L-Alanine absorption in human intestinal Caco-2 cells driven by the proton electrochemical gradient

In human Caco-2 intestinal epithelial layers, xxxl-alanine absorption can be energized by a proton gradient across the brush-border membrane. Acidification of the apical medium, even in Na⁺-free media, is associated with a saturable net transepithelial absorption of xxxl-alanine. xxxl-Alanine transport causes cytosolic acidification consistent with proton/amino acid symport. xxxl-Alanine transport in Na⁺-free media is rheogenic, stimulating an inward short-circuit current in voltageclamped epithelial monolayers. By measurement of rapid xxxl-alanine influx across the apical membrane, xxxl-alanine-stimulated inward short-circuit current and intracellular acidification in the same cell batch, we estimate xxxl-alanine/proton stoichiometry to be 10.62 ±0.25 (xxxsd) (short-circuit current) or 10.73 ±0.19 (intracellular acidification). From competition studies, it is likely that xxxl-proline, -aminoisobutyric acid, and -alanine, but not xxxl-valine and xxxl-serine, are substrates for protonlinked, substrate transport in the brush border of Caco-2 cells.This study was supported by the Wellcome Trust (to D.T.T. and N.L.S.) and the LINK Programme in Selective Drug Delivery and Targeting (funded by the SERC/MRC/DTI and Industry). Charlotte Ward gave excellent technical assistance.     

Conservation of human Y chromosome sequences among male great apes: Implications for the evolution of Y chromosomes

Nine newly described single-copy and lowcopy-number genomic DNA sequences isolated from a flow-sorted human Y chromosome library were mapped to regions of the human Y chromosome and were hybridized to Southern blots of male and female great ape genomic DNAs (Gorilla gorilla, Pan troglodytes, Pongo pygmaeus). Eight of the nine sequences mapped to the euchromatic Y long arm (Yq) in humans, and the ninth mapped to the short arm or pericentromeric region. All nine of the newly identified sequences and two additional human Yq sequences hybridized to restriction fragments in male but not female genomic DNA from the great apes, indicating Y chromosome localization. Seven of these 11 human Yq sequences hybridized to similarly-sized restriction endonuclease fragments in all the great ape species analyzed. The five human sequences that mapped to the most distal subregion of Yq (deletion of which region is associated with spermatogenic failure in humans) were hybridized to Southern blots generated by pulsed-field gel electrophoresis. These sequences define a region of approximately 1 Mb on human Yq in which HpaII tiny fragment (HTF) islands appear to be absent. The conservation of these human Yq sequences on great ape Y chromosomes indicates a greater stability in this region of the Y than has been previously described for most anonymous human Y chromosomal sequences. The stability of these sequences on great ape Y chromosomes seems remarkable given that this region of the Y does not undergo meiotic recombination and the sequences do not appear to encode genes for which positive selection might occur. Correspondence to: B. Steele Allen     

Fenfluramine Releases Serotonin from Human Brain Nerve Endings by a Dual Mechanism

Abstract: Fenfluramine is the most widely used anorexigenic drug in humans. In animal experiments d -fenfluramine has been shown to act as a potent releaser of brain serotonin [5-hydroxytryptamine (5-HT)]. Here we have investigated the effects of d -fenfluramine on the release of [³H]5-HT from isolated nerve endings of human neocortex. The drug elicited release of unmetabolized [³H]5-HT, and this effect was concentration dependent. However, the mechanism of release seems to differ profoundly depending on the concentrations of d -fenfluramine used. At 5 µ M , the release of [³H]5-HT was blocked by the 5-HT transporter inhibitor fluoxetine and was Ca²⁺ independent and insensitive to the human autoreceptor 5-HT_1D agonist sumatriptan. The release of [³H]5-HT elicited by 0.5 µ M d -fenfluramine was similarly blocked by fluoxetine, but it was strongly Ca²⁺ dependent and sensitive to sumatriptan. It is suggested that, at relatively high concentrations, d -fenfluramine largely diffuses into serotonergic terminals and causes release of 5-HT through the 5-HT carrier working in the inside-outside direction; at relatively low concentrations d -fenfluramine enters the terminals through the 5-HT transporter but elicits release of 5-HT by an exocytotic-like mechanism.     

