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Biomedical subjects

R A Harris

Publications and source records attributed to R A Harris.

At least 145 records · Page 8Linked to original sources
PubMed1997

Sites of alcohol and volatile anaesthetic action on GABA(A) and glycine receptors.

Volatile anaesthetics have historically been considered to act in a nonspecific manner on the central nervous system. More recent studies, however, have revealed that the receptors for inhibitory neurotransmitters such as gamma-aminobutyric acid (GABA) and glycine are sensitive to clinically relevant concentrations of inhaled anaesthetics. The function of GABA(A) and glycine receptors is enhanced by a number of anaesthetics and alcohols, whereas activity of the related GABA rho1 receptor is reduced. We have used this difference in pharmacology to investigate the molecular basis for modulation of these receptors by anaesthetics and alcohols. By using chimaeric receptor constructs, we have identified a region of 45 amino-acid residues that is both necessary and sufficient for the enhancement of receptor function. Within this region, two specific amino-acid residues in transmembrane domains 2 and 3 are critical for allosteric modulation of both GABA(A) and glycine receptors by alcohols and two volatile anaesthetics. These observations support the idea that anaesthetics exert a specific effect on these ion-channel proteins, and allow for the future testing of specific hypotheses of the action of anaesthetics.

Alanine↗
PubMed1997

Dihydrolipoamide dehydrogenase-binding protein of the human pyruvate dehydrogenase complex. DNA-derived amino acid sequence, expression, and reconstitution of the pyruvate dehydrogenase complex.

Protein X, recently renamed dihydrolipoamide dehydrogenase-binding protein (E3BP), is required for anchoring dihydrolipoamide dehydrogenase (E3) to the dihydrolipoamide transacetylase (E2) core of the pyruvate dehydrogenase complexes of eukaryotes. DNA and deduced protein sequences for E3BP of the human pyruvate dehydrogenase complex are reported here. With the exception of only a single lipoyl domain, the protein has a segmented multi-domain structure analogous to that of the E2 component of the complex. The protein has 46% amino acid sequence identity in its amino-terminal region with the second lipoyl domain of E2, 38% identity in its central region with the putative peripheral subunit-binding domain of E2, and 50% identity in its carboxyl-terminal region with the catalytic inner core domain of E2. The similarity in the latter domain stands in contrast to E3BP of Saccharomyces cerevisiae, which is quite different from its homologous transacetylase in this region. The putative catalytic site histidine residue present in the inner core domains of all dihydrolipoamide acyltransferases is replaced by a serine residue in human E3BP; thus, catalysis of coenzyme A acetylation by this protein is unlikely. Coexpression of cDNAs for E3BP and E2 resulted in the formation of an E2.E3BP subcomplex that spontaneously reconstituted the pyruvate dehydrogenase complex in the presence of native E3 and recombinant pyruvate decarboxylase (E1).

Amino Acid Sequence↗
PubMed1997

Cost-effectiveness of implantable cardioverter defibrillators relative to amiodarone for prevention of sudden cardiac death.

BACKGROUND: Implantable cardioverter defibrillators (ICDs) are remarkably effective in terminating ventricular arrhythmias, but they are expensive and the extent to which they extend life is unknown. The marginal cost-effectiveness of ICDs relative to amiodarone has not been clearly established. OBJECTIVE: To compare the cost-effectiveness of a third-generation implantable ICD with that of empirical amiodarone treatment for preventing sudden cardiac death in patients at high or intermediate risk. DESIGN: A Markov model was used to evaluate health and economic outcomes of patients who received an ICD, amiodarone, or a sequential regimen that reserved ICD for patients who had an arrhythmia during amiodarone treatment. MEASUREMENTS: Life-years gained, quality-adjusted life-years gained, costs, and marginal cost-effectiveness. RESULTS: For the base-case analysis, it was assumed that treatment with an ICD would reduce the total mortality rate by 20% to 40% at 1 year compared with amiodarone and that the ICD generator would be replaced every 4 years. In high-risk patients, if an ICD reduces total mortality by 20%, patients who receive an ICD live for 4.18 quality-adjusted life-years and have a lifetime expenditure of $88,400. Patients receiving amiodarone live for 3.68 quality-adjusted life-years and have a lifetime expenditure of $51,000. Marginal cost-effectiveness of an ICD relative to amiodarone is $74,400 per quality-adjusted life-year saved. If an ICD reduces mortality by 40%, the cost-effectiveness of ICD use is $37,300 per quality-adjusted life-year saved. Both choice of therapy (an ICD or amiodarone) and the cost-effectiveness ratio are sensitive to assumptions about quality of life. CONCLUSIONS: Use of an ICD will cost more than $50,000 per quality-adjusted life-year gained unless it reduces all-cause mortality by 30% or more relative to amiodarone. Current evidence does not definitively support or exclude a benefit of this magnitude, but ongoing randomized trials have sufficient statistical power to do so.

