Chain Fatty Acid Transport Research Articles

Cellular disulfide-reducing capacity: An integrated measure of cell redox capacity

To assess the disulfide reduction capacity of intact cells, EA.hy926 endothelial cells were incubated with α-lipoic acid in the presence of 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB). α-Lipoic acid was reduced within cells to dihydrolipoic acid, which could be quantified upon efflux from the cells as reduction of DTNB. Uptake of both α-lipoic acid and α-lipoamide occurred at least in part via a medium chain fatty acid transporter, based on inhibition by octanoate. α-Lipoic acid was reduced within cells by pyridine nucleotide-disulfide oxidoreductases, since it is not reduced by GSH and since its reduction was inhibited by carmustine. Nonetheless, reduction was also dependent on the cellular redox environment, since it was inhibited by the redox cycling of menadione, by decreasing intracellular GSH, and by reduction of dehydroascorbate. Together, these results show that α-lipoic acid-dependent DTNB reduction provides a simple method to assess the disulfide-reducing capacity of intact cells, especially as determined by pyridine nucleotide-disulfide oxidoreductases.

Fatty acid transport protein 1 and long-chain acyl coenzyme A synthetase 1 interact in adipocytes

The fatty acid transport proteins (FATP) and long-chain acyl coenzyme A synthetase (ACSL) proteins have been shown to play a role in facilitating long-chain fatty acid (LCFA) transport in mammalian cells under physiologic conditions. The involvement of both FATP and ACSL proteins is consistent with the model of vectorial acylation, in which fatty acid transport is coupled to esterification. This study was undertaken to determine whether the functions of these proteins are coordinated through a protein-protein interaction that might serve as a point of regulation for cellular fatty acid transport. We demonstrate for the first time that FATP1 and ACSL1 coimmunoprecipitate in 3T3-L1 adipocytes, indicating that these proteins form an oligomeric complex. The efficiency of FATP1 and ACSL1 coimmunoprecipitation is unaltered by acute insulin treatment, which stimulates fatty acid uptake, or by treatment with isoproterenol, which decreases fatty acid uptake and stimulates lipolysis. Moreover, inhibition of ACSL1 activity in adipocytes impairs fatty acid uptake, suggesting that esterification is essential for fatty acid transport. Together, our findings suggest that a constitutive interaction between FATP1 and ACSL1 contributes to the efficient cellular uptake of LCFAs in adipocytes through vectorial acylation.

Mass spectrometric identification of apical membrane proteins from perfusion‐biotinylated rat kidney inner medullary collecting ducts

To identify apical plasma membrane proteins of rat kidney inner medullary collecting ducts (IMCD), we developed a technique combining retrograde perfusion of the collecting ducts for surface biotinylation with mass spectrometry of labeled proteins. The inner medullas isolated from the rat kidneys were perfused at 4 °C with sulfo-NHS-LC-biotin to biotinylate apical membrane proteins from the lumen. Apical surface biotinylation was confirmed by fluorescence confocal microscopy using FITC-streptavidin to label sites of biotinylation. Preliminary experiments revealed that pre-perfusion with 4% paraformaldehyde was needed to prevent internalization of the biotin. The biotinylated apical membrane proteins were purified with CaptAvidin agarose beads and separated by SDS-PAGE. The resulting gels were sliced into 16 pieces that were subjected to in-gel trypsin digestion. Extracted peptides were analyzed by liquid chromatography/tandem mass spectrometry. Using this method, we identified 28 proteins known to be plasma membrane proteins or peripheral membrane proteins. Western blotting of selected proteins confirmed IMCD expression of polyserase I, activin A receptor type II, adenylyl cyclase V/VI, long chain fatty acid transporter, and NHE2. Immunofluorescence staining and confocal microscopy confirmed the apical localization in the IMCD of activin A receptor type II, NHE2, and H/K ATPase type I. This study identifies several apical biomarkers that can be used for membrane fractionation studies and introduces a new surface labeling technique that can be used for study of mechanisms whereby vasopressin regulates AQP-2, UT-A, and ENaC in the IMCD.

