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At least 217 records · Page 12Linked to original sources
PubMed2002

Optimizing the tensile properties of polyvinyl alcohol hydrogel for the construction of a bioprosthetic heart valve stent.

Although bioprosthetic heart valves offer the benefits of a natural opening and closing, better hemodynamics, and avoidance of life-long anticoagulant therapy, they nevertheless tend to fail in 10-15 years from tears and calcification. Several authors, including the present ones, have identified the rigid stent as a factor contributing to these failures. The ultimate solution is an artificial heart valve that has mechanical properties that allow it to move in conformity with the aortic root during the cardiac cycle, has superior hemodynamics, is nonthrombogenic, will last more than 20 years, and mitigates the need for anticoagulants. We have identified a polymer, polyvinyl alcohol (PVA) hydrogel, that has mechanical properties similar to soft tissue. The purpose of this research is to match the tensile properties of PVA to the porcine aortic root and to fabricate a stent prototype for a bioprosthetic heart valve with the use of the PVA hydrogel. Specimens of 15% w/w PVA were prepared by processing through 1-6 cycles of freezing (-20 degrees C) at 0.2 degrees C/min freeze rate and thawing (+20 degrees C) at different thawing rates (0.2 degrees C/min and 1 degrees C/min), for different holding times (1 and 6 h) at -20 degrees C. Subsequently tensile tests and stress-relaxation tests were conducted on the specimens. The different holding times at -20 degrees C demonstrated no difference in the result. The slower thawing rate improved the tensile properties but did not produce significant changes on the stress-relaxation properties. The nonlinear stress-strain curve for the PVA after the fourth freeze-thaw cycle matched the porcine aortic root within the physiological pressure range. The stress-relaxation curve for PVA also approximated the shape of the aortic root. The complex geometry of an artificial heart valve stent was successfully injection molded. These results, in combination with other preliminary findings for biocompatibility and fatigue behavior, suggest that PVA hydrogel is a promising biomaterial for implants, catheters, and artificial skin.

Animals↗
PubMed2006

Cyclitols and carbohydrates in leaves and roots of 13 Eucalyptus species suggest contrasting physiological responses to water deficit.

In many tree species, physiological adaptations to drought include the accumulation of osmotically active substances and/or the presence of particular compatible solutes, among them cyclitols. Recently, the cyclitol quercitol was identified in species of Eucalyptus, a diverse genus whose speciation is probably driven by adaptation to water availability. We subjected seedlings of 13 Eucalyptus species from different ecosystems ('mesic' and 'xeric') and different sub-generic taxonomic groups to 10 weeks of water deficit (WD) treatment. Pre-dawn water potentials (psi(pdwn)) and relative water content (RWC) were determined in shoots, and total osmolality, soluble low-molecular-weight carbohydrates and cyclitols were measured in leaves and roots. Responses to water deficit followed two distinct patterns: Eucalyptus species from 'mesic' environments adjusted concentrations of sucrose (through increased levels of sucrose and decreases in RWC) in response to water deficit, whereas 'xeric' species increased concentrations of quercitol (through reductions in RWC). In root tissues, only species from xeric environments contained high levels of quercitol and mannitol, increasing under WD conditions. We suggest that the former (mesic) strategy may be beneficial to respond to short-lasting drought conditions, because sucrose is easily metabolized, whereas the latter (xeric) strategy may relate to an effective acclimation to longer-lasting drought. These physiological response groups are also related to taxonomic groups within the genus.

Adaptation, Physiological↗
PubMed2001

[Biology of root resorption process in deciduous teeth. Review of the literature].

Aim of this paper, is to examine, with a review of the literature the different aspects of physiological process of root resorption of deciduous teeth. The process of development of mouth and teeth and their structure is also described. Studies made during the last period, in most part by Japanese authors, improved our knowledge about the process of root resorption of deciduous teeth, even if many aspects are still unknown. The involvement of the pulp and the periodontal ligament and the presence of enzimatic activity and immunologic cells have been confirmed; all these elements seem to have a definite role in the process of root resorption of the deciduous teeth.

Humans↗
PubMed2001

Neuropathic central pain: epidemiology, etiology, and treatment options.

