The effects of four hours of normobaric hypoxia on the vestibular control of balance.

Whole-body vestibular-evoked balance responses decrease following ~ 55 min of normobaric hypoxia. It is unclear how longer durations of hypoxia affect the vestibular control of balance at the muscle and whole-body levels. This study examined how four hours of normobaric hypoxia influenced the vestibular control of balance. Fifteen participants (4 females; 11 males) stood on a force plate with vision occluded and head rotated rightward while subjected to three blocks of binaural, bipolar stochastic electrical vestibular stimulation (EVS; 0-25 Hz, root mean square amplitude = 1.1 mA) consisting of two, 90-s trials. The relationship between EVS and anteroposterior (AP) forces or medial gastrocnemius (MG) electromyography (EMG) was estimated in the time and frequency domains at baseline (BL; 0.21 fraction of inspired oxygen-FIO2) and following two (H2) and four (H4) hours of normobaric hypoxia (0.11 FIO2). The EVS-MG EMG short-latency peak and peak-to-peak amplitudes were smaller than BL at H2 and H4, but the medium-latency peak amplitude was only lower at H4. The EVS-AP force medium-latency peak amplitude was lower than BL at H4, but the short-latency peak and peak-to-amplitudes were unchanged. The EVS-MG EMG coherence and gain were reduced compared to BL at H2 and H4 across multiple frequencies ≥ 7 Hz, whereas EVS-AP force coherence was blunted at H4 (≤ 4 Hz), but gain was unaffected. Overall, the central nervous system's response to vestibular-driven signals during quiet standing was decreased for up to four hours of normobaric hypoxia, and vestibular-evoked responses recorded within postural muscles may be more sensitive than the whole-body response.

Effect of blood flow occlusion on corticospinal excitability during sustained low-intensity isometric elbow flexion.

Blood flow occlusion (BFO) has been used to study the influence of group III/IV muscle afferents after fatiguing exercise, but it is unknown how BFO-induced activity of these afferents affects motor cortical and motoneuronal excitability during low-intensity exercise. Therefore, the purpose of this study was to assess the acute effect of BFO on peripheral [maximal M wave (Mmax)], spinal [cervicomedullary motor evoked potential (CMEP) normalized to Mmax], and motor cortical [motor evoked potential (MEP) normalized to CMEP] excitability. Nine healthy men completed a sustained isometric contraction of the elbow flexors at 20% of maximal force under three conditions: 1) contractile failure with BFO, 2) a time-matched trial without restriction [free flow (FFiso)], and 3) contractile failure with free flow (FFfail). Time to failure for BFO (and FFiso) were ~80% shorter than that for FFfail (P < 0.05). For FFfail and FFiso, Mmax area decreased ~17% and ~7%, respectively (P < 0.05), with no change during BFO. CMEP/Mmax area increased ~226% and ~80% during BFO and FFfail, respectively (P < 0.05), with no change during FFiso (P > 0.05). The increase in normalized CMEP area was greater for BFO and FFfail compared with FFiso and for BFO compared with FFfail. MEP/CMEP area was not different among the protocols (P > 0.05) and increased ~64% with time (P < 0.05). It is likely that group III/IV muscle afferent feedback to the spinal cord modulates the large increase in motoneuronal excitability for the BFO compared with FFfail and FFiso protocols.NEW & NOTEWORTHY We have observed how blood flow occlusion modulates motor cortical, spinal, and peripheral excitability during and immediately after a sustained low-intensity isometric elbow flexion contraction to failure. We conclude that blood flow occlusion causes a greater and more rapid increase in motoneuronal excitability.

Species-Specific Detection of C. difficile Using Targeted Antibody Design.

Clostridium difficile is a Gram-positive, spore-forming bacterium that continues to present a worldwide problem in healthcare settings. The bacterium causes disease, the symptoms of which include diarrhea, fever, nausea, abdominal pain and even death. Despite the prevalence of the disease, the diagnosis of C. difficile infection is still challenging, with a variety of methods available, each varying in their effectiveness. In this work we sought to identify a new biomarker for C. difficile, develop affinity reagents and design a diagnostic assay for C. difficile infection which could be used in a typical two-step testing algorithm. Initially a bioinformatics pipeline was developed that identified a surface associated biomarker "AKDGSTKEDQLVDALA" present in all C. difficile strains sequenced to-date and unique to the C. difficile species. Monoclonal antibodies were subsequently raised against peptides corresponding to the biomarker sequence. During characterization studies, monoclonal antibody 521 (mAb521) was shown to bind all known C. difficile surface layer types, but not closely related strains. Surface plasmon resonance measurements were used to calculate an apparent equilibrium dissociation constant of 36.5 nM between the purified protein target containing the biomarker (surface layer protein A) and mAb521. We demonstrate a limit of detection of 12.4 ng/mL against surface layer protein A and 1.7 × 106 cells/mL in minimally processed C. difficile cultures. The utility of this computational approach to antibody design for diagnostic tests is the ability to produce antibodies that can act as universal species identifiers while mitigating the likelihood of false-positive detection by intelligently screening potential biomarkers against RefSeq data for other nontarget bacteria.

