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1. The liver cells lose the major part of their carnitine during the commonly used isolation procedure by the collagenase-perfusion method. 2. The cells take up carnitine and the carnitine precursor butyrobetaine when these substances are added to the medium. The carnitine content of isolated liver cells can increase to about 15 mM with no apparent harm to the cells. 3. The data indicate the existence of a common carrier in the plasma membrane which mediates the uphill transport of both carnitine and butyrobetaine. The carrier has a high affinity for butyrobetaine (Km=0.5 mM) and a lower one for carnitine (Km=5.6 mM). 4. The intracellular butyrobetaine is hydroxylated to carnitine with a rate of approximately 0.33 mumol-g wet weight-1-h-1 which is sufficient to cover the turn over of carnitine in the whole rat. Carnitine is effectively esterified in the liver cells to acetylcarnitine and long-chain acylcarnitines. 5. Both carnitine and acetylcarnitine are released from the cells. The release of both compounds is probably physiological since it was found that acetylcarnitine constitutes a similar fraction of the total acid soluble carnitine both in the blood and liver of the intact rat.

1. The metabolism of palmitate and especially of erucate was studied in hepatocytes isolated from rats fed for 3 weeks a diet containing peanut oil (diet, 1), rapeseed oil (diet 2) and partially hydrogenated marine oil (diet 3). 2. The metabolism of palmitate was not significantly influenced by the diet. The rapeseed oil diet caused 1.4 fold and 1.3 fold increase and marine oil diet 3 fold and 2.2 fold increase in the oxidation and chain-shortening respectively of [14-14C]erucic acid in isolated hepatocytes. 3. Cyanide and antimycin A did not inhibit the chain-shortening of erucate in liver cells of rats fed rapeseed oil and peanut oil. The high capacity of the chain-shortening system in hepatocytes of marine oil-fed rats was partially inhibited. 4. Inhibition of the transfer of fatty acids into the mitochondria by lowering the intracellular carnitine concentration and/or by addition of (+)-decanoyl-carnitine resulted in a very pronounced apparent stimulation of the chain-shortening of erucic acid. It is suggested that the chain-shortening system may be virtually independent of the mitochondria, unless the availability of the extramitochondria NAD+ and/or NADP+ is rate-limiting under conditions of extremely low redox potential of the mitochondria. 5. Feeding marine oil or rapeseed oil to the rats induced a 30% increase in catalase activity, a 25--30% increase in urate oxidase activity and a 50% increase in the total CoA in the liver compared to rats fed peanut oil. 6. It is suggested that the increased metabolism of erucate in hepatocytes of marine oil and rapeseed oil-fed rats may be due to the increase in ther peroxisomal beta-oxidation.

1. The mechanism of the inhibitory effect of erucylcarnitine on palmityl-carnitine oxidation in rat heart mitochondria was studied. 2. Erucylcarnitine inhibited in the same time the oxidation of [U-14-C]-palmitylcarnitine and the total rate of oxygen uptake. Other acylcarnitines competed as well for the oxidation with radioactive palmitylcarnitine, but they were well oxidized themselves, so that the total oxygen uptake did not decrease. 3. The presence of erucylcarnitine did not change the distribution pattern of Krebs cycle intermediates derived from [U-minus 14 C] palmitylcarnitine except that succinate/malate ratio increased. 4. The presence of erucylcarnitine did not lead to the formation of any beta-oxidation cycle intermediates from [U-minus 14 C] palymitylcarnitine. The formation of beta-hydroxy-palmityl derivative when rotenon was included into the incubation medium, decreased in the presence of erucylcarnitine. 5. It is postulated, that the inhibited entrance of palmityl groups into the beta-oxidation cycle is due to the fact that erucylcarnitine and palmitylcarnitine behave as substrate-competitive inhibitors for long chain acyl-CoA dehydrogenase. 6. There was observed a latency of 1-2 min in the effect of erucylcarnitine on the palmitylcarnitine oxidation, which seems to correspond to the time required for the formation of high amounts of intramitochondrial erucyl-CoA. 7. Erucylcarnitine inhibited the total oxygen uptake with long, medium and short chain acylcarnitines, pyruvate and alpha-ketoglutarate as substrates, while the oxidation of succinate was not affected. 8. Sequestration of free CoA in the form of very slowly metabolized erucyl-CoA is proposed as the partial explanation of the observed inhibitory effects of erucylcarnitine on the oxidation of CoA-dependent substrates (alternatively to the inhibition at the level of acyl-CoA dehydrogenases in case of acylcarnitines).

1. Carnitine esters of erucic acid (22:1 n-9 cis), cetoleic acid (22:1 n-11 cis), brassidic acid (22:1 n-9 trans), gadoleic acid (20:1 n-9 cis) and oleic acid (18:1 n-9 cis) have been compared as mitochondrial substrates and as inhibitors of palmitoylcarnitine oxidation in heart and liver mitochondria. 2. Both the rate of intramitochondrial-CoA acylation and the rate of beta-oxidation decreases as the chain length increases from C18 to C22. There are no significant differences among the three C22 isomers as oxidizable substrates. 3. All the tested acylcarnitines inhibit palmitoylcarnitine oxidation. The C18 and C20 acylcarnitines inhibit by virtue of being competing substrates; i.e. the respiration is not inhibited. The C22-isomers inhibit also respiration; this shows that the inhibition of palmitolycarnitine oxidation is not compensated for by oxidation of C22-acylcarnitines. Brassidoylcarnitine inhibits the oxidation of palmitoylcarnitine and respiration less than erucoyl-and cetoleoylcarnitine. The different behaviour of the C22-isomers is probably due to the difference in their competitive properties with respect to long-chain acyl-CoA dehydrogenase. 4. All C22 acylcarnitines seem to be relatively better oxidized in the liver than in the heart mitochondria while their inhibitory effect on the usage of the radioactive palmitoylcarnitine is very similar. 5. Palmitoylcarnitine inhibits almost completely the "endogenous" formation of acetyl-CoA presumably from malate via pyruvate in the liver mitochondria while the C22-acylcarnitines cause only a partial inhibiton of this acetyl-CaO formation.