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Biomedical subjects

M W Thompson

Publications and source records attributed to M W Thompson.

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

Molecular properties of ClpAP protease of Escherichia coli: ATP-dependent association of ClpA and clpP.

The ClpAP protease from Escherichia coli consists of the ATP-binding regulatory component, ClpA (subunit Mr 84 165), and the proteolytic component, ClpP (subunit Mr 21 563). Our hydrodynamic studies demonstrate that the predominant forms of these proteins in solution correspond to those observed by electron microscopy. ClpP and proClpP(SA), which in electron micrographs appear to have subunits arranged in rings of seven subunits, were found by ultracentrifugation to have s20,w values of 12.2 and 13.2 S and molecular weights of 300 000 and 324 000 +/- 3000, respectively, indicating that the native form of each consists of two such rings. The two intact rings of ClpP were separated in the presence of >/= 0.1 M sulfate at low temperatures, suggesting that ring-ring contacts are polar in nature and more easily disrupted than subunit contacts within individual rings. Sedimentation equilibrium analysis indicated that ClpA purified without nucleotide exists as an equilibrium mixture of monomers and dimers with Ka = (1.0 +/- 0.2) x 10(5) M-1 and that, upon addition of MgATP or adenosine 5'-O-(3-thiotriphosphate), ClpA subunits associated to a form with Mr 505 000 +/- 5000, consistent with the hexameric structure seen by electron microscopy. Sedimentation velocity and gel-filtration analysis showed that the nucleotide-promoted hexamer of ClpA (s20,w = 17.2 S) binds tightly to ClpP producing species with s20,w values of 21 and 27 S (f/f0 = 1.5 and 1.8, respectively), consistent with electron micrographs of ClpAP that show a single tetradecamer of ClpP associated with either one or two ClpA hexamers [Kessel et al. (1995) J. Mol. Biol. 250, 587-594]. Under assay conditions in the presence of ATP and Mg2+, the apparent dissociation constant of hexameric ClpA and tetradecameric ClpP was approximately 4 +/- 2 nM. By the method of continuous variation, the optimal ratio of ClpA to ClpP in the active complex was 2:1. The specific activities of limiting ClpA and ClpP determined in the presence of an excess of the other component indicated that the second molecule of ClpA provides very little additional activation of ClpP.

Adenosine Triphosphatases↗
PubMed1998

Transient surfactant protein B deficiency in a term infant with severe respiratory failure.

A 38-day-old male infant with persistent pulmonary hypertension and respiratory failure since birth was found to have a complete absence of surfactant protein B (SP-B) along with an aberrant form of SP-C in his tracheal aspirate fluid, findings consistent with the diagnosis of hereditary SP-B deficiency. Surprisingly, SP-B and SP-B messenger ribonucleic acid were present in lung biopsy tissue. However, DNA sequence analysis demonstrated a point mutation in exon 5 of one of the SP-B gene alleles. The infant's mother was found to be a carrier of this mutation. The infant's other SP-B allele did not differ from the published DNA sequence for the SP-B gene. We conclude that this patient had a transient deficiency of SP-B, in contrast to that of previously described infants with irreversible respiratory failure caused by hereditary SP-B deficiency. We recommend that infants with suspected SP-B deficiency have serial analysis of tracheal fluid samples for both SP-B and SP-C before lung biopsy, along with genetic analysis for the known SP-B mutations. We speculate that the new mutation found in one of this patient's SP-B genes was in part responsible for the transient deficiency of SP-B.

Exudates and Transudates↗
PubMed1998

Carbon monoxide mass exposure in a pediatric population.

OBJECTIVES: To describe the outcomes of a mass carbon monoxide (CO) intoxication, and to calculate the CO half-life in a pediatric school-aged population. METHODS: A retrospective chart review was performed based on Regional Poison Center database information, hospital laboratory data, and medical records of the pediatric patients who sought care at one of 3 St. Louis area hospitals, after exposure to high levels of CO. Exposures occurred on January 5, 1996, after evidence of a CO leak was discovered at an area elementary school. Charts were reviewed for major demographics, symptoms reported, carboxyhemoglobin (COHb) levels and times, and level of effect. RESULTS: Information about 177 (35%) of the 504 children in attendance at school that day was available. Mean age was 8.7 +/- 1.8 years (range 4-12 years). Symptoms were present in 155 (88%) of the 177 children for whom data were available. Initial COHb levels were obtained for 147 (83.1%) of the 177 children. First mean COHb level was 7.0% (95% CI = 6.6-7.5%). Second COHb level was obtained for 26 children with a mean of 2.7% (95% CI = 2.2-3.2%). Calculated half-life of COHb, on 100% O2 at 1 atm, was 44.0 minutes (95% CI = 39.6-48.2 minutes). CONCLUSION: Some children had symptoms at COHb levels that traditionally have been considered nontoxic. The elimination of COHb was found to be more rapid in this population of children than reported in other studies.

