Carnitine-induced uptake of l-carnitine into cells from an established cell line from human heart (CCL 27)

l-Carnitine is actively transported into Girardi human heart cells, an established cell line from human heart. The present study was undertaken to investigate the effect of different concentrations of l-carnitine in the growth medium on the rate of uptake of l-[³H]carnitine.Increasing the concentration of l-carnitine from 2 to 100 μmol/1 in the growth medium of the cells, increased the rate of uptake of l-[³H]carnitine by about 50%. The maximal effect was reached after approx. 72 h incubation. The increase in rate seemed to be caused by synthesis of increased number of carriers, as judged by the increase in $\text{V}$ with unchanged apparent $\text{K}{}_{\mathrm{<mtext>m</mtext>}}$ for the transport process. This effect of l-carnitine could be inhibited by cycloheximide, indicating the dependence on intact protein synthesis. The morphology of the cells was studied by electron microscopy. No myofilaments were found, thus the cells are dedifferentiated and no longer typical muscular cells.     

Effect of dehydroepiandrosterone sulfate on carnitine acetyl transferase activity and l-carnitine levels in oophorectomized rats

Alteration in energy metabolism of postmenopausal women might be related to the reduction of dehydroepiandrosterone sulfate (DHEAS). DHEA and DHEAS decline with age, leveling at their nadir near menopause. DHEA and DHEAS modulate fatty acid metabolism by regulating carnitine acyltransferases and CoA. The purpose of this study was to determine whether dietary supplementation with DHEAS would also increase tissue l-carnitine levels, carnitine acetyltransferase (CAT) activity and mitochondrial respiration in oophorectomized rats. Plasma l-carnitine levels rose following oophorectomy in all groups (P<0.0001). Supplementation with DHEAS was not associated with further elevation of plasma l-carnitine levels, but with increased hepatic total and free l-carnitine (P=0.021 and P<0.0001, respectively) and cardiac total l-carnitine concentrations (P=0.045). In addition, DHEAS supplementation increased both hepatic and cardiac CAT activities (P<0.0001 and P=0.05 respectively). CAT activity positively correlated with the total and free carnitine levels in both liver and heart (r=0.764, r=0.785 and r=0.700, r=0.519, respectively). Liver mitochondrial respiratory control ratio, ADP:O ratio and oxygen uptake were similar in both control and supplemented groups. These results demonstrate that in oophorectomized rats, dietary DHEAS supplementation increases the liver and heart l-carnitine levels and CAT activities. In conclusion, DHEAS may modulate l-carnitine level and CAT activity in estrogen deficient rats. The potential role of DHEAS in the regulation of fatty acid oxidation in postmenopausal women is worthy of investigation.     

The efflux of l-carnitine from cells in culture (CCL 27)

The efflux of l-[³H]carnitine was studied in cells from an established cell line from human heart (Girardi human heart cells, CCL 27). The cells were loaded with 4 μmol/l l-[³H]carnitine for 1 or 24 h, and the efflux of radioactivity into the medium was measured. The amount of intracellular l-[³H]carnitine retained was expressed as a function of time. The results were fitted to an exponential equation, from which efflux rate constants were computed.Increasing the extracellular concentration of butyrobetaine, l-carnitine, d-carnitine, betaine, dl-norcarnitine or 3-dimethylamino-2-hydroxypropionic acid each increased the observed efflux. This is most likely due to accelerated exchange diffusion. The substrate specificity of this accelerated exchange diffusion is different from what previously has been found in competitive uptake studies of l-carnitine. l-Carnitine was preferentially released to l-acetylcarnitine, and blocking the sulfhydryl groups with 5,5-dithiobis(2-nitrobenzoic acid) increased the efflux.     

