Ontogeny of Cardiac and Ventilatory Function in the Crayfish Procambarus clarkii

SYNOPSIS. Ontog eny of cardiac and ventilatory function wasinvestigated in the direct developing crayfish Procambarus clarkiito determine basic developmental patterns and to evaluate diffusionaland convective gas exchange. Animals were exposed to water rangingin Po₂ from 150 to less than 10 mmHg. Ontogeny of cardiac functionfollows a pattern unlike that observed in other developing organisms.Heart rate (f_H) decreases from the mid-point of embryonic developmentuntil hatching, and the decrease in f_H is accompanied by a concomitantloss in cardiac and ventilatory sensitivity to hypoxia. Duringlarval development however, f_H increases until a juvenile stageis reached. Heart rate then decreases again as the animal increasesin mass. Cardiac and ventilatory responses to hypoxia are restoredby the third larval instar. Ventilatory function is initiatedwithin hours of hatching. Scaphognathite movement (f_sc), whichis initially uncoordinated, does not result in appreciable movementof water, but functional pumping is achieved within hours ofhatching. Animals do not exhibit an adult-like response to hypoxicexposure until at least the third larval instar. The ontogenyof both cardiac and ventilatory function indicates that thedirect developing crayfish is not physiologically mature untilan early juvenile stage. The drop in embryonic JFH and lossof hypoxic sensitivity late in development may indicate thatoxygen requirements of embryos exceed the capacity of egg membranescapacity (surface area) to supply oxygen by diffusion.     

The Organic Acid Metabolism of Bramley's Seedling Apple Peel1

1. The effect of various Krebs cycle acids on the respirationofdisks of apple peel at various stages of maturity was measuredin a Warburg respirometer.
2. Peel tissue from apples at thepre-climacteric and early post-climactericstages apparentlycontain sufficient of the Krebs cycle acidsused, with the exceptionof succinate, to maintain oxidativeprocesses at a maximum.
3. The addition of malate causes a large increase in the CO₂-outputof peel from post-climacteric and senescent fruit but not frompre-climacteric fruit, and a close correlation exists betweenthe climacteric and this decarboxylation of malate. The decarboxylationof malate does not affect the rate of O₂-uptake of peel tissue.The possible part played by the decarboxylation of malate inthe increased CO₂-output at the climacteric is discussed.
4. Addedpyruvate is decarboxylated by the tissue at all stagesof storagelife.
5. The decarboxylation of added malate is an aerobic fermentation,resulting in the quantitative production of acetaldehyde. Althoughthe presence of oxygen is necessary, the rate of O₂-uptake isnot affected by the reaction. Pyruvate decar boxylation doesnot require the presence of oxygen.
6. The O₂-uptake of peelfrom senescent apples can be stimulatedby addition of malate,succinate, and a-ketoglutarate. No evidencewas obtained, however,of oxidation of fumarate, citrate, orpyruvate. The additionof malate to senescent tissue restoresthe lower endogenousrate of O₂-uptake to that of early postclimacteric tissue.
7. Succinate and fumarate are toxic to peel tissue at concentrationabove 0.02M.

     

Blood Oxygen Transport and Delivery in Reptiles

Cenozoic reptiles are characterized by physiological morphologicaland ecological systems with low energy requirements comparedto those of mammals. Ectothermy and low resting rates of metabolismare the primary physiological adaptations of reptiles that producelow energy demand. Adjustments of the oxygen-transport systemto different thermoregulatory characteristics among reptilesmay be reflected in blood viscosity oxygen capacity oxygen affinityand the temperature sensitivity of oxygenation. Other adaptationsreduce the energy cost of oxygen transport. Reptiles have lowhematocrits and large, widely spaced capillaries that contributeto a low fluid resistance in the vascular system but also limitthe oxygen transport capacity. The low oxygen affinity characteristicof the blood of most reptiles appears to facilitate diffusionof oxygen to the tissues, overcoming the intrinsic limitationsimposed by the morphological specializations of the cardiovascularsystem. The low blood oxygen affinity permits virtually allof the oxygen carried by the blood to be delivered to the tissuesduring periods of stress. It may also help to maintain a relativelyhigh arterial Po₂ even when a right-to-left shunt occurs inthe heart. Reptilian erythrocytes are capable of reducing methemoglobinrapidly. The high concentrations of methemoglobin and polymerizedhemoglobin that occur in vivo may indicate that these compoundshave a functional role. In their blood physiology as in otheraspects of their biology reptiles are specialized animals thatreflect selective forces quite different from those that haveshaped the evolution of mammals.     

