Bacterivory in seawater samples estimated by a dual radioactive-labelling technique

A dual radioactive-labelled bacteria technique using Vibrio(DRLV), developed for laboratory studies on bacterivory, hasbeen refined for use at the concentrations of prey and predatorstypcially found at sea. Experiments with estuarine water collectedin spring and in autumn showed that bacterivorous nanoflagellates(HNF) (concentration 1.38±0.35x10³ HNF ml^–1) ingested2.7±0.96 DRLV flagellate1^–1 h^–1 at concentrationsof 0.8–2.2x10⁶ DRLV ml^–1 in the presence of 2.04±0.68x10⁶natural bacteria ml^–1. The method was also applied tosamples collected in October in the Celtic Sea, when on average1 ml of water from the surface layer contained 1.41±0.16x10⁶natural bacteria, 14.6x10³ cyanobacteria, 530±170 HNF,7.3±3.0x103 phototrophic nanoflagellates (1.5–4µm), 49.0±26.5 phototrophic dinoflagellates, 36.3±12.6heterotrophic dinoflagellates and 21.3±9.5 Leucocryptosmarina. Under these conditions the grazing rate in most samplesdid not exceed the coefficient of variation of the method (2%),although we estimate the grazing rate was -1.6 DRLV HNF^–1h^–1 and on one occasion a rate of 2.45 was recorded. Thegross growth efficiency for protein of -30% displayed by naturalHNF means that they could release about     

Measurement of Yield Threshold and Cell Wal Extensibility of Intact Wheat Roots under Different Ionic, Osmotic and Temperature Treatments

Yield stress threshold (Y) and volumetric extensibility () arethe rheological properties that appear to control root growth.In this study they were measured in wheat roots by means ofparallel measurement of the growth rate (r) of intact wheatroots and of the turgor pressures (P) of individual cells withinthe expansion zone. Growth and turgor pressure were manipulatedby immersion in graded osmoticum (mannitol) solutions. Turgorwas measured with a pressure probe and growth rate by visualobservation. The influence of various growth conditions on Yand was investigated; (a) At 27 °C.In 0.5 mol m^–3 CaCl₂ r, P, Y and were20.7±4.6 µm min^–1, 0.77±0.05 MPa,0.07±0.03 MPa and 26±1.9 µm min^–1MPa^–1 (expressed as increase in length), respectively.Following 24 h growth in 10 mol m^–3 KC1 these parametersbecame 12.3±3.5 µm min^–1, 0.72±0.04MPa, 0.13±0.01 MPa and 21±0.7 µm min^–1MPa^–1. After 24 h osmotic adjustment in 150 mol m^–3mannitol/0.5 mol m^–3 CaCl₂ r= 19.6±4.2 µmmin^–1, P = 0.68±0.05 MPa and Y and were 0.07±0.04MPa and 30±0.2 µm min^–1 MPa^–01, respectively.After 24 h growth in 350 mol m^–3 mannitol/0.5 mol m^–3CaCl₂ r= 13.3±4.1 µm min^–1, P= 0.58±0.07MPa, Y=0.12±0.01 MPa and ø 32±0.2 tim min^–1MPa^–1. During osmotic adjustment in 200 mol m^–3mannitol/0.5 mol m^–3 CaCl₂, with or without KCl, the recoveryof growth rate corresponded to turgor pressure recovery (t1/2approximately 3 h). (b) At 15 °C. Lowered temperature dramatically influencedthe growth parameters which became r= 8.3±2.8 um min^–1,P=0.78 MPa, r=<0.2 MPa and =15±0.1 µm min^–1MPa^–1. Therefore, Y and are influenced by 10 mol m^–3 K⁺ ionsand low temperature. In each case the effective pressure forgrowth (P-Y) was large indicating that small fluctuations ofsoil water potential will not stop root elongation. Key words: Yield threshold, cell wall extensibility, wheat root growth, temperature, turgor pressur     

