Effects of palmitoyl CoA and palmitoyl carnitine on the membrane potential and Mg2+ content of rat heart mitochondria

A number of reports indicate that a long-chain free fatty acid export system may be operating in mitochondria. In this study, we sought evidence of its existence in rat heart mitochondria. To determine its potential role, we also sought evidence of its activation or inhibition in streptozotocin (STZ)-induced diabetic rat heart mitochondria. If confirmed, it could be a novel mechanism for regulation of long-chain fatty acid oxidation (FAO) in mitochondria. To obtain evidence of its existence, we tested whether heart mitochondria presented with palmitoyl-carnitine can generate and export palmitate. We found that intact mitochondria indeed generate and export palmitate. We have also found that the rates of these processes are markedly higher in STZ-diabetic rat heart mitochondria, in which palmitoyl-carnitine oxidation is also increased. Since mitochondrial thioesterase-1 (MTE-1) hydrolyzes acyl-CoA to CoA-SH + free fatty acid, and uncoupling protein-3 (UCP-3), reconstituted in liposomes, transports free fatty acids, we examined whether these proteins are also increased in STZ-diabetic rat heart mitochondria. We found that both of these proteins are indeed increased. Gene expression profile analysis revealed striking expression of mitochondrial long-chain fatty acid transport and oxidation genes, accompanying overexpression of MTE-1 and UCP-3 in STZ-diabetic rat hearts. Our findings provide the first direct evidence for the existence of a long-chain free fatty acid generation and export system in mitochondria and its activation in STZ-diabetic rat hearts in which FAO is enhanced. We suggest that its activation may facilitate, and inhibition may limit, enhancement of FAO.

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4-Bromocrotonic acid, an effective inhibitor of fatty acid oxidation and ketone body degradation in rat heart mitochondria. On the rate-determining step of beta-oxidation and ketone body degradation in heart.

Journal of Biological Chemistry ◽

10.1016/s0021-9258(19)83791-2 ◽

1982 ◽

Vol 257 (10) ◽

pp. 5408-5413

Author(s):

Y Olowe ◽

H Schulz

Keyword(s):

Fatty Acid ◽

Fatty Acid Oxidation ◽

Rat Heart ◽

Ketone Body ◽

Heart Mitochondria ◽

Acid Oxidation ◽

Effective Inhibitor ◽

Beta Oxidation ◽

Rate Determining Step ◽

Rat Heart Mitochondria

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Effects of hydrogen peroxide and hypochlorite on membrane potential of mitochondria in situ in rat heart cells

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y91-253 ◽

1991 ◽

Vol 69 (11) ◽

pp. 1705-1712 ◽

Cited By ~ 10

Author(s):

Noburu Konno ◽

K. J. Kako

Keyword(s):

Hydrogen Peroxide ◽

Membrane Potential ◽

Mitochondrial Membrane Potential ◽

Rat Heart ◽

Mitochondrial Membrane ◽

Isolated Rat Heart ◽

Heart Mitochondria ◽

High Concentrations ◽

Isolated Rat

Hydrogen peroxide (H2O2) and hypochlorite (HOCl) cause a variety of cellular dysfunctions. In this study we examined the effects of these agents on the electrical potential gradient across the inner membrane of mitochondria in situ in isolated rat heart myocytes. Myocytes were prepared by collagenase digestion and incubated in the presence of H2O2 or HOCl. Transmembrane electrical gradients were measured by distribution of [3H]triphenylmethylphosphonium+, a lipophilic cation. The particulate fraction was separated from the cytosolic compartment first by permeabilization using digitonin, followed by rapid centrifugal sedimentation through a bromododecane layer. We found that the mitochondrial membrane potential (161 ± 7 mV, negative inside) was relatively well maintained under oxidant stress, i.e., the potential was decreased only at high concentrations of HOCl and H2O2 and gradually with time. The membrane potential of isolated rat heart mitochondria was affected similarly by H2O2 and HOCl in a concentration- and time-dependent manner. High concentrations of oxidants also reduced the cellular ATP level but did not significantly change the matrix volume. When the extra-mitochondrial free calcium concentration was increased in permeabilized myocytes, the transmembrane potential was decreased proportionally, and this decrease was potentiated further by H2O2. These results support the view that heart mitochondria are equipped with well-developed defense mechanisms against oxidants, but the action of H2O2 on the transmembrane electrical gradient is exacerbated by an increase in cytosolic calcium. Keywords: ATP, calcium, cardiomyocyte, cell defense, mitochondrial membrane potential, oxidant, triphenylmethylphosphonium.

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