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F H Leibach

Publications and source records attributed to F H Leibach.

At least 73 records · Page 4Linked to original sources
PubMed1998

Valacyclovir: a substrate for the intestinal and renal peptide transporters PEPT1 and PEPT2.

Valacyclovir is a prodrug of the antiviral agent acyclovir and it does not contain a peptide bond in its structure. We studied the interaction of valacyclovir with the peptide transporters in the human intestinal cell line Caco-2 and the rat kidney proximal tubular cell line SKPT which differentially express peptide transporters PEPT1 and PEPT2. The results of the studies done with these cell lines were confirmed with the cloned peptide transporters human PEPT1 and rat PEPT2, expressed heterologously in HeLa cells. The activity of the peptide transporters was assessed by measuring the uptake of radiolabeled glycylsarcosine in the presence of a H+ gradient. Valacyclovir inhibited the uptake of glycylsarcosine with an inhibition constant (Ki) of 0.49 +/- 0.04 mM in Caco-2 cells and 0.17 +/- 0.01 mM in SKPT cells. In both cell types, the inhibition was competitive. Acyclovir, in contrast to valacyclovir, did not interact with the peptide transporters. Similar results were obtained with heterologously expressed human PEPT1 and rat PEPT2. Valacyclovir inhibited the hPEPT1-mediated glycylsarcosine transport competitively with a Ki value of 0.74 +/- 0.14 mM. The rPEPT2-mediated transport of glycylsarcosine was also inhibited by valacyclovir competitively and the Ki value for the process was 0.39 +/- 0.03 mM. Acyclovir did not interact with either of these cloned peptide transporters. We conclude that valacyclovir is a substrate for the peptide transporters PEPT1 and PEPT2 and that a peptide bond is not a prerequisite for recognition as a substrate by the peptide transporters.

Acyclovir↗
PubMed1998

Identification of a potential substrate binding domain in the mammalian peptide transporters PEPT1 and PEPT2 using PEPT1-PEPT2 and PEPT2-PEPT1 chimeras.

The mammalian peptide transporters PEPT1 and PEPT2 are energized by a transmembrane electrochemical H+ gradient and exhibit similar broad substrate specificity. These transporters however differ in their affinity for substrates, PEPT1 being a low-affinity transporter and PEPT2 being a high-affinity transporter. To identify the substrate binding domain in PEPT1 and PEPT2 which is responsible for the differing affinities, we constructed a series of PEPT1-PEPT2 and PEPT2-PEPT1 chimeras using an in vivo restriction site-independent procedure and determined their substrate affinities. A comparison of these kinetic data for different chimeras with those of the wild-type PEPT1 and PEPT2 in conjunction with the specific structural PEPT1/PEPT2 crossover regions in these chimeras has led to the identification of a putative substrate binding site, which is comprised of the transmembrane domains 7, 8 and 9 of the transporters.

Animals↗
PubMed1998

Sodium-dependent homo- and hetero-exchange of neutral amino acids mediated by the amino acid transporter ATB degree.

We have investigated the functional characteristics of the human amino acid transporter ATB degree using the Xenopus laevis oocyte expression system. When expressed in oocytes, ATB degree mediates the uptake of neutral amino acids in an Na(+)-dependent manner. In addition, this transporter is able to mediate the efflux of intracellular neutral amino acids in exchange with extracellular neutral amino acids. This homo- and hetero-exchange of amino acids is absolutely Na(+)-dependent and conforms strictly to the substrate specificity of ATB degree. Kinetic analysis indicates that the affinity of ATB degree for a given amino acid substrate is similar whether ATB degree catalyzes the influx of the amino acid or the amino acid-induced efflux of intracellular amino acids. These results demonstrate for the first time the ability of ATB degree to function as a homo- and hetero-exchanger for its substrates.

Amino Acid Transport Systems↗
PubMed1998

Cloning and functional expression of a cDNA encoding a mammalian sodium-dependent vitamin transporter mediating the uptake of pantothenate, biotin, and lipoate.

