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Biomedical subjects

A R Evans

Publications and source records attributed to A R Evans.

At least 19 recordsLinked to original sources
PubMed2006

Functional analysis of CHX21: a putative sodium transporter in Arabidopsis.

The functional role of CHX21, a member of the Arabidopsis thaliana CHX cation transporter family, has been investigated in plants growing under "ideal" conditions and in the presence of elevated NaCl levels. In public databases, AtCHX21 (At2g31910) is annotated as a putative Na+/H+ antiporter. In this study, Southern analysis was used to identify a genotype that contained a single transposon insertion within its genome; using PCR, this insertion was shown to be within the CHX21 locus. No CHX21 transcript was detectable in Atchx21 (mutant) plants using RT-PCR. In the absence of salt stress, Atchx21 showed significant quantitative differences from the wild type (AtCHX21) in development with respect to characters such as rosette width and flowering time. In the presence of 50 mM NaCl, (i) roots of Atchx21 elongated more slowly than the wild type, (ii) the leaf sap Na+ concentration was significantly lower in Atchx21 compared with the wild type, and (iii) the concentra) in the xylem was lower compared with the wild type. The concentration of Na+ exported from the leaf in the phloem was unchanged. Thus, loading of Na+ into the root xylem could explain changes in leaf concentration of Na+. This hypothesis was supported by immunolocalization which demonstrated that the AtCHX21 transporter could only be detected in root endodermal cells. Immunogold labelling of ultra-thin sections, followed by transmission electron microscopy, demonstrated the localization of the protein in the plasma membrane. The data demonstrate that the CHX21 transporter may play a role in regulation of xylem Na+ concentration and, consequently, Na+ accumulation in the leaf.

Arabidopsis↗
PubMed2003

Interactions between proteins bound to biomembranes.

We study a physical model for the interaction between general inclusions bound to fluid membranes that possess finite tension gamma, as well as the usual bending rigidity kappa. We are motivated by an interest in proteins bound to cell membranes that apply forces to these membranes, due to either entropic or direct chemical interactions. We find an exact analytic solution for the repulsive interaction between two similar circularly symmetric inclusions. This repulsion extends over length scales approximately sqrt[kappa/gamma] and contrasts with the membrane-mediated contact attraction for similar inclusions on tensionless membranes. For noncircularly symmetric inclusions we study the small, algebraically long-ranged, attractive contribution to the force that arises. We discuss the relevance of our results to biological phenomena, such as the budding of caveolae from cell membranes and the striations that are observed on their coats. These, and other, "gnarly buds" may prove fascinating to study further.

Biophysical Phenomena↗
PubMed2001

Confocal imaging, visualization and 3-D surface measurement of small mammalian teeth.

The difficulties traditionally faced by functional morphologists in representing and interpreting three-dimensional objects can now be mostly overcome using available laser and computer imaging technologies. A practical method for three-dimensional imaging of small mammalian teeth using confocal microscopy is reported. Moulding and casting of the teeth were first performed, followed by confocal fluorescence imaging. Accuracy and precision of the scanned structures were tested in morphometric studies by using a new technique to measure the noise in the scan of a three-dimensional surface, and linear and angular dimensions of the scans were compared with measurements made using traditional morphological tools. It is shown that measurements can be taken with less than 4% difference from the original object. Teeth of the microchiropteran bat Chalinolobus gouldii were scanned and measured to show the potential of the techniques. Methods for visualizing the small teeth in three-dimensional space, and animating the teeth in occlusion, show the power of this approach in aiding a three-dimensional understanding of the structure and function of teeth and other three-dimensional structures.

Animals↗
PubMed2000

Going APE over ref-1.

