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Biomedical subjects

S Stevens

Publications and source records attributed to S Stevens.

At least 37 records · Page 2Linked to original sources
PubMed1998

Aborted implantable cardioverter defibrillator shock during facial electrosurgery.

A patient with a fourth-generation transvenous implantable cardioverter-defibrillator system nearly received an inappropriate defibrillation discharge while undergoing electrofulguration of keratotic facial skin lesions. The incident was confirmed by analyses of the implantable cardioverter-defibrillator's time/date stamped event log and stored electrogram record. Therapy was withheld by the noncommitted implantable cardioverter-defibrillator as the pulsed electrocautery was not continued beyond the charging period.

Aged↗
PubMed1998

Coactivation by OCA-B: definition of critical regions and synergism with general cofactors.

Molecular dissection of the B-cell-specific transcription coactivator OCA-B has revealed distinct regions important, respectively, for recruitment to immunoglobulin promoters through interaction with octamer-bound Oct-1 and for subsequent coactivator function. Further analysis of general coactivator requirements showed that selective removal of PC4 from the essential USA fraction severely impairs Oct-1 and OCA-B function in a cell-free system reconstituted with partially purified factors. Full activity can be restored by the combined action of recombinant PC4 and the PC4-depleted USA fraction, thus suggesting a joint requirement for PC4 and another, USA-derived component(s) for optimal function of Oct-1/OCA-B in the reconstituted system. Indeed, USA-derived PC2 was found to act synergistically with PC4 in reproducing the function of intact USA in the assay system. Consistent with the requirement for PC4 in the reconstituted system, OCA-B was found to interact directly with PC4. Surprisingly, however, removal of PC4 from the unfractionated nuclear extract has no detrimental effect on OCA-B/Oct-1-dependent transcription. These results lead to a general model for the synergistic function of activation domains in Oct-1 and OCA-B (mediated by the combined action of the multiple USA components) and, further, suggest a functional redundancy in general coactivators.

Amino Acid Sequence↗
PubMed1997

Margatoxin binds to a homomultimer of K(V)1.3 channels in Jurkat cells. Comparison with K(V)1.3 expressed in CHO cells.

Voltage-gated potassium (K(V)) channels play key roles in setting the resting potential and in the activation cascade of human peripheral T lymphocytes. Margatoxin (MgTX), a 39-amino acid peptide from Centruroides margaritatus, is a potent inhibitor of lymphocyte K(V) channels. The binding of monoiodotyrosinyl margatoxin ([125I]MgTX) to plasma membranes prepared from either Jurkat cells, a human leukemic T cell line, or CHO cells stably transfected with the Shaker-type voltage-gated K+ channel, K(V)1.3, has been used to investigate the properties of lymphocyte K(V) channels. These data were compared with [125I]MgTX binding to heterotetrameric K(V) channels in rat brain synaptic plasma membranes [Knaus, H. G., et al. (1995) Biochemistry 34, 13627-13634]. The affinity for [125I]MgTX is 100-200 fM in either Jurkat or CHO/K(V)1.3 membranes, and the receptor density is 20-120 fmol/mg in Jurkat membranes or 1000 fmol/mg in CHO/K(V)1.3 membranes. In contrast to rat brain, [125I]MgTX binding to Jurkat and CHO/K(V)1.3 membranes exhibits an absolute requirement for K+, with no potentiation of binding by Na+. K(V)1.3 was the only K(V)1 series channel present in either CHO/K(V)1.3 or Jurkat plasma membranes as determined by immunoprecipitation of [125I]MgTX binding or by Western blot analyses using sequence-specific antibodies prepared against members of the K(V)1 family. The relative potencies of a series of peptidyl K(V) channel inhibitors was essentially the same for inhibition of [125I]MgTX binding to Jurkat, CHO, or rat brain membranes and for blocking 86Rb+ efflux from the CHO/K(V)1.3 cells, except that alpha-dendrotoxin was more potent at blocking binding to rat brain membranes than in the other assays. The characteristics of [125I]MgTX binding, the antibody profiles, and the effects of the peptidyl K(V) inhibitors all indicate that the [125I]MgTX receptor in Jurkat lymphocytes is comprised of a homomultimer of K(V)1.3, unlike the heteromultimeric arrangement of the receptor in rat brain.