Acid Metabolism and Respiration in Succulent Compositae: III. Further Experiments with Kleinia radicans Haw

Evidence has been obtained that starving leaves of Kleinia radicansin the summer condition produce a volatile substance, whichreacts with potassium permanganate, and which accumulates andpoisons the leaves when they are enclosed, as in a Dixon respirometer.A microrespirometer has been designed for use with continuousair-currents. Using this, the course of oxygen intake by leavesin darkness resembles that of CO₂ output (previous results)and shows an initial phase of diurnal fluctuation of O₂ intake.Humidity has also some effect, for an early increase in O₂ intakeoccurs under dry conditions.     

The effects of endothelin-1 on the cardiorespiratory physiology of the freshwater trout (Oncorhynchus mykiss) and the marine dogfish (Squalus acanthias)

The aim of the present study was to evaluate the effects of endothelin-1-elicited cardiovascular events on respiratory gas transfer in the freshwater rainbow trout (Oncorhynchus mykiss) and the marine dogfish (Squalus acanthias). In both species, endothelin-1 (666 pmol kg^-1) caused a rapid (within 4 min) reduction (ca. 30-50 mmHg) in arterial blood partial pressure of O₂. The effects of endothelin-1 on arterial blood partial pressure of CO₂ were not synchronised with the changes in O₂ partial pressure and the responses were markedly different in trout and dogfish. In trout, arterial CO₂ partial pressure was increased transiently by ~1.0 mmHg but the onset of the response was delayed and occurred 12 min after endothelin-1 injection. In contrast, CO₂ partial pressure remained more-or-less constant in dogfish after injection of endothelin-1 and was increased only slightly (~0.1 mmHg) after 60 min. Pre-treatment of trout with bovine carbonic anhydrase (5 mg ml^-1) eliminated the increase in CO₂ partial pressure that was normally observed after endothelin-1 injection. In both species, endothelin-1 injection caused a decrease in arterial blood pH that mirrored the changes in CO₂ partial pressure. Endothelin-1 injection was associated with transient (trout) or persistent (dogfish) hyperventilation as indicated by pronounced increases in breathing frequency and amplitude. In trout, arterial blood pressure remained constant or was decreased slightly and was accompanied by a transient increase in systemic resistance, and a temporary reduction in cardiac output. The decrease in cardiac output was caused solely by a reduction in cardiac frequency; cardiac stroke volume was unaffected. In dogfish, arterial blood pressure was lowered by ~10 mmHg at 6-10 min after endothelin-1 injection but then was rapidly restored to pre-injection levels. The decrease in arterial blood pressure reflected an increase in branchial vascular resistance (as determined using in situ perfused gill preparations) that was accompanied by simultaneous decreases in systemic resistance and cardiac output. Cardiac frequency and stroke volume were reduced by endothelin-1 injection and thus both variables contributed to the changes in cardiac output. We conclude that the net consequences of endothelin-1 on arterial blood gases result from the opposing effects of reduced gill functional surface area (caused by vasoconstriction) and an increase in blood residence time within the gill (caused by decreased cardiac output.     