Metabolism of labeled carnitine in the rat

In two series of rats, the concentration of carnitine in plasma was 39.9 and 37.8 μmol/ liter, in skeletal muscle tissue 2.97 and 3.26 μmol/g dry wt and the urinary excretion 3.2 and 2.4 μmol/24 h. The renal clearance of carnitine was calculated to 88 and 76 ml/24 h. L-[Me-¹⁴C]Carnitine and DL-[Me-¹⁴C]carnitine have been administered to rats. Only labeled l-carnitine has been found on chromatographic analysis of plasma, urine, and muscle tissue. The specific radioactivity of carnitine in plasma, urine, and muscle tissue has been followed for up to 16 days. A two-compartment metabolic model has been used to interpret the result of the experiment with labeled l-carnitine and the rate constants and compartment sizes have been calculated. The total body content of carnitine was 57 μmol (about 35 μmol/100 g body wt) and the daily turnover was about 7% of the body pool. The daily synthesis of carnitine in the rat is estimated to about 2 μmol/100 g body wt.     

Effects of l-carnitine in the distillers dried grains with solubles diet of sows on reproductive performance and antioxidant status of sows and their offspring

Distillers dried grains with solubles (DDGS) are highly susceptible to lipid oxidation because DDGS contain about 10% crude fat, which is largely composed of polyunsaturated fatty acids. l-carnitine serves an important function in fatty acids β-oxidation, and also has antioxidant properties. The objective of this study was to examine the effects of l-carnitine in the DDGS diet of gestating and lactating sows on reproductive performance, milk composition and antioxidant status of sows and their offspring. One hundred and twenty sows (Landrace×Large white, mean parity 4.2, initial BW 230 kg) were randomly allotted to 1 of 4 dietary treatments (n=30 sows/treatment). Treatments were arranged as a 2×2 factorial with two levels of dietary DDGS (0 v. 250 g/kg in gestating diets and 400 g/kg in lactating diets) and two levels of dietary l-carnitine (0 v. 100 mg/kg in gestating diets and 0 v. 200 mg/kg in lactating diets). Distillers dried grains with solubles had no significant effect on litter size but significantly reduced the birth weights and weaning weights of piglets (P<0.05). Distillers dried grains with solubles reduced the antioxidant enzyme activities (P<0.05) and increased the malondialdehyde level in the plasma of sows on day 60 of gestation (P=0.004) and day 14 of lactation (P=0.008). The compositions of colostrum and milk were not affected by inclusion of DDGS and dietary l-carnitine (P>0.05). Supplementing the diets with l-carnitine had no significant effect of total litter size (P>0.05) but increased the number of piglets born alive and piglets weaned, birth weight and weaning weight of piglets and litter weight at birth and weaning (P<0.05). l-carnitine supplementation also increased the concentration of l-carnitine in milk and l-carnitine status of piglets (P<0.05). The antioxidant enzyme activities of new born and weaning piglets were increased (P<0.05) by maternal dietary l-carnitine but this did not extend to finishing pigs. In conclusion, including DDGS in the sows diet could induce oxidative stress, which may be associated with the reduced individual birth and weaning weight of piglets. Dietary l-carnitine supplementation improved the antioxidant and l-carnitine status of sows, which may be associated with the improved reproduction and piglet performance and the antioxidant status of piglets at birth and weaning. There were no interactions between DDGS and l-carnitine.     

Mechanism of the inhibitory effect of zwitterionic drugs (levofloxacin and grepafloxacin) on carnitine transporter (OCTN2) in Caco-2 cells

l-Carnitine plays an important role in lipid metabolism by facilitating the transport of long-chain fatty acids across the mitochondrial inner membrane followed by fatty acid beta-oxidation. It is known that l-carnitine exists as a zwitterion and that member of the OCTN family play an important role in its transport. The aims of this study were to characterize l-carnitine transport in the intestine by using Caco-2 cells and to elucidate the effects of levofloxacin (LVFX) and grepafloxacin (GPFX), which are zwitterionic drugs, on l-carnitine uptake. Kinetic analysis showed that the half-saturation Na⁺ concentration, Hill coefficient and K_m value of l-carnitine uptake in Caco-2 cells were 10.3 ± 4.5 mM, 1.09 and 8.0 ± 1.0 μM, respectively, suggesting that OCTN2 mainly transports l-carnitine. LVFX and GPFX have two pK_a values and the existence ratio of their zwitterionic forms is higher under a neutral condition than under an acidic condition. Experiments on the inhibitory effect of LVFX and GPFX on l-carnitine uptake showed that LVFX and GPFX inhibited l-carnitine uptake more strongly at pH 7.4 than at pH 5.5. It was concluded that the zwitterionic form of drugs plays an important role in inhibition of OCTN2 function.     

