[Measurements of extracellular water space in healthy children].
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Adolescent↗
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Ultrastructural cytochemistry of iron absorption.
Conventional ultrastructural autoradiographic and morphologic studies of the duodenal mucosal cell have generally corroborated physiologic observations of iron absorption, but such methods have limited resolution and fail to distinguish ferric and ferrous iron. This study describes the application of the Prussian blue reaction as an electron microscopic cytochemical stain to the investigation of inorganic iron absorption in iron-deficient, normal, and iron-loaded rats. Ferrous iron is converted to ferric iron at the microvillus membrane. Subsequently intraepithelial ferric iron appears bound to a non-heme acceptor substance in microvilli and later appears as small non-membrane-bound stain deposits which are concentrated in the apical cytoplasm. The appearance of larger stain deposits in the lateral intercellular spaces, in the basal extracellular spaces, and along the intraluminal and extraluminal outer plasmalemma of adjacent endothelial cells of the lamina propria suggests passage of iron from epithelial cells through the lamina propria to blood vessels. The extreme sensitivity of the method compared with simultaneous ultrastructural autoradiographic techniques is demonstrated and suggests usefulness of the method in further studies of iron metabolism.
Animals↗
Identification and characterization of a cDNA encoding a neuronal glutamate transporter from Drosophila melanogaster.
Sodium-dependent glutamate transporters influence neurotransmission in the central nervous system by removing synaptically released glutamate from the extracellular space and by maintaining extracellular glutamate concentrations below neurotoxic levels. In insects, glutamate also serves as the neurotransmitter at the neuromuscular junction, but the mechanism for neurotransmitter clearance at this synapse has not well-established. Here we report that cloning and characterization of a sodium-dependent glutamate transporter, dEAAT, from Drosophila melanogaster. The 479 amino acid dEAAT gene product is 40-50% homologous to mammalian members of this carrier family. A 3.3 kilobase (kb) transcript for dEAAT was detected in adult fly heads and to a lesser extent in bodies by Northern-blot analysis and was also localized to neurons in the central nervous system by in situ hybridization. The transport activity observed following express of dEAAT in Xenopus oocytes or COS-7 cells shows a high affinity for L-glutamate, L-aspartate and D-aspartate, an absolute dependence on external sodium ions, and considerable stereoselectivity for the transport of L-glutamate over D-glutamate. As has been observed for the human carriers, EAAT 4 and EAAT 5, a significant component of the current activated by L-glutamate application to dEAAT-expressing oocytes appears to arise from the activation of a chloride channel associated with the carrier.
ATP-Binding Cassette Transporters↗
Effect of venous stasis and physical exercise on plasma extracellular-superoxide dismutase.
The secretory protein extracellular-superoxide dismutase is the major superoxide dismutase (SOD) isoenzyme in the extracellular space. There is evidence to suggest that most extracellular-superoxide dismutase in the vascular system is bound to endothelial cell surfaces. Venous stasis and physical exercise is known to induce release of several endothelium-associated factors into the plasma. However, venous stasis and physical exercise were not found to induce any release of extracellular-superoxide dismutase into plasma. The plasma activity of the intracellular isoenzyme CuZn SOD was doubled by venous stasis.
Adult↗
Adenoma of type 2 pneumocytes with oncocytic features.
An adenoma of type 2 pneumocytes in the periphery of the left lung was an incidental finding at the autopsy of a 28-year-old woman. Light microscopy revealed a predominantly papillary growth with oncocytic features. Ultrastructurally, multilaminated bodies and many mitochondria were found in the tumor cells and tubular myelin in the extracellular spaces. Immunohistochemistry revealed surfactant apoprotein in tumor cells and extracellularly.
Adenoma↗
A stopped flow capillary perfusion method to evaluate contraluminal transport parameters of methylsuccinate from interstitium into renal proximal tubular cells.