Photosynthesis, Respiration, and Carbon Assimilation in Water-Stressed Maize at Two Oxygen Concentrations

Photosynthesis decreased with decreasing leaf water potentialas a consequence of stomatal closure and possibly non-stimataleffects of severe stress. Assimilation ceased at c. 16x 10⁵Pa. Photo-respiration, in 21% O₂, was small in relation to assimilationin unstressed leaves and decreased as leaf water potential fellbut it was much larger in proportion to photosynthesis at severestress. Decreasing the O₂ content to 1.5% increased photosynthesisslightly and decreased photo-respiration but did not changethe stress at which assimilation stoped. Dark respiration wasinsensitive to both O₂ and stress. Less ¹⁴C accumulated in stressedleaves but in 21% O₂ a greater proportion of it was in aminoacids, particularly glycine and serine. 1.5% O₂ decreased the¹⁴C in glycine to 10% and in serine to 50% of their levels in21% O₂. In both O₂ concentrations the proportion of ¹⁴C in serineincreased only at the most severe stress. Gas exchange measurementsand changes in the ¹⁴C flux to glycine are interpreted as theresult of glycolate pathway metabolism increasing as a proportionof assimilation in stressed leaves in high O₂. The small absoluterate of photorespiration in high O₂ and at low leaf water potentialmay be due to slow rates of glycine decarbodylation as wellas efficient fixation of any CO₂ produced. Serine is synthesizedby an O₂-sensitive pathway and an O₂-insensitive pathway, whichis most active at severe stress. Synthesis of alanine competeswith that of glycine and serine for a common precursor suppliedby the photo-synthetic carbon reduction cycle. The relativespecific radioactivities of aspartate and alanine suggest thatthey are derived from a common precursor pool, probably pyruvatefrom 3-PGA. The amounts of 3-PGA, aspartate, malate, alanine,and sucrose decreased with increasing water stress as a consequenceof slower assimilation and pool filling. Other amino acids,glycine, serine, glutamate, and proline, accumulated at lowwater potential possibly due to increased synthesis and slowerrates of consumption. Changes in pool sizes, carbon fludes,and specific activities of metabolites are related to the mechanismof C₄ photosynthesis and current concepts of glycolate pathwaymetabolism.     

Inducible nitric oxide synthase augments injury elicited by oxidative stress in rat cardiac myocytes

The effects of nitric oxide (NO) produced by cardiac inducibleNO synthase (iNOS) on myocardial injury after oxidative stress wereexamined. Interleukin-1 induced cultured rat neonatal cardiac myocytes to express iNOS. After induction of iNOS,L-arginine enhanced NOproduction in a concentration-dependent manner. Glutathione peroxidase(GPX) activity in myocytes was attenuated by elevated iNOS activity andby an NO donor,S-nitroso-N-acetyl-penicillamine (SNAP). Although NO production by iNOS did not induce myocardial injury, NO augmented release of lactate dehydrogenase from myocyte cultures after addition ofH₂O₂(0.1 mM, 1 h). Inhibition of iNOS withN-nitro-L-argininemethyl ester ameliorated the effects of NO-enhancing treatments onmyocardial injury and GPX activity. SNAP augmented the myocardialinjury induced byH₂O₂.Inhibition of GPX activity with antisense oligodeoxyribonucleotide forGPX mRNA increased myocardial injury byH₂O₂.Results suggest that the induction of cardiac iNOS promotes myocardialinjury due to oxidative stress via inactivation of the intrinsicantioxidant enzyme, GPX.

     

Changes in caridac output and hemolymph flow during hypoxic exposure in the gravid grass shrimp, <Emphasis Type="Italic">Palaemonetes pugio</Emphasis>

