ͻ400 m) were excised and subsequently transferred to the calorimeter. These preparations were shown recently to be composed chiefly of myocytes accompanied by parallel perimysial collagen fibers (13). Af...

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