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L M Hall

Publications and source records attributed to L M Hall.

At least 55 records · Page 3Linked to original sources
PubMed1997

Agonist-specific coupling of a cloned Drosophila melanogaster D1-like dopamine receptor to multiple second messenger pathways by synthetic agonists.

The mechanism of coupling of a cloned Drosophila D1-like dopamine receptor, DopR99B, to multiple second messenger systems when expressed in Xenopus oocytes is described. The receptor is coupled directly to the generation of a rapid, transient intracellular Ca2+ signal, monitored as changes in inward current mediated by the oocyte endogenous Ca2+-activated chloride channel, by a pertussis toxin-insensitive G-protein-coupled pathway. The more prolonged receptor-mediated changes in adenylyl cyclase activity are generated by an independent G-protein-coupled pathway that is pertussis toxin-sensitive but calcium-independent, and Gbetagamma-subunits appear to be involved in the transduction of this response. This is the first evidence for the direct coupling of a cloned D1-like dopamine receptor both to the activation of adenylyl cyclase and to the initiation of an intracellular Ca2+ signal. The pharmacological profile of both second messenger effects is identical for a range of naturally occurring catecholamine ligands (dopamine > norepinephrine > epinephrine) and for the blockade of dopamine responses by a range of synthetic antagonists. However, the pharmacological profiles of the two second messenger responses differ for a range of synthetic agonists. Thus, the receptor exhibits agonist-specific coupling to second messenger systems for synthetic agonists. This feature could provide a useful tool in the genetic analysis of the roles of the multiple second messenger pathways activated by this receptor, given the likely involvement of dopamine in the processes of learning and memory in the insect nervous system.

Animals↗
PubMed1997

The seizure locus encodes the Drosophila homolog of the HERG potassium channel.

Mutations in the seizure (sei) locus cause temperature-induced hyperactivity, followed by paralysis. Gene cloning studies have established that the seizure gene product is the Drosophila homolog of HERG, a member of the eag family of K+ channels implicated in one form of hereditary long QT syndrome in humans. A series of five null alleles with premature stop codons are all recessive, but viable. A missense mutation in the sei gene, which changes the charge at a conserved glutamate residue near the outer mouth of the pore, has a semidominant phenotype, suggesting that the mutant seizure protein acts as a poison in a multimeric complex. Transformation rescue of a null allele with a cDNA under the control of an inducible promoter demonstrates that induced expression of seizure potassium channels in adults rescues the paralytic phenotype. This rescue decays with a t1/2 of approximately 1-1.5 d after gene induction is discontinued, providing the first estimate of ion channel stability in an intact, multicellular animal.

Amino Acid Sequence↗
PubMed1997

Bases of variation in resistance to beta-lactams in Klebsiella oxytoca isolates hyperproducing K1 beta-lactamase.

Nineteen isolates of Klebsiella oxytoca were examined, representing 18 distinct strains. All were from a 1994 survey of resistance amongst klebsiellae in intensive care units in Europe, and all had reduced susceptibility, or were resistant, to cefuroxime, ceftriaxone and aztreonam, suggesting hyperproduction of the chromosomal K1 beta-lactamase. We sought to confirm this mechanism and to identify why the levels of resistance varied between isolates. Possible reasons for variation were differences in the quantity or subtype of the K1 enzyme or differences in this enzyme's interplay with permeability. Spectrophotometric assays showed that all 19 isolates had K1-like beta-lactamases and that these were present at > or = 15-fold higher levels than in beta-lactam-sensitive K. oxytoca isolates. Fourteen of the 19 isolates had the OXY-2 form of K1 enzyme, while the remaining five had the OXY-1 form, as determined by isoelectric focusing and PCR amplification. Most isolates with the OXY-2 enzyme were more resistant than those with the OXY-1 subtype, but this difference partly reflected enzyme quantity rather than subtype. More generally, and irrespective of enzyme subtype, levels of resistance were broadly related to beta-lactamase specific activity, and the degree of hyperproduction was a major determinant of the level of resistance. Nevertheless, other factors had a role too: several isolates had reduced susceptibility or were resistant to cefoxitin, which is not a substrate for K1 enzyme, and examination of outer membrane protein profiles revealed considerable strain-to-strain diversity in the molecular weight range typical of the major enterobacterial porins (40-48 kDa).

Anti-Bacterial Agents↗
PubMed1997

Staff mix models: complementary or substitution roles for nurses.