In order to study the transport of dicarboxylic acids through the contraluminal cell membrane of proximal tubular cells, 3H- methylsuccinate has been synthetized by catalytic hydration of methylfumarate . As the chromatography of radioactive material excreted in the urine after i.v. injection of 3H- methylsuccinate shows, no metabolite is detectable during the first 3 min. After 10 min, less than 10% of the excreted radiolabel is metabolized. To measure the contraluminal influx of 3H- methylsuccinate from the interstitium into cortical tubular cells, the renal vessels were clamped so that the proximal tubular lumina collapsed. Then Ringer solution was injected into the blood capillaries. It contained different concentrations of 3H- methylsuccinate and 14C-inulin as extracellular space marker. After contact times between 1 and 10 s, this fluid was withdrawn from the capillaries and the disappearance of 3H- methylsuccinate relative to 14C-inulin was measured. The morphological compartments in the outer cortex of the clamped glutaraldehyde-fixed kidney were evaluated by a stereological method. For proximal tubular cells a ratio of extracellular water space to intracellular space of 1:3.1 and a ratio extracellular water space to free cell water space of 1:2 was found. It was tested whether the experimental disappearance curves with 4 different starting concentrations of 3H- methylsuccinate fit with the data from four model calculations. It was found that the data and the conditions of transport are consistent with the predictions of a facilitated diffusion model.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Alteration of hepatic tissue spaces by platelet-activating factor and phenylephrine.
Mean transit times for the movement of extracellular and intracellular reference compounds through isolated perfused rat livers were determined during exposure of livers to platelet-activating factor (AGEPC; 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine) and the alpha-adrenergic agonist phenylephrine, using the multiple indicator dilution technique. From the outflow profiles of rapid bolus injections of 3H-sucrose and 14C-urea given to the liver, the estimated intracellular volume of distribution of small freely permeant substances, Vi, and the ratio of intracellular to extracellular space, were computed. Exposure of the liver to AGEPC decreased Vi and by 32 and 34%, respectively, from control values, whereas infusion of phenylephrine increased Vi by 16% and by 33%. The results indicate that the hemodynamic effects of AGEPC in perfused rat liver cause the apparent loss of tissue space accessible to small permeant compounds. Phenylephrine, although increasing hepatic vascular resistance, measured at the portal vein, by the same magnitude as AGEPC, led to an increase in the apparent tissue space accessible to this same species.
Animals↗
Long-term sodium balance in humans in a terrestrial space station simulation study.
BACKGROUND: Sodium accumulation has been considered to take place in the extracellular space, leading to water retention and weight gain. This traditional view has been questioned by recent studies that showed sodium accumulation in humans without expansion of the extracellular volume. We investigated sodium balance and its impact on body weight (BW) during a long-term balance study. METHODS: Three healthy subjects were confined to a terrestrial MIR simulator for 135 days under conditions simulating a long-term spaceflight. During the entire isolation period, we meticulously measured daily sodium balance and its contribution to BW. RESULTS: During the study period, subjects accumulated between 2,973 and 7,324 mmol of sodium and gained between 5.1 and 9.3 kg in weight. In all subjects, there was a positive correlation between changes in total-body sodium (DeltaTBS) content and BW, reflecting sodium-associated volume expansion. However, toward the end of isolation, sodium gain exceeded weight gain, suggesting that sodium accumulated in an osmotically inactive form. Especially at the onset of the experiment, two subjects showed inverse correlations between DeltaTBS and BW. CONCLUSION: The finding of sodium gain without weight gain is in contradiction to the widely accepted theory that changes in TBS levels are accompanied by changes in extracellular volume. We suggest the existence of a sodium reservoir with the ability to store significant amounts of sodium in an osmotically inactive form. This reservoir might be located in bone, dense connective tissue, or cartilage.
Adult↗
Ca2+ influx into leech glial cells and neurones caused by pharmacologically distinct glutamate receptors.
The effect of glutamatergic agonists on the intracellular free Ca2+ concentration ([Ca2+]i) of neuropile glial cells and Retzius neurones in intact segmental ganglia of the medicinal leech Hirudo medicinalis was investigated by using iontophoretically injected fura-2. In physiological Ringer solution the [Ca2+]i levels of both cell types were almost the same (glial cells: 58 +/- 30 nM, n = 51; Retzius neurones: 61 +/- 27 nM, n = 64). In both cell types glutamate, kainate, and quisqualate induced an increase in [Ca2+]i which was inhibited by 6,7-dinitroquinoxaline-2,3-dione (DNQX). This increase was caused by a Ca2+ influx from the extracellular space because the response was greatly diminished upon removal of extracellular Ca2+. The glutamate receptors of neuropile glial cells and Retzius neurones differed with respect to the relative effectiveness of the agonists used, as well as with regard to the inhibitory strength of DNQX. In Retzius neurones the agonist-induced [Ca2+]i increase was abolished after replacing extracellular Na+ by organic cations or by mM amounts of Ni2+, whereas in glial cells the [Ca2+]i increase was largely preserved under both conditions. It is concluded that in Retzius neurones the Ca2+ influx is predominantly mediated by voltage-dependent Ca2+ channels, whereas in neuropile glial cells the major influx occurs via the ion channels that are associated with the glutamate receptors.