Animals↗
PubMed1996

Deletion in HCDR3 rescues T15 antibody mutants from a secretion defect caused by mutations in HCDR2.

We recently described mutants of the murine anti-phosphocholine Ab T15, with changes in heavy chain complementarity determining region 2 (HCDR2) that caused loss of secretion. Surprisingly, the T15 HCDR2 mutations did not alter secretion when placed into the related anti-phosphocholine Ab D16, which differs from T15 only in HCDR3 and light (L) chain. Here, we exploit the differences between these two Abs to assess the basis of the secretion defect. The T15 L chain is not secreted in the absence of heavy (H) chain. In contrast, D16 L chain is secreted in the absence of H chain, as are most L chains. We co-expressed the T15 wild-type (wt) and mutant H chains with the D16 L chain, as well as with another secreted L chain, J558L. The mutant H chains were not secreted when expressed with either heterologous L chain. These results establish that the T15 L chain is not uniquely associated with the defect. The T15 and D16 Abs also differ in HCDR3 length in that D16 lacks four amino acid residues (Ser99, Ser100, Tyr100a, Trp100b) present in T15. We deleted these four residues from T15 wt and mutant H chains. Secretion of T15 wt was unaffected by the deletion, but shortening HCDR3 restored secretion in the HCDR2 mutants regardless of L chain association. Together these data demonstrate that both the HCDR2 and HCDR3 domains contain structural information that may affect the secretion competence of Abs.

Amino Acid Sequence↗
PubMed1996

HMG box-activating factors 1 and 2, two HMG box transcription factors that bind the human Ig heavy chain enhancer.

We present the isolation of two cDNAs that encode distinct, yet related, proteins that bind the HE2 region of the human Ig heavy chain (IgH) enhancer. Designated HMG box-activating factors (HAF) 1 and 2, the two proteins are new members of the HMG box family of DNA binding proteins. Both are potent transcription activators when expressed 1) as GAL4 fusions targeted to promoters containing GAL4 operators, or 2) as intact proteins targeted to minimal promoters containing binding sites derived from the IgH enhancer. HAF-1 and HAF-2 mRNAs are apparently expressed in both B cells and non-B cells. However, activity generated by the isolated HE2 region in B cells is dependent on both an intact HAF-1/HAF-2 binding site and at least one additional site that has been reported previously to bind a B cell-restricted protein. Our results suggest a collaborative role for either or both HAF-1 and HAF-2 in establishing the B cell activity of the human IgH enhancer.

Amino Acid Sequence↗
PubMed1996

The B-cell-specific transcription coactivator OCA-B/OBF-1/Bob-1 is essential for normal production of immunoglobulin isotypes.

OCA-B was initially identified as a B-cell-restricted coactivator that functions with octamer binding transcription factors (Oct-1 and Oct-2) to mediate efficient cell type-specific transcription of immunoglobulin promoters in vitro. Subsequent cloning studies led to identification of the coactivator as a single polypeptide, designated either as OCA-B (ref. 3), OBF-1 (ref. 4) or Bob-1 (ref. 5). OCA-B itself does not bind to DNA directly, but interacts with either Oct-1 or Oct-2 to potentiate transcriptional activation. To determine the biological role of OCA-B, we generated OCA-B-deficient mice by gene targeting. Mice lacking OCA-B undergo normal antigen-independent, B-cell differentiation, including appropriate expression of both immunoglobulin genes and other early B-cell-restricted genes. However, antigen-dependent maturation of B cells is greatly affected. The proliferative response to surface IgM crosslinking is impaired, and there is a severe deficiency in the production of secondary immunoglobulin isotypes including IgG1, IgG2a, IgG2b, IgG3, IgA and IgE in OCA-B-deficient B cells. This defect is not due to a failure of the isotype switching process, but rather to reduced levels of transcription from normally switched immunoglobulin heavy-chain loci. In accord with the defective isotype production, germinal centre formation is absent in these mutant mice.

Animals↗
PubMed1995

Enhancement and destruction of antibody function by somatic mutation: unequal occurrence is controlled by V gene combinatorial associations.