In response to the need to improve health care efficiency and effectiveness, hospital organizations are exploring and implementing restructured patient care delivery models. The shift away from traditional patterns creates an opportunity for redesign of health care resource utilization and creation of new staff mixes. Many emerging models appear to provide substitute workers for the RN rather than complement the nursing role. One concern evident in the literature is the lack of evaluation of these staff mix models as they become more prevalent. The outcomes for patient, hospital system, and nurse remain unclear.

Hospital Restructuring↗
PubMed1997

Plasma beta-endorphin, adrenocorticotropin hormone, and cortisol in autism.

Plasma levels of the hypothalamo-pituitary-adrenal axis hormones beta-endorphin (BE), adrenocorticotropin hormone (ACTH), and cortisol were measured in autistic (N = 48), mentally retarded/cognitively impaired (MR/CI, N = 16), and normal control (N = 26) individuals. Comparison of log transformed data from the three groups revealed that levels of BE and ACTH were significantly higher (p < .05) in the autistic individuals than in normal controls. The higher means in the autistic group were due to significantly higher plasma levels of BE and ACTH, indices of acute stress response, in the more severely affected individuals. The data support the idea that individuals with severe autism have a heightened response to acute stressors rather than chronic hyperarousal or elevated basal stress response system functioning.

Adolescent↗
PubMed1997

Mechanism of sulfonamide resistance in clinical isolates of Streptococcus pneumoniae.

The genetic basis of sulfonamide resistance in six clinical isolates of Streptococcus pneumoniae was demonstrated to be 3- or 6-bp duplications within sulA, the chromosomal gene encoding dihydropteroate synthase. The duplications all result in repetition of one or two amino acids in the region from Arg58 to Tyr63, close to but distinct from the sul-d mutation, a duplication previously reported in a resistant laboratory strain (P. Lopez, M. Espinosa, B. Greenberg, and S. A. Lacks, J. Bacteriol. 169:4320-4326, 1987). Six sulfonamide-susceptible clinical isolates lacked such duplications. The role of the duplications in conferring sulfonamide resistance was confirmed by transforming 319- or 322-bp PCR fragments into the chromosome of a susceptible recipient. Two members of a clone of serotype 9V, one susceptible and one resistant to sulfonamide, which are highly related by other criteria, were shown to have sulA sequences that differ in 7.2% of nucleotides in addition to the duplication responsible for resistance. It is postulated that horizontal gene exchange has been involved in the acquisition (or loss) of resistance within this clone. However, five of the six resistant isolates have distinct duplications and other sequence polymorphisms, suggesting that resistance has arisen independently on many occasions.

Amino Acid Sequence↗
PubMed1997

OXA-15, an extended-spectrum variant of OXA-2 beta-lactamase, isolated from a Pseudomonas aeruginosa strain.

Pseudomonas aeruginosa AH, isolated in Ankara, Turkey, was highly resistant to ceftazidime (MIC, 128 microg/ml) and produced a beta-lactamase that gave a doublet of bands at pIs 8.7 and 8.9. beta-Lactamase production was transferable to P. aeruginosa PU21 by conjugation and was determined by a ca. 450-kb plasmid, pMLH54. The transconjugant and Escherichia coli transformed with the cloned gene showed increased resistance to ceftazidime (especially) and to cefpirome, ceftazidime, ceftriaxone, moxalactam, and aztreonam, but not to carbapenems. Resistance was not reversed by clavulanic acid or tazobactam. Sequencing revealed that the beta-lactamase responsible for this resistance was identical to OXA-2 except that glycine replaced aspartate at position 150. Compared to OXA-2, the new enzyme, named OXA-15, had greater cephalosporinase activity, with increased relative hydrolysis rates for cephaloridine and cephalothin and, most dramatically, for ceftazidime. Cefotaxime and carbapenems remained stable to hydrolysis. Thus, as in the TEM, SHV, and OXA-10 (PSE-2) beta-lactamase families, a minor sequence change in OXA-2 gave a major extension of cephalosporinase activity and contingent resistance. The gene encoding the new beta-lactamase, bla(OXA-15), lay close to the highly conserved 3' end of an integron and had flanking sequences typical of an integron-associated gene cassette. Restriction mapping and partial sequence data indicated that pMLH54 carries an integron with three putative gene cassettes: bla(OXA-15) itself, aadB [coding aminoglycoside nucleotidyltransferase (2")-1a], and an uncharacterized cassette.