Animals↗
Relationship of cerebral blood flow disturbances with brain oedema formation.
Brain oedema is an important factor which compromises maintenance of the cerebral blood flow. Conversely, primary blood flow disturbances are leading to brain oedema. The mechanisms underlying blood flow impairment by brain oedema are associated with an increased regional tissue pressure in proportion to the degree of water accumulation in the parenchyma. The release of vasoactive mediator compounds might be considered in addition. Primary disturbances of the cerebral blood flow, such as focal or global cerebral ischaemia are leading to an increased cerebral water content. A decrease of the cerebral blood flow to ca. 40% of normal or below has been found to result in the development of brain oedema. This flow threshold is in the neighbourhood of the ischaemic flow level causing irreversible tissue damage. Whereas in focal ischaemia oedema formation is a function of the severity of the flow decrease, it is a pathophysiological hallmark of early postischaemic recirculation in global cerebral ischaemia. Nevertheless, during complete interruption of cerebral blood flow translocation of interstitial fluid into the intracellular compartment occurs as manifestation of ischaemic cell swelling. Cell swelling under these conditions may, however, not necessarily indicate cell damage, but more likely a compensatory response attributable to the uptake of excitotoxic transmitters such as glutamate, and of K(+)-ions which are excessively released at the onset of ischaemia into the extracellular space. Purpose of the swelling process, thus, is clearance of extracellular fluid from this material to re-establish homeostasis.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Nigericin enhances mafosfamide cytotoxicity at low extracellular pH.
The cytotoxicity of many alkylating anticancer drugs is increased at reduced intracellular pH (pHi). The therapeutic index of such agents could therefore be improved by lowering pHi in the target cells prior to their application. We have previously demonstrated that the formation of lactic acid can be selectively enhanced in malignant tissues via glucose-mediated stimulation of tumor cell glycolysis. However, the resulting reduction in pHi is partly compensated by the extrusion of H+ equivalents into the extracellular space, with pHi remaining closer to the physiological value than extracellular pH (pHe). For full exploitation of the proton-mediated increase in the cytotoxicity of alkylating agents, pHi should therefore be equilibrated with pHe in lactic acid-producing cells. In the present study we investigated the question as to whether nigericin, an H+/K+ antiporter enabling the entry into cells of H+ ions at low pHe, can be used to enhance the cytotoxic effect of mafosfamide (MAFO; a precursor of "activated" cyclophosphamide) on cultured M1R rat mammary carcinoma cells. At pHe 7.4, the cytotoxic effect of combined treatment with MAFO and nigericin was not superior to treatment with MAFO alone. At acidic pHe, however, MAFO cytotoxicity was potentiated by nigericin as indicated by the colony-forming capacity of M1R cells. For example, at pHe 6.2 (corresponding to the approximate mean "aggregated pH" in actively glycolyzing tumors), the colony-forming fraction of cells treated with a combination of MAFO and nigericin was 3 x 10(-5) that of controls, as compared with a value of 5 x 10(-2) found for cells exposed to MAFO alone. These results suggest that agents counteracting cellular mechanisms that control pHi may be candidate compounds for investigations aimed at the enhancement of alkylating drug cytotoxicity following glucose-mediated pH reduction in malignant tumors in vivo.
Animals↗
Extracellular superoxide dismutase.
The extracellular space is protected from oxidant stress by the antioxidant enzyme extracellular superoxide dismutase (EC-SOD), which is highly expressed in selected tissues including blood vessels, heart, lungs, kidney and placenta. EC-SOD contains a unique heparin-binding domain at its carboxy-terminus that establishes localization to the extracellular matrix where the enzyme scavenges superoxide anion. The EC-SOD heparin-binding domain can be removed by proteolytic cleavage, releasing active enzyme into the extracellular fluid. In addition to protecting against extracellular oxidative damage, EC-SOD, by scavenging superoxide, preserves nitric oxide bioactivity and facilitates hypoxia-induced gene expression. Loss of EC-SOD activity contributes to the pathogenesis of a number of diseases involving tissues with high levels of constitutive extracellular superoxide dismutase expression. A thorough understanding of the biological role of EC-SOD will be invaluable for developing novel therapies to prevent stress by extracellular oxidants.
Animals↗
Modelling the periodicity of cardiac muscle.