Serrated Pathway and APC (Conventional)-Type Colorectal Polyps

This review addresses the genetic mutations and cell signaling pathway alterations in colorectal premalignant polyps, focusing on the link between molecular changes and morphologic features. Biallelic APC (adenomatous polyposis coli) mutations are directly responsible for the specific and characteristic cytologic features of dysplastic cells in conventional tubular adenomas. Sessile serrated adenomas (SSAs) are the precursor lesions of the serrated neoplasia pathway. The BRAF activating mutation and hypermethylation of SLC5A8, which mediates short chain fatty acid transport, may be the important events in the genesis of SSAs. Intracellular butyrate inhibits histone deacetylase, allowing histone hyperacetylation and, eventually, transcriptional activation of specific genes. Decreased p21(WAF1/CIP1) and activation of the mitogen-activated protein kinase pathway may be the key intermediary alterations. Progressive loss of cell cycle control and decreased and altered cytoplasmic differentiation produce the characteristic constellation of morphologic changes of SSAs and traditional serrated adenomas.

Bacterial Long Chain Fatty Acid Transport: Gateway to a Fatty Acid-responsive Signaling System

Bacterial Long Chain Fatty Acid Transport: Gateway to a Fatty Acid-responsive Signaling System

A Novel Function for Fatty Acid Translocase (FAT)/CD36: INVOLVEMENT IN LONG CHAIN FATTY ACID TRANSFER INTO THE MITOCHONDRIA

Fatty acid translocase (FAT)/CD36 is a long chain fatty acid transporter present at the plasma membrane, as well as in intracellular pools of skeletal muscle. In this study, we assessed the unexpected presence of FAT/CD36 in both subsarcolemmal and intermyofibril fractions of highly purified mitochondria. Functional assessments demonstrated that the mitochondria could bind (14)C-labeled palmitate, but could only oxidize it in the presence of carnitine. However, the addition of sulfo-N-succinimidyl oleate, a known inhibitor of FAT/CD36, resulted in an 87 and 85% reduction of palmitate oxidation in subsarcolemmal and intermyofibril fractions, respectively. Further studies revealed that maximal carnitine palmitoyltransferase I (CPTI) activity in vitro was inhibited by succinimidyl oleate (42 and 48% reduction). Interestingly, CPTI immunoprecipitated with FAT/CD36, indicating a physical pairing. Tissue differences in mitochondrial FAT/CD36 protein follow the same pattern as the capacity for fatty acid oxidation (heart >> red muscle > white muscle). Additionally, chronic stimulation of hindlimb muscles (7 days) increased FAT/CD36 expression and also resulted in a concomitant increase in mitochondrial FAT/CD36 content (46 and 47% increase). Interestingly, with acute electrical stimulation of hindlimb muscles (30 min), FAT/CD36 expression was not altered, but there was an increase in the mitochondrial content of FAT/CD36 compared with the non-stimulated control limb (35 and 37% increase). Together, these data suggest a role for FAT/CD36 in mitochondrial long chain fatty acid uptake and demonstrate system flexibility to match FAT/CD36 mitochondrial content with an increased capacity for fatty acid oxidation, possibly involving translocation of FAT/CD36 to the mitochondria.

Carnitine Supplementation Fails to Maximize Fat Mass Loss Induced by Endurance Training in Rats

Background/Aims: Carnitine is a co-factor of the enzymatic system involved in long chain fatty acid transport across the mitochondrial membrane. This physiological role of carnitine raised the hypothesis that this compound could act as a ‘fat burner’ by optimizing fat oxidation and consequently reducing its availability for storage. Our aim was to verify whether carnitine supplementation could maximize fat mass loss in trained rats. Methods: Male Wistar rats (200 g) were divided into four groups: control (C), sedentary supplemented (S), trained (T) and trained supplemented (TS). The training protocol consisted of bouts of swimming exercise (60 min·day^–1) for 6 weeks. During the last 14 days, before sacrifice, the supplemented groups received a daily dose of 28 mg· kg^–1 of L-carnitine. Carcass fat content, weight and fat content of adipose tissues were evaluated in all experimental groups. Results: Our results indicate that carnitine feeding, per se, failed to promote fat mass loss. Endurance training successfully induced a decrease in the fat content in the carcass (28%) and the weight of adipose tissues (retroperitoneal and mesenteric depots by 41 and 20%, respectively) in comparison to C. Despite the augmented carnitine content in the soleus mitochondria (2-fold) observed in TS, the higher content did not maximize the fat loss induced by endurance training. Conclusions: Our data strongly suggest that endurance training, rather than carnitine content, is the major factor involved in fat mass loss.

