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Biomedical subjects

E M Jones

Publications and source records attributed to E M Jones.

At least 19 recordsLinked to original sources
PubMed2000

GABA receptor rho1 subunit interacts with a novel splice variant of the glycine transporter, GLYT-1.

Ionotropic gamma-aminobutyric acid (GABA(A) and GABA(C)) receptors mediate fast synaptic inhibition in the central nervous system. GABA(C) receptors are expressed predominantly in the retina on bipolar cell axon terminals, and are thought to mediate feedback inhibition from GABAergic amacrine cells. Utilizing the yeast two-hybrid system, we previously identified MAP1B as a binding partner of the GABA(C) receptor rho1 subunit. Here we describe the isolation of an additional rho1 interacting protein: a novel C-terminal variant of the glycine transporter GLYT-1. We show that GLYT-1 exists as four alternatively spliced mRNAs which encode proteins expressing one of two possible intracellullar N- and C-terminal domains. Variants containing the novel C terminus efficiently transport glycine when expressed in COS cells, but with unusual kinetics. We have confirmed the interaction between the novel C terminus and rho1 subunit and demonstrated binding in heterologous cells. This interaction may be crucial for the integration of GABAergic and glycinergic neurotransmission in the retina.

Alternative Splicing↗
PubMed1999

The role of Ca2+-activated K+ channel spliced variants in the tonotopic organization of the turtle cochlea.

1. Turtle auditory hair cells contain multiple isoforms of the pore-forming alpha-subunit of the large-conductance Ca2+-activated K+ (KCa) channel due to alternative splicing at two sites. Six splice variants were studied by expression in Xenopus oocytes. 2. The isoforms possessed differences in apparent Ca2+ sensitivity and kinetics. The lowest Ca2+ sensitivity was observed in a novel variant resulting from a 26 amino acid deletion around one of the splice sites. 3. Co-expression of a bovine beta-subunit slowed the current relaxation 10-fold compared with channels formed from alpha-subunits alone but preserved the original order of kinetic differences. The beta-subunit also increased the Ca2+ sensitivity of isoforms to bring them nearer the range of sensitivity of the native KCa channels of the hair cell. 4. With channels formed from alpha-subunits or alpha + beta-subunits, the half-activation voltage in a fixed Ca2+ concentration, and the time constant of the current relaxation, varied linearly with the combined size of the insertions/deletions at the splice sites. 5. Experiments in which the beta/alpha concentration ratio was varied indicated that the beta-subunit exerts an all-or-none effect on the Ca2+ sensitivity and kinetics of the channel. 6. Co-expression of an avian beta2-subunit had effects on kinetics and Ca2+ sensitivity of several alpha-isoforms which were qualitatively similar to those produced by the bovine beta-subunit. 7. We conclude that differential expression of alternatively spliced alpha-subunit variants and a non-uniform distribution of a beta-subunit can produce a range of KCa channel properties needed to explain the tonotopic organization of the turtle cochlea.

Acoustic Stimulation↗
PubMed1999

The functional role of alternative splicing of Ca(2+)-activated K+ channels in auditory hair cells.

Turtle auditory hair cells are frequency tuned by the activity of large-conductance calcium-activated potassium (KCa) channels, the frequency range being dictated primarily by the channel kinetics. Seven alternatively spliced isoforms of the KCa channel alpha-subunit, resulting from exon insertion at two splice sites, were isolated from turtle hair cells. These, when expressed in Xenopus oocytes, produced KCa channels with a range of apparent calcium sensitivities and channel kinetics. However, most expressed channels were less calcium sensitive than the hair cells' native KCa channels. Coexpression of alpha-subunit with a bovine beta-subunit substantially increased the channel's calcium sensitivity while markedly slowing its kinetics, but kinetic differences between isoforms were preserved. These data suggest a molecular mechanism for hair cell frequency tuning involving differential expression of different KCa channel alpha-subunits in conjunction with an expression gradient of a regulatory beta-subunit.

Alternative Splicing↗
PubMed1999

Molecular cloning and pharmacological characterization of a somatostatin receptor subtype in the gymnotiform fish Apteronotus albifrons.