Carbon Dioxide↗
PubMed1998

Nutritional and fluid intake in a 100-km ultramarathon.

The fluid and food intakes of 7 male participants in a 100-km ultramarathon were recorded. The mean exercise time was 10 hr 29 min. Nutrient analysis revealed a mean intrarace energy intake of 4,233 kJ, with 88.6% derived from carbohydrate, 6.7% from fat, and 4.7% from protein. Fluid intake varied widely, 3.3-11.1 L, with a mean of 5.7 L. The mean decrease in plasma volume at 100 km was 7.3%, accompanied by an estimated mean sweat rate of 0.86 L.hr-1. Blood glucose concentrations remained normal during the event, and free fatty acids and glycerol were elevated both during and at the conclusion of the event. No significant correlations were found between absolute amounts and rates of ingestion of carbohydrate and/or fluid and race performance.

Adult↗
PubMed1997

Expired air temperature during prolonged exercise in cool- and hot-humid environments.

The purpose of this investigation was to measure expired air temperature under cool- and hot-humid environmental conditions at rest and during prolonged exercise to: (1) establish if significant increases in body core temperature affected expired air temperature, and (2) to determine if the temperature setting for heating the pneumotachometer in an open-circuit system requires adjustment during prolonged exercise tests to account for changes in expired air temperature. Six male distance runners completed two tests in cool-humid [dry bulb temperature (Tdb) 15.5 (SD 1.3) degrees C, wet bulb temperature (TWb) 12.1 (SD 1.4) degrees C] and hot-humid [Tdb 31.6 (SD 0.6) degrees C, TWb 24.9 (SD 0.6) degrees C, black globe temperature (Tg) 34.3 (SD 0.3) degrees C] environments, running at a velocity corresponding to 65% [67.1 (SD 2.82)%] of their maximal oxygen uptake. Rectal temperature and expired air temperatures were compared at rest, and after 30 min and 60 min of exercise for each environment. The main finding of this investigation was a significant (P < 0.05) but small increase in expired air temperature between the 30-min and 60-min measures in the hot-humid environment. No significant differences in expired air temperature were found between the 30-min and 60-min measures in the cool-humid environment. These findings suggest that: (1) expired air temperature is influenced by elevations in body core temperature during prolonged exercise in hot-humid conditions, and (2) that the temperature setting for heating the head of the pneumotachometer (after determining the appropriate temperature through measuring expired air temperature for the set environmental condition) may require adjustment during prolonged exercise trials in hot-humid environmental conditions.

Adult↗
PubMed1997

Impaired calcium pump function does not slow relaxation in human skeletal muscle after prolonged exercise.

This study examined the effects of prolonged exercise on human quadriceps muscle contractile function and homogenate sarcoplasmic reticulum Ca2+ uptake and Ca2+-adenosinetriphosphatase activity. Ten untrained men cycled at 75 +/- 2% (SE) peak oxygen consumption until exhaustion. Biopsies were taken from the right vastus lateralis muscle at rest, exhaustion, and 20 and 60 min postexercise. Peak tension and half relaxation time of the left quadriceps muscle were measured during electrically evoked twitch and tetanic contractions and a maximal voluntary isometric contraction at rest, exhaustion, and 10, 20, and 60 min postexercise. At exhaustion, homogenate Ca2+ uptake and Ca2+ adenosinetriphosphatase activity were reduced by 17 +/- 4 and 21 +/- 5%, respectively, and remained depressed after 60 min recovery (P </= 0.01). Muscle ATP, creatine phosphate, and glycogen were all depressed at exhaustion (P </= 0.01). Peak tension during a maximal voluntary contraction, a twitch, and a 10-Hz stimulation were reduced after exercise by 28 +/- 3, 45 +/- 6, 65 +/- 5%, respectively (P </= 0.01), but no slowing of half relaxation times were found. Thus fatigue induced by prolonged exercise reduced muscle Ca2+ uptake, but this did not cause a slower relaxation of evoked contractions.