The intracellular localization and properties of carnitine acetyltransferase from ram spermatozoa

Although spermatozoa possess a very active carnitine acetyltransferase, there is no satisfactory explanation for such a high activity. In order to help elucidate possible roles for carnitine acetyltransferase in spermatozoa, we examined the intracellular location and properties of carnitine acetyltransferase from ejaculated ram spermatozoa. The spermatozoa were disrupted by hypotonic treatment with 10 mm phosphate buffer (pH 7.4), followed by mild sonication. The resulting homogenate was separated by sucrose step-gradient centrifugation into soluble, plasma membrane, acrosomal membrane, and mitochondrial fractions. These fractions were characterized by electron microscopy and marker enzyme assays. The particulate fractions were made soluble by treatment with 0.1% deoxycholate and then were assayed for carnitine acetyltransferase activity. Carnitine acetyltransferase activity was found exclusively in the mitochondrial fraction with a specific activity of 0.151 μmol CoASH · min^?1 · mg^?1. The apparent K_m values for acetyl-CoA and l-carnitine were 1.1 × 10^?5 and 1.3 × 10^?4m respectively.     

Effect of orally administered l-carnitine on selected biochemical indicators of lactating Tuj-ewes

The effect of orally administered l-carnitine on biochemical parameters was examined in lactating Tuj-ewes. Ewes were orally given 500 mg of l-carnitine daily for 3 weeks. To evaluate the changes on selected blood indicators (total protein, albumin, glucose, triglyceride, cholesterol, urea, aspartate amino transferase, alanine amino transferase, lipase, triiodothyronine and thyroxine), blood samples were collected at the beginning of the study, and at the end of 1st, 2nd and 3rd week of study. Oral administration of supplemental carnitine significantly decreased serum triglyceride (P < 0.05), glucose (P < 0.05), cholesterol (P < 0.05) and triiodothyronine (P < 0.05) concentrations. In addition, serum thyroxine (P < 0.001) and albumin (P < 0.01) concentrations were significantly elevated as a result of oral carnitine treatment. These results suggest that supplemental l-carnitine improves selected biochemical indicators in Tuj-ewes.     

The effects of substrates on the optical rotatory dispersion of carnitine acetyltransferase

1. The optical rotatory dispersion of carnitine acetyltransferase is altered in the presence of l-carnitine or acetyl-l-carnitine. These changes, which include an increase in the reduced mean residue rotation at 233nm. ([M'](233)), suggest that substrate binding causes the enzyme to unfold. 2. CoA and acetyl-CoA have no immediate effect on [M'](233) and CoA has no effect on the change in this parameter induced by l-carnitine. 3. The change in [M'](233) was used as a measure of the degree of saturation of the enzyme with carnitine substrates. Dissociation constants for the enzyme complexes with l-carnitine, d-carnitine and acetyl-l-carnitine were determined in this way. 4. Prolonged incubation of carnitine acetyltransferase in the presence of CoA leads to a small increase in the value of [M'](233) accompanied by irreversible inhibition of the enzyme. 5. Optical-rotatory-dispersion studies of two specifically inhibited enzyme forms are reported.     

Chronotropic and inotropic effects of atrial peptides on the isolated systemic heart ofOctopus vulgaris

Summary The chronotropic and inotropic effects of four atrial peptides (cardiodilatin 1–16, atrial natriuretic factor 8–33 and atriopeptin I and III) on the isolated systemic heart ofOctopus vulgaris were studied.Using a preparation that produces a physiological stroke volume at physiological input pressures, it was found that ANF, atriopeptin I and atriopeptin III exerted both negative chronotropic and inotropic effects. In contrast, cardiodilatin produced a positive inotropic effect.A dose-response curve of ANF is reported, showing a threshold concentration of about 10^–12 M.The pharmacological and physiological implications of these results are discussed in relation to some characteristics of the cephalopod systemic heart.     