Amino Acid Sequence↗
PubMed1997

Association of enzyme inhibition with methods of museum skin preparation.

Enzyme inhibition is commonly encountered when using molecular biological techniques on museum-prepared animal skin samples, and this problem is exacerbated by a lack of information on how particular skins have been prepared for preservation. This report: (i) demonstrates that while some methods of museum preparation inhibit both proteinase K digestion and the PCR, others do not; (ii) describes a change in buffer conditions that reduces proteinase K enzyme inhibition during tissue digestion: and (iii) uses electron-dispersive X-ray microanalysis (EDXA) to show that the preparation methods for museum-preserved skin are often more complex than the treatment description provided with samples and also suggests that some of these descriptions are incorrect.

Animals↗
PubMed1996

A Drosophila calcium channel alpha1 subunit gene maps to a genetic locus associated with behavioral and visual defects.

We have cloned cDNAs that encode a complete open reading frame for a calcium channel alpha1 subunit from Drosophila melanogaster. The deduced 1851 amino acid protein belongs to the superfamily of voltage-gated sodium and calcium channels. Phylogenetic analysis shows that the sequence of this subunit is relatively distant from sodium channel alpha subunits and most similar to genes encoding the A, B, and E isoforms of calcium channel alpha1 subunits. To indicate its similarity to this subfamily of vertebrate isoforms, we name this protein Dmca1A, for Drosophila melanogaster calcium channel alpha1 subunit, type A. Northern blot analysis detected a single 10. 5 kb transcript class that is regulated developmentally, with expression peaks in the first larval instar, midpupal, and late pupal stages. In late-stage embryos, Dmca1A is expressed preferentially in the nervous system. Variant transcripts are generated by alternative splicing. In addition, single nucleotide variations between cDNAs and genomic sequence are consistent with RNA editing. Dmca1A maps to a chromosomal region implicated in, and is the likely candidate for, the gene involved in the generation of behavioral, physiological, and lethal phenotypes of the cacophony, nightblind-A, and lethal(1)L13 mutants.

Amino Acid Sequence↗
PubMed1996

Adenosine diphosphate inhibits the serotonin transporter.

Adenosine 5'-diphosphate (ADP) caused rapid and significant reductions in the rates of [3H]serotonin uptake observed for human platelets, human platelet vesicles, and rat brain synaptic vesicles. Estimated Vmax values in platelets (N = 15). platelet vesicles (N = 3), and synaptic vesicles (N = 3) exposed to 100 microM ADP were 42.3 +/- 11.4%, 78.8 +/- 1.4%, and 56.8 +/- 9.9% of control values, respectively. The EC50 values observed for ADP in platelets and platelet vesicles were 10-24 microM. Exposure to 100 microM ADP had small, inconsistent effects on KM values observed for the platelet transporter. ADP (100 microM) caused only a slight competitive inhibition of the platelet membrane binding of [3H]citalopram, a ligand for the 5HT uptake site of the transporter (5.0% displacement of 1.0 nM [3H]citalopram, 13% increase in apparent KD). The ADP analogue 2-methylthioADP caused similar decreases in the rates of platelet [3H]serotonin uptake, while a number of other related compounds had little or no effect on rates of platelet uptake. The ADP-effect on uptake was rapid, occurring in less than 2.5 s. and was additive with reductions produced by protein kinase C (PKC) activation. The ADP-induced decreases in uptake did not appear to occur through the ADP receptor or known platelet second messenger systems. The exact mechanism of the ADP-effect and its functional significance remain to be determined.

Adenosine Diphosphate↗
PubMed1996

Cloning and functional characterization of a novel dopamine receptor from Drosophila melanogaster.

