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Biomedical subjects

P Taylor

Publications and source records attributed to P Taylor.

At least 253 records · Page 14Linked to original sources
PubMed1996

Lateral bone density measurements in osteoarthritis of the lumbar spine.

OBJECTIVE: To investigate whether spinal osteoarthritis (OA) is responsible for the common finding that lumbar spine bone mineral density (BMD) is greater when measured in the anteroposterior plane than when measured in the lateral plane. METHODS: We studied lateral spine radiographs from 63 women who attended a hospital outpatient department for bone density measurement and who also underwent lumbar spine radiography. Osteoarthritis was assessed using both the Kellgren and Lawrence scale and a scoring system for osteophytosis. Bone density was measured in the anteroposterior and lateral planes using a Hologic QDR-2000 instrument. RESULTS: The mean anteroposterior BMD (0.92 g/cm2) was significantly greater than the lateral BMD (0.59 g/cm2) (p < 0.01), and the difference between antero-posterior and lateral measurements was significantly associated with both increasing Kellgren and Lawrence score and osteophyte score, even after adjustment for age. CONCLUSION: These data suggest that spinal OA is a major cause of the difference between anteroposterior and lateral BMD and that lateral BMD may provide a more accurate representation of true vertebral body bone density in patients with OA of the lumbar spine.

Absorptiometry, Photon↗
PubMed1996

Spinal nicotinic receptor expression in spontaneously hypertensive rats.

Intrathecal administration of nicotinic agonists previously has been shown to result in exaggerated pressor and heart rate responses as well as greater nociceptive behavior in adult (12-week-old) spontaneously hypertensive rats (SHR) than in age-matched normotensive Wistar-Kyoto rats (WKY). Paradoxical to these augmented responses to nicotinic agonists in SHR, nicotinic receptor number in the spinal cord as measured by cytisine binding sites is lower in adult SHR than normotensive WKY and Sprague-Dawley rats. Using the high-affinity agonist epibatidine, we found similar differences in receptor number between strains in both in vitro ligand binding experiments with spinal cord membranes and in situ autoradiographic analyses. Spinal nicotinic receptor number did not differ in 5-week-old prehypertensive SHR and age-matched WKY; however, receptor numbers were higher in young rats of both strains than in their adult counterparts. Antihypertensive treatment (25 mg/kg per day hydralazine PO) in 6-week-old SHR from 6 to 12 weeks of age markedly reduced the progressive rise in blood pressure yet did not alter nicotinic receptor number compared with untreated rats. Similar treatment of WKY with hydralazine produced a slight fall in blood pressure but no change in receptor number. Thus, normalization of blood pressure by hydralazine in SHR does not result in a return of receptor expression to levels seen in normotensive rats. Higher centrally mediated pressor activity or augmented postcoupling events after neuronal nicotinic receptor stimulation may slowly downregulate expression of spinal nicotinic receptors in this genetically hypertensive rat strain.

Animals↗
PubMed1996

Potential toxicity of retrograde uterine passage of particulate matter.

Dusting powders are commonly used on surgical gloves, examination gloves, and condoms. In addition, they are used in diaphragms, sanitary napkins, and toiletries. These dusting powders can gain access to the abdominal cavity through the vagina or through surgical intervention. The toxicity of these dusting powders in the abdominal cavity can be divided into acute and chronic complications that may be life-threatening. The use of medical and surgical products without dusting powders is strongly recommended.

Condoms↗
PubMed1996

Intrathecal nicotinic agonist-elicited release of excitatory amino acids as measured by in vivo spinal microdialysis in rats.

The nicotinic agonists, nicotine and cytisine, when administered intrathecally elicit an increase in blood pressure and heart rate as well as a nociceptive response. By using a novel microdialysis procedure, in which a 4-cm dialysis tubing is inserted proximal to the intrathecal injection site, we have examined the release of excitatory amino acids associated with agonist stimulation. The nicotinic agonists, nicotine, cytisine and epibatidine, elicit dose-dependent increases in spinal release of Asp and Glu. The rank order of potencies of the nicotinic agonists in eliciting the cardiovascular and irritation responses correlates with the order of agonist potency in inducing Asp and Glu release in spinal microdialysates. In addition, a correlation is observed between the nociceptive and blood pressure response evoked by the nicotinic agonists and the spinal release of the excitatory amino acids. By examining the position of the permeable dialysis surface in relation to the agonist injection port, we found that the response to nicotine is localized to 5 to 10 mm distances, whereas the cytisine response may be elicited over longer distances. The marked desensitization observed upon repeated administration of cytisine is also reflected in diminished amino acid release. Amino acid release by nicotine can be antagonized by a channel blocking antagonist, mecamylamine, and by a competitive antagonist, dihydro-beta-erythroidine. Mecamylamine also inhibited the amino acid release elicited by epibatidine and cytisine. Hence, excitatory amino acid release is an appropriate response marker for the cellular events associated with nicotinic receptor stimulation in the spinal cord.