Effect of L-carnitine administration on the seminal characteristics of oligoasthenospermic stallions

The effect of orally administered l-carnitine on the quality of semen obtained from stallions with different semen qualities was investigated. Four stallions with proven fertility (high motility group, HM) and with normal seminal characteristics (>50% progressive motility and > 80 x 10(6) spermatozoa/ml), and four questionable breeders (low motility group, LM) with <50% of sperm progressive motility and < 80 x 10(6) spermatozoa/ml, received p.o. 20 g of l-carnitine for 60 days. Blood and semen samples were collected before treatment (T0) and after 30 (T1) and 60 days (T2). Semen evaluation were performed on five consecutive daily ejaculates (n = 120 ejaculates) and conventional semen analysis was carried out on each ejaculate, both at collection and after refrigeration for 24, 48, and 72 h. Furthermore l-carnitine, acetylcarnitine, pyruvate, and lactate concentrations, and carnitine acetyltransferase activity (CAT) were determined both in raw semen and seminal plasma. There were an increase in progressive motile spermatozoa only in the LM group (26.8 +/- 12.9, 39.1 +/- 15.5, and 48.8 +/- 8.6 for T0, T1, and T2, respectively). Free seminal plasma carnitine concentration was higher in the LM group compared to the HM one. Both pyruvate and lactate were higher in the LM group. Raw semen and seminal plasma carnitine and acetylcarnitine levels correlate positively with both sperm concentration and progressive motility; moreover, acetylcarnitine content was positively correlated with total motile morphologically normal spermatozoa. In conclusion, oral administration of l-carnitine to stallions with questionable seminal characteristics may improve spermatozoa kinetics and morphological characteristics; whereas, it seem to be ineffective in normospermic animals.     

Purification and properties of carnitine acetyltransferases from bovine spermatozoa and heart

To investigate the physical and kinetic properties of sperm carnitine acetyltransferase, the enzyme was purified from bovine spermatozoa and heart muscle. Carnitine acetyltransferase was purified 580-fold from ejaculated bovine spermatozoa to a specific activity of 85 units/mg protein (95% homogeneity). Sperm carnitine acetyltransferase was characterized as a single polypeptide of M_r 62,000 and pI 8.2. Heart carnitine acetyltransferase was purified 650-fold by the same procedure to a final specific activity of 71 units/mg protein. The kinetic properties of purified bovine sperm carnitine acetyltransferase were consistent with the proposed function of this enzyme in acetylcarnitine pool formation. Product inhibition by either acetyl-l-carnitine or CoASH was not sufficient to predict significant in vivo inhibition of acetyl transfer. At high concentrations of l-carnitine, bovine sperm and heart carnitine acetyltransferases were most active with propionyl- and butyryl-CoA substrates, although octanoyl-, iso-butyryl-, and iso-valeryl-CoA were acceptable substrates. Binding of one substrate was enhanced by the presence of the second substrate. Carnitine analogs that have significance in reproduction, such as phosphorylcholine and taurine, did not inhibit carnitine acetyltransferase. Bovine sperm and heart carnitine acetyltransferases were indistinguishable on the basis of purification behavior, pI, pH optima, kinetic properties, acyl-CoA specificity, and sensitivity to sulfhydryl reagents and divalent cations; thus there was no indication that bovine sperm carnitine acetyltransferase is a sperm-specific isozyme.     

Expression and localization of organic cation/carnitine transporter OCTN2 in Caco-2 cells

l-Carnitine is derived both from dietary sources and biosynthesis. Dietary carnitine is absorbed in the small intestine and then distributed to other organs. Previous studies using Caco-2 cells demonstrated that the transport of l-carnitine in the intestine involves a carrier-mediated system. The purpose of this study was to determine whether the uptake of l-carnitine in Caco-2 cells is mediated by the recently identified organic cation/carnitine transporter (OCTN2). Kinetics of l-[(3)H]carnitine uptake were investigated with or without specific inhibitors. l-Carnitine uptake in mature cells was sodium dependent and linear with time. K(m) and V(max) values for saturable uptake were 14.07 +/- 1.70 micro M and 26.3 +/- 0.80 pmol. mg protein(-1). 6 min(-1), respectively. l-carnitine uptake was inhibited (P < 0.05-0.01) by valproate and other organic cations. Anti-OCTN2 antibodies recognized a protein in the brush-border membrane (BBM) of Caco-2 cells with an apparent molecular mass of 60 kDa. The OCTN2 expression was confirmed by double immunostaining. Our results demonstrate that l-carnitine uptake in differentiated Caco-2 cells is primarily mediated by OCTN2, located on the BBM.     

