Photosystem 2 (PS 2) reaction centre can be considered as a water-plastoqninone oxido-reductase. Using four photons it transfers four electrons from two molecules of water to plastoquinone (PQ), producing the molecular oxygen and two molecules of double reduced PQ. PS 2 is the site of the antagonistic action of bicarbonate and formáte on PS 2 electron flow; incubation of isolated chloroplasts with formáte results in full inhibition of electron flow actívity, which can be restored by addition of bicarbonate. This bicarbonate effect is located at the Dl protein and affects the electron flow between the primary quinone and the PQ pool. Bicarbonate is probably involved in stabilizatíon of tíie semireduced secondary quinone Qb, and in the protonation reactions at this site. Under physiological conditions bicarbonate is boimd to thylakoid membranes. Addition of formáte to thylakoids appears to release CO2. The bicarbonate effect is not only observed in isolated chloroplasts, but also in intact organisms as green algae and leaves. Bicarbonate Controls PS 2 electron flow in order to cope with stress conditions leading to, for instance, photoinhibition or to the high rates of photorespiration.
Although playing an important role in shaping the environment, the mechanisms responsible for runoff initiation and yield in arid and semiarid regions are not yet fully explored. With infiltration-excess overland flow, known also as Hortonian overland flow (HOF) taking place in these areas, the uppermost surface 'skin' plays a cardinal role in runoff initiation and yield. Over large areas, this skin is composed of biocrusts, a variety of autotrophs (principally cyanobacteria, green algae, lichens, mosses) accompanied by heterotrophs (such as fungi, bacteria, archaea), which may largely dictate the infiltration capability of the surface. With most biocrust organisms being capable of excreting extracellular polymeric substances (EPS or exopolymers), and growing evidence pointing to the capability of certain EPS to partially seal the surface, EPS may play a cardinal role in hindering infiltration and triggering HOF. Yet, despite this logic thread, great controversy still exists regarding the main mechanisms responsible for runoff generation (runoff initiation and yield). Elucidation of the possible role played by EPS in runoff generation is the focus of the current review.
Primary amoebic meningoencephalitis (PAM) was induced in mice by intranasal inoculation of Naegleria fowleri (Singh et Das, 1970) to study the role of the blood vessels and lungs in the early and later stages in this disease. Upon culturing blood and lung tissue obtained at 24-, 36-, 48-, 72-, 96-, and 120-hour time periods, it was found that amoebae grew only from blood and lung tissue obtained at the 96 and 120 hour time periods. Paraffin sections of the head revealed small foci of acute inflammation and amoebae within the olfactory bulb of the central nervous system (CNS) at 24 hours. Amoebae were not observed within blood vessels of the CNS until 96 and 120 hours. Also, amoebae were observed within the connective tissue surrounding blood vessels and sutures of the skull, bone marrow, and venous sinusoids between the skull bone tables at 96 and 120 hours. No amoebae or acute inflammatory reactions were observed in the lung sections from any time period and indirect immunofluorescence microscopy was negative for N. fowleri. This study provides evidence that neither blood vessels nor lungs provide routes for N. fowleri to the CNS during the early stages of PAM and that amoebae enter veins of the CNS and bone marrow during later stages of the disease.
Carbon dioxide interacts both with reactive nitrogen species and reactive oxygen species. In the presence of superoxide, NO reacts to form peroxynitrite that reacts with CO2 to give nitrosoperoxycarbonate. This compound rearranges to nitrocarbonate which is prone to further reactions. In an aqueous environment, the most probable reaction is hydrolysis producing carbonate and nitrate. Thus the net effect of CO2 is scavenging of peroxynitrite and prevention of nitration and oxidative damage. However, in a nonpolar environment of membranes, nitrocarbonate undergoes other reactions leading to nitration of proteins and oxidative damage. When NO reacts with oxygen in the absence of superoxide, a nitrating species N2O3 is formed. CO2 interacts with N2O3 to produce a nitrosyl compound that, under physiological pH, is hydrolyzed to nitrous and carbonic acid. In this way, CO2 also prevents nitration reactions. CO2 protects superoxide dismutase against oxidative damage induced by hydrogen peroxide. However, in this reaction carbonate radicals are formed which can propagate the oxidative damage. It was found that hypercapnia in vivo protects against the damaging effects of ischemia or hypoxia. Several mechanisms have been suggested to explain the protective role of CO2 in vivo. The most significant appears to be stabilization of the iron-transferrin complex which prevents the involvement of iron ions in the initiation of free radical reactions., A. Veselá, J. Wilhelm., and Obsahuje bibliografii
Chronic heart failure has become a significant health problem. Cardiac surgery has an important role in the treatment of patients with heart failure. There are traditional surgical techniques in cardiac surgery – coronary revascularization, valve surgery, ventricular reconstructive surgery as well as new surgical techniques – cardiac support device (CorCap), mechanical circulatory support and resynchronization therapy. Cardiac surgery has a definitive role in the treatment algorithm for chronic heart failure., J. Pirk., and Obsahuje seznam literatury
To evaluate the role of chloride in the pathogenesis of salt-dependent deoxycorticosterone (DOC) hypertension, we studied young Wistar rats chronically loaded with sodium bicarbonate (NaHCO3) or sodium chloride (NaCl) which were administered either in the diet or in the drinking fluid. Selective sodium loading (without chloride) increased blood pressure (BP) in DOC-treated animals only if NaHCO3 was provided in the diet. In contrast, no significant blood pressure changes were induced by DOC treatment in rats drinking NaHCO3 solution. Hypernatremia and high plasma osmolality occurred only in rats drinking NaCl or NaHCO3 solutions. Compared to great volume expansion in NaCl-loaded DOC-treated rats, the degree of extracellular fluid volume expansion (namely of its interstitial fraction) was substantially lower in both NaHCO3-loaded groups in which significant hypokalemia was observed. NaHCO3-drinking rats without significant blood pressure response to DOC treatment represented the only experimental group in which blood volume was not expanded. In conclusion, our data confirm previous observations that NaHCO3 loading is less potent in eliciting DOC hypertension than NaCl loading, but blood pressure rise in rats fed NaHCO3 diet clearly demonstrated that selective sodium loading could potentiate the development of DOC hypertension if NaHCO3 is offered within the appropriate dietary regimen. The reasons for the failure of NaHCO3-drinking rats to elevate blood pressure in response to chronic mineralocorticoid treatment are not obvious. However, the absence of a significant plasma volume expansion together with hypernatremia and increased plasma osmolality suggest a considerable degree of dehydration in these animals which fail to increase their fluid consumption compared to water drinking rats.