Amino Acid Residues 226–240 of τ Which Encompass the First Lys-Ser-Pro Site of τ, Are Partially Phosphorylated in Alzheimer Paired Helical Filament-τ

Abstract: A synthetic peptide corresponding to residues 226–240 (E9 peptide) of human τ, which contains an Lys-Ser-Pro motif, was used to raise a polyclonal antibody. The antibody, E9, was 10-fold less reactive with phospho-E9 peptide than with native E9 peptide. E9 antibody was used to study the extent of phosphorylation in a modified form of τ (PHF-τ) that is found in Alzheimer's disease brain and is incorporated into paired helical filaments (PHFs). E9 immunolabeled Alzheimer's disease neurofibrillary tangles and abnormal neurites in brain sections intensely, with increased immunoreactivity detected after pretreatment of sections with phosphatase. On immunoblots and ELISA, E9 reacted with PHF-τ and recombinant human τ but not with the high and middle molecular weight neurofilament proteins. Phosphatase treatment of PHF-τ improved the E9 immunoreactivity by 30–50%. Dephosphorylated high but not middle molecular weight neurofilament protein became reactive with E9. These results indicate that <50% of the PHF-T is phosphorylated in the subregion corresponding to residues 226–240 of τ and suggest that the phosphorylation of this region may not be essential for PHF formation.     

Identification of Endothelin Receptor Subtype (ETB) in Human Cerebral Cortex Using Subtype-Selective Ligands

Abstract: Specific endothelin (ET) binding sites were characterized in membranes prepared from human cerebral cortices using binding assay and cross-linking analysis. The presence of immunoreactive (IR) ET-1 was studied by radioimmunoassay. Saturation binding experiments revealed that the K _D and B _max for ¹²⁵I-ET-1 and ¹²⁵l-ET-3 to membranes from gray matter were 25 ± 6 pM and 115 ± 15 fmol/mg of protein and 24 ± 5 p M and 108 ± 13 fmol/mg of protein, respectively. Similar results were obtained for white matter. In the presence of 10 n M sarafotoxin-6c, which is selective for ET_B receptors, ¹²⁵I-ET-1 and ¹²⁵l-ET-3 binding was totally abolished. However, in the presence of 1 μ M BQ123, which is selective for ET_Areceptors, both bindings were not affected. These results suggest that the human cerebral cortex contains only ET_Breceptors. Cross-linking of ¹²⁵I-ET-1 and ¹²⁵l-ET-3 to membranes with disuccinimidyl suberate resulted in the labeling of two bands of 48 and 31 kDa. Concentrations of IR-ET-1 in the gray and white matter were 7.0 ± 3.2 and 2.5 ± 1.7 fmol/g wet weight, respectively. The demonstration of high-affinity ET_B receptors and the presence of IRET-1 suggest that the peptide may act as a neurotransmitter or neuromodulator in the human cerebral cortex.     

Molecular Cloning, Expression, and Pharmacological Characterization of humEAA1, a Human Kainate Receptor Subunit

Abstract: Kainate is a potent neuroexcitatory agent; its neurotoxicity is thought to be mediated by an ionotropic receptor with a nanomolar affinity for kainate. In this report, we describe the cloning of a cDNA encoding a human glutamate ionotropic receptor subunit protein from a human hippocampal library. This cDNA, termed humEAA1, is most closely related to rat and human cDNAs for kainate receptor proteins and, when expressed in COS or Chinese hamster ovary cells, is associated with high-affinity kainate receptor binding. We have successfully established cell lines stably expressing humEAA1. This is the first report of establishment of stable cell lines expressing a glutamate receptor subunit. The relative potency of compounds for displacing [³H] kainate binding of humEAA1 receptors expressed in these stable cell lines was kainate > quisqualate > domoate > L-glutamate > ( RS )-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid > dihydro-kainate > 6, 7-dinitroquinoxaline-2, 3-dione > 6-cyano-7-nitroquinoxaline-2, 3-dione. Homooligomeric expression of humEAA1 does not appear to elicit ligand-gated ion channel activity. Nevertheless, the molecular structure and pharmacological characterization of high-affinity kainate binding of the humEAA1 expressed in the stable cell line (ppEAA1–16) suggest that the humEAA1 is a subunit protein of a human kainate receptor complex.     