Amiodarone↗
PubMed1997

Epitope cleavage by Leishmania endopeptidase(s) limits the efficiency of the exogenous pathway of major histocompatibility complex class I-associated antigen presentation.

The activation of CD8+ T cell responses is commonplace during infection with a number of nonviral pathogens. Consequently, there has been much interest in the pathways of presentation of such exogenous antigens for major histocompatibility complex class I-restricted recognition. We had previously shown that Leishmania promastigotes transfected with the ovalbumin (OVA) gene could efficiently target OVA to the parasitophorous vacuole (PV), with subsequent recognition by class II-restricted T cells. We now report the results of studies aimed at evaluating the PV as a route of entry into the exogenous class I pathway. Bone marrow-derived macrophages can present soluble OVA (albeit at high concentrations) to the OVA(257-264)-specific T cell hybridoma 13.13. In contrast, infection with OVA-transfected Leishmania promastigotes failed to result in the stimulation of this hybridoma. This appeared unrelated to variables such as antigen concentration, parasite survival, and macrophage activation status. These results prompted an analysis of the effects of promastigotes on class I peptide binding using RMA-S cells and OVA(257-264). Our data indicate that the major surface protease of Leishmania, gp63, inhibits this interaction by virtue of its endopeptidase activity against the OVA(257-264) peptide. The data suggest that this activity, if maintained within the PV, would result in loss of the OVA(257-264) epitope. Although we can therefore draw no conclusions from these studies regarding the efficiency of the PV as a site of entry of antigen into the exogenous class I pathway, we have identified a further means by which parasites may manipulate the immune repertoire of their host.

Animals↗
PubMed1997

Prevention of recurrences of erosive reflux esophagitis: a cost-effectiveness analysis of maintenance proton pump inhibition.

PURPOSE: To determine the cost-effectiveness of three management strategies for healed erosive reflux esophagitis: maintenance therapy with a proton pump inhibitor (PPI) from the outset; no maintenance therapy unless a patient's symptoms recur once over a year; and no maintenance therapy unless a patient's symptoms recur twice over a year. MATERIALS AND METHODS: Decision analysis using data from randomized trials of lansoprazole, case series, and expert opinion. RESULTS: For patients with grade 4 esophagitis, maintenance from the outset is the most efficient approach. For all other patients, providing maintenance PPI after a patient experiences two recurrences is the least costly but least effective approach. The other two approaches prevent more recurrences: waiting to initiate maintenance therapy until symptoms recur once requires an additional $73 for each recurrence prevented whereas maintenance PPI from the outset requires an additional $819 for each recurrence prevented. Maintenance therapy from the outset is cost effective if symptoms of esophagitis cause a 22% or greater decrement in quality of life (using $50,000 per quality-adjusted life year gained as a cost-effectiveness definition). However, withholding maintenance until the time of a first recurrence is cost effective if symptoms cause a 2% or greater decrement in quality of life. CONCLUSION: For grades 2 and 3 esophagitis, providing maintenance therapy after a patient experiences a further recurrence is a preferred option that appears cost-effective across a wide array of assumptions. Maintenance therapy from the outset, however, appears cost-effective only for those patients who report a significant decline in quality of life associated with esophagitis or for those patients with baseline grade 4 esophagitis.

2-Pyridinylmethylsulfinylbenzimidazoles↗
PubMed1997

Implications of new dry fibrin sealant technology for trauma surgery.