Metabolism of pyruvate and carnitine esters in bovine epididymal sperm mitochondria

Filipin-treated bovine epididymal spermatozoa have been used to study mitochondrial l-acetylcarnitine, l-palmitoylcarnitine, and pyruvate metabolism. The cells were supplemented with malate to allow rapid rates of substrate oxidation. The rate of l-palmitoylcarnitine-supported state 3 respiration was slow. In contrast, pyruvate, acetylcarnitine, or lactate supported rapid and approximately equal respiratory rates. l-Palmitoylcarnitine was a weak inhibitor of pyruvate-supported respiration and pyruvate use and a more potent inhibitor of l-acetylcarnitine. l-Carnitine was an effective inhibitor of l-acetylcarnitine oxidation; however, it did not influence l-palmitoylcarnitine oxidation or inhibit pyruvate utilization. Pyruvate (1.4 mm) disappearance was rapid and was complete within 6–7 min; the lactate produced during pyruvate metabolism was then oxidized. ATP synthesis was constant throughout the 20-min incubation. With pyruvate plus l-acetylcarnitine as substrate, the l-acetylcarnitine concentration initially dropped and then recovered to a level that was dependent on free carnitine addition. Data obtained from experiments using [2-¹⁴C]pyruvate indicated that the ¹⁴C label from pyruvate and lactate entered the l-acetylcarnitine pool and labeling was maximal when free l-carnitine was added. The rate of citrate synthesis was maximal when pyruvate was being metabolized; the largest total accumulation occurred when all three substrates were included in the incubation. The data suggest that the high NAD⁺/ NADH maintained during pyruvate metabolism may restrict flux through the citric acid cycle. The relationships of l-carnitine and the l-carnitine esters to pyruvate metabolism are discussed.     

Salient effects of l-carnitine on adenine-nucleotide loss and coenzyme A acylation in the diabetic heart perfused with excess palmitic acid: A phosphorus-31 NMR and chemical extract study

The beneficial effects of l-carnitine perfusion on energy metabolism and coenzyme A acylation were studied in isolated hearts from control and diabetic rats. All hearts were perfused at a constant flow rate with a glucose/albumin buffer which contained 2.0 mM palmitate. ³¹P-NMR was utilized to assess sequential phosphocreatine and ATP metabolism during 1 h of recirculation perfusion. l-Carnitine (5.0 mM final concentration) was added after 12 min of baseline recirculation perfusion. Frozen samples were taken after 1 h of recirculation perfusion for spectrophotometric analysis of high-energy phosphates and the free and acylated fractions of coenzyme A. l-Carnitine perfusion of diabetic hearts attenuated or prevented the reduction of ATP observed in untreated diabetic hearts. It also attenuated the accumulation of long-chain fatty-acyl coenzyme A. Although l-carnitine improved myocardial function in diabetic hearts, this was independent of any direct effect on physiological indices. Thus, the salutory effect of acute perfusion with l-carnitine on energy metabolism in the isolated perfused diabetic rat heart appears to be a direct effect on lipid metabolism.     

l-Carnitine attenuates angiotensin II-induced proliferation of cardiac fibroblasts: role of NADPH oxidase inhibition and decreased sphingosine-1-phosphate generation