The cardiovascular response of decapod crustaceans to hypoxic exposure is well documented; however, information is limited concerning the influence of reproductive state on cardiovascular demands during hypoxic exposure. Given the additional metabolic demand of reproduction, we investigated the cardiovascular adjustments employed by gravid grass shrimp Palaemonetes pugio to maintain oxygen delivery during hypoxic stress. Cardiac output values were elevated in gravid compared to nongravid grass shrimp. Gravid grass shrimp were exposed to hypoxia and the stroke volume, heart rate, cardiac output and hemolymph flow were determined using video-microscopy and dimensional analysis. Oxygen consumption rates were determined using respirometry. There where no changes in the cardiac output values of gravid females until reaching 6.8 kPa O₂, with a significant redistribution of hemolymph flow at 13.7 kPa O₂. Flow was significantly decreased to the anterior lateral arteries that supply the ovaries and hepatopancreas, the anterior aorta and the posterior aorta. The redistribution of hemolymph flow away from these vessels results in an enhanced hemolymph flow to the sternal artery that supplies the ventral segmental system, the gills, the buccal apparatus and the ventral nerve cord. The data suggest that during hypoxic stress, gravid females place a priority on survival.     

Synthesis of Isozymes of Superoxide Dismutase in Maize Leaves in Response to O3, SO2 and Elevated O2

Matters, G. L. and Scandalios, J. G. 1987. Synthesis of isozymesof superoxide dismutase in maize leaves in response to O₃ SO₂and elevated O₂.—J. exp. Bot 38: 842–852. The activities of the enzymes superoxide dismutase (SOD) andcatalase were determined in maize leaves treated with O₃or SO₂for8 h, or with elevated levels of oxygen for up to 96 h. NeitherO₃nor SO₂significantly increased the levels of superoxide dismutaseor catalase activity. However, after 72 h in an atmosphere containing90% oxygen, superoxide dismutase activity was increased, butnot the activities of catalase, ascorbate pcroxidase, and malatedehydrogenase. Immunological analysis showed that amounts ofthe cytosolic superoxide dismutase isozymes, SOD-2 and SOD-4,were increased by the elevated oxygen but not the chroloplast(SOD-1) or mitochondrial (SOD-3) isozymes. Immunoprecipitationof translation products of leaf polysomes indicated that thehigher levels of SOD-2 and SOD-4 were due to increased amountsof polysome-bound mRNA coding for these proteins. The specificresponse of SOD-2 and SOD-4 to 90% oxygen treatments contrastswith the increase in all SOD isozymes in maize leaves treatedwith the herbicide paraquat. Key words: Air pollutants, maize, oxidative stress, oxygen, superoxide dismutase     

Reactive oxygen species formation in the transition to hypoxia in skeletal muscle

Many tissues produce reactive oxygen species (ROS) during reoxygenation after hypoxia or ischemia; however, whether ROS are formed during hypoxia is controversial. We tested the hypothesis that ROS are generated in skeletal muscle during exposure to acute hypoxia before reoxygenation. Isolated rat diaphragm strips were loaded with dihydrofluorescein-DA (Hfluor-DA), a probe that is oxidized to fluorescein (Fluor) by intracellular ROS. Changes in fluorescence due to Fluor, NADH, and FAD were measured using a tissue fluorometer. The system had a detection limit of 1 µM H₂O₂ applied to the muscle superfusate. When the superfusion buffer was changed rapidly from 95% O₂ to 0%, 5%, 21%, or 40% O₂, transient elevations in Fluor were observed that were proportional to the rise in NADH fluorescence and inversely proportional to the level of O₂ exposure. This signal could be inhibited completely with 40 µM ebselen, a glutathione peroxidase mimic. After brief hypoxia exposure (10 min) or exposure to brief periods of H₂O₂, the fluorescence signal returned to baseline. Furthermore, tissues loaded with the oxidized form of the probe (Fluor-DA) showed a similar pattern of response that could be inhibited with ebselen. These results suggest that Fluor exists in a partially reversible redox state within the tissue. When Hfluor-loaded tissues were contracted with low-frequency twitches, Fluor emission and NADH emission were significantly elevated in a way that resembled the hypoxia-induced signal. We conclude that in the transition to low intracellular PO₂, a burst of intracellular ROS is formed that may have functional implications regarding skeletal muscle O₂-sensing systems and responses to acute metabolic stress. dihydrofluorescein; tissue fluorometer; ebselen; N-acetylcysteine; rat     