Chronic Leptin Administration Decreases Fatty Acid Uptake and Fatty Acid Transporters in Rat Skeletal Muscle

Chronic leptin administration reduces triacylglycerol content in skeletal muscle. We hypothesized that chronic leptin treatment, within physiologic limits, would reduce the fatty acid uptake capacity of red and white skeletal muscle due to a reduction in transport protein expression (fatty acid translocase (FAT/CD36) and plasma membrane-associated fatty acid-binding protein (FABPpm)) at the plasma membrane. Female Sprague-Dawley rats were infused for 2 weeks with leptin (0.5 mg/kg/day) using subcutaneously implanted miniosmotic pumps. Control and pair-fed animals received saline-filled implants. Leptin levels were significantly elevated (approximately 4-fold; p < 0.001) in treated animals, whereas pair-fed treated animals had reduced serum leptin levels (approximately -2-fold; p < 0.01) relative to controls. Palmitate transport rates into giant sarcolemmal vesicles were reduced following leptin treatment in both red (-45%) and white (-84%) skeletal muscle compared with control and pair-fed animals (p < 0.05). Leptin treatment reduced FAT mRNA (red, -70%, p < 0.001; white, -48%, p < 0.01) and FAT/CD36 protein expression (red, -32%; p < 0.05) in whole muscle homogenates, whereas FABPpm mRNA and protein expression were unaltered. However, in leptin-treated animals plasma membrane fractions of both FAT/CD36 and FABPpm protein expression were significantly reduced in red (-28 and -34%, respectively) and white (-44 and -56%, respectively) muscles (p < 0.05). Across all experimental treatments and muscles, palmitate uptake by giant sarcolemmal vesicles was highly correlated with the plasma membrane FAT/CD36 protein (r = 0.88, p < 0.01) and plasma membrane FABPpm protein (r = 0.94, p < 0.01). These studies provide the first evidence that protein-mediated long chain fatty acid transport is subject to long term regulation by leptin.

Regulation of CD36 expression in human melanoma cells.

CD36 is a suspected facilitator of long chain fatty acid transport and as a thrombospondin (TSP) receptor, thereby being implicated in cell proliferation, angiogenesis and tumor metastasis. The human amelanotic melanoma cell line, C32, is known to express CD36 and has been as a model for studying TSP binding. The purpose of this study was to investigate the regulation of CD36 expression in the C32 cell line. C32 cells were treated with 12-O-tetradecanoylphorobol-13-acetate (TPA)(10 microM), insulin (174 nM), ibuprofen (0.3 mM) and oleic acid. CD36 mRNA levels were determined by Northern Blot analysis using human CD36 cDNA probe. Western blot analysis utilized the human anti-CD36 antibody. Protein and mRNA concentration was determined by autoradiography, densitometry and NIH image software. Statistical analysis was by Student's t-test with P < 0.05 considered significant. CD36 mRNA levels were decreased 2.2 fold in C32 cells treated with TPA (p < 0.05) compared to control cells. Insulin treated cells showed a 30% increase (p < 0.05) in CD36 mRNA levels. Ibuprofen, a regulator of peroxisomal proliferation activated receptor (PPAR) alpha, was found to increase CD36 protein levels by 50% (p < 0.05). Oleic acid had no effect on CD36 mRNA or protein levels. The finding that the tumor promoter TPA significantly decreases CD36 mRNA levels, while insulin and ibuprofen increase CD36 expression, may have important implications in tumor biology. The regulation of CD36 expression in tumor cells may play an important role in tumor growth, metastasis and angiogenesis.

Coupling of Mitochondrial Fatty Acid Uptake to Oxidative Flux in the Intact Heart

The coordination of long chain fatty acid (LCFA) transport across the mitochondrial membrane ( V PAL) with subsequent oxidation rate through β-oxidation and the tricarboxylic acid (TCA) cycle ( V tca) has been difficult to characterize in the intact heart. Kinetic analysis of dynamic 13C-NMR distinguished these flux rates in isolated rabbit hearts. Hearts were perfused in a 9.4 T magnet with either 0.5 mM [2,4,6,8,10,12,14,16- 13C 8] palmitate ( n = 4), or 0.5 mM 13C-labeled palmitate plus 0.08 mM unlabeled butyrate ( n = 4). Butyrate is a short chain fatty acid (SCFA) that bypasses the LCFA transporters of mitochondria. In hearts oxidizing palmitate alone, the ratio of V TCA to V PAL was 8:1. This is consistent with one molecule of palmitate yielding eight molecules of acetyl-CoA for the subsequent oxidation through the TCA cycle. Addition of butyrate elevated this ratio; V TCA/ V PAL = 12:1 due to an SCFA-induced increase in V TCA of 43% ( p < 0.05). However, SCFA oxidation did not significantly reduce palmitate transport into the mitochondria: V PAL = 1.0 ± 0.2 μmol/min/g dw with palmitate alone versus 0.9 ± 0.1 with palmitate plus butyrate. Thus, the products of β-oxidation are preferentially channeled to the TCA cycle, away from mitochondrial efflux via carnitine acetyltransferase.