Adult↗
PubMed1996

Chronic hypertension and altered baroreflex responses in transgenic mice containing the human renin and human angiotensinogen genes.

We have generated a transgenic model consisting of both the human renin and human angiotensinogen genes to study further the role played by the renin-angiotensin system in regulating arterial pressure. Transgenic mice containing either gene alone were normotensive, whereas mice containing both genes were chronically hypertensive. Plasma renin activity and plasma angiotensin II levels were both markedly elevated in the double transgenic mice compared with either single transgenic or nontransgenic controls. The elevation in blood pressure caused by the human transgenes was independent of the genotype at the endogenous renin locus and was equal in mice homozygous for the Ren-1c allele or in mice containing one copy each of Ren-1c, Ren-1d, or Ren-2. Chronic overproduction of angiotensin II in the double transgenic mice resulted in a resetting of the baroreflex control of heart rate to a higher pressure without significantly changing the gain or sensitivity of the reflex. Moreover, this change was not due to the effects of elevated pressure itself since angiotensin-converting enzyme inhibition had minimal effects on the baroreflex in spontaneously hypertensive BPH-2 control mice, which exhibit non-renin-dependent hypertension. This double transgenic model should provide an excellent tool for further studies on the mechanisms of hypertension initiated by the renin-angiotensin system.

Angiotensinogen↗
PubMed1996

Marked hypocalcemia and ventricular fibrillation in two pediatric patients exposed to a fluoride-containing wheel cleaner.

In two separate cases, pediatric patients exposed to Armor-All Quicksilver Wheel Cleaner exhibited systemic toxicity including mental status changes, marked hypocalcemia, and ventricular fibrillation. One child also demonstrated profound hypomagnesemia. These are the first pediatric reports of near-fatal outcomes after ingestion or inhalation of a hydrofluoric acid-like product, namely, ammonium bifluoride.

Ammonium Compounds↗
PubMed1996

Regulation of human renin mRNA expression and protein release in transgenic mice.

The renin-angiotensin system plays a major role in the regulation of blood pressure and electrolyte homeostasis in mammals. In this study, we subjected transgenic mice containing a human renin genomic construct to a variety of pharmacological and physiological manipulations to test whether expression of the human renin gene and release of active human renin in appropriately regulated in this model. These manipulations were designed to test major regulators of renin release, including angiotensin II, the macula densa, renal perfusion pressure, and beta-adrenergic receptors. We used human plasma renin concentration and human renal renin mRNA levels to document the response of the transgene to these stimuli. Human plasma renin concentration increased in response to both angiotensin-converting enzyme inhibition with captopril and isoproterenol and decreased after a high salt diet. A low salt or sodium-deficient diet did not stimulate renin release. Human renin mRNA levels in kidney increased after captopril but were unchanged in the other experimental groups. We also measured the levels of human renin mRNA in double transgenic mice containing the same human renin gene in addition to the human angiotensinogen gene. These mice are chronically hypertensive and have increased circulating levels of angiotensin II. Human renin mRNA levels in the kidney were paradoxically elevated compared with their single transgenic normotensive counterparts. These transgenic mice provide a model for examination of human renin regulation and may help elucidate the molecular mechanisms that regulate the gene in response to physiological cues.

Animals↗
PubMed1995

Treatment of respiratory failure in an infant with bronchopulmonary dysplasia infected with respiratory syncytial virus using inhaled nitric oxide and high frequency ventilation.

A 2-month-old, former 28-week premature infant with bronchopulmonary dysplasia infected with respiratory syncytial virus was treated with nitric oxide and high frequency oscillatory ventilation after conventional therapy failed. Nitric oxide and high frequency oscillatory ventilation rapidly improved oxygenation allowing recovery without the need for extracorporeal membrane oxygenation. This treatment regimen should be considered as an option in high-risk infants with respiratory syncytial virus infection who meet extracorporeal membrane oxygenation criteria.