Whole-body and splanchnic amino acid metabolism in sheep during an acute endotoxin challenge.

Supplemented protein or specific amino acids (AA) are proposed to help animals combat infection and inflammation. The current study investigates whole-body and splanchnic tissue metabolism in response to a lipopolysaccharide (LPS) challenge with or without a supplement of six AA (cysteine, glutamine, methionine, proline, serine and threonine). Eight sheep were surgically prepared with vascular catheters across the gut and liver. On two occasions, four sheep were infused through the jugular vein for 20 h with either saline or LPS from Escherichia coli (2 ng/kg body weight per min) in a random order, plus saline infused into the mesenteric vein; the other four sheep were treated with saline or LPS plus saline or six AA infused via the jugular vein into the mesenteric vein. Whole-body AA irreversible loss rate (ILR) and tissue protein metabolism were monitored by infusion of [ring-2H2]phenylalanine. LPS increased (P<0·001) ILR (+17 %), total plasma protein synthesis (+14 %) and lymphocyte protein synthesis (+386 %) but decreased albumin synthesis (-53 %, P=0·001), with no effect of AA infusion. Absorption of dietary AA was not reduced by LPS, except for glutamine. LPS increased the hepatic removal of leucine, lysine, glutamine and proline. Absolute hepatic extraction of supplemented AA increased, but, except for glutamine, this was less than the amount infused. This increased net appearance across the splanchnic bed restored arterial concentrations of five AA to, or above, values for the saline-infused period. Infusion of key AA does not appear to alter the acute period of endotoxaemic response, but it may have benefits for the chronic or recovery phases.

Examining non-syndromic autosomal recessive intellectual disability (NS-ARID) genes for an enriched association with intelligence differences.

Two themes are emerging regarding the molecular genetic aetiology of intelligence. The first is that intelligence is influenced by many variants and those that are tagged by common single nucleotide polymorphisms account for around 30% of the phenotypic variation. The second, in line with other polygenic traits such as height and schizophrenia, is that these variants are not randomly distributed across the genome but cluster in genes that work together. Less clear is whether the very low range of cognitive ability (intellectual disability) is simply one end of the normal distribution describing individual differences in cognitive ability across a population. Here, we examined 40 genes with a known association with non-syndromic autosomal recessive intellectual disability (NS-ARID) to determine if they are enriched for common variants associated with the normal range of intelligence differences. The current study used the 3511 individuals of the Cognitive Ageing Genetics in England and Scotland (CAGES) consortium. In addition, a text mining analysis was used to identify gene sets biologically related to the NS-ARID set. Gene-based tests indicated that genes implicated in NS-ARID were not significantly enriched for quantitative trait loci (QTL) associated with intelligence. These findings suggest that genes in which mutations can have a large and deleterious effect on intelligence are not associated with variation across the range of intelligence differences.

Twitch interpolation: superimposed twitches decline progressively during a tetanic contraction of human adductor pollicis.

The assessment of voluntary activation of human muscles usually depends on measurement of the size of the twitch produced by an interpolated nerve or cortical stimulus. In many forms of fatiguing exercise the superimposed twitch increases and thus voluntary activation appears to decline. This is termed 'central' fatigue. Recent studies on isolated mouse muscle suggest that a peripheral mechanism related to intracellular calcium sensitivity increases interpolated twitches. To test whether this problem developed with human voluntary contractions we delivered maximal tetanic stimulation to the ulnar nerve (≥60 s at physiological motoneuronal frequencies, 30 and 15 Hz). During the tetani (at 30 Hz) in which the force declined by 42%, the absolute size of the twitches evoked by interpolated stimuli (delivered regularly or only in the last second of the tetanus) diminished progressively to less than 1%. With stimulation at 30 Hz, there was also a marked reduction in size and area of the interpolated compound muscle action potential (M wave). With a 15 Hz tetanus, a progressive decline in the interpolated twitch force also occurred (to ∼10%) but did so before the area of the interpolated M wave diminished. These results indicate that the increase in interpolated twitch size predicted from the mouse studies does not occur. Diminution in superimposed twitches occurred whether or not the M wave indicated marked impairment at sarcolemmal/t-tubular levels. Consequently, the increase in superimposed twitch, which is used to denote central fatigue in human fatiguing exercise, is likely to reflect low volitional drive to high-threshold motor units, which stop firing or are discharging at low frequencies.