Animals↗
PubMed1996

Developmental versus conventional care: a comparison of clinical outcomes for very low birth weight infants.

The purpose of this research was to describe the clinical profile of very low birth weight (VLBW) infants receiving conventional versus developmental care during their hospitalization and to determine the appropriateness of developmental-care interventions. A phase-lag study with 124 preterm infants indicated that although there were no significant differences in individual clinical outcomes, developmental care had a significant effect on the physiologic stability of the infant over time. Developmental interventions were used for all infants receiving the developmental-care intervention, with varying frequency.

Developmental Biology↗
PubMed1995

Acetylcholinesterase inhibition by fasciculin: crystal structure of the complex.

The crystal structure of the snake toxin fasciculin, bound to mouse acetylcholinesterase (mAChE), at 3.2 A resolution reveals a synergistic three-point anchorage consistent with the picomolar dissociation constant of the complex. Loop II of fasciculin contains a cluster of hydrophobic residues that interact with the peripheral anionic site of the enzyme and sterically occlude substrate access to the catalytic site. Loop I fits in a crevice near the lip of the gorge to maximize the surface area of contact of loop II at the gorge entry. The fasciculin core surrounds a protruding loop on the enzyme surface and stabilizes the whole assembly. Upon binding of fasciculin, subtle structural rearrangements of AChE occur that could explain the observed residual catalytic activity of the fasciculin-enzyme complex.

Animals↗
PubMed1995

Transcription factor repression and activation of the human acetylcholinesterase gene.

Acetylcholinesterase in man is encoded by a single gene, ACHE, located on chromosome 7q22. In this study, the transcription start sites and major DNA promoter elements controlling the expression of this gene have been characterized by structural and functional studies. Immediately upstream of the first untranslated exon of the gene are GC-rich sequences containing consensus binding sites for several transcription factors, including Sp1, EGR-1 and AP2. In vitro transcription studies and RNase protection analyses of mRNA isolated from human NT2/D1 teratocarcinoma cells reveal that two closely spaced transcription cap sites are located at a consensus initiator (Inr) element similar to that found in the terminal transferase gene. Transient transfection of mutant genes shows that removal of three bases of this initiator sequence reduces promoter activity by 98% in NT2/D1 cells. In vitro transcription studies and transient transfection of a series of 5' deletion mutants of the ACHE promoter linked to a luciferase reporter show an Sp1 site at -71 to be essential for promoter activity. Purified Sp1 protein protects this site from DNase cleavage during in vitro footprinting experiments. A conserved AP2 consensus binding site, located between the GC box elements and the Inr, is protected by recombinant AP2 protein in DNase footprinting experiments, induces a mobility shift with AP2 protein and AP2-containing cell extracts, and fosters inhibition of transcription by AP2 as measured by transient transfection in mouse and human cell lines and in in vitro transcription reactions. These results indicate that AP2 functions as a repressor of human ACHE and mouse Ache transcription.

Acetylcholinesterase↗
PubMed1995

Specificity and orientation of trigonal carboxyl esters and tetrahedral alkylphosphonyl esters in cholinesterases.

We have examined the specificity of planar carboxyl and tetrahedral phosphonyl esters for mouse cholinesterases and have delineated the orientation of these ligands in the enzyme active center. The approach involved altering acyl pocket dimensions by site-specific mutagenesis of two phenylalanines and varying ligand size and enantiomer presentation. Substrate catalysis rates by wild type acetylcholinesterase (AChE) of acetyl-, butyryl-, and benzoylthiocholine diminished with increasing size of the acyl moiety. In contrast, substitution of the acyl pocket phenylalanines giving the mutants F295L and F297I of AChE yielded more efficient catalysis of the larger substrates and a specificity approaching that of butyrylcholinesterase. Extension from planar substrates to enantiomerically pure organophosphonates allowed for an analysis of enantiomeric selectivity. We found that AChE reactions are 200-fold faster with the Sp than the Rp enantiomer of of cycloheptyl methylphosphonyl thiocholine. Upon the acyl pocket size being enlarged, the Rp enantiomer became more reactive while reaction with the Sp enantiomer was slightly reduced. In fact, the F297I mutant displayed inverted stereospecificity. A visual correlation with the kinetic data has been developed by docking the ligands in the active site. Upon placement of the phosphonyl oxygen in the oxyanion hole and the leaving group being directed out of the gorge, the Rp, but not the Sp, enantiomer engendered steric hindrance between the alkoxyl group and the acyl pocket. Replacing F297 with Ile accommodated the bulky alkoxyl group of the Rp isomer in the acyl pocket, allowing similar orientations of the phosphonyl oxygen and the leaving group to the Sp isomer.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholinesterase↗
PubMed1995

