Calorimetric Studies of Behavior, Metabolism and Energetics of Sessile Intertidal Animals

SYNOPSIS: Behaviors to conserve water during intertidal exposureat the same time impair respiratory gas exchange, so that observedresponses to emersion may reflect compromises between theseincompatible needs. Behavioral isolation of the tissues fromair results in the complete or partial reliance on anoxic energymetabolism, which is most reliably measured directly as heatdissipation. Combined direct calorimetry and indirect calorimetry(respirometry) enable the partitioning of total metabolic heatdissipation into its aerobic and anoxic components, which mayvary according to physical and biological factors. The musselMytilus edulis is tolerant of anoxia and saves water and energyduring aerial exposure in its rocky intertidal habitat by closingits shell valves and becoming largely anoxic. Like most suspensionfeeders in this habitat, its compensation for reduced feedingtime involves energy conservation; there is little evidencefor energy supplementation such as increases in feeding rateor absorption efficiency. Ammonia production continues duringaerial exposure and is involved in acid-base balance in thehemolymph and mantle cavity fluid. Infaunal cockles (Cardiumedule) and mussels (Geukensia demissa) gape their shell valves,remain largely aerobic and have high rates of heat dissipationduring intertidal exposure, a response which appears relatedto the lower desiccation potential and exploitation of richertrophic resources in their soft-sediment habitats. The variableexpansion of the symbiotic sea anemone Anthopleura elegantissimareflects interaction among the responses to desiccation, irradianceand continued photosynthesis by its zooxanthellae during exposureto air.     

Relationship of Cellular Energetics to RNA Metabolism in Tetrahymena pyriformis W.*

Cultures of Tetrahymena pyriformis in a non-nutrient buffer degrade RNA and excrete hypoxanthine, uracil and orthophosphate. Glucose addition leads to the retention of a portion of the purine, pyrimidine, and orthophosphate by the cells; however, the hexose has little influence on the RNA level. Acetate supplementation has no effect on RNA degradation or on the distribution of the catabolic products between the cells and the environment. Interruption of oxidative phosphorylation by 2,4-dinitrophenol results in an increase in RNA degradation. This action is annulled by the glycolytic substrate, glucose, but not by acetate. A combination of iodoacetic acid and glucose blocks glycolysis and increases cellular RNA loss which can be reversed by the addition of the citric acid cycle substrate, acetate. These findings suggest that the available cellular energy supply in starved cells is sufficient to regulate the rate of RNA degradation. Disruption of ATP generation by the appropriate inhibitors, however, allows the demonstration of the importance of energy-yielding reactions in the determination of the amount of nucleic acid loss. It appears that glycolysis and oxidative phosphorylation are equally efficient in sustaining the regulatory process. RNA synthesis during starvation conditions is a discontinuous process with a sharp rate change after 30 min of incubation. 2,4-Dinitrophenol inhibits [2-¹⁴C] uracil incorporation into the nucleic acid. Glucose does not annul the inhibition of synthesis in contrast to the influence of the hexose on RNA degradation. This observation demonstrates that the synthetic and degradative processes are not directly coupled. Glycogen synthesis and RNA degradation appear to compete for the available energy supply and respond in a similar fashion to the metabolic inhibitors and carbon sources.     

Using Cellular Automata for Parking Recommendations in Smart Environments

In this work, we propose an innovative adaptive recommendation mechanism for smart parking. The cognitive RF module will transmit the vehicle location information and the parking space requirements to the parking congestion computing center (PCCC) when the driver must find a parking space. Moreover, for the parking spaces, we use a cellular automata (CA) model mechanism that can adjust to full and not full parking lot situations. Here, the PCCC can compute the nearest parking lot, the parking lot status and the current or opposite driving direction with the vehicle location information. By considering the driving direction, we can determine when the vehicles must turn around and thus reduce road congestion and speed up finding a parking space. The recommendation will be sent to the drivers through a wireless communication cognitive radio (CR) model after the computation and analysis by the PCCC. The current study evaluates the performance of this approach by conducting computer simulations. The simulation results show the strengths of the proposed smart parking mechanism in terms of avoiding increased congestion and decreasing the time to find a parking space.     