Altered muscle development and expression of the insulin-like growth factor system in growth retarded fetal pigs.

We have used a porcine model of spontaneous differential fetal growth to investigate the effects of fetal size on muscle development. We hypothesized that altered muscle development may occur in small fetuses as a consequence of modified expression of selected genes of the insulin-like growth factor system. We examined the development of the Longissimus muscle (m. Longissimus) in small fetuses and their average sized littermates. We collected small for gestational age fetuses and their average sized sibling on days 45, 65 and 100 of gestation (term is 113-116 days). Small fetuses had significantly lower body weight at all three stages of gestation (p<0.05) and significantly reduced secondary to primary muscle fibre ratio in m. Longissimus on day 100 (p<0.05) compared to their littermates. On day 65, the expression of insulin-like growth factor receptor 1 and insulin-like growth factor binding protein 3 were significantly higher (p<0.05) in m. Longissimus of the small fetuses compared with their average sized littermates. On day 100, the expression of insulin-like growth factor receptor 1 remained significantly higher (p=0.001), in addition to significantly higher levels of insulin-like growth factor receptor 2 and insulin-like growth factor binding protein 5 in the small fetuses (p<0.05). No difference in levels of myogenin was observed between the small and average sized littermates. In conclusion, we demonstrate that reduced fetal muscle development is associated with an increased expression of several genes of the insulin-like growth factor system in small fetuses in mid to late gestation.

Activation of peroxisome proliferator-activated receptor gamma and retinoid X receptor results in net depletion of cellular cholesteryl esters in macrophages exposed to oxidized lipoproteins.

OBJECTIVE: Peroxisome proliferator-activated receptor gamma (PPARgamma), a ligand-activated transcription factor, has pleiotropic effects, including regulation of macrophage differentiation and lipid homeostasis. The PPARgamma ligands, thiazolidinediones (TZDs), attenuate atherosclerosis in mice by uncertain mechanisms. The objective of this study was to determine whether activation of PPARgamma or its obligate heterodimer, retinoid X receptor (RXR), modulates macrophage foam cell formation induced by oxidized (ox) lipoproteins. METHODS AND RESULTS: Incubation of THP-1 macrophages with oxHTG-VLDL, oxREM, or oxLDL increased cellular cholesteryl ester over 6-fold. Preincubation with the TZD, ciglitazone, the RXR-specific ligand, 9-cis retinoic acid (9cRA) or the combination reduced CE mass accumulation by up to 65%. Ciglitazone and 9cRA increased CD36 mRNA (up to 4-fold); however, uptake of [125I]oxLDL was only modestly enhanced (up to 1.8-fold) becaues of a concomitant PPARgamma:RXR-induced decrease in SRAI/II activity (up to 40%). This suggested that PPARgamma:RXR activation inhibited cholesteryl ester accumulation by enhancing cholesterol efflux. Ciglitazone and 9cRA were found to increase the expression of ATP-binding cassette proteins A1 and G1, resulting in enhanced cholesterol efflux to lipoprotein-deficient serum, apoAI and HDL3. CONCLUSIONS: PPARgamma and/or RXR activation inhibit foam cell formation through enhanced cholesterol efflux despite increased oxLDL uptake. These observations explain the reduced atherosclerosis in TZD-treated mice and may extend the therapeutic implications of these ligands.

alpha-melanocyte-stimulating hormone modulates nitric oxide production in melanocytes.