Allosteric control of acetylcholinesterase catalysis by fasciculin.

The interaction of fasciculin 2 was examined with wild-type and several mutant forms of acetylcholinesterase (AChE) where Trp86, which lies at the base of the active center gorge, is replaced by Tyr, Phe, and Ala. The fasciculin family of peptides from snake venom bind to a peripheral site near the rim of the gorge, but at a position which still allows substrates and other inhibitors to enter the gorge. The interaction of a series of charged and uncharged carboxyl esters, alkyl phosphoryl esters, and substituted trifluoroacetophenones were analyzed with the wild-type and mutant AChEs in the presence and absence of fasciculin. We show that Trp86 is important for the alignment of carboxyl ester substrates in the AChE active center. The most marked influence of Trp86 substitution in inhibiting catalysis is seen for carboxyl esters that show rapid turnover. The extent of inhibition achieved with bound fasciculin is also greatest for efficiently catalyzed, charged substrates. When Ala is substituted for Trp86, fasciculin becomes an allosteric activator instead of an inhibitor for certain substrates. Analysis of the kinetics of acylation by organophosphates and conjugation by trifluoroacetophenones, along with deconstruction of the kinetic constants for carboxyl esters, suggests that AChE inhibition by fasciculin arises from reductions of both the commitment to catalysis and diffusional entry of substrate into the gorge. The former is reflected in the ratio of the rate constant for substrate acylation to that for dissociation of the initial complex. The action of fasciculin appears to be mediated allosterically from its binding site at the rim of the gorge to affect the orientation of the side chain of Trp86 which lies at the gorge base.

Acetylcholinesterase↗
PubMed1995

Morning peak in ventricular tachyarrhythmias detected by time of implantable cardioverter/defibrillator therapy. The CPI Investigators.

BACKGROUND: A morning peak in occurrence of sudden cardiac death has been identified in epidemiological studies, but the studies are subject to selection bias, with the exclusion of unwitnessed deaths, which are more likely to occur at night. The recent availability of implantable cardioverter/defibrillators that record the time of ventricular tachyarrhythmias requiring either pacing or shock therapy provides an opportunity to clarify the timing of ventricular tachyarrhythmias predisposing to sudden cardiac death. Analysis of the timing of arrhythmias in different patient subgroups, such as patients with poor left ventricular function, may provide further insight into the mechanism of onset of sudden cardiac death. METHODS AND RESULTS: We studied patients in whom a cardioverter/defibrillator (Ventak PRx) was implanted between September 1990 and September 1993 in US centers. Events that could be timed occurred in 483 patients. With an RR cycle length of 240 ms as a cutoff, corresponding to a heart rate of 250 beats per minute, episodes were categorized as rapid (n = 1217) or less rapid (n = 9266) ventricular tachyarrhythmias. A higher proportion of both rapid and less rapid ventricular tachyarrhythmias began in the late morning compared with other times of the day. The subgroup of patients with ejection fraction < 20% at the time of implantation demonstrated a more uniform 24-hour distribution of tachycardias < or = 250 beats per minute than patients with higher left ventricular ejection fraction. CONCLUSIONS: Further investigation of the late morning peak and of precipitants of ventricular tachyarrhythmias by use of data from the implantable cardioverter/defibrillator may provide insight into the pathophysiological mechanisms causing sudden cardiac death.

Circadian Rhythm↗
PubMed1995

Amino acid residues controlling reactivation of organophosphonyl conjugates of acetylcholinesterase by mono- and bisquaternary oximes.