Role of calreticulin in the sensitivity of myocardiac H9c2 cells to oxidative stress caused by hydrogen peroxide

Calreticulin (CRT), a Ca²⁺-binding molecular chaperone in the endoplasmic reticulum, plays a vital role in cardiac physiology and pathology. Oxidative stress is a main cause of myocardiac apoptosis in the ischemic heart, but the function of CRT under oxidative stress is not fully understood. In the present study, the effect of overexpression of CRT on susceptibility to apoptosis under oxidative stress was examined using myocardiac H9c2 cells transfected with the CRT gene. Under oxidative stress due to H₂O₂, the CRT-overexpressing cells were highly susceptible to apoptosis compared with controls. In the overexpressing cells, the levels of cytoplasmic free Ca²⁺ ([Ca²⁺]_i) were significantly increased by H₂O₂, whereas in controls, only a slight increase was observed. The H₂O₂-induced apoptosis was enhanced by the increase in [Ca²⁺]_i caused by thapsigargin in control cells but was suppressed by BAPTA-AM, a cell-permeable Ca²⁺ chelator in the CRT-overexpressing cells, indicating the importance of the level of [Ca²⁺]_i in the sensitivity to H₂O₂-induced apoptosis. Suppression of CRT by the introduction of the antisense cDNA of CRT enhanced cytoprotection against oxidative stress compared with controls. Furthermore, we found that the levels of activity of calpain and caspase-12 were elevated through the regulation of [Ca²⁺]_i in the CRT-overexpressing cells treated with H₂O₂ compared with controls. Thus we conclude that the level of CRT regulates the sensitivity to apoptosis under oxidative stress due to H₂O₂ through a change in Ca²⁺ homeostasis and the regulation of the Ca²⁺-calpain-caspase-12 pathway in myocardiac cells. apoptosis; calcium; endoplasmic reticulum     

A Connection between the Self-Incompatibility Mechanism and the Stress Response in Lily

An attempt was made to examine the possible connection betweenself-incompatibility in Lilium longiflorum and the stress responseusing pistils after self-incompatible pollination. The growthof pollen tubes in the pistil after self-incompatible pollinationwas promoted by treatment with germanium compounds [(GeCH₂CH₂COOH)₂O₃and GeO₂], which are scavengers of active oxygen species, suchas O₂^– and H₂O₂. The promotion by germanium compoundsof the growth of pollen tubes after self-incompatible pollinationwas reflected by the detection of elevated levels of activityof superoxide-forming NADPH-dependent oxidase, xanthine oxidase,superoxide dismutase, catalase and ascorbate peroxidase, allof which are associated with stress responses, in pistils uponself-incompatible pollination as compared to the activitiesof these enzymes after cross-compatible pollination. A possibleconnection between self-incompatibility and stress in pistilsupon self-incompatible pollination is discussed on the basisof these results. (Received October 9, 1995; Accepted November 11, 1996)     

Optimization of the Oxygen Transport System

Emphasizing the over-all performance of the O₂ transport system, as well as the interactions between its various subsystems, a method for a parametric performance analysis has been developed. The purpose of such an analysis is three-fold: 1. It permits an evaluation of those parameters which are critical for the performance of the system under conditions of stress. 2. It leads to an assessment of the ranking of individual members within the hierarchy of biological control systems. 3. It permits an objective assessment of the severity and prognosis of cardiovascular and respiratory diseases and of the degree of disability resulting therefrom. Starting with the principle of conservation of mass, two equations are derived which express the balance of oxygen in terms of supply, consumption, and waste. These equations are then developed in terms of the parameters of the system; namely, ventilation, inspired O₂ concentration, cardiac output, O₂ capacity of the blood, energy requirements of the two pumps, fractional extraction of O₂ from alveolar air (ventilation-perfusion ratio), and the oxygen utilization fraction in the periphery. The results indicate that the normal system attempts to maximize the oxygen utilization fraction while minimizing ventilatory and cardiac energy requirements. Changes in the ventilation-perfusion ratio are relatively less important. Possible extensions of the model are discussed.     