Trauma patients have been bleeding to death for thousands of years. The methods used to control hemorrhage (tourniquets, pressure, bandages, and ligatures) have not changed for 2000 years. Technology now exists to amplify the normal clotting system with human proteins, thus providing almost instant hemorrhage control in the face of bleeding. The increasing body of clinical and animal research and safety data regarding new fibrin sealant technologies is compelling. When combined with the evolving concepts of extended trauma resuscitation, acceptance of this technology will finally add a new method of rapid, easy hemostasis to the armamentarium of the surgeon faced with an unstable hemorrhaging patient. Several important issues remain unresolved, such as optimal thrombin and fibrinogen content, amount of material required for hemostasis, long-term effects, distribution of breakdown products, and role of recombinant proteins. These issues are under active investigation. Despite these unanswered questions, the field of absorbable, off-the-shelf, rapidly active hemostatic agents that do not require refrigeration is an exciting area that should yield significant improvements in the care of injured patients.

Bandages↗
PubMed1997

Spatio-temporal properties of motion detectors matched to low image velocities in hovering insects.

Our recent study [O'Carroll et al. (1996). Nature 382, 63-66) described a correlation between the spatio-temporal properties of motion detecting neurons in the optic lobes of flying insects and behaviour. We consider here theoretical properties of insect motion detectors at very low image velocities and measure spatial and temporal sensitivity of neurons in the lobula complex of two specialised hovering insects, the bee-fly Bombylius and the hummingbird hawkmoth, Macroglossum. The spatio-temporal optima of direction-selective neurons in these insects lie at lower velocities than those of other insects which we have studied, including large syrphid flies, which are also excellent hoverers. We argue that spatio-temporal optima reflect a compromise between the demands of diverse behaviour, which can involve prolonged periods of stationary, hovering flight followed by spectacular high speed pursuits of conspecifics. Males of the syrphid Eristalis which engage in such behaviour, have higher temporal frequency optima than females. High contrast sensitivity in these flies nevertheless results in reliable responses at very low image velocities. Neurons of Bombylius have two distinct velocity optima, suggesting that they sum inputs from two classes of motion correlator with different time constants. This also provides sensitivity to a large range of velocities.

Animals↗
PubMed1997

Studies on the regulation of the mitochondrial alpha-ketoacid dehydrogenase complexes and their kinases.

Five mitochondrial protein kinases, all members of a new family of protein kinases, have now been identified, cloned, expressed as recombinant proteins, and partially characterized with respect to catalytic and regulatory properties. Four members of this unique family of eukaryotic protein kinases correspond to pyruvate dehydrogenase kinase isozymes which regulate the activity of the pyruvate dehydrogenase complex, an important regulatory enzyme at the interface between glycolysis and the citric acid cycle. The fifth member of this family corresponds to the branched-chain alpha-ketoacid dehydrogenase kinase, an enzyme responsible for phosphorylation and inactivation of the branched-chain alpha-ketoacid dehydrogenase complex, the most important regulatory enzyme in the pathway for the disposal of branched-chain amino acids. At least three long-term control mechanisms have evolved to conserve branched chain amino acids for protein synthesis during periods of dietary protein insufficiency. Increased expression of the branched-chain alpha-ketoacid dehydrogenase kinase is perhaps the most important because this leads to phosphorylation and nearly complete inactivation of the liver branched-chain alpha-ketoacid dehydrogenase complex. Decreased amounts of the liver branched-chain alpha-ketoacid dehydrogenase complex secondary to a decrease in liver mitochondria also decrease the liver's capacity for branched-chain keto acid oxidation. Finally, the number of E1 subunits of the branched-chain alpha-ketoacid dehydrogenase complex is reduced to less than a full complement of 12 heterotetramers per complex in the liver of protein-starved rats. Since the E1 component is rate-limiting for activity and also the component of the complex inhibited by phosphorylation, this decrease in number further limits overall enzyme activity and makes the complex more sensitive to regulation by phosphorylation in this nutritional state. The branched-chain alpha-ketoacid dehydrogenase kinase phosphorylates serine 293 of the E1 alpha subunit of the branched-chain alpha-ketoacid dehydrogenase complex. Site-directed mutagenesis of amino acid residues surrounding serine 293 reveals that arginine 288, histidine 292 and aspartate 296 are critical to dehydrogenase activity, that histidine 292 is critical to binding the coenzyme thiamine pyrophosphate, and that serine 293 exists at or in close proximity to the active site of the dehydrogenase. Alanine scanning mutagenesis of residues in the immediate vicinity of the phosphorylation site (serine 293) indicates that only arginine 288 is required for recognition of serine 293 as a phosphorylation site by the branched-chain alpha-ketoacid dehydrogenase kinase. Phosphorylation appears to inhibit dehydrogenase activity by introducing a negative charge directly into the active site pocket of the E1 dehydrogenase component of the branched-chain alpha-ketoacid dehydrogenase complex. A model based on the X-ray crystal structure of transketolase is being used to predict residues involved in thiamine pyrophosphate binding and to help visualize how phosphorylation within the channel leading to the reactive carbon of thiamine pyrophosphate inhibits catalytic activity. The isoenzymes of pyruvate dehydrogenase kinase differ greatly in terms of their specific activities, kinetic parameters and regulatory properties. Chemically-induced diabetes in the rat induces significant changes in the pyruvate dehydrogenase kinase isoenzyme 2 in liver. Preliminary findings suggest hormonal control of the activity state of the pyruvate dehydrogenase complex may involves tissue specific induced changes in expression of the pyruvate dehydrogenase kinase isoenzymes.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1997