Previous studies have shown that a Na+-dependent transport system is responsible for the transplacental transfer of the vitamins pantothenate and biotin and the essential metabolite lipoate. We now report the isolation of a rat placental cDNA encoding a transport protein responsible for this function. The cloned cDNA, when expressed in HeLa cells, induces Na+-dependent pantothenate and biotin transport activities. The transporter is specific for pantothenate, biotin, and lipoate. The Michaelis-Menten constant (Kt) for the transport of pantothenate and biotin in cDNA-transfected cells is 4.9 +/- 1.1 and 15.1 +/- 1.2 microM, respectively. The transport of both vitamins in cDNA-transfected cells is inhibited by lipoate with an inhibition constant (Ki) of approximately 5 microM. The nucleotide sequence of the cDNA (sodium-dependent multivitamin transporter (SMVT)) predicts a protein of 68.6 kDa with 634 amino acids and 12 potential transmembrane domains. Protein data base search indicates significant sequence similarity between SMVT and known members of the Na+-dependent glucose transporter family. Northern blot analysis shows that SMVT transcripts are present in all of the tissues that were tested. The size of the principal transcript is 3.2 kilobases. SMVT represents the first Na+-dependent vitamin transporter to be cloned from a mammalian tissue.

Amino Acid Sequence↗
PubMed1998

Transport mechanisms for vitamin C in the JAR human placental choriocarcinoma cell line.

We investigated the transport pathways available for the uptake of vitamin C in the human placental choriocarcinoma cell line, JAR. These cells were found to possess the capacity to accumulate the vitamin when presented either in the oxidized form (dehydroascorbic acid) or in the reduced form (ascorbate). Dithiothreitol and 5,5'-dithiobis(2-nitrobenzoic acid) were used to maintain vitamin C as ascorbate and dehydroascorbic acid, respectively. The uptake of these two forms of vitamin C in JAR cells was found to occur by different mechanisms. The uptake of the dehydroascorbic acid was Na(+)-independent and was mediated by facilitative glucose transporters as evidenced from the inhibition of the uptake process by glucose. On the other hand, the uptake of ascorbate was Na(+)-dependent and was not sensitive to inhibition by glucose. Substitution of Na+ with other monovalent cations abolished the uptake of ascorbate completely. The uptake process was, however, not influenced by anions. Kinetic analysis indicated the presence of a single saturable transport system for ascorbate with a Michaelis-Menten constant of 22 +/- 1 microM. The dependence of the uptake rare of ascorbate on Na+ concentration exhibited sigmoidal kinetics, suggesting interaction of more than one Na+ ion with the transporter. The Hill coefficient for the Na+ interaction was 2, indicating that the Na(+)-dependent ascorbate transport is electrogenic. The Na(+)-dependent stimulation of ascorbate uptake was primarily due to an increase in the affinity of the transporter for ascorbate in the presence of Na+. It is concluded that the JAR placental trophoblast cell line expresses two different transport systems for vitamin C: one for the reduced form of the vitamin ascorbate; and the other for the oxidized form of the vitamin dehydroascorbic acid.

Ascorbic Acid↗
PubMed1998

Molecular and structural features of the proton-coupled oligopeptide transporter superfamily.

Work in the area of molecular biology of transport proteins has unveiled the presence of a distinct peptide transporter superfamily whose members extend from the prokaryotic to the eukaryotic kingdom. There are two subgroups within this superfamily, one subgroup harnessing the energy necessary for active transport from a transmembrane H+ gradient and the other subgroup relying directly on ATP hydrolysis. In addition to the use of different driving forces, the two subgroups are also distinguishable with regard to molecular structure and operational mechanism. This review is intended to analyze critically the molecular nature of the members of the H+ gradient-dependent peptide transporter subgroup, with emphasis on the cloning strategies utilized in the isolation of the individual transporter cDNAs or genes; on the structural patterns, motifs, and conserved amino acid residues common to constituent members of the subgroup; and on the characteristic topological features of the individual members.

ATP-Binding Cassette Transporters↗
PubMed1998

Improvement of L-dopa absorption by dipeptidyl derivation, utilizing peptide transporter PepT1.