Swelling of Etiolated Oat Protoplasts Induced by cAMP and Red Light

Etiolated oat protoplasts were treated with dibutyryl cAMP tostudy possible function of cAMP in the development by measuringthe protoplast swelling. The mean diameter of protoplasts inthe absence of any chemical treatment was 33.58±1.26(SE) µm, which increased to 36.96±0.86 µmin the presence of 100 µM dibutyryl cAMP. Prostacyclin,a potent activator of adenyl cyclase, also showed a significantswelling effect (diameter 38.01±0.98 µm). Red lightalso elicited the swelling of protoplasts (40.26±0.8µm). ¹Present address: Department of Biology, Pusan National University,Pusan 607, Korea. ²Present address: Department of Horticulture, Cheju NationalUniversity, Cheju 590, Korea. ³Present address: Department of Biological Sciences, Texas TechUniversity, Lubbock, TX 79409, U.S.A. (Received June 29, 1985; Accepted November 18, 1985)     

WATER EXCHANGE, TEMPERATURE TOLERANCE, OXYGEN CONSUMPTION AND ACTIVITY OF THE NAMIB DESERT SNAIL, TRIGONEPHRUS SP.

Water exchange, temperature tolerance and oxygen consumptionof the snail, Trigonephrus sp., from the southern Namib desertof Namibia were examined and related to activity. At 25°Cand 15% R.H. mean water loss and food and water uptake were5.95 mg. day^–1 and 630 mg.day^–1, respectively. Bodytemperature tracked sand temperature. Snails tolerated sandtemperatures as high as 45°C. Mean ± S.D. oxygenconsumption rates were 32.0 ± 2.94 µlO₂.g totalbody mass^–1.h^–1 at 15°C, when the snails wereactive, and 11.27 µlO₂.g total body mass^–1.h^–1at 25°C, when the snails were inactive. These values are2-6 times lower than those recorded for the similarly sizedmesic snail, Helix aspersa. Activity experiments indicated thatlow ambient temperatures and high humidities were favoured bythe snails. This, together with the burying behaviour of thesesnails during high temperatures, suggests that they limit stressby restricting activity to physiologically-favourable periods,even though more-extreme conditions may be tolerated. (Received 7 June 1990; accepted 20 November 1990)     

Evidence for Symplasmic Ion Transport in Maize Roots

Excised maize roots, placed in saturated water vapour to limitthe external ionic supply, continued to produce exudates attheir basal ends for at least 24 h. The mean rate of fluid exudationfrom roots in water vapour was about 28 per cent of the correspondingrate in ‘control’ roote placed in a solution containing0.1 mil CaCl₂ and 1 mM KC1. Moreover, the net fluxes (mean ±S.E.)of potassium and calcium ions into the exudate were reducedfrom (35.8±3.2) x 10^– and (4.37±0.39) xlO^–9 mole cm^–2 h^– for roots in solution to(10.9±0.6) x 10^–9 and (l.00±0.06)x 10^–9molecm^–2 h^–1 respectively for roots in vapour. It isconsidered that the observation of a prolonged exudation ofwater and ions from the roots placed in water vapour demonstratesthe existence of an alternative ionic supply within the roottissue itself and that this parallel route of ion transportto the exudate constitutes the cortical symplasmic pathway. Pre-treatment of the excised roots with 0.8 M mannitol beforeexudation studies in water vapour and solution led to a significantreduction in the rates of fluid and ion exudation which hadbeen observed in untreated roots under similar conditions. Itis concluded that the plas-molysis, induced by mannitol, disruptedthe symplasmic connections between root cells and that thisperturbation significantly reduced the operation of the symplasmicmode of ion transport into the exudate.     

