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Biomedical subjects

A E Stewart

Publications and source records attributed to A E Stewart.

16 recordsLinked to original sources
PubMed2004

alpha2-Adrenergic receptor-mediated modulation of calcium current in neocortical pyramidal neurons.

Noradrenergic projections to the cortex modulate a variety of cortical activities and calcium channels are one likely target for such modulation. We used the whole-cell patch-clamp technique to study noradrenergic modulation of barium currents in acutely dissociated pyramidal neurons from rat sensorimotor cortex. Extracellular application of specific agonists and antagonists revealed that norepinephrine (NE) reduced Ca2+ current. A major component of this modulation was due to activation of alpha2 receptors. Activation of alpha2-adrenergic receptors resulted in a fast, voltage-dependent pathway involving Gi/Go G-proteins. This pathway targeted N- and P-type calcium channels The alpha2 modulation was partially reversed by repeated action potential waveforms (APWs). N- and P-type channels have been implicated in synaptic transmission and activation of afterhyperpolarizations in these cells. Our findings suggest that NE can regulate these cellular processes by mechanisms sensitive to spike activity.

Action Potentials↗
PubMed2001

Effects of spike parameters and neuromodulators on action potential waveform-induced calcium entry into pyramidal neurons.

Neocortical pyramidal neurons express several different calcium channel types. Previous studies with square voltage steps have found modest biophysical differences between these calcium channel types as well as differences in their modulation by transmitters. We used acutely dissociated neocortical pyramidal neurons to test whether this diversity extends to different activation by physiological stimuli. We conclude that 1) peak amplitude, latency to peak, and the total charge entry for the Ca(2+) channel current is dependent on the shape of the mock action potential waveforms (APWs). 2) The percent contribution of the five high-voltage-activated currents to the whole cell current was not altered by using an APW as opposed to a voltage step to elicit the current. 3) The identity of the charge carrier affects the amplitude and decay of the whole cell current. With Ca(2+), there was a greater contribution of T-type current to the whole cell current. 4) Total Ba(2+) charge entry is linearly dependent on the number of spikes in the stimulating waveform and relatively insensitive to spike frequency. 5) Current decay was greatest with Ca(2+) as the charge carrier and with minimal internal chelation. 6) Voltage-dependent neurotransmitter-mediated modulations can be reversed by multiple spikes. The extent of the reversal is dependent on the number of spikes in the stimulating waveform. Thus the neuronal activity pattern can determine the effectiveness of voltage-dependent and -independent modulatory pathways in neocortical pyramidal neurons.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1999

Crystal structure of the MAPK phosphatase Pyst1 catalytic domain and implications for regulated activation.

The crystal structure of the catalytic domain from the MAPK phosphatase Pyst1 (Pyst1-CD) has been determined at 2.35 A. The structure adopts a protein tyrosine phosphatase (PTPase) fold with a shallow active site that displays a distorted geometry in the absence of its substrate with some similarity to the dual-specificity phosphatase cdc25. Functional characterization of Pyst1-CD indicates it is sufficient to dephosphorylate activated ERK2 in vitro. Kinetic analysis of Pyst1 and Pyst1-CD using the substrate p-nitrophenyl phosphate (pNPP) reveals that both molecules undergo catalytic activation in the presence of recombinant inactive ERK2, switching from a low- to high-activity form. Mutation of Asp 262, located 5.5 A distal to the active site, demonstrates it is essential for catalysis in the high-activity ERK2-dependent conformation of Pyst1 but not for the low-activity ERK2-independent form, suggesting that ERK2 induces closure of the Asp 262 loop over the active site, thereby enhancing Pyst1 catalytic efficiency.

Amino Acid Sequence↗
PubMed1999

Complicated bereavement and posttraumatic stress disorder following fatal car crashes: recommendations for death notification practice.