Traditionally, the dorsal column-medial lemniscus system has been viewed as a pathway not involved in pain perception. However, recent clinical and experimental studies have provided compelling evidence that implicates an important role of the dorsal column pathway in relaying visceral nociceptive information. Several clinical studies have shown that a small lesion that interrupts fibers of the dorsal columns (DC) that ascend close
to the midline of the spinal cord significantly relieves pain and decreases analgesic requirements in patients suffering from cancer originating in
visceral organs. Behavioral, electrophysiological and immunohistochemical methods used under experimental situations in animals showed that DC lesion lead to decreased activation of thalamic and gracile neurons by visceral stimuli, suppressed inhibition of exploratory activity induced by visceral noxious stimulation and prevented potentiation of visceromotor reflex evoked by colorectal distention under inflammatory conditions. Whereas the surgical lesion of the DC tract has proven to be clinically successful, a pharmacological approach would be a better strategy to block this pathway and thus to improve visceral pain conditions under less dramatic circumstances than cancer pain. Our finding that PSDC neurons start to express receptors for substance P after colon inflammation suggests new targets for the development of pharmacological strategies for the control of visceral pain.
a1_Vascular resistance in the mammalian pulmonary circulation is affected by many endogenous agents that influence vascular smooth muscle, right ventricular myocardium, endothelial function, collagen and elastin deposition, and fluid balance. When the balance of these agents is disturbed, e.g. by airway hypoxia from high altitude or pulmonary obstructive disorders, pulmonary hypertension ensues, as characterized by elevated pulmonary artery pressure (PPA). Among neuropeptides with local pulmonary artery pressor effects are endothelin-1 (ET-1), angiotensin II (AII), and substance P, and among mitigating peptides are calcitonin gene-related peptide (CGRP), adrenomedullin (ADM), atrial natriuretic peptide (ANP), vasoactive intestinal peptide (VIP) and ET-3. Moreover, somatostatin28 (SOM28) exacerbates, whereas SOM14 decreases PPA in hypoxic rats, with lowering and increasing of lung CGRP levels, respectively. Pressure can also be modulated by increasing or decreasing plasma volume (VIP and ANP, respectively), or by induction or suppression of vascular tissue remodeling (ET-1 and CGRP, respectively). Peptide bioavailability and potency can be regulated through hypoxic up- and down- regulation of synthesis or release, activation by converting enzymes (ACE for AII and ECE for ET-1), inactivation by neutral endopeptidase and proteases, or by interaction with nitric oxide (NO). Moreover, altered receptor density and affinity can account for changed peptide efficacy. For example, upregulation of ETA receptors and ET-1 synthesis occurs in the hypoxic lung concomitantly with reduced CGRP release. Also, receptor activity modifying protein 2 (RAMP2) has been shown to confer ADM affinity to the pulmonary calcitonin-receptor-like receptor (CRLR). We recently detected the mRNA encoding for RAMP2, CRLR, and the CGRP receptor RDC-1 in rat lung., a2_The search for an effective, lung selective treatment of pulmonary hypertension will likely benefit from exploring the imbalance and restoring the balance between these native modulators of intrapulmonary pressure. For example, blocking of the ET-1 receptor ETA and vasodilation by supplemental CGRP delivered i. v. or via airway gene transfer, have proven to be useful experimentally., I. M. Keith., and Obsahuje bibliografii
Gastrointestinal hormones play an important role in the neuroendocrine regulation of food intake and postprandial satiety. Ghrelin is a 28-amino acid orexigenic peptide produced mainly by the stomach that is involved in both the long-term regulation of body weight and the short-term regulation of postprandial satiety. Impairments in ghrelin secretion may in concert with other factors play an important role in the development of both obesity and anorexia nervosa. Despite an intensive research the critical factors regulating physiological postprandial ghrelin response in healthy individuals and its modification by the presence of obesity and anorexia nervosa are only partially understood. The potential contribution of ghrelin to the differences of diet- vs. surgical-induced weight losses in morbidly obese patients is now also being recognized. The aim of this review is to summarize the current knowledge about the physiology and pathophysiology of ghrelin and to discuss its potential in the prevention and/or treatment of obesity and anorexia nervosa., I. Dostálová, M. Haluzík., and Obsahuje seznam literatury
This paper looks at housing strategy in a wider social and economic context and argues that a household’s (class) position in society depends on important life decisions, one of the most important of which is a person’s employment strategy and preparation for the period of retirement (pensions), which is related to housing decisions. The main context of these decisions is the welfare regime, but also a country’s economic structure (varieties of capitalism) and housing system (tax and subsidy elements of programmes). However, as the paper argues, these systems are also changing in relation to the macro effect of individual decisions.