Pulmonary blood flow distribution has a hilar-to-peripheral gradient in awake, prone sheep

Walther, Sten M., Karen B. Domino, Robb W. Glenny, Nayak L. Polissar, and Michael P. Hlastala. Pulmonary blood flow distribution has a hilar-to-peripheral gradient in awake, prone sheep.J. Appl. Physiol. 82(2): 678-685, 1997.We examined the pulmonary blood flow distribution withintravenous fluorescent microspheres (15 µm) in nine prone,unanesthetized, lambs. Lungs flushed free of blood were air-dried attotal lung capacity and sectioned into~2-cm³ pieces. The pieces wereweighed, identified by lobe, and assigned spatial coordinates.Fluorescence was read on a spectrophotometer, and signals werecorrected for piece weight and normalized to mean flow. Pulmonary bloodflow heterogeneity was assessed by using the coefficient of variationof the flow data. The number of pieces (±SD) analyzed were 1,249 ± 150/animal. Heterogeneity of blood flow was 29.5 ± 6.5%(coefficient of variation = SD/mean). Pulmonary blood flow decreasedwith distance from hilus (P < 0.002) but did not change significantly with vertical height. Distance fromthe hilus was the best predictor of pulmonary blood flow (R² = 0.201) and,together with spatial coordinates and lobe, accounted for 33.7 ± 12.0% of blood flow variability. We conclude that pulmonary blood flowin the awake, prone sheep is distributed with a hilar-to-peripheral gradient but no significant vertical gradient.

     

Maintenance and Growth Components of Carbon Dioxide Efflux from Growing Pea Fruits

Carbon dioxide efflux from 5- to 20-day-old pea fruits was measuredfor plants grown in controlled environment at 15 °C and600 µmol s^–1 m^–2 photon flux density in a16 h photoperiod. The rate of CO₂ output per fruit increasedquickly from 0.005 to 0.018 mg CO₂ min^–1 during fruitelongation and subsequently more slowly to 0.030 mg CO₂ min^–1as the fruits inflated. On a d. wt basis the rate was highest,0.175 mg CO₂ g^–1 min^–1, in the youngest fruits anddeclined curvilinearly with increasing fruit weight to 0.02mg CO₂ g^–1 min^–1. Separation of maintenance andgrowth components was achieved by starvation methods and bymultiple regression analysis. From the latter method estimatesof the maintenance coefficient declined hyperbolically from150±8.7 mg carbohydrate g^–1 d. wt day^–1 inthe very young fruits (0.05 g) to 10.4±0.36 mg carbohydrateg^–1 d. wt day^–1 in older fruits (2.0 g). On a nitrogenbasis maintenance costs decreased from 2240 to 310 mg carbohydrateg^–1 nitrogen day^–1 while nitrogen concentrationfell from 6.7 to 3 per cent d. wt. A simple linear relationshipbetween maintenance cost per unit d. wt and nitrogen concentrationwas not observed. A growth coefficient of 50±6.7 mg carbohydrate g^–1growth (equivalent to a conversion efficiency, Y_G, of 0.95)was estimated for all fruits examined. The overall efficiency, Y, increased from a mean of 0.70 to0.85 during fruit elongation and subsequently declined to 0.80.For a given fruit weight, efficiency increased asymptoticallywith relative growth rate; both asymptote and slope of the relationshipincreased as the fruits grew. Pisum sativum L., garden pea, legume fruit, carbon dioxide efflux, maintenance respiration, growth respiration     

Structure, function, and genomic organization of human Na(+)-dependent high-affinity dicarboxylate transporter