We have previously observed that melanocytes produce nitric oxide in response to ultraviolet radiation and lipopolysaccharide and in this study have examined how these responses are affected by alpha-melanocyte-stimulating hormone. Nitric oxide production by cultured cells was measured electrochemically in real time using an ISO-nitric oxide sensor probe. B16 mouse melanoma cells released nitric oxide in response to lipopolysaccharide and the effects were enhanced in cells that had been grown in the presence of 10-11-10-9 M alpha-melanocyte-stimulating hormone prior to stimulation. At concentrations in excess of 10-9 M alpha-melanocyte-stimulating hormone decreased nitric oxide production. Preincubation with lipopolysaccharide, a well-known inducer of inducible nitric oxide synthase, also increased nitric oxide production but this response was reduced by alpha-melanocyte-stimulating hormone. alpha-Melanocyte-stimulating hormone also increased the levels of nitric oxide produced in response to ultraviolet radiation (20-100 mJ per cm2) in B16 cells. The same effect was seen in human melanocytes and as this was inhibited by aminoguanidine would appear to involve an induction of inducible nitric oxide synthase. Reverse transcription-polymerase chain reaction showed that melanocytic cells express inducible nitric oxide synthase mRNA. Western blotting analysis and immunocytochemistry confirmed the presence of inducible nitric oxide synthase protein in B16 cells and FM55 human melanoma cells and that the levels were increased in response to alpha-melanocyte-stimulating hormone. alpha-Melanocyte-stimulating hormone, however, decreased inducible nitric oxide synthase protein expression, which occurred in response to lipopolysaccharide. These results suggest that alpha-melanocyte-stimulating hormone regulates nitric oxide production in melanocytic cells by modulating the induction of inducible nitric oxide synthase. Additional experiments showed that nitric oxide increased melanin production by B16 cells and human melanocytes. This is in keeping with a melanogenic role for nitric oxide but whether its production by melanocytes in response to alpha-melanocyte-stimulating hormone is associated with such a role or whether it has some other significance relating to melanocyte differentiation or in mediating immunomodulatory actions of alpha-melanocyte-stimulating hormone remains to be seen.

Direct, real-time sensing of free radical production by activated human glioblastoma cells.

Primary brain injury initiates a cascade of events which result in secondary brain damage. Although, at present, the biochemical and molecular mechanisms of nerve cell death are not well understood, sufficient evidence now exists to implicate free radicals in this brain injury response. In the light of the current understanding on the role of free radicals in cell mortality, we report on the use of two specific sensors, which we use to measure the direct, simultaneous and real time electrochemical detection of both superoxide (O2.-) and nitric oxide (NO), produced by activated glioblastoma cells. The development and application of these novel methods has enabled us to show that both the cytokine-mediated induction of the enzymes responsible for the generation of these radical species, and the metabolic requirements of the cell can modulate cell messenger release. Importantly, the data collected provides dynamic information on the time course of free radical production, as well as their interactions and their involvement in the process of cell death. In particular, one of the major advances afforded by this technology is the demonstration that suppression of one of either of the two cellular generated radical species (NO and O2.-) leads directly to a corresponding increase in the species that was not being deliberately inhibited or scavenged. This finding may indicate a mechanism involving inter-enzyme regulation of free radical production in glial cells (a phenomenon which may, in future, also be shown to operate in other relevant cell models).

Superoxide generation from constitutive nitric oxide synthase in astrocytes in vitro regulates extracellular nitric oxide availability.

Oxygen-derived free radicals play an important role in the physiology and pathophysiology of brain cell function. Because of their labile nature, however, it has been difficult to investigate their actions directly. This problem has been addressed, in primary rat brain cell cultures, in this study by utilization of two novel electrochemical sensors. It has been demonstrated that extracellular superoxide originates from the astrocytic subpopulation in a calcium/calmodulin dependent manner and responds to constitutive nitric oxide synthase inhibition. The results indicate a novel function for the astrocytic constitutive nitric oxide synthase in regulating extracellular superoxide release and, therefore, controlling neuronal nitric oxide availability.

Superoxide electrode based on covalently immobilized cytochrome c: modelling studies.

We have recently described an optimised electrode for the detection of enzymatic and cellular superoxide (O2*-) production based on cytochrome c immobilized covalently at a surface-modified gold electrode and applied this system to the study of free radical production by activated human glioblastoma cells. In this paper we report the development of a mathematical model for the O2*- electrode responding to enzymically produced O2*- which should enable the determination of absolute concentrations of O2*- in biological systems when this electrode is employed for direct, real-time monitoring of free radical release and interactions.

Amplified electrochemical immunoassay for thyrotropin using thermophilic beta-NADH oxidase.