In the present study, possible enhancement of intestinal absorption of L-dopa by utilizing intestinal peptide transporter was examined using Caco-2 cells and Xenopus oocytes expressing human peptide transporter (hPepT1). To see whether this peptide transporter could be utilized for the improvement of L-dopa absorption, we employed a dipeptide-mimetic derivative of L-dopa, L-dopa-L-Phe. L-Dopa-L-Phe inhibited the uptake of [14C]Gly-Sar, but not that of L-[3H]-dopa by Caco-2 cells. Uptake of L-dopa-L-Phe was increased by expression of hPepT1 in Xenopus oocytes. The appearance of L-dopa and its metabolite, dopamine, on the basolateral side of Caco-2 cells was significantly higher after addition of L-dopa-L-Phe than after that of L-dopa and was reduced by the presence of Gly-Sar on the apical side. These results indicate that the L-dopa-L-Phe is absorbed more efficiently than L-dopa and is taken up via the peptide transporter, but not via the amino acid transporter, demonstrating the possibility of targeting the peptide transporter as a means for improving intestinal absorption of peptide-like drugs.

Amino Acid Transport Systems↗
PubMed1998

Exon-intron structure, analysis of promoter region, and chromosomal localization of the human type 1 sigma receptor gene.

Sigma receptor is a protein that interacts with a variety of psychotomimetic drugs including cocaine and amphetamines and is believed to play an important role in the cellular functions of various tissues associated with the endocrine, immune, and nervous systems. Here we report on the structure and organization of the human gene coding for this receptor. The gene is approximately 7 kbp long and contains four exons, interrupted by three introns. Exon 3 is the shortest (93 bp), and exon 4 is the longest (1,132 bp). Among the introns, intron 3 is the longest (approximately 1,250 bp). Exon 2 codes for the single transmembrane domain present in the receptor. 5' rapid amplification of cDNA end reactions with mRNA from the JAR human trophoblast cell line have identified 56 bp upstream of the translation start codon as the initiation site for transcription. This transcription start site has been confirmed by RNase protection analysis. Structural analysis of the 5' flanking region has revealed that the gene is TATA-less. This region, however, contains a CCAATC box in the reverse complement and several GC boxes that are recognition sites for SP1. There are also consensus sequences for the liver-specific transcription factor nuclear factor-1/L, for a variety of cytokine responsive factors, and for the xenobiotic responsive factor called the arylhydrocarbon receptor. Southern blot analysis of the genomic DNA from Chinese hamster-human and mouse-human hybrid cell lines and fluorescent in situ hybridization with human metaphase chromosome spreads have shown that the gene is located on human chromosome 9, band p13, a region known to be associated with different psychiatric disorders.

Amino Acid Sequence↗
PubMed1998

Cloning and functional characterization of a sigma receptor from rat brain.

We have cloned a sigma receptor from rat brain and established its functional identity using a heterologous expression system. The cloned cDNA (1,582 bp long) codes for a protein of 223 amino acids that possesses a single putative transmembrane domain. The amino acid sequence of the rat brain sigma receptor is highly homologous to that of the sigma receptor recently cloned from guinea pig liver and a human placental cell line but is not related to any other known mammalian receptors. When expressed in HeLa cells, the rat brain sigma receptor cDNA leads to a two- to threefold increase in haloperidol binding, and this cDNA-induced binding is sensitive to inhibition by several sigma receptor-specific ligands. Kinetic analysis using the heterologous expression system has revealed that the rat brain sigma receptor interacts with haloperidol with an apparent dissociation constant (K(D)) of 3 nM. Functional expression of the cloned rat brain sigma receptor in HeLa cells also leads to an increase in the binding of two other sigma ligands, namely, (+)-pentazocine and (+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine (PPP). Pharmacological characterization of the cloned rat brain sigma receptor reveals that it exhibits severalfold higher affinity for clorgyline than for 1 ,3-di(2-tolyl)guanidine, it interacts with progesterone and testosterone, and its interaction with PPP is markedly enhanced by phenytoin. In addition, transfection of MCF-7 cells, which do not express type 1 sigma receptor mRNA or activity, with the cloned rat brain cDNA leads to the appearance of haloperidol-sensitive binding of (+)-pentazocine, a selective type 1 sigma receptor ligand. These data show that the cloned rat brain cDNA codes for a functional type 1 sigma receptor. Northern blot analysis with poly(A)+ RNA isolated from various rat tissues has indicated that the sigma receptor-specific transcript, 1.6 kb in size, is expressed abundantly in liver and moderately in intestine, kidney, brain, and lung.

Amino Acid Sequence↗
PubMed1998

Electrophysiological characteristics of the proton-coupled peptide transporter PEPT2 cloned from rat brain.