We have clonedand functionally characterized the human Na⁺-dependenthigh-affinity dicarboxylate transporter (hNaDC3) from placenta. ThehNaDC3 cDNA codes for a protein of 602 amino acids with 12 transmembrane domains. When expressed in mammalian cells, the clonedtransporter mediates the transport of succinate in the presence ofNa⁺ [concentration of substrate necessary for half-maximaltransport (K_t) for succinate = 20 ± 1 µM]. Dimethylsuccinate also interacts with hNaDC3. TheNa⁺-to-succinate stoichiometry is 3:1 and concentration ofNa⁺ necessary for half-maximal transport(K^Na+_0.5) is 49 ± 1 mM as determined by uptake studies withradiolabeled succinate. When expressed in Xenopuslaevis oocytes, hNaDC3 induces Na⁺-dependent inwardcurrents in the presence of succinate and dimethylsuccinate. At amembrane potential of 50 mV,K^Suc_0.5 is 102 ± 20 µM andK^Na+_0.5 is 22 ± 4 mM as determined by the electrophysiological approach. Simultaneous measurements of succinate-evoked charge transfer andradiolabeled succinate uptake in hNaDC3-expressing oocytes indicate acharge-to-succinate ratio of 1:1 for the transport process, suggestinga Na⁺-to-succinate stoichiometry of 3:1. pH titration ofcitrate-induced currents shows that hNaDC3 accepts preferentially thedivalent anionic form of citrate as a substrate. Li⁺inhibits succinate-induced currents in the presence of Na⁺.Functional analysis of rat-human and human-rat NaDC3 chimeric transporters indicates that the catalytic domain of the transporter lies in the carboxy-terminal half of the protein. The humanNaDC3 gene is located on chromosome20q12-13.1, as evidenced by fluorescent in situ hybridization. Thegene is >80 kbp long and consists of 13 exons and 12 introns.

     

The role of faecal material in the particulate organic carbon flux in the northern Humboldt Current, Chile (23{degrees}S), before and during the 1997-1998 El Nino

Sedimentation rates of faecal material, phytoplankton and microzooplanktonand production rates of faecal material from crustaceans andpelagic tunicates were estimated during the austral summer andwinter 1997, and summer 1998, in the northern Humboldt Current(23°S, off Antofagasta, Chile). Sampling periods coveredpre-El Niño (January 1997) and El Niño 1997–98(July 1997 and January 1998). Samples were collected using floatingsediment traps deployed at 65, 100, 200 and 300 m depth in oceanicand coastal areas. Sedimentation rates during January 1997 were,on average, 152 ± 23 and 85 ± 57 mg C m^–2day^–1 at 65 and 300 m depth, respectively. During July,these rates averaged 93 ± 56 mg C m^–2 day^–1at 65 m depth and 35 ± 12 mg C m^–2 day^–1at 300 m depth, while in January 1998 they were 98 and 109 ±37 mg C m^–2 day^–1 at 65 and 200 m depth, respectively.Recognizable faecal material made up the bulk of the sedimentingmatter, accounting for 8 ± 5% (n = 14), 31 ± 26%(n = 16) and 8 ± 5% (n = 5) of the average total organiccarbon recorded from all sediment trap samples collected duringJanuary and July 1997 and January 1998, respectively. However,at300 m depth, the contribution of recognizable faecal materialto total sedimented organic carbon increased to 43 ±33% (n = 4) during July 1997. The remaining sedimenting particlesconsisted mainly of tintinnids, crustacean exuviae, heterotrophicdinoflagellates (both thecated and athecated) and diatom cells.During this study, we estimated that only a minor fraction (average± SD = 5 ± 8%) of the copepod faecal materialproduced within the photic zone sedimented down to 300 m depth,suggesting an efficient recycling within the overlaying watercolumn. On the other hand, an important fraction (47 ±30%) of the euphausiid faecal strings was collected in the 300m depth trap, suggesting that this material would enhance thedownward flux of particulate organic matter (POC). POC fluxesto 65 and 300 m depth traps were in the range of 4–20%and 3–8% of the estimated primary production during thewhole study period. It is postulated that the overall verticalflux of particulates and, in particular, faecal pellets wasdetermined by a combination of three factors. The first wasthe composition of the zooplankton assemblages in the studyarea. When the dominant group was calanoid copepods, their faecesseemed to contribute poorly to the vertical flux of particulates.On the other hand, when the dominant group was euphausiids,a significant proportion of their faecal material was collectedin the sediment trap located at 300 m depth. The second wasthe relatively high abundance of cyclopoid copepods from thegenera Oncaea, Corycaeus and Oithona, which are reported tofeed on aggregates of phytodetritus and faecal pellets producedby calanoid copepods, suggesting that they may act as a naturalfilter to sedimenting particulates. The third was the compositionand size spectrum of the phyto- and microzooplankton assemblageswhich are potential food sources for the meso- and macrozooplankton.These factors were partially modulated by both the 1997–1998El Niño and seasonality.     