Administration, Inhalation↗
PubMed1995

Transgenic animals in the study of blood pressure regulation and hypertension.

It is generally accepted that the etiology of essential hypertension is due to a complex interplay of genetic and environmental factors. A great deal of research effort over the past ten years has been focused on the identification of genes the variants of which predispose individuals to high blood pressure. Consequently, transgenic and knockout animals have become important research tools, providing experimental systems in which defined genetic manipulations can be introduced on uniform genetic backgrounds while minimizing environmental variation. These animal models have provided the means by which candidate genes thought to be involved in blood pressure regulation have been studied. Furthermore, these models can be used to test the significance of genes and gene variants identified via genome-wide searches as potential causes of hypertension. The purpose of this review is to provide a brief discussion of transgenic and knockout methodology and its application to study the genetic basis of hypertension.

Angiotensinogen↗
PubMed1994

Functional expression of the human angiotensinogen gene in transgenic mice.

The renin-angiotensin system is a major determinant of arterial pressure and volume homeostasis in mammals through the actions of angiotensin II, the proteolytic digestion product of angiotensinogen. Molecular genetic studies in several human populations have revealed genetic linkage between the angiotensinogen gene and both hypertension and increased plasma angiotensinogen. Transgenic mice were generated with a human angiotensinogen genomic clone to develop an animal model to examine tissue- and cell-specific expression of the gene and to determine if overexpression of angiotensinogen results in hypertension. Human angiotensinogen mRNA was expressed in transgenic mouse liver, kidney, heart, adrenal gland, ovary, brain, and white and brown adipose tissue and, in kidney, was exclusively localized to epithelial cells of the proximal convoluted tubules. Plasma levels of human angiotensinogen were approximately 150-fold higher in transgenic mice than that found normally in human plasma. The blood pressure of mice bearing the human angiotensinogen gene was normal but infusion of a single bolus dose of purified human renin resulted in a transient increase in blood pressure of approximately 30 mm Hg within 2 min. These results suggest that abnormalities in the angiotensinogen gene resulting in increased circulating levels of angiotensinogen could potentially contribute in part to the pathogenesis of essential hypertension.

Angiotensinogen↗
PubMed1994

Activity and specificity of Escherichia coli ClpAP protease in cleaving model peptide substrates.

Escherichia coli ClpAP protease is an ATP-dependent protease composed of the proteolytic component ClpP and a regulatory ATPase, ClpA. ClpAP protease degraded a variety of peptide bonds in protein and peptide substrates at a slow rate (kcat < or = 30 min-1/subunit of ClpP), but showed very high activity (kcat > or = 800 min-1) for a synthetic peptide composed of the first 19 amino acids of ClpP, MSYSGERDNFAPHMALVPV, referred to as the propeptide. The propeptide was not degraded by ClpP alone, but was degraded in the presence of ClpA and ClpP. Degradation was activated by nonhydrolyzable analogs of ATP, indicating that nucleotide-promoted interaction between ClpA and ClpP is sufficient to activate ClpP for propeptide cleavage. The propeptide, as well as truncated forms lacking either the first 9 or the last 3 amino acids, was cleaved at the same Met-Ala bond at which autoprocessing occurs in vivo. No hydrolysis of FAPHMALVPV derivatives was observed when Met was replaced by Glu, Lys, Ser, Tyr, Ile, and D-Met, but cleavage at the same position did occur with Leu or Trp substitutions. A peptide composed of a tandem repeat of FAPHMALVPV was cleaved between both Met-Ala bonds (Kcat values > or = 39 min-1). Propeptides inhibited degradation of alpha-casein by competition for a binding site on ClpA, and they stimulated the basal ATPase activity of ClpA in the absence of ClpP. Peptides and protein substrates interact at an allosteric site on ClpA, which appears to be the site at which specific substrates are recognized by the Clp protease.

ATP-Dependent Proteases↗
PubMed1994

Processive degradation of proteins by the ATP-dependent Clp protease from Escherichia coli. Requirement for the multiple array of active sites in ClpP but not ATP hydrolysis.