This article reviewed how four characteristics of car crash deaths--suddenness, untimeliness, preventability, and violent, mutilating injuries--may contribute to complicated bereavement syndromes or to the development of posttraumatic stress disorder (PTSD). The Fatality Analysis Reporting System was then used to assess the proportion of car crashes from 1990-1996 that involved one or more of these characteristics. At least 75% of all deaths involved suddenness, untimeliness, or were preventable, that is, due to alcohol or drug use. Twenty-eight percent of crash deaths involved 2 of these characteristics and 6% involved all 3. Recommendations for performing death notifications were provided with an emphasis on identifying and responding to circumstances that may lead to complicated bereavement or PTSD. Recommendations for further research also were provided.

Accidents, Traffic↗
PubMed1999

Muscarine modulates Ca2+ channel currents in rat sensorimotor pyramidal cells via two distinct pathways.

We used the whole cell patch-clamp technique and single-cell reverse transcription-polymerase chain reaction (RT-PCR) to study the muscarinic receptor-mediated modulation of calcium channel currents in both acutely isolated and cultured pyramidal neurons from rat sensorimotor cortex. Single-cell RT-PCR profiling for muscarinic receptor mRNAs revealed the expression of m1, m2, m3, and m4 subtypes in these cells. Muscarine reversibly reduced Ca2+ currents in a dose-dependent manner. The modulation was blocked by the muscarinic antagonist atropine. When the internal recording solution included 10 mM ethylene glycol-bis(beta-aminoethyl ether)-N, N,N',N'-tetraacetic acid (EGTA) or 10 mM bis-(o-aminophenoxy)-N,N,N', N'-tetraacetic acid (BAPTA), the modulation was rapid (tauonset approximately 1.2 s). Under conditions where intracellular calcium levels were less controlled (0.0-0.1 mM BAPTA), a slowly developing component of the modulation also was observed (tauonset approximately 17 s). Both fast and slow components also were observed in recordings with 10 mM EGTA or 20 mM BAPTA when Ca2+ was added to elevate internal [Ca2+] ( approximately 150 nM). The fast component was due to a reduction in both N- and P-type calcium currents, whereas the slow component involved L-type current. N-ethylmaleimide blocked the fast component but not the slow component of the modulation. Preincubation of cultured neurons with pertussis toxin (PTX) also greatly reduced the fast portion of the modulation. These results suggest a role for both PTX-sensitive G proteins as well as PTX-insensitive G proteins in the muscarinic modulation. The fast component of the modulation was reversed by strong depolarization, whereas the slow component was not. Reblock of the calcium channels by G proteins (at -90 mV) occurred with a median tau of 68 ms. We conclude that activation of muscarinic receptors results in modulation of N- and P-type channels by a rapid, voltage-dependent pathway and of L-type current by a slow, voltage-independent pathway.

Animals↗
PubMed1996

A mouse amidase specific for N-terminal asparagine. The gene, the enzyme, and their function in the N-end rule pathway.

The N-end rule relates the in vivo half-life of a protein to the identity of its N-terminal residue. In both fungi and mammals, the tertiary destabilizing N-terminal residues asparagine and glutamine function through their conversion, by enzymatic deamidation, into the secondary destabilizing residues aspartate and glutamate, whose destabilizing activity requires their enzymatic conjugation to arginine, one of the primary destabilizing residues. We report the isolation and analysis of a mouse cDNA and the corresponding gene (termed Ntan1) that encode a 310-residue amidohydrolase (termed NtN-amidase) specific for N-terminal asparagine. The approximately 17-kilobase pair Ntan1 gene is located in the proximal region of mouse chromosome 16 and contains 10 exons ranging from 54 to 177 base pairs in length. The approximately 1.4-kilobase pair Ntan1 mRNA is expressed in all of the tested mouse tissues and cell lines and is down-regulated upon the conversion of myoblasts into myotubes. The Ntan1 promoter is located approximately 500 base pairs upstream of the Ntan1 start codon. The deduced amino acid sequence of mouse NtN-amidase is 88% identical to the sequence of its porcine counterpart, but bears no significant similarity to the sequence of the NTA1-encoded N-terminal amidohydrolase of the yeast Saccharomyces cerevisiae, which can deamidate either N-terminal asparagine or glutamine. The expression of mouse NtN-amidase in S. cerevisiae nta1Delta was used to verify that NtN-amidase retains its asparagine selectivity in vivo and can implement the asparagine-specific subset of the N-end rule. Further dissection of mouse Ntan1, including its null phenotype analysis, should illuminate the functions of the N-end rule, most of which are still unknown.

