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Biomedical subjects

N F Barley

Publications and source records attributed to N F Barley.

5 recordsLinked to original sources
PubMed2001

Epithelial calcium transporter expression in human duodenum.

Calcium absorption in intestine and kidney involves transport through the apical membrane, cytoplasm, and basolateral membrane of the epithelial cells. Apical membrane calcium influx channels have recently been described in rabbit (epithelial calcium channel, ECaC) and rat (calcium transport protein, CaT1). We amplified from human duodenum a 446-base partial cDNA probe (ECAC2) having a predicted amino acid similarity of 97% to rat CaT1. Duodenum, but not ileum, colon, or kidney, expressed a 3-kb transcript. A larger transcript was also found in placenta and pancreas, and a different, faint transcript was found in brain. In duodenal biopsies from 20 normal volunteers, expression varied considerably but was not significantly correlated with vitamin D metabolites. This signal correlated with calbindin-D(9k) (r = 0.48, P < 0.05) and more strongly with the plasma membrane calcium ATPase PMCA1 (r = 0.83, P < 0.001). These data show that although individual variations in calcium channel transcripts are not vitamin D dependent, expression of genes governing apical entry and basolateral extrusion are tightly linked. This may account for some of the unexplained variability in calcium absorption.

Amino Acid Sequence↗
PubMed2000

Glucagon-like peptide-2 increases sucrase-isomaltase but not caudal-related homeobox protein-2 gene expression.

To determine the effect of glucagon-like peptide-2 (GLP-2) on sucrase-isomaltase and caudal-related homeobox protein-2 (Cdx-2) gene expression, male Wistar rats were divided into total parenteral nutrition (TPN)-fed and GLP-2-treated, TPN-fed groups. TPN was given via a jugular line, inserted under anesthesia, for 7 days. The treatment group received 40 microg/day of GLP-2 intravenously with the TPN diet. The small intestine and colon were weighed and measured. Tissue was obtained from the jejunum, terminal ileum, and midcolon. RNA analysis, morphometry, and microdissection were performed. The weight of the small intestine of GLP-2-treated rats was greater than that of TPN-fed rats (P < 0.001). GLP-2 increased the mean metaphase arrests/crypt in both the jejunum and ileum (P < 0.001). Ileal expression of sucrase-isomaltase was increased by 1. 6-fold (P < 0.05). Jejunal expression was increased by a similar amount, although not significantly (P = 0.08). There was no change in Cdx-2 gene expression. Thus GLP-2 can maintain small intestinal morphology and function, but effects on gene expression are not mediated by gross changes in the level of the mRNA for the homeobox protein Cdx-2.

Animals↗
PubMed1999

Factors involved in the duodenal expression of the human calbindin-D9k gene.

Calbindin-D9k is expressed in the cytoplasm of intestinal cells, where it is critical for dietary calcium absorption. Two striking aspects of the expression of this gene are its vitamin-D dependency and regional differences in expression, with high levels only in duodenum. We report studies of the human calbindin-D9k promoter. Differences between the reported sequences of the human calbindin-D9k promoter were first clarified before undertaking a functional analysis of this sequence. Studies of the rat gene have indicated that several transcription factors, including the caudal-related homeobox factor (CDX-2), hepatic nuclear factor-4 and CCAAT-enhancer-binding protein alpha (C/EBPalpha), could interact with elements in the promoter. Although these elements are conserved in the human gene, we show here that their intestinal distribution makes them unlikely to be critical positive factors. The calbindin-D9k gene contains multiple potential binding sites for homeobox transcription factors; one of these, known as IPF-1 or PDX-1, co-localizes in the intestine with calbindin-D9k. We show in gel-shift assays that the sequence within a putative vitamin-D-response element in the human calbindin-D9k promoter can bind expressed IPF-1/PDX-1 protein, although we cannot confirm binding of the vitamin-D-receptor protein. CDX-2 binds to the region around the TATA box, as in the rat gene, and may act as a negative factor in the distal intestine. Transfection studies in Caco-2 and MCF-7 cells with heterologous reporter vectors containing up to 1303 bp of the gene showed that this functioned as a weak promoter and indicated the presence of suppressor sequences, but did not show vitamin-D responsiveness. This indicates that other elements are also needed for the control of human calbindin-D9k expression.

Animals↗
PubMed1994

Plasma-membrane calcium-pump isoforms in human and rat liver.

Plasma-membrane Ca(2+)-pumping ATPases (PMCAs) extrude Ca2+ from the cytoplasm of all cells. Some previous studies of ATP-dependent Ca2+ transport by liver membranes suggested there exist specific properties of the hepatic PMCA, including regulation by hormones which affect calcium signalling. Multiple PMCA isoforms are now known to result from expression of four different genes (known as PMCA 1-4) and alternative RNA splicing at three possible sites (A, B and C). We investigated which isoforms are expressed in adult human and rat liver RNA using reverse-transcription polymerase chain reaction with mixed primers designed to amplify parts of all the known PMCA transcripts. In human liver, products were identified by sequencing from PMCA1, PMCA2 and PMCA4, but not from PMCA3 or from any new gene. In rat liver, by contrast, only PMCA1 and PMCA2 were detectable, although we confirmed that the primers were able to amplify from rat lung a new sequence which is part of rat PMCA4. Of the alternatively spliced variants, at site A in the PMCA2 sequences, all the exons were included in both adult and fetal human liver. In human liver, the exon at site B was excluded in some products from PMCA1 and PMCA4, and at site C, only PMCA1b and one form of PMCA4 were found. Blots of human liver RNA showed PMCA1 and PMCA4 were abundantly expressed, unlike PMCA2. On blots of rat liver RNA, PMCA1 was more abundant than PMCA2, and purified rat parenchymal cell RNA gave similar findings. In summary, no new hepatic PMCA isoforms have been demonstrated, but differences between the predominant human and rat isoforms may have consequences for Ca2+ signalling or the response to liver cell injury.

Adult↗