ClpP, the proteolytic component of the ATP-dependent ClpAP protease, is composed of 12 identical subunits and has intrinsic degradative activity against short peptides. Degradation of proteins and some peptides by ClpP requires the regulatory component ClpA and ATP. Peptide and protein substrates have been used to distinguish the roles of nucleotide binding and nucleotide hydrolysis in the activation of ClpAP protease. ATP binding alone promoted interaction between ClpA and ClpP, affected the substrate response curves for very short peptides, and activated degradation of larger peptides that were not degraded by ClpP alone. ATP hydrolysis did not increase in proportion to the increase in peptide bond hydrolysis of short peptides. However, ATP hydrolysis was strictly required for degradation of proteins such as alpha-casein; there was no indication of even limited cleavage of protein substrates when nonhydrolyzable analogs of ATP were used. Most large peptides and proteins were degraded in multiple sites without release of high molecular weight intermediates. Partial inactivation of ClpP with diisopropyl fluorophosphate produced ClpP with one to three active subunits/dodecamer. When only a few active sites were available in the active complex of ClpAP, degradation of large peptides and proteins released significant amounts of high molecular weight intermediates. Thus, processive degradation of protein substrates is a function of the multiple array of proteolytic active sites within the ClpP dodecamer.

ATP-Dependent Proteases↗
PubMed1994

Acetaminophen ingestion in childhood--cost and relative risk of alternative referral strategies.

Acetaminophen is the pharmaceutical most frequently ingested by small children. Although past research has allowed the safe management of 90% of these ingestions at home, several thousand are still referred to emergency departments annually. With the goal of further reducing the number of unnecessary referrals, the risk/benefit considerations of alternate referral strategies were analyzed. In a retrospective poison center chart review study from 11 centers, the records of children between the ages 1 and 6 years who acutely ingested acetaminophen and were referred to a hospital for determination of serum acetaminophen concentration in 1986 and 1987 were identified using the database of the American Association of Poison Control Centers. Risk of hepatic injury was assigned on the basis of the Rumack-Matthew acetaminophen toxicity nomogram. The cohort was stratified in terms of the amount ingested and whether a pediatric or adult preparation was ingested. The direct cost of an evaluation was estimated from four centers. Sensitivity, specificity and direct cost of each risk identification strategy were calculated. Eight hundred sixty six of 2091 patients had a timed serum acetaminophen concentration recorded. Of these, three patients had results in the "probable risk" area of the nomogram. A referral reduction strategy which would refer only children who ingest 200 mg/kg or more of an adult preparation could eliminate 82% of referrals without missing any of these "probable risk" patients. Six other children were determined to have serum acetaminophen concentrations in an area of the nomogram labeled "possible risk". No referral reduction strategy explored identified all of these patients. The average charge for an emergency department evaluation in 1992 was $272.00. These data suggest that children less than six years of age who ingest pediatric acetaminophen products other than those from packages containing greater than 30 tablets or who ingest less than 200 mg/kg of an adult preparation may be safely managed at home without referral to a hospital. This strategy would result in significant cost savings and prevent unnecessary inconvenience to many patients and families.

Acetaminophen↗
PubMed1993

Influence of time until emesis on the efficacy of decontamination using acetaminophen as a marker in a pediatric population.

STUDY OBJECTIVE: To determine the extent of drug removal by emesis at different times after the ingestion of a toxic substance. DESIGN: Multicenter retrospective chart review. METHODS: Using the American Association of Poison Control Centers' aggregate data base, children who had ingested acetaminophen and who were referred to a health care facility by one of 11 poison centers during a two-year period were identified. Charts of these patients were reviewed to determine the quantity ingested per kilogram of body weight, method of decontamination used, the timing of decontamination, and the serum acetaminophen concentration obtained four hours after ingestion. RESULT: Charts of 455 patients met all requirements for inclusion. When emesis occurred within one-half hour after ingestion, mean serum acetaminophen concentration drawn four hours after ingestion was approximately half that in a control group that received no decontamination. Emesis had less impact when it was delayed further and had no demonstrable impact when it occurred more than 90 minutes after ingestion. CONCLUSION: Many factors must be considered when deciding if and by what method a given patient should receive decontamination. When delayed gastric emptying is not expected, emesis can at best decrease a toxic burden by half if it occurs early. Medical care givers must continue to scrutinize management practice to ensure that syrup of ipecac is given only in situations in which it is likely to make a difference in outcome and in which it is the most effective agent to achieve this goal.

Acetaminophen↗