Amidohydrolases↗
PubMed1996

Incorporating anomalous scattering centres into macromolecules.

The widespread application of multiwavelength anomalous diffraction (MAD) for phase evaluation has been hampered in the past by the small selection of anomalous scattering centres that could be introduced into macromolecules. Recently, the use of chemical modification, protein engineering or biosynthetic labelling has provided suitable tools to overcome the previous limitations, thereby making most structural analyses amenable to a MAD approach.

Animals↗
PubMed1995

Eukaryotic methionyl aminopeptidases: two classes of cobalt-dependent enzymes.

Using partial amino acid sequence data derived from porcine methionyl aminopeptidase (MetAP; methionine aminopeptidase, peptidase M; EC 3.4.11.18), a full-length clone of the homologous human enzyme has been obtained. The cDNA sequence contains 2569 nt with a single open reading frame corresponding to a protein of 478 amino acids. The C-terminal portion representing the catalytic domain shows limited identity with MetAP sequences from various prokaryotes and yeast, while the N terminus is rich in charged amino acids, including extended strings of basic and acidic residues. These highly polar stretches likely result in the spuriously high observed molecular mass (67 kDa). This cDNA sequence is highly similar to a rat protein, termed p67, which was identified as an inhibitor of phosphorylation of initiation factor eIF2 alpha and was previously predicted to be a metallopeptidase based on limited sequence homology. Model building established that human MetAP (p67) could be readily accommodated into the Escherichia coli MetAP structure and that the Co2+ ligands were fully preserved. However, human MetAP was found to be much more similar to a yeast open reading frame that differed markedly from the previously reported yeast MetAP. A similar partial sequence from Methanothermus fervidus suggests that this p67-like sequence is also found in prokaryotes. These findings suggest that there are two cobalt-dependent MetAP families, presently composed of the prokaryote and yeast sequences (and represented by the E. coli structure) (type I), on the one hand, and by human MetAP, the yeast open reading frame, and the partial prokaryotic sequence (type II), on the other.

Amino Acid Sequence↗
PubMed1995

The sequence of porcine protein NH2-terminal asparagine amidohydrolase. A new component of the N-end Rule pathway.

Co- and post-translational amino-terminal processing of proteins is one mechanism by which intracellular proteins can be either protected from or targeted to degradation by the N-end Rule pathway (Bachmair, A., Finley, D., and Varshavsky, A. (1986) Science 234, 179-186). A novel enzyme, protein NH2-terminal asparagine amidohydrolase, which can function in this pathway by potentially directing critical regulatory proteins possessing an amino-terminal asparagine residue formed from the removal of N-acetylmethionine, has recently been purified and characterized (Stewart, A.E., Arfin, S. M., and Bradshaw, R. A. (1994) J. Biol. Chem. 269, 23509-23517). Here, we report the isolation and characterization of a cDNA for porcine protein NH2-terminal asparagine amidohydrolase, which indicates that it is a new type of enzyme, not homologous to any previously identified protein. This provides strong evidence for the importance of regulated protein degradation in cellular functioning.

Amino Acid Sequence↗
PubMed1994

Protein NH2-terminal asparagine deamidase. Isolation and characterization of a new enzyme.