The intractable problem of modelling cardiac muscle of arbitrary extent while preserving cellular structure has been solved using an analytical rather than numerical approach with a method called two-scale asymptotic analysis. In this method, the myocardium was modelled as a collection of bundles arranged periodically in space and connected by junctions, and the distribution of the steady-state potential and current density was determined. The potential both along and across fibers was found to contain a distinct periodic component that determines the transmembrane potential. The magnitude of the transmembrane potential depends on the gradient of applied potential, the dimensions of the bundles, and their internal conductivity. Current flows primarily in the extracellular space, and the extracellular pathway also determines the apparent conductivity of cardiac muscle.
Electric Conductivity↗
[So-called fibrous long-spacing collagen in a murine osteosarcoma (author's transl) ].
Peculiar periodically banded structures were found in the extracellular spaces of a vascular type of a murine osteosarcoma. The structures consisted of fine almost parallely arranged filaments with electron-dense cross-bands of about 35-50 nm thickness. The periodicity of the bands was about 85-100 nm. Similar structures have been found by many authors in various tissues of different species. Commonly, they have been referred to as "fibrous long-spacing collagen".
Animals↗
Collagen phagocytosis by fibroblasts in the periodontal ligament of the mouse molar during the initial phase of hypofunction.
This study was undertaken in order to determine whether hypofunction of teeth is associated with changes in collagen phagocytosis by fibroblasts of the periodontal ligament. In mice, the lower right molars were extracted and the animals killed one, two, three, four, or seven days later. The maxillary first molars with their surrounding periodontium were processed for electron microscopy and their periodontal ligament subjected to morphometric analysis. It was observed that, whereas the volume density of extracellular collagen in the ligament of the hypofunctional molars decreased from 50% to 30% during the course of the experiment, the fraction of fibrillar collagen ingested by the cells increased over two-fold. This increase was already manifest very shortly after the onset of the experiment and offers an explanation for the net loss of collagen fibrils from the extracellular space.
Animals↗
Diffusion from gel in brain: modelisation and identification.
A mathematical model is proposed for describing the mechanism of diffusion from gel (Tissucol) into the extracellular space. After diffusion of the antibiotic in one dimension, the gradient concentration was determined with microvoltametric electrodes. These microelectrodes measure the free diffusible form of electroactive antibiotics in the extracellular brain space. The aim of this study was to find simultaneously the coefficient of diffusion and extraction of some antibiotics (in our case the Fotemustin) using the Alienor Algorithm. These coefficients are useful for predicting the concentration gradient into abscesses, fibrin, etc.
Algorithms↗
The role of extracellular potassium in hippocampal epilepsy.
It has been proposed that the notable capacity for epileptogenesis in the hippocampus may be related to potassium accumulation in extracellular spaces. To investigate this hypothesis more directly, we measured changes in extracellular potassium concentration ([K+]o) during focal hippocampal epilepsy using potassium-sensitive microelectrodes. Interictal and ictal electroencephalographic events were accompanied by increases in [K+]o that varied systematically with depth from the ependymal surface and lateral distance from the focus. Maximal [K+]o changes during interictal and ictal discharges occurred in the stratum pyramidale. Initiation of ictal activity did not correlate with a particular "threshold" [K+]o. Comparing these results with similar data from neocortex, we observed that interictal K+ responses in hippocampus lasted longer and had slower rise times, and that peak interictal and ictal [K+]o values were consistently lower. Increases in [K+]o cannot be the sole explanation for regional variations in seizure susceptibility, interictal-ictal transitions, or termination of ictal episodes.
Animals↗
Intracellular pH of isolated rat diaphragm muscle with metabolic and respiratory changes of extracellular pH.
Relationships between intracellular and extracellular pH isolated rat diaphragms were determined both during respiratory and metabolic changes of extracellular pH. Metabolic changes of extracellular pH were produced by varying bicarbonate concentration of the suspending Krebs-Ringer solution and respiratory changes were produced by varying PCO2 of the suspending medium. At any defined extracellular pH, the bicarbonate concentration ratios between intracellular and extracellular space were the same during both metabolic and respiratory changes of extracellular pH. However, when extracellular pH varied within 7.15 and 7.4 intracellular pH remained essentially constant. In order to maintain the intracellular pH constant during extracellular pH changes, a bicarbonate efflux during metabolic changes from the intracellular compartment, and a bicarbonate influx during respiratory changes to the intracellular compartment must occur. The maintenance of identical intracellular/extracellular bicarbonate concentration ratios regardless of the mechanisms of extracellular pH changes (metabolic or respiratory) suggests an active mechanism for the transport of bicarbonate or H-+ ions.
Acid-Base Equilibrium↗