The actions of the various forms of somatostatin (SRIF), including those of the tetradecapeptide SRIF(14), are mediated by specific receptors. In mammals, five subtypes of SRIF receptors, termed sst(1-5), have been cloned. Using a combination of reverse transcriptase-polymerase chain reaction and genomic library screening in the gymnotiform fish Apteronotus albifrons, a gene encoding the first-known nonmammalian SRIF receptor has been isolated. The deduced amino acid sequence displays 59% identity with the human sst(3) receptor protein; hence, the gene is termed "Apteronotus sst(3)." The predicted protein consists of 494 amino acid residues exhibiting a putative seven-transmembrane domain topology typical of G protein-coupled receptors. A signal corresponding to the Apteronotus sst(3) receptor was detected in brain after amplification of poly(A)(+)-RNA by reverse transcriptase-polymerase chain reaction, but not by Northern blot analysis or in situ hybridization, suggesting a low level of expression. Membranes prepared from CCL39 cells stably expressing the Apteronotus sst(3) receptor gene bound [(125)I][Leu(8),d-Trp(22), (125) I-Tyr(25)]SRIF(28) with high affinity and in a saturable manner (B(max) = 4470 fmol/mg protein; pK(D) = 10.5). SRIF(14) and various synthetic SRIF receptor agonists produced a dose-dependent inhibition of radioligand binding, with the following rank order of potency: SRIF(14) approximately SRIF(28) > BIM 23052 > octreotide > BIM 23056. Under low stringency conditions, an Apteronotus sst(3) probe hybridized to multiple DNA fragments in HindIII or EcoRI digests of A. albifrons DNA, indicating that the Apteronotus sst(3) receptor is a member of a larger family of Apteronotus SRIF receptors.

Amino Acid Sequence↗
PubMed1999

Pancreatic expression of keratinocyte growth factor leads to differentiation of islet hepatocytes and proliferation of duct cells.

Keratinocyte growth factor, (KGF), a member of the fibroblast growth factor (FGF) family, is involved in wound healing. It also promotes the differentiation of many epithelial tissues and proliferation of epithelial cells as well as pancreatic duct cells. Additionally, many members of the highly homologous FGF family (including KGF), influence both growth and cellular morphology in the developing embryo. We have previously observed elevated levels of KGF in our interferon-gamma transgenic mouse model of pancreatic regeneration. To understand the role of KGF in pancreatic differentiation, we generated insulin promoter-regulated KGF transgenic mice. Remarkably, we have found that ectopic KGF expression resulted in the emergence of hepatocytes within the islets of Langerhans in the pancreas. Additionally, significant intra-islet duct cell proliferation in the pancreata of transgenic KGF mice was observed. The unexpected appearance of hepatocytes and proliferation of intra-islet duct cells in the pancreata of these mice evidently stemmed directly from local exposure to KGF.

Aging↗
PubMed1999

Transgenic expression of epidermal growth factor and keratinocyte growth factor in beta-cells results in substantial morphological changes.

The upregulation of a limited number of growth factors in our interferon-gamma transgenic model for regeneration within the pancreas lead us to propose that these factors are important during pancreatic regeneration. In this study, we have assessed the influence of two growth factors within the pancreas, epidermal growth factor (EGF) and keratinocyte growth factor (KGF), by ectopically expressing these proteins under the control of the human insulin promoter in transgenic mice. This beta-cell-targeted expression of either EGF or KGF resulted in significant morphological changes, including cellular proliferation and disorganized islet growth. Intercrossing the individual Ins-EGF and Ins-KGF transgenic mice resulted in more profound changes in pancreatic morphology including proliferation of pancreatic cells and extensive intra-islet fibrosis. Insulin-producing beta-cells were found in some of the ducts of older Ins-EGF and Ins-EGFxKGF transgenic mice, and amylase-producing cells were observed within the islet structures of the double transgenic mice. These data suggest that both EGF and KGF are capable of affecting pancreatic differentiation and growth, and that co-expression of these molecules in islets has a more substantial impact on the pancreas than does expression of either growth factor alone.

Animals↗
PubMed1998

Identification of Ca(2+)-activated K+ channel splice variants and their distribution in the turtle cochlea.

Turtle auditory-hair cells are frequency-tuned by the activity of calcium-activated potassium (KCa) channels, a cell's characteristic frequency being determined by the KCa channel density and kinetics which both vary systematically along the cochlea. As a first step towards identifying the source of KCa channel variation, we have isolated, by reverse-transcription polymerase chain reaction on dissociated hair cells, the main cDNAs homologous to the slo gene which encodes the channel's alpha-subunit. A total of six alternatively spliced variants were identified, the smallest of which is 94% identical to a mouse Slo sequence. Variation occurs by insertion of exons at only two splice sites, two of these exons encoding novel 31- and 61-amino acid sequences. As we were unable to detect splicing at other potential sites, we infer that the six variants correspond to naturally occurring combinations. The spatial distribution of the variants, defined by isolating hair cells from different regions of the cochlea, indicated that some isoforms were non-uniformly distributed. Those containing large inserts in the first splice site were notably absent from the highest-frequency region. We suggest that alternative splicing of the slo gene may contribute to variation in KCa channel properties.