The DNA base excision repair (BER) pathway is responsible for the repair of cellular alkylation and oxidative DNA damage. A crucial and the second step in the BER pathway involves the cleavage of baseless sites in DNA by an AP endonuclease. The major AP endonuclease in mammalian cells is Ape1/ref-1. Ape1/ref-1 is a multifunctional protein that is not only responsible for repair of AP sites, but also functions as a reduction-oxidation (redox) factor maintaining transcription factors in an active reduced state. Ape1/ref-1 has been shown to stimulate the DNA binding activity of numerous transcription factors that are involved in cancer promotion and progression such as Fos, Jun, NF(B, PAX, HIF-1(, HLF and p53. Ape1/ref-1 has also been implicated in the activation of bioreductive drugs which require reduction in order to be active and has been shown to interact with a subunit of the Ku antigen to act as a negative regulator of the parathyroid hormone promoter, as well as part of the HREBP transcription factor complex. Ape1/ref-1 levels have been found to be elevated in a number of cancers such as ovarian, cervical, prostate, rhabdomyosarcomas and germ cell tumors and correlated with the radiosensitivity of cervical cancers. In this review, we have attempted to try and assimilated as much data concerning Ape1/ref-1 and incorporate the rapidly growing information on Ape1/ref-1 in a wide variety of functions and systems.

Animals↗
PubMed2000

Isoprostanes, novel eicosanoids that produce nociception and sensitize rat sensory neurons.

Isoprostanes are a novel class of eicosanoids primarily formed by peroxidation of arachidonic acid. Because of their potential as inflammatory and/or hyperalgesic agents whose formation is largely independent of cyclooxygenases, we examined whether 8-iso prostaglandin E(2) (8-iso PGE(2)) or 8-iso prostaglandin F(2alpha) (8-iso PGF(2alpha)) reduces mechanical and thermal withdrawal threshold in rats, and whether they sensitize rat sensory neurons. Injection of 1 microg of 8-iso PGE(2) (in 2.5 microl) into the hindpaw of rats significantly reduced mechanical and thermal withdrawal thresholds, whereas 1 microg of 8-iso PGF(2alpha) elicited a transient decrease in only the mechanical withdrawal threshold. Both isoprostanes enhanced the firing of C-nociceptors in a concentration-dependent manner when injected into peripheral receptive fields. Exposing sensory neurons grown in culture to 1 microM 8-iso PGE(2) or 8-iso PGF(2alpha) augmented the number of action potentials elicited by a ramp of depolarizing current. In contrast, 8-iso PGE(2) but not 8-iso PGF(2alpha) enhanced the release of substance P- and calcitonin gene-related peptide-like immunoreactivity from isolated sensory neurons. Ten micromolar 8-iso PGE(2) stimulated peptide release directly, whereas treatment with 1 microM 8-iso PGE(2) augmented the release evoked by either bradykinin or capsaicin. Pretreating neuronal cultures with the nonsteroidal anti-inflammatory drug ketorolac did not alter the sensitizing action of 8-iso PGE(2) on peptide release, suggesting that this action of the isoprostane was not secondary to the production of prostaglandins via the cyclooxygenase pathway. These data support the notion that isoprostanes are an important class of inflammatory mediators that augment nociception.

Action Potentials↗
PubMed1999

The cAMP transduction cascade mediates the PGE2-induced inhibition of potassium currents in rat sensory neurones.

1. The role of the cyclic AMP (cAMP) transduction cascade in mediating the prostaglandin E2 (PGE2)-induced decrease in potassium current (IK) was investigated in isolated embryonic rat sensory neurones using the whole-cell patch-clamp recording technique. 2. Exposure to 100 microM chlorophenylthio-adenosine cyclic 3', 5'-monophosphate (cpt-cAMP) or 1 microM PGE2 caused a slow suppression of the whole-cell IK by 34 and 36 %, respectively (measured after 20 min), without a shift in the voltage dependence of activation for this current. Neither of these agents altered the shape of the voltage-dependent inactivation curve indicating that the suppression of IK did not result from alterations in the inactivation properties. 3. To determine whether the PGE2-mediated suppression of IK depended on activation of the cAMP pathway, cells were exposed to this prostanoid in the presence of the protein kinase A (PKA) inhibitor, PKI. The PGE2-induced suppression of IK was prevented by PKI. In the absence of PGE2, PKI had no significant effect on the magnitude of IK. 4. Results obtained from protocols using different conditioning prepulse voltages indicated that the extent of cpt-cAMP- and PGE2-mediated suppression of IK was independent of the prepulse voltage. The subtraction of control and treated currents revealed that the cpt-cAMP- and PGE2-sensitive currents exhibited little time-dependent inactivation. Taken together, these results suggest that the modulated currents may be delayed rectifier-like IK. 5. Exposure to the inhibitors of IK, tetraethylammonium (TEA) or 4-aminopyridine (4-AP), reduced the control current elicited by a voltage step to +60 mV by 40-50 %. In the presence of 10 mM TEA, treatment with cpt-cAMP did not result in any further inhibition of IK. In contrast, cpt-cAMP reduced IK by an additional 25-30 % in the presence of 1 mM 4-AP. This effect was independent of the conditioning prepulse voltage. 6. These results establish that PGE2 inhibits an outward IK in sensory neurones via activation of PKA and are consistent with the idea that the PGE2-mediated sensitization of sensory neurones results, in part, from an inhibition of delayed rectifier-like IK.