The heart is unable to synthesize l-carnitine and is strictly dependent on the l-carnitine provided by the blood stream; however, additional studies are needed to better understand the mechanism of l-carnitine supplementation to the heart. The aim of this study was to evaluate the effects of l-carnitine on angiotensin II (Ang II)-induced cardiac fibroblast proliferation and to explore its intracellular mechanism(s). Cultured rat cardiac fibroblasts were pretreated with l-carnitine (1-30 mM) then stimulated with Ang II (100 nM). Ang II increased fibroblast proliferation and endothelin-1 expression, which were partially inhibited by l-carnitine. l-Carnitine also attenuated Ang II-induced NADPH oxidase activity, reactive oxygen species formation, extracellular signal-regulated kinase phosphorylation, activator protein-1-mediated reporter activity and sphingosine-1-phosphate generation. In addition, l-carnitine increased prostacyclin (PGI₂) generation in cardiac fibroblasts. siRNA transfection of PGI₂ synthase significantly reduced l-carnitine-induced PGI₂ and its anti-proliferation effects on cardiac fibroblasts. Furthermore, blockading potential PGI₂ receptors, including immunoprecipitation (IP) receptors and peroxisome proliferator-activated receptors alpha (PPARα) and delta , revealed that siRNA-mediated blockage of PPARα considerably reduced the anti-proliferation effect of l-carnitine. In summary, these results suggest that l-carnitine attenuates Ang II-induced effects (including NADPH oxidase activation, sphingosine-1-phosphate generation and cell proliferation) in part through PGI₂ and PPARα-signaling pathways.     

Isoproterenol effects on the contractility of papillary muscles in the heart of ground squirrel

This paper presents a study of the influence of isoproterenol (1 μM) on the force of isometric contractions (0.1–1.0 Hz; 30 ± 1°C; 1.8 mM Ca²⁺) of papillary muscles of the right ventricle in the heart of a ground squirrel during summer activity (n = 5) and hibernation season (activity between hibernation bouts, n = 4; torpor, n = 4; and arousal, n = 5). It is shown that isoproterenol increases the force of contraction (a positive inotropic effect) by 20 ± 3% and 61 ± 7% at stimulation frequencies of 0.4 and 1.0 Hz, respectively. In animals of hibernating period the isoproterenol-induced increase in the force of contraction is rather brief (within 3 min after onset of the influence) and is accompanied by a 30–50% decrease in the force from the control level (a negative inotropic effect) at stimulation frequencies from 0.3 to 0.8 Hz. The positive isoproterenol inotropic effect in active summer ground squirrels is associated with a decrease in a relative value of the pause potentiating effect (a qualitative indicator of calcium content in sarcoplasmic reticulum), and the negative inotropic effect, with its increase. In all groups of animals under examination the isoproterenol inotropic effect (regardless of its direction) is accompanied by the acceleration of the temporal parameters of the contraction—relaxation cycle. The dependence of isoproterenol effects in the heart of hibernating animals on both seasonal changes in calcium homeostasis and the activity of the sympathetic nervous system is under discussion.     

Effects of l-carnitine supplementation to suckling piglets on carcass and meat quality at market age

In a previous study, carnitine supplementation to piglets during the suckling period resulted in an increased total muscle fibre number at weaning in piglets of low birth weight. The objective of the present study was to investigate whether this effect is maintained until market age and whether this would attenuate the negative consequences of low birth weight on carcass and meat quality. Using a split-plot design with litter as block, sex as whole plot and treatment as subplot, the effects of early-postnatal l-carnitine supplementation on female and castrated male piglets of low birth weight were investigated on a total of 56 German Landrace piglets from 14 litters. From days 7 to 27 of age piglets were orally supplemented once daily with 400 mg of l-carnitine dissolved in 1 ml of water or received an equal volume of water without carnitine. From weaning (day 28) until slaughter (day 166 of age) all pigs were fed standard diets. At weaning, carnitine-supplemented piglets had a twofold increased concentration of free carnitine (P < 0.001) and a lower concentration of non-esterified fatty acids (P < 0.05) in blood plasma indicating that carnitine became bioavailable and increased fatty acid utilization during the period of supplementation. Growth performance was not influenced by treatment in any growth period. Dual-energy X-ray absorptiometry revealed no differences in body composition between groups in weeks 12, 16 and 20 of age. LW at slaughter, carcass weight, measures of meat yield and fat accretion, as well as body composition by chemical analyses and dissection of primal cuts did not differ between treatments. No differences between control and carnitine-treated pigs in total fibre number (P = 0.85) and fibre cross-sectional area (P = 0.68) in m. semitendinosus (ST) measured at slaughter could be observed. The carnitine group tended to exhibit a smaller proportion of slow-twitch oxidative fibres (P = 0.08), a greater proportion of fast-twitch glycolytic fibres (P = 0.11), and increased specific lactate dehydrogenase activity (P = 0.09) in ST indicating a more glycolytic muscle metabolism. Compared with the controls, a lower pH₂₄ value was observed (P = 0.05) in ST muscle of carnitine-supplemented pigs, which – in castrates only – was associated with an increased drip loss (P < 0.01). Meat quality traits in m. longissimus were not influenced by treatment. In conclusion, our hypothesis that early-postnatal carnitine supplementation to piglets of low birth weight permanently increases myofibre number and improves later carcass and meat quality could not be confirmed by this experiment.     