Single and multiple site mutants of recombinant mouse acetylcholinesterase (rMoAChE) were inhibited with racemic 7-(methylethoxyphosphinyloxy)-1-methylquinolinium iodide (MEPQ) and the resulting mixture of two enantiomers, CH3PR,S(O)(OC2H5)-AChE(EMPR,S-AChE), were subjected to reactivation with 2-(hydroxyiminomethyl)-1-methylpyridinium methanesulfonate (P2S) and 1-(2'-hydroxyiminomethyl-1'-pyridinium)-3-(4"-carbamoyl-1"- pyridinium)-2-oxapropane dichloride (HI-6). Kinetic analysis of the reactivation profiles revealed biphasic behavior with an approximate 1:1 ratio of two presumed reactivatable enantiomeric components. Equilibrium dissociation and kinetic rate constants for reactivation of site-specific mutant enzymes were compared with those obtained for wild-type rMoAChE, tissue-derived Torpedo AChE and human plasma butyrylcholinesterase. Substitution of key amino acid residues at the entrance to the active-site gorge (Trp-286, Tyr-124, Tyr-72, and Asp-74) had a greater influence on the reactivation kinetics of the bisquaternary reactivator HI-6 compared with the monoquaternary reactivator P2S. Replacement of Phe-295 by Leu enhanced reactivation by HI-6 but not by P2S. Of residues forming the choline-binding subsite, the E202Q mutation had a dominant influence where reactivation by both oximes was decreased 16- to 33-fold. Residues Trp-86 and Tyr-337 in this subsite showed little involvement. These kinetic findings, together with energy minimization of the oxime complex with the phosphonylated enzyme, provide a model for differences in the reactivation potencies of P2S and HI-6. The two kinetic components of oxime reactivation of MEPQ-inhibited AChEs arise from the chirality of O-ethyl methylphosphonyl moieties conjugated with Ser-203 and may be attributable to the relative stability of the phosphonyl oxygen of the two enantiomers in the oxyanion hole.

Acetylcholinesterase↗
PubMed1995

Molecular determinants conferring alpha-toxin resistance in recombinant DNA-derived acetylcholine receptors.

Sequences of the alpha-subunits of the nicotinic acetylcholine receptor from the snake and mongoose contain several differences in the region between amino acids 183 and 200. Receptors from both of these species reveal resistance to the snake alpha-toxins presumably arising as a protective evolutionary mechanism. Sequence differences include the added glycosylation signals at residue 187 in the mongoose and at residues 189 and 111 in snake. Although previous observations with peptides and fusion proteins either synthesized chemically or in a bacterial expression system indicate that certain amino acid residues may contribute to the resistance, our findings with the intact receptor in an eukaryotic expression system indicate the major role for glycosylation. In this study, we show that addition of glycosylation signals gives rise to virtually complete glycosylation at the added sites, although heterogeneity of oligosaccharide processing is evident. By analysis of combinations of mutants, we document that glycosylation exerts the predominant influence on alpha-toxin binding. Substitutions at other residues are largely without influence as single mutations but appear to decrease affinity further in multiple mutants, particularly where the receptor is glycosylated at the 187 and 189 positions. Glycosylation exerts a major influence on the dissociation as well as the association rates of the alpha-toxin-receptor complex, suggesting that the decrease for alpha-toxin affinity is not simply a consequence of restricted diffusional access, rather glycosylation affects the conformation and stability of the bound complex.

Amino Acid Sequence↗
PubMed1995

Promoter elements of the mouse acetylcholinesterase gene. Transcriptional regulation during muscle differentiation.

The increase in acetylcholinesterase expression during muscle differentiation from myoblasts to myotubes was shown previously to reflect primarily a greater stability of the messenger RNA (mRNA). Here, we investigate the regulation of the acetylcholinesterase gene during early determination of the muscle phenotype. (i) We employ myogenic transcription factors to transform non-muscle cells into myoblasts in order to assess the role of the myogenic transcription factors in this regulation. (ii) We analyze the Ache promoter region by deletion analysis, point mutagenesis, and gel mobility shift assays. The myogenic transcription factors do not accelerate transcription of the Ache gene in spite of the presence of E-boxes at -335 base pairs from the start of transcription and in the first intron, and they are not able to trigger stabilization of the Ache mRNA when constitutively expressed in 10T1/2 fibroblasts. A GC-rich region (at -105 to -59 base pairs from the start of transcription) containing overlapping binding sites for the transcription factors Sp1 and Egr-1 is essential for promoter activity. Mutation of the Sp1 sites dramatically reduces the promoter activity while mutation of the Egr-1 sites has little effect. Sp1 and Egr-1 compete for binding to overlapping sites and an increase in Egr-1 decreases the expression of the Ache gene.

3T3 Cells↗