4-Aminopyridine↗
PubMed1999

The epidemiology of pediatric glaucoma: the Toronto experience.

BACKGROUND: This study was conceived to provide an insight into the spectrum of glaucoma in the pediatric population. We also set out to compare the success of disease control and the prognosis for vision within the different diagnostic subgroups. This is the largest single population of children with glaucoma that has been so described and compared. METHODS: The charts of children who were first seen between birth and age 16 years and who attended the Hospital for Sick Children with any form of glaucoma between January 1974 and January 1995 were reviewed and entered into the study. RESULTS: Data are presented for 306 children. Congenital glaucoma was the most common subtype, accounting for 38%. Patients with congenital glaucoma were young, had surgery, and had more operations than any other group except those with aniridia. Goniotomy offered a cure in 47.8% of the patients. A bimodal distribution reflected their visual performance. Patients with aphakic glaucoma, the next most prevalent group (20%), presented at an older age (4.5 years). Surgical intervention was performed in 50% of these children. Nearly all patients with Sturge-Weber syndrome (80%) had surgery. The following glaucoma groups were associated with a poor visual outcome: aniridia, anterior segment developmental anomalies involving the cornea, uveitis with glaucoma other than steroid induced, retinopathy of prematurity, and persistent hyperplastic primary vitreous. Steroid-induced glaucoma and anterior segment dysgenesis, excluding Peters anomaly, had uniformly good outcomes. CONCLUSION: The ability to control glaucoma in childhood and visual prognosis is highly variable. Particular diagnostic categories do consistently well and some do poorly.

Adolescent↗
PubMed1998

Necrotising fasciitis as a complication of botulinum toxin injection.

PURPOSE: To highlight the need for early diagnosis and treatment of the rare condition of necrotising fasciitis as a complication of botulinum toxin injection, and to illustrate that injections in immunocompromised patients carry a rare but serious risk. RESULTS AND METHODS: A case report is presented of an 80-year-old woman suffering from blepharospasm and chronic myeloid leukaemia, who developed necrotising fasciitis 3 days after a botulinum toxin injection. CONCLUSIONS: Chronic debilitating processes such as diabetes, alcoholism and polymyositis have been suggested as predisposing factors in the development of necrotising fasciitis. We believe this is the first reported case of necrotising fasciitis occurring secondary to a botulinum toxin injection. The fact that this infection extended through the fascial planes and led to the death of muscle was, probably, because an inoculum was introduced directly into the muscle at the time of botulinum toxin treatment. This may have led to its deep spread and difficulty in debriding the area. Chronic myeloid leukaemia does not in itself cause significant immunosuppression, but our patient was on anti-proliferative treatment and had a low leucocyte count, which may have been a predisposing factor in this case.

Aged↗
PubMed1997

Prostaglandins suppress an outward potassium current in embryonic rat sensory neurons.