Selective Up-regulation of Fatty Acid Uptake by Adipocytes Characterizes Both Genetic and Diet-induced Obesity in Rodents

Long chain fatty acid transport is selectively up-regulated in adipocytes of Zucker fatty rats, diverting fatty acids from sites of oxidation toward storage in adipose tissue. To determine whether this is a general feature of obesity, we studied [(3)H]oleate uptake by adipocytes and hepatocytes from 1) homozygous male obese (ob), diabetic (db), fat (fat), and tubby (tub) mice and from 2) male Harlan Sprague-Dawley rats fed for 7 weeks a diet containing 55% of calories from fat. V(max) and K(m) were compared with controls of the appropriate background strain (C57BL/6J or C57BLKS) or diet (13% of calories from fat). V(max) for adipocyte fatty acid uptake was increased 5-6-fold in ob, db, fat, and tub mice versus controls (p < 0.001), whereas no differences were seen in the corresponding hepatocytes. Similar changes occurred in fat-fed rats. Of three membrane fatty acid transporters expressed in adipocytes, plasma membrane fatty acid-binding protein mRNA was increased 9-11-fold in ob and db, which lack a competent leptin/leptin receptor system, but was not increased in fat and tub, i.e. in strains with normal leptin signaling capability; fatty acid translocase mRNA was increased 2.2-6.5-fold in tub, ob, and fat adipocytes, but not in db adipocytes; and only marginal changes in fatty acid transport protein 1 mRNA were found in any of the mutant strains. Adipocyte fatty acid uptake is generally increased in murine obesity models, but up-regulation of individual transporters depends on the specific pathophysiology. Leptin may normally down-regulate expression of plasma membrane fatty acid binding protein.

Substitution of Alanine for Serine 250 in the Murine Fatty Acid Transport Protein Inhibits Long Chain Fatty Acid Transport

The murine fatty acid transport protein (FATP) was identified on the basis of its ability to facilitate uptake of long chain fatty acids (LCFAs) when expressed in mammalian cells. To delineate FATP domains important for transport function, we cloned the human heart FATP ortholog. Comparison of the human, murine, and yeast amino acid sequences identified a highly conserved motif, IYTSGTTGXPK, also found in a number of proteins that form adenylated intermediates. We demonstrate that depletion of intracellular ATP dramatically reduces FATP-mediated LCFA uptake. Furthermore, wild-type FATP specifically binds [alpha-32P]azido-ATP. Introduction of a serine to alanine substitution (S250A) in the IYTSGTTGXPK motif produces an appropriately expressed and metabolized mutant FATP that demonstrates diminished LCFA transport function and decreased [alpha-32P]azido-ATP binding. These results are consistent with a mechanism of action for FATP involving ATP binding that is dependent on serine 250 of the IYTSGTTGXPK motif.

Fatty acid uptake by Caco-2 human intestinal cells

The Caco-2 human enterocytic cell line was used to study the kinetics and mechanism of intestinal long chain fatty acid uptake. Initial rates of palmitate (16:0), oleate (18:1), and octanoate (8:0) uptake were determined for adherent cells at greater than 7 days confluence. Uptake of long chain 18:1 and 16:0 by cells grown on coverslips was saturable with an apparent Km of 0.3 microM, but also included a notable diffusive component. Uptake of short chain 8:0, on the other hand, was linear up to 10 microM. Cells grown on permeable Transwell filters were used to study uptake at the apical versus the basolateral membrane. Uptake of long chain (18:1 and 16:0), but not short chain (8:0), fatty acid was saturable at both surfaces with a similar Km of 0.3 microM. In addition, long chain but not short chain fatty acid uptake was competitively inhibitable. Western blot analysis demonstrated that Caco-2 cells express a protein immunoreactive with antibodies to the rat liver plasma membrane fatty acid binding protein (FABPpm), which is thought to be involved in long chain fatty acid transport. Nevertheless, long chain fatty acid uptake was not inhibited by pretreatment of the cells with an FABPpm antibody, nor by pretreatment with two proteases. These data support a saturable component in the transport of long chain but not short chain fatty acids by human intestinal epithelial cells, which may involve an as yet unknown plasma membrane protein.