We have cloned a peptide transporter from rat brain and found it to be identical to rat kidney PEPT2. In the present study we characterize the transport function of the rat brain PEPT2, with special emphasis on electrophysiological properties and interaction with N-acetyl-L-aspartyl-L-glutamate (NAAG). When heterologously expressed in HeLa cells and in SK-N-SH cells, PEPT2 transports several dipeptides but not free amino acids in the presence of a proton gradient. NAAG competes with other peptides for the PEPT2-mediated transport process. When PEPT2 is expressed in Xenopus laevis oocytes, substrate-induced inward currents are detectable with dipeptides of differing charge in the presence of a proton gradient. Proton activation kinetics are similar for differently charged peptides. NAAG is a transportable substrate for PEPT2, as evidenced by NAAG-induced currents. The Hill coefficient for protons for the activation of the transport of differently charged peptides, including NAAG, is 1. Although the peptide-to-proton stoichiometry for negatively charged peptides is 1, the transport nonetheless is associated with transfer of positive charge into the oocyte, as indicated by peptide-induced inward currents.

Amino Acids↗
PubMed1997

Cloning and structural analysis of the cDNA and the gene encoding the murine type 1 sigma receptor.

We have isolated a mouse cDNA which codes for a functional type 1 sigma receptor. The functional identity of the cDNA was established by expressing the cDNA in mammalian cells and measuring the cDNA-induced binding of haloperidol. Using this cDNA as the probe, we have isolated a murine genomic clone which contains the type 1 sigma receptor gene in its entirety. We have sequenced the gene completely, deduced the exon-intron organization and analyzed the promoter region sequence for transcription factor binding sites. The gene (approximately 7 kbp) is TATA-less but contains CCAATC and GC boxes immediately upstream of the transcription start site. The gene consists of 4 exons and 3 introns. The 5'-flanking region contains putative binding sites for AP-1, AP-2, GATA-1 and steroid receptors.

Amino Acid Sequence↗
PubMed1997

Tyrosine phosphorylation-and epidermal growth factor-dependent regulation of the sodium-coupled amino acid transporter B0 in the human placental choriocarcinoma cell line JAR.

We have recently cloned an amino acid transporter from the human placental choriocarcinoma cell line JAR which, when functionally expressed in HeLa cells, induces an amino acid transport activity with characteristics known to be associated with the amino acid transport system B(0) (R. Kekuda, P.D. Prasad, Y.J. Fei, V. Torres-Zamorano, S. Sinha, T.L. Yang-Feng, F.H. Leibach, and V. Ganapathy, J. Biol. Chem. 271, 18657-18661, 1996). The presence of the amino acid transport system B(0) (ATB(0)) has however not been previously described in these cells by functional studies. In the present investigation, we have obtained evidence for the existence of ATB(0) in JAR cells and delineated the functional characteristics of the transporter. The identifying characteristics include Na(+)-dependence and preference for neutral amino acids. In addition, we have used the JAR cells as a model system to investigate the regulatory aspects of ATB(0). Treatment of the cells with the neuroprotective agent aurintricarboxylic acid (ATA) for 16 h leads to a significant increase in ATB(0) activity. This increase is associated with enhanced maximal velocity of the transporter and with increased steady state levels of the transporter mRNA. The effect of ATA is blocked by the tyrosine kinase inhibitor genistein. ATA treatment results in increased tyrosine phosphorylation of two major proteins, 180 kDa and 140 kDa in size. The 180 kDa protein is likely to be the epidermal growth factor (EGF) receptor because exposure of the cells to EGF also leads to enhanced tyrosine phosphorylation of a protein of similar molecular size. Furthermore, the effects of ATA on ATB(0) activity and on ATB(0) mRNA levels can be reproduced by EGF. Treatment of the cells with EGF for 24 h results in a significant increase in ATB(0) activity and this effect is associated with an increase in the maximal velocity of the transporter and with an increase in the steady state levels of the transporter mRNA. These data suggest that ATA influences ATB(0) activity in JAR cells most likely by activating the EGF receptor through tyrosine phosphorylation. It is concluded that the human placental choriocarcinoma cells functionally express the amino acid transport system B(0) and that the expression of the system in these cells is stimulated by EGF.

Alanine↗
PubMed1997

Functional link between tyrosine phosphorylation and human serotonin transporter gene expression.