BACKGROUND: Nociceptive pain is a major problem in clinical neurology. Peripheral nerve injury may change the physiology of the dorsal horn so that pain becomes progressively centralized. OBJECTIVE: To review mechanisms underlying the plasticity of dorsal root ganglia and dorsal horn neurons that lead to central pain from a peripheral nerve injury. RESULTS: Evidence is reviewed that points to molecular changes in nociceptive terminals, ectopic firing of afferent pain fibers at the level of the dorsal root ganglia, and physiologic changes of the N-methyl-D-aspartate receptor that cause chronic nociceptive pain. CONCLUSIONS: Central sensitization is the physiologic manifestation of many severe peripherally induced pain states. It is maintained by nociceptive input and a physiologic change in the N-methyl-D-aspartate receptor. It consists of: (1) hypersensitivity at the site of injury; (2) mechanoallodynia; (3) thermal hyperalgesia; (4) hyperpathia; (5) extraterritoriality in the case of complex regional pain syndrome/reflex sympathetic dystrophy; and (6) associated neurogenic inflammation, autonomic dysregulation, and motor phenomena.

Central Nervous System Diseases↗
PubMed2005

Plant cell growth and ion flux responses to the streptomycete phytotoxin thaxtomin A: calcium and hydrogen flux patterns revealed by the non-invasive MIFE technique.

Thaxtomin A, a key phytotoxin produced by plant pathogenic Streptomyces sp., is implicit in common scab disease expression in potato. Primary targets and modes of action of thaxtomin A toxicity in plant cells are not well understood. In this work, early signalling events associated with thaxtomin A toxicity were studied using the ion-selective microelectrode ion flux estimation (MIFE) technique. Thaxtomin A-induced changes in net ion fluxes were measured across the plasma membrane (PM) of root and pollen tube tissue in Arabidopsis thaliana and tomato. Within a minute after toxin application, a rapid and short-lived Ca2+ influx was observed. Well ahead of the marked inhibition of root growth, a significant shift towards net H+ efflux across the PM occurred in all tissues. Similar to root tissues, thaxtomin A significantly modified ion flux profiles from growing pollen tubes. Thaxtomin A was more effective in young, physiologically active tissues (root elongation zone or pollen tube apex), suggesting a higher density of thaxtomin A-binding sites in these regions. Overall, our data provide the first evidence that thaxtomin A triggers an early signalling cascade, which may be crucial in plant-pathogen interactions. It also suggests a possible interaction between thaxtomin A and PM auxin receptors, as revealed from experiments on the auxin-sensitive ucu2-2/gi2 A. thaliana mutant.

Arabidopsis↗
PubMed2004

Calcitonin in human odontoclasts regulates root resorption activity via protein kinase A.

Calcitonin is a known inhibitor of osteoclastic bone resorption, but it remains uncertain whether calcitonin also regulates human odontoclastic activity, particularly during the physiological process of root resorption. In this study, we examined the expression of calcitonin receptors in human odontoclasts and the effect of calcitonin on root resorption, using immunocytochemistry and reverse transcription-polymerase chain reaction (RT-PCR). Actin-ring formation was used to assess cytostructural changes during resorption activity. Our results show that calcitonin receptors are expressed in human odontoclasts freshly isolated from deciduous teeth of the periodontal region. Calcitonin inhibited actin-ring formation and resorption activity. This calcitonin-induced inhibition was mimicked by forskolin and dibutyryl-adenosine 3',5'-cyclic monophosphate (db-cAMP), which are protein kinase A (PKA) activators, but not by phorbol 12-myristate 13-acetate, a protein kinase C activator. Pretreatment with adenosine 3',5'-cyclic monophosphothioate Rp diastereomer (Rp-cAMPS), a PKA inhibitor, suppressed the calcitonin-induced inhibition of actin-ring formation. These results indicate that calcitonin receptor activation suppresses odontoclastic root resorption via PKA, a signaling pathway different from that in human osteoclasts.

Acid Phosphatase↗
PubMed1995

Possible branching of myelinated primary afferent fibres in the dorsal root of the rat.

A combined physiological and morphological examination of rat dorsal root ganglion cells revealed branching of the central process of neurones with myelinated fibres (conduction velocity > 2 m/s; n = 24). Single shock electrical stimulation of spinal dorsal roots triggered double action potentials (early and late spike) in two dorsal root ganglion cells recorded by intracellular electrodes in the in vitro spinal cord-dorsal root ganglion preparation from 12-20 day-old rats. The action potentials had different stimulus thresholds (lower for the late spike). In one dorsal root ganglion cell the differences in delay between the two spikes inhibited the soma invasion of the second spike, when both action potentials were evoked at resting membrane potential. Depolarization of the soma membrane by DC current, injected through the electrode, recovered the blocked action potential. Membrane depolarization by GABA reduced the threshold for the early spike and changed the pattern of activation. After electrophysiological characterisation, intracellular biotin/avidin staining of the neurone revealed branching of the central axon in the dorsal root. None of the other cells, which responded with single action potentials after dorsal root stimulation showed secondary branching (n = 5). This rare observation shows that differences between the conduction velocities and activation thresholds in branches of individual dorsal root ganglion cell axons may produce block of spike invasion into the soma and perhaps the spinal terminal field of large primary afferents.