The use of the highly stable, pH insensitive flavoenzyme, reduced nicotinamide adenine dinucleotide oxidase (NADH oxidase) from the thermophilic organism Thermus aquaticus in combination with alcohol dehydrogenase in an amperometric amplified immunoassay for thyrotropin (TSH) is described. NADH oxidase catalyses the oxidation of reduced nicotinamide adenine dinucleotide (NADH) with concomitant two electron reduction of di-oxygen to hydrogen peroxide. Hydrogen peroxide can be detected by oxidation at a platinum electrode poised at +650mV vs. Ag/AgCl. The enzyme amplification system described has advantages over existing amplification techniques in terms of sensitivity, specificity and operational pH dependence. The electrochemical enzyme-amplified assay for TSH was compared with a spectrophotometric enzyme-amplified system and with a non-amplified electrochemical immunoenzymometric TSH assay. The dynamic range of the electrochemical enzyme-amplified TSH immunoassay was 0.2-100 mIU/l, which was four times that of the enzyme-amplified spectrophotometric assay while the detection limits of both techniques were comparable.

Parathyroid hormone induces superoxide anion burst in the osteoclast: evidence for the direct instantaneous activation of the osteoclast by the hormone.

We have shown that superoxide anion (O2-) production by the osteoclast can be used as an index of the osteoclast activity since the agents that inhibit and stimulate the osteoclast also diminish and stimulate O2- production respectively. Therefore, we have investigated the mechanism of parathyroid hormone (PTH)-mediated stimulation of osteoclast function in terms of its effect on O2- generation. The determination of O2- generation was carried out by employing cytochrome c immobilised on a surface-modified gold electrode. The basal level of free radical production by the osteoblast-like cells (ROS 17/2.8) was 10(4)-fold lower than by osteoclasts cultured on bone. PTH had no acute effect on free radical production by the osteoblasts. The exposure of the osteoclasts cultured on bone to PTH led to a dramatic and immediate stimulation of O2- generation which was unaffected by the presence of ROS 17/2.8 cells. The osteoclasts co-cultured with ROS 17/2.8 cells and exposed to PTH for 3 h were also found to produce greater stimulation of O2- than the osteoclasts exposed to PTH alone. A competitive leukotriene D4 antagonist REV 5901, which also inhibits 5-lipoxygenase, did not block O2- generation by osteoclasts cultured alone or in the presence of osteoblasts. Therefore, we conclude that PTH directly stimulates osteoclasts to produce O2-; this may be the main mode of activation of the osteoclasts, although an osteoblast-mediated effect of the hormone cannot be ruled out.

Separation-free electrochemical immunosensor for rapid determination of atrazine.

A separation-free electrochemical immunoassay method for the detection of the pesticide atrazine is described. The method developed is a competitive ELISA incorporating disposable screen printed horseradish peroxidase modified electrodes as the detector element in conjunction with single-use atrazine immuno-membranes. Screen printed carbon electrodes were prepared using carbon ink incorporating horseradish peroxidase. A monoclonal antibody for atrazine was immobilised onto Biodyne C membranes which were, in turn, placed over the electrode surface. The assay was based on competition for available binding sites between free atrazine and an atrazine-glucose oxidase conjugate prepared 'in-house'. In the presence of glucose, H2O2 formed by the conjugate was reduced by enzyme-channelling via the HRP electrode. The HRP was in turn re-reduced by a direct electron transfer mechanism at a potential of +50 mV Vs Ag/AgCl. Any H2O2 formed in the bulk solution by unbound atrazine-GOD conjugate was scavenged by excess catalase thus removing the requirement for a washing step. The performance of the method was compared with a commercial immunoassay kit for atrazine.

Direct electron transfer bioelectronic interfaces: application to clinical analysis.

Bioelectronic interfaces based on direct electron transfer to proteins and enzymes immobilised at functional electrode surfaces are currently under development and the potential of two such systems for application to clinical measurement will be outlined. The first is the detection of free radical production via direct electrochemistry of cytochrome c immobilised covalently at modified gold electrodes. The redox protein cytochrome c has been immobilised covalently to gold electrodes surface-modified with N-acetyl cysteine via carbodiimide condensation. The electrodes thus produced were used to measure directly the enzymatic and cellular production of the superoxide anion radical (O2(-). The superoxide radical reduced the immobilised cytochrome c which was immediately re-oxidised by the surface-modified gold electrode poised at a potential of +25 mV (vs Ag/AgCl). The electron transfer rate constant (ket) of this process was 3.4 +/- 1.2 s(-1). The rate of current generation was directly proportional to the rate of O2(-) production. The essentially reagentless system produced was designed to be applied ultimately to continuous monitoring of free radical activity in vivo since there is evidence that oxygen-derived free radical species act as mediators which cause and perpetuate inflammation in disease states, including rheumatoid arthritis and neurodegenerative disorders. The second systems are pseudo-homogeneous immunoassays based on direct electron transfer to horseradish peroxidase. Horseradish peroxidase enzyme electrodes based on activated carbon (HRP-ACE) have been constructed by simple passive adsorption.(ABSTRACT TRUNCATED AT 250 WORDS)

Amperometric detection of alkaline phosphatase activity at a horseradish peroxidase enzyme electrode based on activated carbon: potential application to electrochemical immunoassay.