An apparently unique enzyme, designated protein NH2-terminal asparagine deamidase (PNAD), that specifically converts NH2-terminal asparagine residues of peptide and protein substrates to aspartic acid, has been isolated to homogeneity from porcine liver by an eight-step procedure. PNAD is a relatively low abundance protein, is readily solubilized, and exists as a monomeric species of approximately 33 kDa. PNAD does not act on internal asparagine residues and requires a free N alpha-amino group. It has reduced or no activity on NH2-terminal asparagine dipeptides and no activity toward free asparagine or asparagine amide. It does not act on any NH2-terminal glutamine substrates. PNAD does not show a strong pH dependence suggesting that the enzyme can act equally well on substrates with ionized or unionized alpha-amino groups. The properties and specificity of PNAD are consistent with those expected for the enzyme required for the ubiquitin-dependent turnover of intracellular proteins that initiate with Met-Asn-. Such proteins should be N alpha-acetylated on the retained initiator methionine and can subsequently be modified by the removal of N-acetyl methionine by acylaminoacid hydrolase. Conversion of the resulting NH2-terminal asparagine to aspartic acid by PNAD would render the protein susceptible to arginylation, polyubiquitinylation and degradation as specified by the N-end rule.

Amidohydrolases↗
PubMed1992

The disulfide bond pairing of the pheromones Er-1 and Er-2 of the ciliated protozoan Euplotes raikovi.

The disulfide pairings of the two Euplotes raikovi pheromones Er-1 and Er-2 have been determined by chemical and mass spectrometric analyses. Cystine-linked peptides from thermolytic digestions of the native molecules were purified by reverse-phase high performance liquid chromatography and identified in the known sequences to make the assignments. The same pairing, Cys(I)-Cys(IV), Cys(II)-Cys(VI), and Cys(III)-Cys(V), was found in both pheromones, suggesting that this pattern occurs commonly throughout this family of molecules. This arrangement of disulfides indicates that the three-dimensional structure is defined by three loops, which can vary in size and charge distribution from one pheromone to another.

Amino Acid Sequence↗
PubMed1992

Effects of group membership on perception of risk for AIDS.

The role of social identity as a moderator for perception of risk for AIDS has not been examined. The purpose of this study was to examine perception of risk for AIDS as a function of membership in an identified risk group. 34 subjects who were homosexual, 58 intravenous drug users (IV), and 34 college students rated a 21-item list of behaviors for perception of AIDS risk. The findings indicate that the IV drug-use group significantly underestimated five risk behaviors, four of which are high probability behaviors of IV drug-users and two of which are exclusively IV drug-use behaviors. The homosexual group significantly underestimated four risk behaviors, all of which are primarily characteristic of that group. The college group was generally more accurate in assessing risk than either of the other two groups. These findings support the hypothesis that membership in a perceived risk group is related to differential perceptual bias associated with the need for positive social identity for one's group.

Acquired Immunodeficiency Syndrome↗
PubMed1968

Detection of bacteriuria in women attending local authority antenatal clinics using the dip-inoculum transport medium spoon method.

Four hundred and seventy-eight pregnant women attending local authority clinics in Portsmouth were screened for bacteriuria using the dip-inoculum transport medium (DITM) spoon method. The detection of asymptomatic bacteriuria in 5% of the patients with a very low proportion of equivocal results (0.83%) suggests that this is an efficient method; and large numbers of urine specimens could be sampled with relatively little work for the laboratory. A cystine-MacConkey medium was devised for incorporation in the spoons. General practitioners treated the women with bacteriuria, and remained responsible for home delivery and postpartum examinations. The possibility of successful cooperation between non-hospital clinics, a bacteriological laboratory, and general practitioners is demonstrated.

Bacteriological Techniques↗
PubMedDate not supplied

A survey of professionals' training and experiences in delivering death notifications.

A mail survey was conducted of 240 people from different professions that routinely encountered death to assess their previous training and experiences in delivering death notifications. Nearly 40% of these persons had received neither classroom nor experiential training in death notification, although 70% of respondents had performed at least one notification. The causes of death that contributed to notifiers' distress during notification included (a) violent crime, (b) drunk driving crashes, (c) suicide, and (d) the death of a child. Survivor reactions that were the most difficult for notifiers to manage during the notification included (a) attempts to harm self or others (b) physical acting-out, and (c) intense anxiety. Notifiers indicated that they most frequently coped with the stresses of notification by (a) spending time with family, (b) talking with coworkers, and (c) spending time alone. The implications of the results and the needs for systematic death notification education were discussed.

Adult↗