Direct and indirect effects of recombinant human granulocyte-colony stimulating factor on in vitro colony formation of human bladder cancer cells

Although the present experimental use of recombinant human granulocyte-colony-stimulating factor (rG-CSF) has been proven to alleviate the myelosuppression induced by antitumor chemotherapy, it is also believed to stimulate growth of some nonhematopoietic tumor cells. We investigated both the direct and indirect effects of rG-CSF on in vitro colony formation of human bladder cancer cell lines using a modified human tumor clonogenic assay. Peripheral blood mononuclear cells (PBMC) were used as feeder cells (a mixture of 5×10⁴ monocytes/dish and 5×10⁵ lymphocytes/dish obtained from healthy donors). Human bladder cancer cell lines KK-47, TCCSUP and T24, all derived from human transitional-cell carcinomas, were incubated continuously with various concentrations of rG-CSF ranging from 0.01 ng/ml to 10 ng/ml both with and without PBMC for 7–21 days. The concentrations of rG-CSF used were chosen as being in the range of achievable serum concentrations in patients treated with rG-CSF. At the end of incubation, colonies were counted under an inverted phase-contrast microscope, and an increase in the number of colonies in comparison with the control was used to evaluate the effects of rG-CSF. Results were expressed as a percentage of controls. rG-CSF in the upper layer at concentrations ranging from 0.1 ng/ml to 10 ng/ml stimulated the colony formation of all the cancer cell lines tested in the absence of PBMC in the feeder layer, whereas cells with PBMC in the feeder layer were significantly stimulated more than those without PBMC in the feeder layer (P<0.05) up to a certain concentration, which varied from cell line to cell line. At higher concentrations of rG-CSF, no further stimulation but, on the contrary, a decrease in colony formation was observed in cells with PBMC in the feeder layer in all the cell lines tested. Colony formation in KK-47 and T24 cell lines was significantly inhibited at 5 ng/ml and/or 10 ng/ml rG-CSF compared with cells without PBMC in the feeder layer. Our results suggest that rG-CSF may have both direct and indirect stimulatory effects on the growth of human bladder cancer cell lines in vitro. The results obtained also raise the possibility of adverse effects of rG-CSF in bladder cancer patients whose malignant cells may be directly and indirectly stimulated by this factor while it is being used clinically to alleviate the myelosuppression induced by antitumor chemotherapy.     

Genomic organization, sequence and polymorphism of the human chromosome 4-specific a-satellite DNA

Two -satellite fragments specific for human chromosome 4 have been cloned and characterized. Under stringent annealing conditions, they hybridized in situ only to the pericentromeric region of chromosome 4, but under nonstringent conditions they hybridized to all chromosomes containing the sequences of -satellite suprachromosomal family 2 (viz., chromosomes 2, 4, 8, 9, 13, 14, 15, 18, 20, 21 and 22). Southern blot analysis reveals the 3.2-kb higher-order repeated unit which exists in two forms: as a single MspI fragment or a combination of the 2.6-kb and 0.6-kb MspI fragments. The two chromosome-4-specific cloned sequences appear to be different parts of this repeated unit. Taken together they constitute about 60% of its length. The primary structure of the higher-order repeated unit is characterized by a dimeric periodicity of the D1-D2 type which is usual to suprachromosomal family 2. At least in one site this regularity is disrupted by monomer deletion leading to the D2-D2 monomeric order. The most likely mechanism of this monomer excision is homologous unequal crossing-over. These sequences may serve as both cytogenetic and restriction-fragment length polymorphism (RFLP) markers for the pericentromeric region of chromosome 4.