Amperometric detection of alkaline phosphatase activity has been achieved using 5-bromo-4-chloro-3-indolyl phosphate (BCIP) as the enzyme substrate. The production of hydrogen peroxide from the dephosphorylation of BCIP was measured using an activated carbon electrode with horseradish peroxidase immobilised to its surface by simple passive adsorption. This method was easily capable of measuring 10(-12) M alkaline phosphatase and had a calculated detection limit of 2.2 x 10(-14) M. The horseradish peroxidase electrode system was investigated further as a method for non-competitive electrochemical enzyme immunoassay using thyrotropin (TSH) as the model analyte. This was realised by co-immobilization to the electrode surface of both horseradish peroxidase and an anti-thyrotropin monoclonal antibody. After addition of the analyte, a second biotinylated anti-thyrotropin monoclonal antibody and the substrate, streptavidin-labelled alkaline phosphatase was added and the current (generated by enzyme channelling of hydrogen peroxide) measured as a function of TSH concentration. Thus, the activated carbon electrode was used as a combined immunological capture phase and amperometric detection system.

Amperometric enzyme electrode for determination of theophylline in serum.

This paper describes an amperometric enzyme electrode for the rapid determination of theophylline in serum. The method is based on the catalysed oxidation of theophylline by the haem-containing enzyme theophylline oxidase. Results are presented for two approaches. First, ferrocene monocarboxylic acid was used as a mediator. The second-order rate constant was 1.1 x 10(3) 1 mol-1 s-1. Secondly, the organic conducting salt NMP.TCNQ was used to construct enzyme electrodes. These electrodes were employed for the rapid (60 s) measurement of theophylline in serum at a working potential of +100 mV versus Ag/AgCl. Linear calibration curves were obtained over the clinically relevant range (y = 0.13x + 0.22, n = 8). Caffeine, theobromine and 3-methylxanthine at levels up to 100 mg l-1 do not interfere and 1-methylxanthine shows cross-reactivity at concentrations greater than 50 mg l-1.

Biosensor based on enzyme-catalysed degradation of thin polymer films.

A biosensor based on the enzyme-catalysed dissolution of biodegradable polymer films has been developed. Three polymer-enzyme systems were investigated for use in the sensor: a poly(ester amide), which is degraded by the proteolytic enzyme alpha-chymotrypsin; a dextran hydrogel, which is degraded by dextranase; and poly(trimethylene) succinate, which is degraded by a lipase. Dissolution of the polymer films was monitored by Surface Plasmon Resonance (SPR). The rate of degradation was directly related to enzyme concentration for each polymer/enzyme couple. The poly(ester amide)/alpha-chymotrypsin couple proved to be the most sensitive over a concentration range from 4 x 10(-11) to 4 x 10(-7) mol l(-1) of enzyme. The rate of degradation was shown to be independent of the thickness of the poly(ester amide) films. The dextran hydrogel/dextranase couple was less sensitive than the poly(ester amide)/alpha-chymotrypsin couple but showed greater degradation rates at low enzyme concentrations. Enzyme concentrations as low as 2 x 10(-11) mol l(-1) were detected in less than 20 min. Potential fields of application of such a sensor system are the detection of enzyme concentrations and the construction of disposable enzyme based immunosensors, which employ the polymer-degrading enzyme as an enzyme label.

Potential glucose sensor for perioperative blood glucose control in diabetes mellitus.

A glucose sensor intended for future use in diabetic patients undergoing major surgery is described. It involves glucose oxidase immobilised at a platinised activated carbon electrode (PACE). The sensor gave a nonoxygen dependent amperometric response in whole undiluted blood and did not require the use of electron mediators. In vitro studies in protein containing buffer using a flow cell indicated current densities of approximately 160 nA mm-2 mM-1 and a linear response over the range 0-20 mM. The operational stability of the sensor was at least 49 h in continuous use. In addition the sensor had a 90-99% response time of 1 min when used at a flow rate of 3 ml min-1 and showed a temperature dependence of 2.4% C-1. The results reported suggest significant advantages of this approach, for future use as a perioperative intra-vascular sensor for diabetic subjects, over previously reported glucose sensors.