Dehydration markedly impairs cardiovascular function in hyperthermic endurance athletes during exercise

González-Alonso, José, RicardoMora-Rodríguez, Paul R. Below, and Edward F. Coyle.Dehydration markedly impairs cardiovascular function inhyperthermic endurance athletes during exercise. J. Appl. Physiol. 82(4): 1229-1236, 1997.Weidentified the cardiovascular stress encountered by superimposingdehydration on hyperthermia during exercise in the heat and themechanisms contributing to the dehydration-mediated stroke volume (SV)reduction. Fifteen endurance-trained cyclists [maximalO₂ consumption(O_{2 max}) = 4.5 l/min] exercised in the heat for 100-120 min and either became dehydrated by 4% body weight or remained euhydrated by drinkingfluids. Measurements were made after they continued exercise at 71%O_{2 max} for 30 minwhile 1) euhydrated with anesophageal temperature (T_es) of38.1-38.3°C (control); 2)euhydrated and hyperthermic (39.3°C);3) dehydrated and hyperthermic withskin temperature (T_sk) of34°C; 4) dehydrated withT_es of 38.1°C and T_sk of 21°C; and5) condition4 followed by restored blood volume. Compared withcontrol, hyperthermia (1°C T_esincrease) and dehydration (4% body weight loss) each separatelylowered SV 7-8% (11 ± 3 ml/beat;P < 0.05) and increased heart ratesufficiently to prevent significant declines in cardiac output.However, when dehydration was superimposed on hyperthermia, thereductions in SV were significantly (P < 0.05) greater (26 ± 3 ml/beat), and cardiac output declined 13% (2.8 ± 0.3 l/min). Furthermore, mean arterialpressure declined 5 ± 2%, and systemic vascular resistanceincreased 10 ± 3% (both P < 0.05). When hyperthermia wasprevented, all of the decline in SV with dehydration was due to reducedblood volume (~200 ml). These results demonstrate that thesuperimposition of dehydration on hyperthermia during exercise in theheat causes an inability to maintain cardiac output and blood pressurethat makes the dehydrated athlete less able to cope with hyperthermia.

     

Effects of Oxidative Stress Caused by Oxygen and Hydrogen Peroxide on Energy Metabolism and Senescence in Oat Leaves

In attached oat leaves the levels of adenine nucleotides decreasedduring leaf development and senescence. However, the energycharge (EC) only decreased from 0.90 in 4-cm leaves to 0.80in senescent leaves. In detached leaves the levels of adeninenucleotides increased for 48 h, in association with an increasein RNase activity and a decrease in levels of RNA. The EC remainedhigh until late senescence when levels of adenine nucleotidesfell to about 30% of initial values. A decrease in energy parametersinduced by transfer from light to darkness and from high (21%)to low (0.5% and anoxia) concentrations of oxygen resulted inan increase in membrane permeability. Oxidative stress (above 0.5% O₂ induced an increase in levelsof malondialdehyde (MDA) and then in permeability, associatedwith a decrease in levels of adenine nucleotides. Oxidativestress provoked by 0.05 and 0.10 M H₂O₂ caused a more rapiddecrease in energy parameters than O₂. Under oxidative stress(above 0.5% O₂) there is, first of all, an increase in membranepermeability and then a decrease in energy parameters, whichin turn are involved with senescence via increases in oxidationof membranes and degradation of energy-producing systems. (Received October 6, 1987; Accepted October 19, 1988)     