Expression cloning and characterization of a novel adipocyte long chain fatty acid transport protein: Schaffer JE, Lodish HF. Cell 1994; 79: 427–436

Long chain fatty acids (LCFAs) are an important energy substrate used by cardiac myocytes and other cells, but the mechanism whereby these molecules cross the plasma membrane is poorly understood. We used an expression cloning strategy and a cDNA library from 3T3-L1 adipocytes to identify a cDNA that, when expressed in cultured cells, augments uptake of LCFAs. This cDNA encodes a novel 646 amino acid fatty acid transport protein (FATP) with six predicted membrane spanning regions and that is integrally associated with membranes. Immunocytochemistry and subcellular fractionation of 3T3-L1 adipocytes show that FATP is localized to the plasma membrane. We propose that FATP is a plasma membrane transporter for LCFAs.

Expression cloning and characterization of a novel adipocyte long chain fatty acid transport protein

Long chain fatty acids (LCFAs) are an important energy substrate used by cardiac myocytes and other cells, but the mechanism whereby these molecules cross the plasma membrane is poorly understood. We used an expression cloning strategy and a cDNA library from 3T3-L1 adipocytes to identify a cDNA that, when expressed in cultured cells, augments uptake of LCFAs. This cDNA encodes a novel 646 amino acid fatty acid transport protein (FATP) with six predicted membrane-spanning regions and that is integrally associated with membranes. Immunocytochemistry and subcellular fractionation of 3T3-L1 adipocytes show that FATP is localized to the plasma membrane. We propose that FATP is a plasma membrane transporter for LCFAs.

On the Mechanism of Long Chain Fatty Acid Transport in Cardiomyocytes as Facilitated by Cytoplasmic Fatty Acid-binding Protein

Fatty acid-binding protein (FABP) is abundantly present in the cytoplasm of the cardiomyocyte, i.e. the cell which causes the contractile activity of the heart. Although FABP is thought to act as an intracellular long chain fatty acid (FA) carrier, definite experimental proof on this putative function has yet to be obtained. In the present study, experimental results from several authors were combined in an attempt to elucidate the precise physiological function of heart-type FABP in cardiac FA transport. It was calculated that, under normal conditions, the major part of FA in the cardiomyocyte is dissolved in lipid bilayers and that the presence of FABP in the heart enhances the aqueous solubility of FA more than 700-fold despite the fact that only a minor part (<2%) of the total FABP content is then complexed with FA. Moreover, it is shown that, as a result of the enhanced cytoplasmic solubility, the FA flux from sarcolemma (the cellular membrane of the cardiomyocyte) to mitochondria is increased at least 17-fold in the presence of physiological amounts of FABP compared with the hypothetical situation in which FABP is absent. These calculations indicate the involvement of FABP in the transport of FA from the sarcolemma to those mitochondria lying in the innermost region of the cardiomyocyte. The extent to which FABP facilitates FA trafficking through the cytoplasm of the cardiomyocyte under physiological circumstances remains, however, to be established.

Photoaffinity labeling of fatty acid-binding proteins involved in long chain fatty acid transport in Escherichia coli.

The photoreactive fatty acid 11-m-diazirinophenoxy-[11-3H]undecanoate was shown to be taken up specifically by the fatty acid transport system expressed in Escherichia coli grown on oleate. This photoreactive fatty acid analogue was therefore used to identify proteins involved in fatty acid uptake in E. coli. The fadL protein was labeled by the probe, confirmed to be exclusively in the outer membrane and to exhibit the heat modifiable behavior typical of outer membrane proteins. The apparent pI of the incompletely denatured form of the protein having the mobility of a 33-kDa protein was 4.6 while that of the fully denatured form was consistent with the calculated value of 5.2. The denaturation was reversible depending upon the protein to detergent ratios. The photoreactive fatty acid partitions into the outer membrane, resulting in extensive photolabeling of the lipid; a high affinity fatty acid-binding site is not apparent in total membranes labeled using free fatty acids due to this large binding capacity of the outer membrane. However, when the free fatty acid concentration was controlled by supplying it as a bovine serum albumin complex, the fadL protein exhibited saturable high affinity fatty acid binding, having an apparent Kd for the probe of 63 nM. The methods described very readily identify fatty acid-binding proteins: the fact that even when the sensitivity was increased 500-fold, no evidence was found for the presence of a fatty acid-binding protein in the inner membrane is consistent with the proposal that fatty acid permeation across the plasma membrane is not protein mediated but occurs by a simple diffusive mechanism.