The cellular mechanisms giving rise to the enhanced excitability induced by prostaglandin E2 (PGE2) and carba prostacyclin (CPGI2) in embryonic rat sensory neurons were investigated using the whole cell patch-clamp recording technique. Exposing sensory neurons to 1 microM PGE2 produced a twofold increase in the number of action potentials elicited by a ramp of depolarizing current, but this eicosanoid had no effect on the resting membrane potential or the amplitude of the slow afterhyperpolarization. Characterization of the outward potassium currents in the embryonic sensory neurons indicated that the composition of the total current was variable among these neurons. A steady-state inactivation protocol was used to determine the extent of residual noninactivating current. A conditioning prepulse to +20 mV demonstrated that some of these neurons exhibited only a sustained potassium current with little steady-state inactivation whereas other exhibited some combination of a sustained as well as a rapidly inactivating IA-type current. Treatment with 1 microM PGE2 or 1 microM CPGI2, but not 1 microM prostaglandin F2 alpha (PGF2 alpha) produced a time-dependent suppression of the total potassium current. After a 20-min exposure, PGE2 and CPGI2 inhibited the maximal current obtained at +60 mV by 48 and 40%, respectively. The prostaglandin-induced suppression of the potassium current was not associated with a shift in the voltage dependence for activation. Subtraction of the currents remaining after PGE2 or CPGI2 treatment from their respective control recordings revealed that the prostaglandin-sensitive current had characteristics that were consistent with a sustained-type of potassium current. This idea is supported by the following observation. The steady-state inactivation protocol revealed that for prepulse voltages activating both rapidly inactivating and sustained currents, the relaxation of the current was accelerated after treatment with PGE2 or CPGI2 suggesting the removal of a slower component. This effect was not observed in neurons exhibiting only the sustained type current. These results suggest that pro-inflammatory prostaglandins enhance the excitability of rat sensory neurons, in part, through the suppression of an outward potassium current that may modulate the firing threshold for generation of the action potential.

Animals↗
PubMed1996

Differential regulation of evoked peptide release by voltage-sensitive calcium channels in rat sensory neurons.

To determine whether the sensitizing action of prostaglandins on sensory neurons are due to modulation of voltage-sensitive calcium channels (VSCC) we examined the effects of inhibiting these channels on PGE2-induced enhancement of evoked peptide release from isolated dorsal root ganglion neurons. The inhibitory effects of the VSCC blockers on stimulated release were dependent upon the type of chemical agent used to evoke the release. Bradykinin-stimulated release of immunoreactive substance P (iSP) and calcitonin gene-related peptide (iCGRP) was attenuated by the N-type VSCC blocker, omega-conotoxin GVIA (100 nM), but was unaffected by blockade of L-type (1 microM nifedipine) or P-type (200 nM omega-agatoxin IVA) VSCC. In contrast, potassium-stimulated release of peptides was inhibited by nifedipine, but not by omega-conotoxin GVIA or omega-agatoxin IVA. None of the VSCC blockers tested attenuated capsaicin-stimulated release of iSP and iCGRP. The combination of 1 microM nifedipine and 100 nM omega-conotoxin GVIA reduced the whole cell calcium current 89% +/- 1.7%. Administration of 100 nM PGE2 potentiated bradykinin- and capsaicin-evoked peptide release by 2-3-fold. Neither nifedipine nor omega-conotoxin GVIA attenuated the PGE2-mediated potentiation of bradykinin-evoked release, and neither omega-conotoxin GVIA nor omega-agatoxin IVA blocked the potentiation of capsaicin-evoked release induced by PGE2. These results indicate that the sensitizing actions of PGE2 as measured by enhanced peptide release, are not mediated by L-, N-, or P-type VSCC.

Animals↗
PubMed1994

Effects of vagal afferent nerve stimulation on noxious heat-evoked Fos-like immunoreactivity in the rat lumbar spinal cord.

Electrophysiological and behavioral studies have described modulation of nociception by vagal afferent fibers. The objectives of this study were to 1) use Fos-like immunoreactivity as a marker for neuronal activity to examine populations of neurons in the spinal cord that are activated by a noxious heat stimulus, 2) determine whether heat-evoked Fos-like immunoreactivity can be modulated by vagal afferent stimulation, and 3) determine whether vagally-mediated effect on heat-evoked Fos-like immunoreactivity can be blocked by intrathecally administered serotoninergic receptor and alpha-adrenergic receptor antagonists. Neurons demonstrating Fos-like immunoreactivity were located in the ipsilateral superficial and deep dorsal horn laminae extending from the caudal L3 through the rostral L6 region of the spinal cord. Stimulation of the right cervical vagus nerve attenuated significantly (42%) heat-evoked Fos-like immunoreactivity in the superficial laminae. The reduction in Fos-like immunoreactivity by vagal stimulation was abolished by intrathecal administration of methysergide, a nonselective serotoninergic receptor antagonist, but not by phentolamine, a nonselective alpha-adrenoceptor antagonist. These results suggest that vagal afferent modulation of spinal nociceptive transmission is mediated, at least in part, by serotonin receptors.

Adrenergic alpha-Antagonists↗