Treatment of the JAR human placental choriocarcinoma cells with herbimycin A, an inhibitor of tyrosine kinases, led to an increase in the activity of the serotonin transporter. This effect was accompanied by an increase in the serotonin transporter density and in the steady-state levels of the serotonin transporter mRNA. A treatment time of > 4 h was necessary for herbimycin A to elicit its effect. Actinomycin D and cycloheximide blocked the effect. There was no increase in the steady-state levels of the serotonin transporter mRNA when cells were treated with herbimycin A in the presence of actinomycin D. The herbimycin A-induced increase in the transporter activity was abolished by genistein, another inhibitor of tyrosine kinases. But the increase in the transporter mRNA levels caused by herbimycin A was not affected by genistein. Treatment of cells with herbimycin A resulted in an increase in the tyrosine phosphorylation of specific cellular proteins, suggesting that herbimycin A directly or indirectly activates specific tyrosine kinases. It is concluded that tyrosine phosphorylation is an essential component in the signaling pathways participating in the regulation of the human serotonin transporter gene expression.

Benzoquinones↗
PubMed1997

Influence of proton and essential histidyl residues on the transport kinetics of the H+/peptide cotransport systems in intestine (PEPT 1) and kidney (PEPT 2).

The mechanism by which H+ alters the kinetics of the H+-coupled peptide transporters PEPT 1 and PEPT 2 was investigated in two different cell lines which differentially express these transporters, namely Caco-2 cells (PEPT 1) and SKPT cells (PEPT 2). The effects of H+ on the affinity and the maximal velocity of Gly-Sar uptake were analyzed in these cells under identical conditions. In both cells, H+ influenced only the maximal velocity of uptake and not the apparent affinity. The effects of H+ on the IC50 values (i.e., concentration necessary to cause 50% inhibition) of the cationic dipeptide Ala-Lys and the anionic dipeptide Ala-Asp for inhibition of Gly-Sar uptake were also investigated. H+ did not change the IC50 value for Ala-Lys but did decrease the IC50 value for Ala-Asp considerably. The influence of diethylpyrocarbonate (DEP) on the kinetic parameters of PEPT 1 and PEPT 2 was then studied. Histidyl residues are the most likely amino acid residues involved in H+ binding and translocation in H+-coupled transport systems and DEP is known to chemically modify histidyl residues and block their function. DEP treatment altered the maximal velocity of Gly-Sar uptake but had no effect on its K(t) (Michaelis-Menten constant) or the IC50 values of Ala-Lys or Ala-Asp for the inhibition of Gly-Sar uptake. It is concluded that H+ stimulates PEPT 1 and PEPT 2 primarily by increasing the maximal velocity of the transporters with no detectable influence on the substrate affinity.

Animals↗
PubMed1997

Interaction of anionic cephalosporins with the intestinal and renal peptide transporters PEPT 1 and PEPT 2.

The present study was undertaken to investigate the interaction of anionic cephalosporins (cefixime, ceftibuten, and cefdinir) with the renal peptide transporter (PEPT 2) and the intestinal peptide transporter (PEPT 1) using four different experimental model systems. In the first approach, the human colon carcinoma cell line Caco-2 which expresses PEPT 1 and the SHR rat kidney cell line SKPT which expresses PEPT 2 were used. The uptake of the dipeptide Gly-Sar mediated by PEPT 1 or PEPT 2 in these cells was inhibited significantly by the anionic cephalosporins, with the following order of potency: ceftibuten > cefixime > cefdinir. The inhibition was competitive in nature. Even though the order of potency was the same for PEPT 1 and PEPT 2, PEPT 1 exhibited much lesser sensitivity to inhibition than PEPT 2. In the second approach, the cloned human PEPT 1 and PEPT 2 were functionally expressed in HeLa cells following which the cells were used to study the interaction of anionic cephalosporins with PEPT 1 and PEPT 2. Again, Gly-Sar uptake mediated by the human PEPT 1 and PEPT 2 in HeLa cells was found to be inhibited by the anionic cephalosporins with the same order potency as in Caco-2 and SKPT cells. In the third approach, brush border membrane vesicles isolated from rat kidneys were employed. In this approach also it was found that PEPT 2-mediated Gly-Sar uptake was inhibited by cefixime and ceftibuten. In the fourth approach, the human PEPT 1 was expressed in Xenopus laevis oocytes and PEPT 1-mediated transport of ceftibuten was investigated directly by electrophysiological methods. Ceftibuten evoked inward currents in PEPT 1-expressing oocytes but not in water-injected oocytes, showing that the transport of the anionic cephalosporin via PEPT 1 is associated with transfer of positive charge. The ceftibuten-evoked currents were saturable with respect to ceftibuten concentration and were markedly dependent on membrane potential. It is concluded that anionic cephalosporins interact with the peptide transporters expressed in the intestine (PEPT 1) as well as in the kidney (PEPT 2).