Cardiac output estimated noninvasively from oxygen uptake during exercise

Stringer, William W., James E. Hansen, and K. Wasserman.Cardiac output estimated noninvasively from oxygen uptake duringexercise. J. Appl. Physiol. 82(3):908-912, 1997.Because gas-exchange measurements duringcardiopulmonary exercise testing allow noninvasive measurement ofoxygen uptake (O₂), whichis equal to cardiac output (CO) × arteriovenous oxygencontent difference [C(a-vD_O2)],CO and stroke volume could theoretically be estimated if theC(a-vD_O2)increased in a predictable fashion as a function of %maximumO₂(O_{2 max}) duringexercise. To investigate the behavior ofC(a-vD_O2)during progressively increasing ramp pattern cycle ergometry exercise,5 healthy subjects performed 10 studies to exhaustion while arterialand mixed venous blood were sampled. Samples were analyzed forblood gases (pH, PCO₂,PO₂) and oxyhemoglobin and hemoglobinconcentration with a CO-oximeter. TheC(a-vD_O2)(ml/100 ml) could be estimated with a linear regression [C(a-vD_O2) = 5.72 + 0.105 × %O_{2 max};r = 0.94]. The CO estimated fromthe C(a-vD_O2)by using the above linear regression was well correlated withthe CO determined by the direct Fick method(r = 0.96). The coefficient ofvariation of the estimated CO was small (7-9%) between the lacticacidosis threshold and peakO₂. The behaviorof C(a-vD_O2),as related to peakO₂, was similar regardless of cardiac function compared with similar measurements fromstudies in the literature performed in normal and congestive heartfailure patients. In summary, CO and stroke volume can be estimatedduring progressive work rate exercise testing from measured O₂ (in normal subjects andpatients with congestive heart failure), and the resultant linearregression equation provides a good estimate ofC(a-vD_O2).

     

The Metabolism of Acetaldehyde by Plant Tissues

Apples and oranges can absorb appreciable amounts of acetaldehydevapour, but acetaldehyde does not accumulate in the tissues,in the presence or absence of oxygen. When the fruit is givenacetaldehyde the loss of carbon as CO₂ + ethanol equals thatlost from carbohydrate + acid+acetaldehyde. Part of the addedacetaldehyde is reduced to ethanol by NADH₂ and the rate ofglycolysis is increased; the remainder is oxidized to CO₂. Respiration of apples is limited by oxygen; the output of CO₂is only slightly increased at the beginning of the treatmentwith acetaldehyde, but afterwards it declines; acetaldehydespares oxidation of carbohydrate. In oranges, availability of substrate limits respiration, andacetaldehyde stimulates CO₂-production and O₂-uptake. In theabsence of oxygen, acetaldehyde is reduced to ethanol, and thequotient CO₂/ethanol falls.     

Pollutant particles enhanced H2O2 production from NAD(P)H oxidase and mitochondria in human pulmonary artery endothelial cells

Particulate matter (PM) induces oxidative stress and cardiovascular adverse health effects, but the mechanistic link between the two is unclear. We hypothesized that PM enhanced oxidative stress in vascular endothelial cells and investigated the enzymatic sources of reactive oxygen species and their effects on mitogen-activated protein kinase (MAPK) activation and vasoconstriction. We measured the production of extracellular H₂O₂, activation of extracellular signal-regulated kinases1/2 (ERK1/2) and p38 MAPKs in human pulmonary artery endothelial cells (HPAEC) treated with urban particles (UP; SRM1648), and assessed the effects of H₂O₂ on vasoconstriction in pulmonary artery ring and isolated perfused lung. Within minutes after UP treatment, HPAEC increased H₂O₂ production that could be inhibited by diphenyleneiodonium (DPI), apocynin (APO), and sodium azide (NaN₃). The water-soluble fraction of UP as well as its two transition metal components, Cu and V, also stimulated H₂O₂ production. NaN₃ inhibited H₂O₂ production stimulated by Cu and V, whereas DPI and APO inhibited only Cu-stimulated H₂O₂ production. Inhibitors of other H₂O₂-producing enzymes, including N-methyl-L-argnine, indomethacin, allopurinol, cimetidine, rotenone, and antimycin, had no effects. DPI but not NaN₃ attenuated UP-induced pulmonary vasoconstriction and phosphorylation of ERK1/2 and p38 MAPKs. Knockdown of p47phox gene expression by small interfering RNA attenuated UP-induced H₂O₂ production and phosphorylation of ERK1/2 and p38 MAPKs. Intravascular administration of H₂O₂ generated by glucose oxidase increased pulmonary artery pressure. We conclude that UP induce oxidative stress in vascular endothelial cells by activating NAD(P)H oxidase and the mitochondria. The endothelial oxidative stress may be an important mechanism for PM-induced acute cardiovascular health effects. mitogen-activated protein kinase; extracellular signal-regulated kinase; p38; vasoconstriction     