Matriptase Autoactivation Is Tightly Regulated by the Cellular Chemical Environments

The ability of cells to rapidly detect and react to alterations in their chemical environment, such as pH, ionic strength and redox potential, is essential for cell function and survival. We present here evidence that cells can respond to such environmental alterations by rapid induction of matriptase autoactivation. Specifically, we show that matriptase autoactivation can occur spontaneously at physiological pH, and is significantly enhanced by acidic pH, both in a cell-free system and in living cells. The acid-accelerated autoactivation can be attenuated by chloride, a property that may be part of a safety mechanism to prevent unregulated matriptase autoactivation. Additionally, the thio-redox balance of the environment also modulates matriptase autoactivation. Using the cell-free system, we show that matriptase autoactivation is suppressed by cytosolic reductive factors, with this cytosolic suppression being reverted by the addition of oxidizing agents. In living cells, we observed rapid induction of matriptase autoactivation upon exposure to toxic metal ions known to induce oxidative stress, including CoCl₂ and CdCl₂. The metal-induced matriptase autoactivation is suppressed by N-acetylcysteine, supporting the putative role of altered cellular redox state in metal induced matriptase autoactivation. Furthermore, matriptase knockdown rendered cells more susceptible to CdCl₂-induced cell death compared to control cells. This observation implies that the metal-induced matriptase autoactivation confers cells with the ability to survive exposure to toxic metals and/or oxidative stress. Our results suggest that matriptase can act as a cellular sensor of the chemical environment of the cell that allows the cell to respond to and protect itself from changes in the chemical milieu.     

Restoring Cellular Energetics Promotes Axonal Regeneration and Functional Recovery after Spinal Cord Injury

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High NaCl Promotes Cellular Senescence

High extracellular NaCl was previously shown to increase the number of DNA breaks in mammalian cells in tissue culture, renal medullary cells in vivo, C. elegans, and marine invertebrates. It was also shown to increase reactive oxygen species in renal cells, resulting in oxidation of proteins and DNA. Cellular senescence is a common response to such damage. Therefore, in the present studies we looked for signs of senescence in cells exposed to high NaCl. We find that (1) The rate of proliferation of HeLa cells exposed to high NaCl decreases gradually to the point of arrest, and the cells display signs of senescence, including hypertrophy and increased auto fluorescence. (2) High NaCl accelerates the appearance of senescence in primary mouse embryonic fibroblasts, as measured by β-galactosidase activity (SA-β-gal). (3) High NaCl retards growth and markedly decreases the life span of C. elegans, accompanied by features of accelerated aging, such as decreased locomotion and increased number of SA-β-gal positive cells. (4) Mouse renal medullary cells, which are normally continuously exposed to high NaCl, express increased p16^INK4 (another indicator of senescence) much earlier than do cells in the renal cortex, which has the same level of NaCl as peripheral blood. We conclude that high NaCl accelerates cellular senescence and aging, most likely secondary to the DNA breaks and oxidative damage that it causes.     

Energetics of sodium efflux from Escherichia coli

When energy-starved cells of Escherichia coli were passively loaded with 22Na+, efflux of sodium could be initiated by addition of a source of metabolic energy. Conditions were established where the source of energy was phosphate bond energy, an electrochemical proton gradient, or both. Only an electrochemical proton gradient was required for efflux from intact cells. These results are consistent with secondary exchange of Na+ for H+ catalyzed by a sodium/proton antiporter.     

A 3-D Propagation Model for Emerging Land Mobile Radio Cellular Environments

A tunable stochastic geometry based Three-Dimensional (3-D) scattering model for emerging land mobile radio cellular systems is proposed. Uniformly distributed scattering objects are assumed around the Mobile Station (MS) bounded within an ellipsoidal shaped Scattering Region (SR) hollowed with an elliptically-cylindric scattering free region in immediate vicinity of MS. To ensure the degree of expected accuracy, the proposed model is designed to be tunable (as required) with nine degrees of freedom, unlike its counterparts in the existing literature. The outer and inner boundaries of SR are designed as independently scalable along all the axes and rotatable in horizontal plane around their origin centered at MS. The elevated Base Station (BS) is considered outside the SR at a certain adjustable distance and height w.r.t. position of MS. Closed-form analytical expressions for joint and marginal Probability Density Functions (PDFs) of Angle-of-Arrival (AoA) and Time-of-Arrival (ToA) are derived for both up- and down-links. The obtained analytical results for angular and temporal statistics of the channel are presented along with a thorough analysis. The impact of various physical model parameters on angular and temporal characteristics of the channel is presented, which reveals the comprehensive insight on the proposed results. To evaluate the robustness of the proposed analytical model, a comparison with experimental datasets and simulation results is also presented. The obtained analytical results for PDF of AoA observed at BS are seen to fit a vast range of empirical datasets in the literature taken for various outdoor propagation environments. In order to establish the validity of the obtained analytical results for spatial and temporal characteristics of the channel, a comparison of the proposed analytical results with the simulation results is shown, which illustrates a good fit for 10⁷ scattering points. Moreover, the proposed model is shown to degenerate to various notable geometric models in the literature by an appropriate choice of a few parameters.     