Relative importance of malonyl CoA and carnitine in maturation of fatty acid oxidation in newborn rabbit heart

After birth, a dramatic increase in fatty acid oxidation occurs in the heart, which has been attributed to an increase in l-carnitine levels and a switch from the liver (L) to muscle (M) isoform of carnitine palmitoyltransferase (CPT)-1. However, because M-CPT-1 is more sensitive to inhibition by malonyl CoA, a potent endogenous regulator of fatty acid oxidation, a switch to the M-CPT-1 isoform should theoretically decrease fatty acid oxidation. Because of this discrepancy, we assessed the contributions of myocardial l-carnitine content and CPT-1 isoform expression and kinetics to the maturation of fatty acid oxidation in newborn rabbit hearts. Although fatty acid oxidation rates increased between 1 and 14 days after birth, myocardial l-carnitine concentrations did not increase. Changes in the expression of L-CPT-1 or M-CPT-1 mRNA after birth also did not parallel the increase in fatty acid oxidation. The K(m) of CPT-1 for carnitine and the IC(50) for malonyl CoA remained unchanged between 1 and 10 days after birth. However, malonyl CoA levels dramatically decreased, due in part to an increase in malonyl CoA decarboxylase activity. Our data suggest that a decrease in malonyl CoA control of CPT-1 is primarily responsible for the increase in fatty acid oxidation seen in the newborn heart.     

Effects of serum,its protein and lipid extracts,and commercial serum proteins and lipid on the isolated frog heart

Summary This study investigates the inotropic effects of serum, its protein and lipid extracts, and commercial serum proteins and lipid on the isolated, spontaneously-beating heart and superfused, hypodynamic ventricle of the frog. Serum taken from either man, horse, calf, frog, or rabbit evoked marked positive inotropic responses which were unaffected by cholinergic, serotonergic, and adrenergic receptor antagonists. Dialysed serum (dialisand) and void volume fractions from Sephadex G200–120 columns corresponding to large molecular weight constituents evoked marked positive inotropic responses. When serum was separated into fractions containing either proteins or lipids/lipoproteins by high-density ultracentrifugation or activated charcoal, both extracts evoked marked positive inotropic responses. Commerical serum globulins and serum containing a high proportion of immunoglobulins elicited large increases in contractile force, whereas serum albumin evoked a negative inotropic effect. Serum which was either boiled and/or treated with chymotrypsin to denature proteins also caused a marked increase in isometric twitch tension in the frog heart. Similar inotropic response was obtained with fractions of boiled serum eluted on columns of Sephadex G200–120. These fractions corresponded to molecular weight in the region of 60–70 kDa. However, the inotropic effect of boiled serum was abolished following pretreatment with lipase. Superfusion of frog hearts with commercial cardiolipin resulted in marked dose-dependent increases in contractile force. The results demonstrate the presence of at least two large molecular weight cardioactive principles in serum. These substances are comparable in size to constituents of serum proteins (e.g., globulins and immuno-globulins) and serum lipids/lipoproteins (e.g., cardiolipin) and may serve as physiological regulators of cardiac function.Abbreviations Ca ²⁺ Calcium - Da dalton - IgG immunoglobulins - Na ⁺ Sodium - K ⁺ potassium