The importance of patient preferences for comorbidities in cost-effectiveness analyses.

When using cost-effectiveness analyses to prioritize the allocation of health care resources across patients, a standard definition of effectiveness must be used. In an informal review of cost-effectiveness analyses, we found a heterogeneity in the methods used to qualify adjust years of life. Many studies do not account for the morbid conditions that patients experience other than the index condition being studied. These studies systematically overstate health benefit relative to studies that do for comorbidities. We recommend that patient preferences for comorbid conditions be incorporated into analyses to allow a consistent and facile comparison of cost-utility ratios for societal decision making.

Comorbidity↗
PubMed1997

Glycine receptors from long-sleep and short-sleep mice: genetic differences in drug sensitivity.

The long-sleep (LS) and short-sleep (SS) mice were selected for differences in sensitivity to ethanol but also differ in response to propofol and some neurosteroids. To determine the role of strychnine-sensitive glycine receptors in genetic differences between these mice, effects of propofol, ethanol and pregnenolone sulfate on glycine responses were compared in Xenopus oocytes expressing mRNA extracted from spinal cord of LS and SS mice. The two lines of mice did not differ in sensitivity to glycine, ethanol or pregnenolone sulfate. However, receptors expressed from LS mRNA were more sensitive to the potentiation induced by propofol than those from SS. Binding of [3H]strychnine to spinal cord membranes demonstrated a similar affinity and density of receptors in LS and SS. These results suggest that glycine receptor function could account for differences in propofol sensitivity between LS and SS mice, but may not be responsible for the differences in behavioral sensitivity to ethanol or steroids previously reported.

Animals↗
PubMed1997

Serological diagnosis of Trypanosoma rangeli infected patients. A comparison of different methods and its implications for the diagnosis of Chagas' disease.

Venous blood from 65 Panamanian schoolchildren living in an area endemic for both Trypanosoma cruzi and T. rangeli were screened for the presence of these parasites. Trypanosoma rangeli were isolated and cultured from four individuals. Serological tests of all 65 sera were performed, including immunohaemagglutination (IHA), indirect immunofluorescence assay (IF) and ELISA using both T. rangeli and T. cruzi as antigens, as well as T. cruzi synthetic peptides in an ELISA assay. Results indicated a higher immunoreactivity to T. rangeli preparations than to T. cruzi within the studied population, which could be divided into four 'serological responder' groups. Interestingly, the panel of SAPA and other T. cruzi synthetic peptides were not useful in the discrimination of patients. Furthermore, patients from whom parasites had been isolated could not be distinguished from those of two other groups. Significant immunoreactivity to T. cruzi preparations was displayed in all responder sera, despite total lack of evidence of infection with this parasite. The immunobiological significance of T. rangeli infection is unclear, but these data indicate that it is a compounding problem in the accurate diagnosis of pathological T. cruzi infection by serological analysis. The relationship of these cohabiting species, in respect to infection outcome and immunological activation, is discussed.