The Tonoplast Impedance of Chara

The capacitance and conductance of the plasmalemma and tonoplastof Chara were measured simultaneously in space-clamped cells.At a frequency of 5 Hz the capacitance and conductance of thetonoplast were 60 ± 5 mF m^–2 (i. e. 6.0 µF cm^–2) and 6.5 ± 0.6 S m^–2 respectively.These values were respectively 2.9 ± 0.3 and 3.7 ±0.4 times greater than those of the plasmalemma. It is shownthat any leakage of current around the cytoplasmic electrodewill not drastically affect the calculated area-specific valuesof the tonoplast parameters under the experimental conditionsused, providing that the cytoplasm possesses a reasonable longitudinalconductivity. An examination of the relative measured impedancesof the plasmalemma and tonoplast supports this conclusion. Key words: Chara tonoplast: Plasmalemma, Capacitance/ conductance     

Phosphorylation of p70S6k correlates with increased skeletal muscle mass following resistance exercise

High-resistance exercise training results in an increase inmuscle wet mass and protein content. To begin to address the acute changes following a single bout of high-resistance exercise, a newmodel has been developed. Training rats twice a week for 6 wk resultedin 13.9 and 14.4% hypertrophy in the extensor digitorum longus (EDL)and tibialis anterior (TA) muscles, respectively. Polysome profilesafter high-resistance lengthening contractions suggest that the rate ofinitiation is increased. The activity of the 70-kDa S6 protein kinase(p70^S6k), a regulator oftranslation initiation, is also increased following high-resistancelengthening contractions (TA, 363 ± 29%; EDL, 353 ± 39%).Furthermore, the increase inp70^S6k activity 6 h after exercisecorrelates with the percent change in muscle mass after 6 wk oftraining (r = 0.998). The tightcorrelation between the activation ofp70^S6k and the long-term increasein muscle mass suggests thatp70^S6k phosphorylation may be agood marker for the phenotypic changes that characterize musclehypertrophy and may play a role in load-induced skeletal muscle growth.

     

Effect of cell flotation on growth of Anabaena circinalis under diurnally stratified conditions

We tested the hypothesis that the growth rate of Anabaena circinalis,under diurnally stratified conditions, would increase as flotationvelocity increased owing to higher light availability. An insitu experiment compared the growth of diurnally stratifiedpopulations of A. circinalis with flotation velocities of 0.5and 1.0 m h^–1, with neutrally buoyant populations thatwere exposed to either mixed or persistently stratified conditions.The experiment was conducted in the turbid lower Murray Riverin South Australia (vertical attenuation coefficient = 4.52± 0.36 m^–1). To represent the mixing patterns,A. circinalis was contained in diffusion chambers that weremoved to different positions in the water column throughoutthe day. Diurnal populations with flotation velocities of 1.0and 0.5 m h^–1 grew at 0.23 ± 0.01 and 0.15 ±0.01 day^–1, respectively. Mixed populations grew at 0.19± 0.01 day^–1, whereas persistently stratified populationsgrew at 0.43 ± 0.01 day^–1. Results were used toextend a model that predicts growth of A. circinalis when exposedto the different mixing patterns. The model showed that bloomsare unlikely to be formed when the period of diurnal stratificationis <1 week, regardless of flotation velocity. When the diurnallystratified period is >1 week, flotation velocity is importantand a bloom may form depending on values assigned to the growthperiod and maximum mixed depth (Z_m).     