We examined the positive and negative effects of somatic mutation on antibody function using saturation mutagenesis in vitro to mimic the potential of the in vivo process to diversify antibodies. Identical mutations were introduced into the second complementarity determining region of two anti-phosphocholine antibodies, T15 and D16, which share the same germline VH gene sequence. T15 predominates in primary responses and does not undergo affinity maturation. D16 is representative of antibodies that co-dominate in memory responses and do undergo affinity maturation. We previously reported that > 50% of T15 mutants had decreased antigen binding capacity. To test if this high frequency of binding loss was unique to T15 or a consequence of random point mutations applicable to other combining sites, we analyzed the same mutations in D16. We show that D16 suffers a similar loss of function, indicating an equally high potential for B-cell wastage. However, only D16 displayed the capacity for somatic mutation to improve antigen binding, which should enhance its persistence in memory responses. Mutation of residues contacting the haptenic group, as determined by molecular modeling, did not improve binding. Instead, productive mutations occurred in residues that either contacted carrier protein or were distant from the antigen binding site, possibly increasing binding site flexibility through long-range effects. Targeting such residues for mutation should aid in the rational design of improved antibodies.

Amino Acid Sequence↗
PubMed1995

Reduction of tissue edema by microdialysis.

OBJECTIVE: This is the first report (to our knowledge) of the use of tissue microdialysis to reduce tissue edema. In this study, a hyperosmotic solution was perfused through microdialysis catheters, allowing direct treatment of interstitial edema by osmosis. DESIGN: First, the catheter and perfusate characteristics were tested in vitro. A physiologic, controlled trial was then performed, with two outcome variables: osmolarity of the effluent and tissue water content. SUBJECTS: Twenty male Sprague-Dawley rats. One rat was withdrawn. INTERVENTIONS: Tissue microdialysis catheters were implanted in the rats. The control side of the animals was not perfused. The experimental side was perfused for 9 hours. RESULTS: Osmolarity of the perfusate was reduced 16.5 mOsm after passing through the catheter, indicating that fluid was removed from the tissue. Tissue edema was reduced by an average 1.8 mL of fluid per 100 g of wet tissue. CONCLUSIONS: Tissue microdialysis removed tissue fluid and reduced edema. This treatment may have a beneficial effect on edematous tissues. Potential use and limitations of this therapeutic modality are discussed.

Animals↗
PubMed1995

Clinical trial of a new lightwand device (Trachlight) to intubate the trachea.

BACKGROUND: Transillumination of the soft tissue of the neck using a lighted stylet (lightwand) is an effective and safe intubating technique. A newly designed lightwand (Trachlight) incorporates modifications to improve the brightness of the light source as well as flexibility. The goal of this study was to determine the effectiveness and safety of this device in intubating the trachea of elective surgical patients. METHODS: Healthy surgical patients were studied. Patients with known or potential problems with intubation were excluded. During general anesthesia, the tracheas were intubated randomly using either the Trachlight or the laryngoscope. Failure to intubate was defined as lack of successful intubation after three attempts. The duration of each attempt was recorded as the time from insertion of the device into the oropharynx to the time of its removal. The total time to intubation (TTI), an overall measure of the ease of intubation, was defined as the sum of the durations of all (as many as three) intubation attempts. Complications, such as mucosal bleeding, lacerations, dental injury, and sore throat, were recorded. RESULTS: Nine hundred fifty patients (479 in the Trachlight group and 471 in the laryngoscope group) were studied. There was a 1% failure rate with the Trachlight, and 92% of intubations were successful on the first attempt, compared with a 3% failure rate and an 89% success rate on the first attempt with the laryngoscope (P not significant). All failures were followed by successful intubation using the alternate device. The TTI was significantly less with the Trachlight compared with the laryngoscope (15.7 +/- 10.8 vs. 19.6 +/- 23.7 s). For laryngoscopic intubation, the TTI was longer for patients with limited mandibular protrusion and mentohyoid distance, with a larger circumference of the neck, and with a high classification according to Mallampatti et al. However, there was no relation between the TTI and any of the airway parameters for Trachlight. There were significantly fewer traumatic events in the Trachlight group than in the laryngoscope group (10 vs. 37). More patients complained of sore throat in the laryngoscope group than in the Trachlight group (25.3% vs. 17.1%). CONCLUSIONS: In contrast to laryngoscopy, the ease of intubation using the Trachlight does not appear to be influenced by anatomic variations of the upper airway. Intubation occasionally failed with the Trachlight but in all cases was resolved with direct laryngoscopy. The failures of direct laryngoscopy were resolved with Trachlight. Thus the combined technique was 100% successful in intubating the tracheas of all patients.