Energetics of transport

Conclusion It has been possible to present in this short review a rather circumscribed picture of the field concerning the utilization of energy for the transport of substances. I have specifically considered metabolic energy and to a large degree have emphasized bulk transport and sodium transport. One important part of the field, the transport of non-electrolytes, has been omitted in this essay. Uphill transport of sugars, for example, is well known to require metabolic energy and certainly merits discussion in an article of this kind. Some idea of matters unwillingly or unwittingly slighted by this author can be derived from any one of numerous excellent recent reviews, e.g. that of the Hokins [43]. The choices of topic that have been made stem from the specific interests of the author, and the major emphasis of the literature. The viewpoint of this essay also stems in marked degree from the atmosphere, discussion and general sense of exploration of the Frascati meeting. The important objective has been to emphasize the nature ot information already achieved, and to point up a few of the matters that should yield to probing in the next few years — especially the matter of the detailed mechanisms of ATP involvement in transport processes.     

Energetics of kayaking

The metabolic cost of paddling at low speeds (v) was measured from oxygen uptake (VO2) and anaerobic glycolysis in an annular pool or calculated from submaximal VO2 measured at higher speeds when the kayaker was assisted in overcoming water resistance. Also calculated were the total drag (D) and the net mechanical efficiency (e). Each of the above variables was determined in male (n = 17) and female (n = 7) kayakers ranging in experience from beginners to elite. The VO2 increased with v to a peak of approximately 3.4 l.min-1 (80%-100% of peak VO2 during running) in men and of approximately 2.8 l.min-1 in women, while at higher speeds the additional energy was accounted for by anaerobic glycolysis. In all subjects the energy cost to paddle a given distance (C) increased according to a power function with increasing v. The C was lower for the elite male paddlers than for the unskilled group, while that for elite women was slightly less than that for the elite men. Also the rates of increase of C appeared to be inversely proportional to the subjects' skill. Total D for elite men increased from approximately 15 to 60 N over a range of speeds from 1 to 2.2 m.s-1 while those of unskilled men and skilled women for the same speed range were 10-20 N greater and slightly less, respectively. The e increased linearly, but at a different rate, with increases in v for the unskilled and the elite kayakers (males and females) being 4.2% and 6%, respectively, at v = 1.2 m.s-1.     

Light-dependent Emission of Hydrogen Sulfide from Plants

With the aid of a sulfur-specific flame photometric detector, an emission of volatile sulfur was detected from leaves of cucumber (Cucumis sativus L.), squash and pumpkin (Cucurbita pepo L.), cantaloupe (Cucumis melo L.), corn (Zea mays L.), soybean (Glycine max [L.] Merr.) and cotton (Gossypium hirsutum L.). The emission was studied in detail in squash and pumpkin. It occurred following treatment of the roots of plants with sulfate and was markedly higher from either detached leaves treated via the cut petiole, or whole plants treated via mechanically injured roots. Bisulfite elicited higher rates of emission than sulfate. The emission was completely light-dependent and increased with light intensity. The rate of emission rose to a maximum and then declined steadily toward zero in the course of a few hours. However, emission resumed after reinjury of roots, an increase in light intensity, an increase in sulfur anion concentration, or a dark period of several hours.

The emission was identified as H₂S by the following criteria: it had the odor of H₂S; it was not trapped by distilled H₂O, but was trapped by acidic CdCl₂ resulting in the formation of a yellow precipitate, CdS; it was also trapped by base and the contents of the trap formed methylene blue when reacted with N,N-dimethyl-p-phenylenediamine and Fe³⁺.

H₂S emission is not the cause of leaf injury by SO₂, since bisulfite produced SO₂ injury symptoms in dim light when H₂S emission was low, while sulfate did not produce injury symptoms in bright light when H₂S emission was high.

The maximum rates of emission observed, about 8 nmol min⁻¹ g fresh weight⁻¹, are about the activity that would be expected for the sulfur assimilation pathway of a normal leaf. H₂S emission may be a means by which the plant can rid itself of excess inorganic sulfur when HS⁻ acceptors are not available in sufficient quantity.