A cDNA clone is described that encodes a novel G-protein-coupled dopamine receptor (DopR99B) expressed in Drosophila heads. The DopR99B receptor maps to 99B3-5, close to the position of the octopamine/tyramine receptor gene at 99A10-B1, suggesting that the two may be related through a gene duplication. Agonist stimulation of DopR99B receptors expressed in Xenopus oocytes increased intracellular Ca2+ levels monitored as changes in an endogenous inward Ca2+-dependent chloride current. In addition to initiating this intracellular Ca2+ signal, stimulation of DopR99B increased cAMP levels. The rank order of potency of agonists in stimulating the chloride current is: dopamine > norepinephrine > epinephrine > tyramine. Octopamine and 5-hydroxytryptamine are not active (< 100 microM). This pharmacological profile plus the second-messenger coupling pattern suggest that the DopR99B receptor is a D1-like dopamine receptor. However, the hydrophobic core region of the DopR99B receptor shows almost equal amino acid sequence identity (40-48%) with vertebrate serotonergic, alpha 1- and beta-adrenergic, and D1-like and D2-like dopaminergic receptors. Thus, this Drosophila receptor defines a novel structural class of dopamine receptors. Because DopR99B is the second dopamine receptor cloned from Drosophila, this work establishes dopamine receptor diversity in a system amenable to genetic dissection.

Amino Acid Sequence↗
PubMed1996

Cyanobacteria carrying an smt-lux transcriptional fusion as biosensors for the detection of heavy metal cations.

The metal-responsive smt operator/promoter region of Synechococcus PCC7942 was fused to the luxCDABE genes of Vibrio fischeri. Plasmid DNA (pJLE23) carrying this fusion conferred metal ion-inducible luminescence to transformed cyanobacteria. Synechococcus PCC7942 (pJLE23) was sensitive to ZnCl2 concentrations within a range of 0.5-4 microM as demonstrated by induction of luminescence. Trace levels of CuSO24 and CdCl2 were also detected.

Bacterial Proteins↗
PubMed1996

Expression of mouse metallothionein in the cyanobacterium Synechococcus PCC7942.

A cDNA encoding mouse metallothionein was cloned into the shuttle vector pUc303, creating a translational fusion with the bacterial chloramphenicol acetyltransferase gene. The resulting fusion protein has been expressed in the cyanobacterium Synechococcus PCC7942. Cyanobacterial transformants expressed mouse metallothionein-specific mRNA species as detected by RNA slot blots. In addition, the transformants expressed a unique cadmium ion-binding protein corresponding to the predicted size of the mouse metallothionein fusion protein. Expression of this fusion protein conferred a two- to five-fold increase in cadmium ion tolerance and accumulation on Synechococcus PCC7942.

Animals↗
PubMed1996

Temporal and spatial expression patterns of two G-protein coupled receptors in Drosophila melanogaster.

Temporal and spatial expression patterns of a muscarinic acetylcholine receptor (Acr60C) and an octopamine/tyramine receptor (Octyr) were determined in Drosophila melanogaster using quantitative Northern analysis and in situ hybridization to tissue sections. Expression of mRNA encoding both of these G-protein coupled receptors peaks initially in 18 to 21 hour embryos following the formation of the mature larval nervous system. Levels of mRNA then decline during larval stages, rising to a second peak in 3 to 4-day-old pupae after a period of major nervous system reorganization. The muscarinic acetylcholine receptor mRNA is expressed throughout the cortical regions of the central nervous system in adults and embryos. Particularly high levels of expression of Acr60C are observed in cell bodies adjacent to the antennal lobes, suggesting a major role for this muscarinic receptor in the processing of olfactory information. In contrast, the octopamine/tyramine receptor mRNA is distributed diffusely throughout the adult brain, with patches of signal concentrated in the cortex of the dorsal protocerebrum near the mushroom bodies. These patches may represent individual cells expressing Octyr receptors.

Animals↗
PubMed1996

Pneumococcal meningitis in the North East Thames Region UK: epidemiology and molecular analysis of isolates.

One hundred and fourteen cases of pneumococcal meningitis were identified by prospective laboratory based surveillance during 1990-3 in the North East Thames Region. Higher rates of disease were seen in Asians (2.1/100000) than Caucasians (0.8/100000) (P = 0.002). The incidence of meningitis was higher in children than adults, while mortality rates were highest in adults over the age of 60 (48%). In 72 cases, both blood and CSF were culture positive. Serotyping of 65 isolates collected identified 22 serotypes (and one non-typable) causing disease, the most common being serotype 6 (13 cases) and serotype 14 (11 cases). Overall, 90% of serotype antigens identified were represented in the 23 valent vaccine. Ribotyping of 62 isolates identified 35 different patterns, of which 26 were single types. Different ribotypes were found among isolates of the same serotypes, with the exception of serotype 14, where 9 of 11 isolates had the same ribotype pattern. Four percent of isolates had reduced susceptibility to penicillin, but no high level penicillin resistance was found.

Adolescent↗