Action Potentials↗
PubMed2002

Electrophysiology of radiculopathies.

The anatomy, pathophysiology, and clinical evaluation of radiculopathies are discussed. Defining whether root injury is present and which roots are involved can be difficult but critical for patient management. In conjunction with clinical and radiological information, studies that establish physiological abnormalities of roots should be helpful and important. Clinical neurophysiological studies for radiculopathies are performed frequently but have yet to achieve a universally accepted role in the evaluation of these patients. Electrophysiological techniques for the evaluation of radiculopathies are reviewed. Needle electromyography is the best established of these procedures but has the disadvantage of requiring injury to motor fibers of both a certain degree and distribution. Nerve conduction studies may rarely be abnormal in radiculopathies but are needed to be certain other conditions that may produce similar symptoms and signs are not present. H reflexes and F waves probably have roles in the evaluation of radiculopathies but published reports about F waves in radiculopathies have been marred by inadequate methodology. There is evidence based on large series of patients that somatosensory evoked potentials can be helpful for evaluating patients with multilevel injury such as spinal stenosis, patients where electrophysiological studies may have their greatest clinical utility. Further work using either electrical stimulation with needles or magnetic stimulation of roots seems warranted. The demonstration of meaningful electrophysiological changes with activities that reproduce radicular symptoms may be a promising experimental approach. Available information does not necessarily answer critical questions about the role of electrophysiology in patients with radiculopathies. This cannot be done using analyses based on current ideas about evidence based medicine given the absence of a 'gold standard' for defining radiculopathies as well the absence of blinded studies. The available information provides strong arguments for further investigations evaluating different clinical neurophysiological techniques in the same patient, and for evaluating the value of these techniques by concentrating on their clinical import.

Electrodiagnosis↗
PubMed1966

CO(2) Fixation in Opuntia Roots.

Nonautotrophic CO(2) metabolism in Opuntia echinocarpa roots was studied with techniques of manometry and radiometry. The roots were grown in a one-quarter strength nutrient solution for several days; the distal 2 cm was used for physiological studies. The roots assimilated significant quantities of (14)CO(2) and appeared to show a crassulacean-type acid metabolism with respect to quality and quantity. Most of the (14)C activity was associated with the distal portion of the elongating root indicating correlation with metabolic activity. The (14)CO(2) assimilation was comparable to a crassulacean leaf succulent, but 3 times greater than that found for stem tissue of the same Opuntia species.The rates of O(2) and CO(2) exchange and estimated CO(2) fixation were 180, 123, and 57 mul/g per hour. A respiratory quotient of 0.66 was found.The products of (14)CO(2) fixation were similar in most respects to reported experiments with leaf succulents. Equilibration of the predominant malic acid with isocitric, succinic, and fumaric acids was not evident. The latter observation was interpreted as metabolic isolation of the fixation products rather than poor citric acid cycle activity.A rapid turnover of the fixed (14)CO(2) was measured by following decarboxlyation kinetics and by product analysis after a postincubation period. The first order rate constant for the steady state release was 4.4 x 10(-3) min(-1) with a half-time of 157.5 minutes. Amino acids decayed at a more rapid rate than organic acids.

Journal Article↗
PubMed2006

Physiological responses of potato (Solanum tuberosum L.) to partial root-zone drying: ABA signalling, leaf gas exchange, and water use efficiency.

The physiological responses of potato (Solanum tuberosum L. cv. Folva) to partial root-zone drying (PRD) were investigated in potted plants in a greenhouse (GH) and in plants grown in the field under an automatic rain-out-shelter. In the GH, irrigation was applied daily to the whole root system (FI), or to one-half of the root system while the other half was dried, for 9 d. In the field, the plants were drip irrigated either to the whole root system near field capacity (FI) or using 70% water of FI to one side of the roots, and shifted to the other side every 5-10 d (PRD). PRD plants had a similar midday leaf water potential to that of FI, whereas in the GH their root water potential (Psi(r)) was significantly lowered after 5 d. Stomatal conductance (g(s)) was more sensitive to PRD than photosynthesis (A) particularly in the field, leading to greater intrinsic water use efficiency (WUE) (i.e. A/g(s)) in PRD than in FI plants on several days. In PRD, the xylem sap abscisic acid concentration ([ABA](xylem)) increased exponentially with decreasing Psi(r); and the relative [ABA](xylem) (PRD/FI) increased exponentially as the fraction of transpirable soil water (FTSW) in the drying side decreased. In the field, the leaf area index was slightly less in PRD than in FI treatment, while tuber biomass was similar for the two treatments. Compared with FI, PRD treatment saved 30% water and increased crop water use efficiency (WUE) by 59%. Restrictions on leaf area expansion and g(s) by PRD-induced ABA signals might have contributed to reduced water use and increased WUE.