Animals↗
PubMed1997

Identification of the histidyl residue obligatory for the catalytic activity of the human H+/peptide cotransporters PEPT1 and PEPT2.

Histidyl residues are known to be essential for the catalytic function of the H(+)-coupled peptide transporters expressed in the intestine and the kidney, most likely participating in the binding and translocation of H+. Three histidyl residues are conserved among the intestinal and renal peptide transporters (PEPT1 and PEPT2, respectively) from different animal species. In hPEPT1, these residues are His-57, His-121, and His-260. The corresponding residues in hPEPT2 are His-87, His-142, and His-278. We have individually mutated each of these histidyl residues in hPEPT1 and in hPEPT2 and compared the catalytic function of the mutants with that of their respective wild type transporters by expressing the transporters in Xenopus laevis oocytes and also in HeLa cells. His-57 in hPEPT1 and His-87 in hPEPT2 were found to be absolutely essential for catalytic activity because the corresponding mutants had no detectable peptide transport activity. His-121 in hPEPT1 is not essential since mutation of this residue did not impair transport function. His-142 in hPEPT2 was found to play a significant role in the maintenance of transport function but was not found to be obligatory because the mutant had appreciable transport activity. The obligatory histidyl residue (His-57 in hPEPT1 and His-87 in hPEPT2) is located in an almost identical topological position in both transporters, near the extracellular surface of the second putative transmembrane domain. The second conserved histidyl residue is located in the fourth putative transmembrane domain in hPEPT1 as well as in hPEPT2. The third conserved histidyl residue is present in the cytoplasmic loop between the transmembrane domains 6 and 7 and is unlikely to play any significant role in the binding and translocation of H+ and this was supported by the findings that mutation of this histidyl residue in hPEPT1 did not interfere with transport function. The loss of transport function of hPEPT1 and hPEPT2, when His-57 in hPEPT1 and His-87 in hPEPT2 were mutated, was not due to alterations in protein expression because the expression levels of these mutants were similar to those of the respective wild type transporters in HeLa cells as assessed by immunoblot analysis. Confocal analysis of immunofluorescence in X. laevis oocytes expressing the wild type and the three histidine mutants of hPEPT1 showed that the transporter protein is expressed exclusively in the plasma membrane and that the level of expression is comparable among the wild type and the three mutants. These site-directed mutagenesis studies clearly show that His-57 in hPEPT1 and His-87 in hPEPT2 are the most critical histidyl residues necessary for the catalytic function of these transporters.

Amino Acid Sequence↗
PubMed1997

Localization of peptide transporter in nuclei and lysosomes of the pancreas.

CONCLUSIONS: These studies show for the first time the localization of a H+/peptide cotrasporter in nuclei of vascular smooth muscle cells and Schwann cells and its localization in lysosomes of the exocrine pancreas. It is likely that the transporter functions to move small peptides from the lysosome to the cytoplasm following intralysosomal protein degradation. The nature of the transporter function in the nucleus remains to be determined, including the possibility that peptide signaling molecules may be transmitted between nucleus and cytoplasm. BACKGROUND: PEPT1 transports di- and tripeptides through plasma membranes. Peptides are cotransported with H+, thus deriving the energy for the active transport process from an electrochemical H+ gradient. The main regions in which PEPT1 has been thought to function are the plasma membranes of the small intestinal epithelial cells for absorption of protein digestion products and in the kidney tubules for recovery of small peptides from the glomerular filtrate. METHODS: Pancreas was removed from rats and quick frozen with liquid nitrogen. Frozen sections were fixed in cold acetone. Sections were incubated with primary antibody against PEPT1, followed by a secondary antibody conjugated with fluorescein, then examined with a fluorescence microscope. RESULTS: Three major structures were immunopositive with the antibody to PEPT1: the nuclei of smooth muscle cells in the wall of arterioles, the nuclei of Schwann cells in unmyelinated pancreatic nerves, and lysosomes in acinar cells.

Animals↗