Adult↗
PubMed1995

Willingness for treatment as a predictor of retention and outcomes.

Retention in drug treatment is important to successful outcomes. The purpose of this study was to test assumptions made in the development and implementation of the ASSET project. The three assumptions were that living conditions of the homeless adult drug user influence willingness for treatment; willingness relates to treatment tenure; and, conditions, willingness and time in treatment influence treatment outcomes. Data on alcohol use, drug use, employment and housing as well as motivation, readiness and suitability of treatment were collected from 494 homeless adults at baseline and at follow-up. Data were subjected to multivariate causal analysis using factor analytic structural equations modeling. Practical fit indices were acceptable. The measurement model confirmed a higher order construct labelled willingness encompassing motivation, readiness and suitability. The structural model demonstrated that willingness positively related to treatment tenure; willingness positively influenced change in drug use and housing; and, tenure related positively to change in housing.

Adult↗
PubMed1994

Defective secretion of an immunoglobulin caused by mutations in the heavy chain complementarity determining region 2.

We have investigated four secretion-deficient antibodies (Abs) derived from a panel of 46 mutant T15 anti-phosphocholine Abs, all of which have point mutations in the heavy chain (H) complementarity determining region 2 (CDR2). The level of secretion for these four Abs was < 10% of wild type when expressed together with the T15 light chain (L) in either SP2/0 or P3X63Ag8.653 myeloma cells although normal levels of H and L chain mRNA were produced. Moreover, abundant intracellular H and L chain proteins were detected. Three of the four mutants had little or no assembled H and L complexes intracellularly whereas one had a significant amount of intracellular immunoglobulin (Ig) which was shown to be capable of binding Ag. Thus, we demonstrate for the first time that point mutations confined to CDR2 of the H chain variable (V) region can impede Ab assembly and secretion. We then introduced the same CDR2 mutations into a related H chain which is encoded by the same T15 VH gene but different diversity (D) and joining (J) genes. When these H chains were expressed with a non-T15 L chain, the resulting Abs were secreted normally. The results thus suggest that the effects of the CDR2 mutations on Ab secretion are dependent on their interactions with L and/or H chain D-J sequences. These results also reveal a novel mechanism that could contribute to B cell wastage.

Amino Acid Sequence↗
PubMed1994

Drug allergies in the surgical population.

Many patients claim to have drug allergies. However, the signs and symptoms of "allergic reactions" are seldom documented and the drug allergies are rarely properly assessed. The goal of this study was to determine the incidence of claimed "drug allergies" in a surgical population. After obtaining institutional approval, the study was carried out at five hospitals affiliated with Dalhousie University. Patients were interviewed by the investigators during the preoperative anaesthetic evaluation over six months and all signs and symptoms of drug reactions were recorded. The validity of the claimed allergy was based on the history. The allergies were assigned to one of three groups: (1) High probability of an allergic reaction: one or more of the signs and symptoms typical of an immunological reaction, with or without a family history, or a history of atopy; (ii) Low probability of an allergic reaction: signs and symptoms of the reaction were predictable reactions or side effects of the drug, without the occurrence of reactions mentioned above; or (iii) Unknown status: no information concerning the reaction of history was available. Of 1818 adult and paediatric patients (914 female/904 male) interviewed, 511 (28.1%) claimed to have one or more drug allergies (a total of 671 allergies). More women than men claimed to have drug allergies (60.3% vs 39.7%) and there was a positive correlation between age, number of medications and reported drug allergies. Antibiotics (50%), opioids (27%), non-steroidal anti-inflammatory agents (10%), and sedatives (5%) accounted for 92% of all claimed drug allergies. Overall, 50% of claimed allergies had a high probability of true allergic reactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