Abscisic Acid↗
PubMed2001

Iron stress-induced changes in root epidermal cell fate are regulated independently from physiological responses to low iron availability.

Iron-overaccumulating mutants were investigated with respect to changes in epidermal cell patterning and root reductase activity in response to iron starvation. In all mutants under investigation, ferric chelate reductase activity was up-regulated both in the presence and absence of iron in the growth medium. The induction of transfer cells in the rhizodermis appeared to be iron regulated in the pea (Pisum sativum L. cv Dippes Gelbe Viktoria and cv Sparkle) mutants bronze and degenerated leaflets, but not in roots of the tomato (Lycopersicon esculentum Mill. cv Bonner Beste) mutant chloronerva, suggesting that in chloronerva iron cannot be recognized by putative sensor proteins. Experiments with split-root plants supports the hypothesis that Fe(III) chelate reductase is regulated by a shoot-borne signal molecule, communicating the iron status of the shoot to the roots. In contrast, the formation of transfer cells was dependent on the local concentration of iron, implying that this shoot signal does not affect their formation. Different repression curves of the two responses imply that the induction of transfer cells occurs after the enhancement of electron transfer across the plasma membrane rather than being causally linked. Similar to transfer cells, the formation of extra root hairs in the Arabidopsis mutant man1 was regulated by the iron concentration of the growth medium and was unaffected by interorgan signaling.

FMN Reductase↗
PubMed2005

Taurine-induced modulation of voltage-sensitive Na+ channels in rat dorsal root ganglion neurons.

The physiological role of taurine, an abundant free amino acid in the neural system, is still poorly understood. The aim of this study was to investigate its effect on TTX-sensitive (TTX-S) and TTX-resistant (TTX-R) Na+ currents in enzymatically dissociated neurons from rat dorsal root ganglion (DRG) with conventional whole-cell recording manner under voltage-clamp conditions. A TTX-S Na+ current was recorded preferentially from large DRG neurons and a TTX-R Na+ current preferentially from small ones. For TTX-S Na+ channel, taurine of the concentration > or = 10 mM shifted the activation curve in the depolarizing direction and the inactivation curve in the hyperpolarizing direction. There was no change in the activation curve for TTX-R Na+ channel and the inactivation curve was shifted in the hyperpolarizing direction slightly in the presence of taurine > or = 20 mM. When the recovery kinetics was examined, the presence of taurine resulted in a slower recovery from inactivation of TTX-S currents and no change of TTX-R ones. All the effects of taurine were weakly concentration-dependent and partly recovered quite slowly after washout. Our data indicate that taurine alters the properties of Na+ currents in intact DRG neurons. These may contribute to the understanding of taurine as a natural neuroprotectant and the potential of taurine as a useful medicine for the treatment of sensory neuropathies.

Algorithms↗
PubMed1986

The electrophysiological and morphological characteristics of feline dorsal root ganglion cells.

The electrophysiological characteristics of physiologically typed L7 and S1 dorsal root ganglion (DRG) cells have been studied in the cat by intracellular recording. The injection of the fluorescent dye Lucifer Yellow has enabled us to study the morphology of these neurons. Our results show that over the entire range of primary sensory afferents there is a linear relationship between the peak rate of rise of somatic action potentials (dv/dt) and axonal conduction velocity. There is a prominent inflexion on the repolarizing phase of the somatic action potentials of group III and group IV afferents. This is not seen in the action potentials of group II or group I afferents. These results correlate with the observation that the total action potential duration (APD) is inversely related to conduction velocity. Primary afferent somata were observed to have an ellipsoidal shape with the long axis in the rostrocaudal dimension. It was observed that for all afferents studied the volume of a dorsal root ganglion cell was linearly related to its peripheral axonal conduction velocity. We were able to show further that group IV somata, some of whose axons supplied nociceptors, were among the smallest in the ganglion.

Action Potentials↗
PubMed1995

Molecular and physiological responses to abscisic acid and salts in roots of salt-sensitive and salt-tolerant Indica rice varieties.