667 L-CARNITINE ON FAT UTILIZATION IN INFANTS

L-carnitine (LC), which is essential for fat utilization, acts by facilitating long chain fatty acid transport into the mitochondrial matrix where B-oxidation occurs. The purpose of this prospective study was to determine if LC supplementation given to carnitine deficient infants would results in improved utilization of exogenously administered IV fat. Seventeen infants (gestational age 35.8±3.7 wks, postnatal age 13.6±7.3 wks, weight 3.3±1.0 kg) requiring a minimum of 7 days of parenteral nutrition (PN) and able to tolerate small quantities of enteral feedings were randomized into treatment and control groups. All infants had received nutritional support devoid of LC. Plasma carnitine (PC) levels did not vary significantly between groups in the pre-study period (control: 10.0±6.3 nM/ml; treatment: 9.4±6.0 nM/ml). Infants received 7 days of continuous nasogastric or gastric tube LC (50uM/k/d) or placebo. Fat was withheld and glucose reduced to 10% for 16 hrs prior to the delivery of a 0.5 gm/k IntralipidR bolus administered over 2 hrs. LC supplementation continued until termination of the fat bolus. Serial blood samples for triglycerides (TGY), free fatty acids (FFA), acetoacetate (AA), B-hydroxybutyrate (BOB) and PC were observed at 0 (start of lipid infusion), 2,4,6 and 8 hrs. Infants receiving carnitine had significantly greater (p<0.05) concentrations of BOB, total ketones (BOB plus AA), and PC at times 0,2,4,6 and 8 hrs when compared to controls. Significantly lower (p<0.05) FFA/BOB ratios were observed in the treatment group at 2 and 4 hours indicating improved ketogenesis. No significant differences were found between groups for TGY or FFA at any observation period. This study demonstrated improved fatty acid oxidation as evidenced by increased ketogenesis with LC supplementation in carnitine deficient infants.

Hepatic Gluconeogenic and Ketogenic Interrelationships in the Lactating Cow

Interrelationships between propionate, palmitate, and butyrate metabolism were investigated in vitro with [1-carbon-14] carboxyl substrates. Production of labeled glucose, ketone bodies, and carbon dioxide was used to estimate rates of bovine hepatic gluconeogenesis and ketogenesis. Incubations were with liver slices from eight lactating Holstein cows fed either a control or high concentrate-low fiber diet. Liver samples were acquired by trochar biopsy at 30, 60, 90, and 180 days postpartum. Ketone production from both palmitate and butyrate was highest in liver slices obtained at 30 days. Glucose production from labeled propionate was also highest in early lactation. The higher rates of gluconeogenesis and ketogenesis in early lactation were associated with higher hepatic carnitine palmitoyltransferase (EC 2.3.1.21) activity. Feeding the high concentrate enhanced gluconeogenesis from propionate and decreased ketogenesis from palmitate. Propionate addition (10mM) to incubation media also decreased the total amount of palmitate oxidized ([carbon-14] dioxide plus [carbon-14] ketones). Diet had no effect on hepatic butyrate metabolism. Results indicated that ketogenesis is regulated via rate of long chain fatty acid transport into the mitochondria. Stage of lactation has a greater influence on long and short chain fatty acid metabolism than does diet composition.

Long Chain Fatty Acid Transport by the Perfused Rat Kidney

Transport of the long chain fatty acid (LCFA), palmitate (C16), was studied in the isolated rat kidney perfused with Krebs-Henseleit bicarbonate buffer containing 1% defatted albumin. Because palmitate was extensively bound to albumin, its filtration was negligible and transport into renal tubular cells occurred across the peritubular membrane. Saturation of peritubular uptake of palmitate was observed with a maximum uptake of 2.4-2.5 mumol . g wet weight -1 . 20 min-1. Under the conditions of these experiments, uptake was not affected by attempts to alter fatty acid metabolism, by substances known to be transported by the organic acid transport system or by other LCFA.