Transport of Oxygen by the Blood of the Land Crab, Gecarcinus lateralis

Parameters relating to transport of oxygen were measured inthe pericardial blood and venous outflow from the first walkingleg of Gecarcinus lateralis. O₂-equilibrium curves of the hemocyaninof G. lateralis were found to be sigmoid and, at 27°C andpH 7.45, to have a half-saturation pressure of about 17 mm Hgoxygen. Average partial pressures of oxygen as measured by O₂-electrodewere 32 mm Hg in pericardial blood and 9 mm Hg in the venoussamples. Analysis of the O₂-content in corresponding samplesby the Van Slyke technique revealed an average of 2.17 volumes% O₂-capacity for whole blood, 1.45 volumes % for pericardialblood, and 0.61 volumes % for venous blood. Estimates basedon the Van Slyke analyses indicated an average pO₂ of 29 and14 mm Hg in pericardial and venous samples, respectively. Thesefigures agree fairly well with those obtained by means of O₂-electrodes.Of the oxygen carried to the tissues, about 94% is carried asoxyhemocyanin and about 6% is carried in physical solution.As the blood passes through the gills, the hemocyanin, on anaverage, becomes 80–85% saturated with oxygen and returnedfrom the tissues 18–45% saturated with oxygen. These resultsindicate that the blood of G. lateralis has a higher O₂-capacitythan the blood of most other decapod crustaceans for which similarinformation is available. In addition, the blood of G. lateralistransports more oxygen to the tissues per unit volume than doother crustacean bloods.     

Differential MAP kinase activation and Na(+)/H(+) exchanger phosphorylation by H(2)O(2) in rat cardiac myocytes

Bursts in reactive oxygen species productionare important mediators of contractile dysfunction duringischemia-reperfusion injury. Cellular mechanisms that mediatereactive oxygen species-induced changes in cardiac myocyte functionhave not been fully characterized. In the present study,H₂O₂ (50 µM) decreased contractility of adultrat ventricular myocytes. H₂O₂ caused aconcentration- and time-dependent activation of extracellularsignal-regulated kinases 1 and 2 (ERK1/2), p38, and c-JunNH₂-terminal kinase (JNK) mitogen-activated protein (MAP)kinases in adult rat ventricular myocytes. H₂O₂ (50 µM) caused transient activation of ERK1/2 and p38 MAP kinase thatwas detected as early as 5 min, was maximal at 20 min (9.6 ± 1.2- and 9.0 ± 1.6-fold, respectively, vs. control), and returned tobaseline at 60 min. JNK activation occurred more slowly (1.6 ± 0.2-fold vs. control at 60 min) but was sustained at 3.5 h. Theprotein kinase C inhibitor chelerythrine completely blocked JNKactivation and reduced ERK1/2 and p38 activation. The tyrosine kinaseinhibitors genistein and PP-2 blocked JNK, but not ERK1/2 and p38,activation. H₂O₂-inducedNa⁺/H⁺ exchanger phosphorylation was blocked bythe MAP kinase kinase inhibitor U-0126 (5 µM). These resultsdemonstrate that H₂O₂-induced activation of MAPkinases may contribute to cardiac myocyte dysfunction duringischemia-reperfusion.