The Indica rice (Oryza sativa L.) varieties Pokkali and Nona Bokra are well-known salt tolerance donors in classical breeding. In an attempt to understand the molecular basis of their tolerance, physiological and gene expression studies were initiated. The effect of abscisic acid (ABA) on total proteins in roots from 12-d-old seedlings of Pokkali, Nona Bokra, and the salt-sensitive cultivar Taichung N1 were analyzed on two-dimensional gels. The abundance of ABA-induced proteins was highest in the most tolerant variety, Pokkali. Three ABA-responsive proteins, present at different levels in roots from tolerant and sensitive varieties, were further characterized by partial amino acid analysis. A novel histidine-rich protein and two types of late embryogenesis abundant (LEA) proteins were identified. Protein immunoblotting revealed that the levels of dehydrins and group 3 LEA proteins were significantly higher in roots from tolerant compared with sensitive varieties. Endogenous ABA levels showed a transient increase in roots exposed to osmotic shock (150 mM NaCl). Peak ABA concentrations were 30-fold higher for Nona Bokra and 6-fold higher for Pokkali compared with Taichung N1. Both the salt-induced endogenous ABA levels and a greater molecular response of root tissue to ABA were associated with the varietal differences in tolerance.

Abscisic Acid↗
PubMed1995

Export of Abscisic Acid, 1-Aminocyclopropane-1-Carboxylic Acid, Phosphate, and Nitrate from Roots to Shoots of Flooded Tomato Plants (Accounting for Effects of Xylem Sap Flow Rate on Concentration and Delivery).

We determined whether root stress alters the output of physiologically active messages passing from roots to shoots in the transpiration stream. Concentrations were not good measures of output. This was because changes in volume flow of xylem sap caused either by sampling procedures or by effects of root stress on rates of whole-plant transpiration modified concentrations simply by dilution. Thus, delivery rate (concentration x sap flow rate) was preferred to concentration as a measure of solute output from roots. To demonstrate these points, 1-aminocyclopropane-1-carboxylic acid (ACC), abscisic acid, phosphate, nitrate, and pH were measured in xylem sap of flooded and well-drained tomato (Lycopersicon esculentum Mill., cv Ailsa Craig) plants expressed at various rates from pressurized detopped roots. Concentrations decreased as sap flow rates were increased. However, dilution of solutes was often less than proportional to flow, especially in flooded plants. Thus, sap flowing through detopped roots at whole-plant transpiration rates was used to estimate solute delivery rates in intact plants. On this basis, delivery of ACC from roots to shoots was 3.1-fold greater in plants flooded for 24 h than in well-drained plants, and delivery of phosphate was 2.3-fold greater. Delivery rates of abscisic acid and nitrate in flooded plants were only 11 and 7%, respectively, of those in well-drained plants.

Journal Article↗
PubMed2002

The tomato fer gene encoding a bHLH protein controls iron-uptake responses in roots.

Iron deficiency is among the most common nutritional disorders in plants. To cope with low iron supply, plants with the exception of the Gramineae increase the solubility and uptake of iron by inducing physiological and developmental alterations including iron reduction, soil acidification, Fe(II) transport and root-hair proliferation (strategy I). The chlorotic tomato fer mutant fails to activate the strategy I. It was shown previously that the fer gene is required in the root. Here, we show that fer plants exhibit root developmental phenotypes after low and sufficient iron nutrition indicating that FER acts irrespective of iron supply. Mutant fer roots displayed lower Leirt1 expression than wild-type roots. We isolated the fer gene by map-based cloning and demonstrate that it encodes a protein containing a basic helix-loop-helix domain. fer is expressed in a cell-specific pattern at the root tip independently from iron supply. Our results suggest that FER may control root physiology and development at a transcriptional level in response to iron supply and thus may be the first identified regulator for iron nutrition in plants.

Amino Acid Sequence↗
PubMed2006

Functional aquaporin diversity in plants.

Due to the fact that most plants are immobile, a rapid response of physiological processes to changing environmental conditions is essential for their survival. Thus, in comparison to many other organisms, plants might need a more sophisticated tuning of water balance. Among others, this is reflected by the comparable large amount of aquaporin genes in plant genomes. So far, aquaporins were shown to be involved in many physiological processes like root water uptake, reproduction or photosynthesis. Their classification as simple water pores has changed according to their molecular function into channels permeable for water, small solutes and/or gases. An adjustment of the corresponding physiological process could be achieved by regulation mechanisms. Concerning aquaporins these range from posttranslational modification, molecular trafficking to heteromerization of aquaporin isoforms. The aim of this review is to underline the function of the four plant aquaporin family subclasses with regard to the substrate specificity, regulation and physiological relevance.

Aquaporins↗