Alternative Splicing↗
PubMed1997

Cell-surface ADP-ribosylation of fibroblast growth factor-2 by an arginine-specific ADP-ribosyltransferase.

Basic fibroblast growth factor (FGF-2) appeared to be ADP-ribosylated on the surface of adult bovine aortic arch endothelial and human hepatoma cells. Further characterization of this reaction with cells expressing an arginine-specific, glycosylphosphatidylinositol-anchored, mono-ADP-ribosyltransferase demonstrated that FGF-2 is ADP-ribosylated on arginine. Incubation of transformed cells with FGF-2 and [adenylate-32P]nicotinamide-adenine dinucleotide (NAD) resulted in the rapid incorporation of [32P]ADP-ribose into FGF-2 in a time- and concentration-dependent manner, with labelling averaging 3 mol of ADP-ribose/mol of FGF-2. Excess ADP-ribose had no effect on these reactions, whereas excess NAD inhibited the ADP-ribosylation of FGF-2, consistent with an enzymic rather than a non-enzymic ADP-ribosylation reaction. Heparin also inhibited the ADP-ribosylation reaction, whereas a neutralizing polyclonal anti-peptide antibody had no effect. Furthermore, the addition of putative receptor binding domain peptide analogues of FGF-2 reduced the maximal ADP-ribosylation of FGF-2. These results identify the cell-surface ADP-ribosylation of FGF-2 as a potentially ubiquitous event.

ADP Ribose Transferases↗
PubMed1997

Control of varicella-zoster infection on renal and other specialist units.

The introduction of chickenpox onto our renal unit recently raised several issues surrounding the management of patient and staff contracts. This paper describes the action taken and makes various recommendations for future management of similar cases. Guidelines are proposed for the management of patients and staff as well as the role of the infection control team in handling a chickenpox problem. Future developments, including the use of VZ vaccine for patient and staff, are also discussed.

Chickenpox↗
PubMed1997

Salt tolerance of EMRSA-16 and its effect on the sensitivity of screening cultures.

The salt (NaCl) tolerance of methicillin-resistant Staphylococcus aureus (EMRSA)-16 was compared with 18 other MRSA isolates by an agar incorporation technique. The NaCl minimum inhibitory concentration (MIC) of EMRSA-16 was 7% which compared with an MIC50 of 7%, MIC90 of 10%, range (5.5-10.5%) for the other isolates. Study of the growth kinetics in broth containing NaCl at concentrations up to 10% indicated complete inhibition of growth by 7 and 10% NaCl and partial inhibition by 5%. Addition of EMRSA-16 at inocula of < or = 1 cfu/mL into salt broths revealed lower than expected EMRSA recovery from broths containing 5, 7.5 and 10% NaCl. Two and a half per cent NaCl broths were not inhibitory. Selective broth containing 2.5% NaCl should be considered for use when screening for EMRSA-16.

Culture Media↗
PubMed1997

Islet regeneration in IFNgamma transgenic mice.

The adult pancreas is a developmentally stable organ with limited mitotic activity. This minimal mitotic activity proves critical in insulin-dependent diabetes mellitus (IDDM) since the pathogenesis is characterized by a selective and permanent destruction of islet beta cells. The IFNgamma transgenic mouse model of islet regeneration elucidates the differentiation pathway involved in the regeneration of functional beta cells from ductal precursors and reveals the functional plasticity of the adult pancreas.

Animals↗
PubMed1997

The pharmacokinetics of intravenous ciprofloxacin 400 mg 12 hourly in patients with severe sepsis: the effect of renal function and intra-abdominal disease.

Serum concentrations of ciprofloxacin were reviewed in 22 patients given ciprofloxacin 400 mg intravenously 12 hourly for severe infection. No dosage modifications were made in patients with renal impairment. Patients who had either bowel or liver pathology in addition to renal failure had significantly higher serum concentrations than all other patients. Dosage reduction of ciprofloxacin in patients with severe sepsis and impaired renal function is not required unless they have co-existent intra-abdominal disease.

Abdomen↗