Amino Acid Sequence↗
PubMed1997

Ethanol, flunitrazepam, and pentobarbital modulation of GABAA receptors expressed in mammalian cells and Xenopus oocytes.

GABAA receptors composed of human alpha 1 beta 2 gamma 2L, alpha 1 beta 2 gamma 2S, alpha 1 beta 3 gamma 2S, alpha 6 beta 3 gamma 2S, and alpha 5 beta 3 gamma 3 subunits as well as bovine alpha 1 beta 1 gamma 2L and alpha 1 beta 1 subunits were stably expressed in mammalian L(tk-) cells and transiently expressed in Xenopus oocytes. Effects of muscimol, ethanol, flunitrazepam, and pentobarbital on receptor function were compared for the two expression systems using a 36Cl- flux assay for cells and an electrophysiological assay for oocytes. Muscimol activated all receptors in both expression systems but was more potent for L(tk-) cells than oocytes; this difference ranged from 2.6-to 26-fold, depending upon subunit composition. The most pronounced differences between receptors and expression systems were found for ethanol. In L(tk-) cells, low (5-50 mM) concentrations of ethanol potentiated muscimol responses only with receptors containing the gamma 2L subunit. In oocytes, concentrations of 30-100 mM produced small enhancements for most subunit combinations. Flunitrazepam enhanced muscimol responses for all receptors except alpha 6 beta 3 gamma 2S and alpha 1 beta 1, and this enhancement was similar for both expression systems. Pentobarbital also enhanced muscimol responses for all receptors, and this enhancement was similar for L(tk-) cells and oocytes, except for alpha 6 beta 3 gamma 2S where the pentobarbital enhancement was much greater in oocytes than cells. The alpha 6 beta 3 gamma 2S receptors were also distinct in that pentobarbital produced direct activation of chloride channels in both expression systems. Thus, the type of expression/assay system markedly affects the actions of ethanol on GABAA receptors and also influences the actions of muscimol and pentobarbital on this receptor. Differences between these expression systems may reflect posttranslational modifications of receptor subunits.

Animals↗
PubMed1997

Intracellular calcium responses in CF/T43 cells: calcium pools and influx pathways.

We studied the intracellular free Ca2+ concentration ([Ca2+]i) response to histamine in a cystic fibrosis airway epithelial cell line (CF/T43). Histamine (100 microM; duration approximately 10 min) biphasically increased [Ca2+]i, with a rapid initial peak (30-45 s) followed by a smaller second peak that lasted for several minutes before returning to baseline. Neither peak specifically depended on Ca2+ influx. Exposure to bradykinin (10 microM) elicited a single peak that lasted 3-3.5 min before returning to baseline. Bradykinin increased intracellular inositol 1,4,5-trisphosphate (IP3), which peaked and returned to baseline within 150 s. Histamine also increased IP3 monophasically, but the peak was brief (< 20 s). Both phases of the Ca2+ response to histamine exhibited similar responsiveness to histamine concentration and sensitivity to antagonists. Cimetidine or thioperamide (1 mM) had no effect on the second peak. Pyrilamine blocked the second peak at concentrations similar to those required to block the initial peak. Activation of the second peak was observed at a threshold concentration of 1 microM comparable with the threshold of the initial peak. Neither adenosine 3',5'-cyclic monophosphate, guanosine 3',5'-cyclic monophosphate, nor cyclic ADP (cADP)-ribose altered the second phase of the histamine response.

Bradykinin↗
PubMed1997

Health promotion for seniors: what is over the horizon?

The health care industry is experiencing tremendous change in terms of health care delivery systems and fiscal pressure to provide high-quality health care at an affordable cost. A significant step forward in this change process will be the recognition of the value of comprehensive health promotion and disease prevention. The managed care model of health care is an excellent vehicle for a systematic health promotion program to flourish and succeed. This article surveys the literature on the topic of health promotion and its impact on the wellness of Medicare managed care beneficiaries and the senior population. The authors address issues, facilitators, benefits, and barriers within the context of health promotion and its potential to greatly impact both the quality and cost of health care for the rapidly growing senior population in the coming years.

Aged↗