Interactions of transmembrane carbonic anhydrase, CAIX, with bicarbonate transporters

Association of some plasma membrane bicarbonate transporters with carbonic anhydrase enzymes forms a bicarbonate transport metabolon to facilitate metabolic CO₂-HCO₃^– conversions and coupled HCO₃^– transport. The transmembrane carbonic anhydrase, CAIX, with its extracellular catalytic site, is highly expressed in parietal and other cells of gastric mucosa, suggesting a role in acid secretion. We examined in transfected HEK293 cells the functional and physical interactions between CAIX and the parietal cell Cl^–/HCO₃^– exchanger AE2 or the putative Cl^–/HCO₃^– exchanger SLC26A7. Coexpression of CAIX increased AE2 transport activity by 28 ± 7% and also activated transport mediated by AE1 and AE3 (32 ± 10 and 37 ± 9%, respectively). In contrast, despite a transport rate comparable to that of AE3, coexpressed CAIX did not alter transport associated with SLC26A7. The CAIX-associated increase of AE2 activity did not result from altered AE2 expression or cell surface processing. CAIX was coimmunoprecipitated with the coexpressed SLC4 polypeptides AE1, AE2, and AE3, but not with SLC26A7. GST pull-down assays with a series of domain-deleted forms of CAIX revealed that the catalytic domain of CAIX mediated interaction with AE2. AE2 and CAIX colocalized in human gastric mucosa, as indicated by coimmunofluorescence. This is the first example of a functional and physical interaction between a bicarbonate transporter and a transmembrane carbonic anhydrase. We conclude that CAIX can bind to some Cl^–/HCO₃^– exchangers to form a bicarbonate transport metabolon. SLC4; SLC26; bicarbonate transport metabolon     

On the causes of interspecific differences in the growth-irradiance relationship for phytoplankton. Part I. A comparative study of the growth-irradiance relationship of three marine phytoplankton species: Skeletonema costatum, Olisthodiscus luteus and Gonyaulax tamarensis

Three marine phytoplankton species (Skeletonema costatum, Olisthodiscusluteus andGonyaulax tamarensis) were grown in batch culturesat 15°C and a 14:10 L:D cycle at irradiance levels rangingfrom 5 to 450 µEinst m^–2 s^–1. At each irradiance,during exponential growth, concurrent measurements were madeof cell division, carbon-specific growth rate, photosyntheticperformance (both O₂ and POC production), dark respiration,and cellular composition in terms of C, N and chlorophyll a.The results indicate that the three species were similar withrespect to chemical composition, C:N (atomic) = 6.9 ±0.4, photo-synthetic quotient, 1.43 ± 0.09, and photosyntheticefficiency, 2.3 ±0.1 x 10^–3 µmol O₂ (µgChl a)^–1 h^–1 (µEinst m^–2 s^–1)^–1.Differences in maximum growth rate varied as the –0.24power of cell carbon. Differences in growth efficiency, werebest explained by a power function of Chl a:C at µ = 0.Compensation intensities, ranged from 1.1 µEinst m^–2s^–1 for S. costatum to 35 forG. tamarensis and were foundto be a linear function of the maintenance respiration rate.The results indicate that interspecific differences in the µ–Irelationship can be adequately explained in terms of just threeparameters: cell carbon at maximum growth rate, the C:Chl aratio (at the limit as growth approaches zero) and the respirationrate at zero growth rate. A light-limited algal growth modelbased on these results gave an excellent fit to the experimentalµ–I curves and explained 97% of the observed interspecificvariability. ¹Present address: Lamont-Doherty Geological Observatory Columbiaof University, Palisades, NY 10964, USA     

The Theory and Practice of Measuring Transport Coefficients and Sap Flow in the Xylem of Red Maple Stems (Acer rubrum)

In this paper we report measurements concerning the conductivityof water and ions and the interaction between the two in excisedpieces of xylem of red maple stems under various conditions.We have also demonstrated that it is possible to detect theflow of solutions through the stems of maple by measuring thedegree of interaction between the flow of water and ions. Inthis technique we apply voltage pulses of ±V volts acrossa length of stem and detect the unequal current pulses resultingfrom the greater frictional drag when current (which is carriedprimarily by cations) is flowing against the water stream thanwhen flowing with the water stream. The hydraulic conductivityof recent maple sapwood ranges from 30 to 90 cm³ s^–1 cm^–2(J cm^–3)^–1 cm; in 2 mM KCl the electrical conductivityis roughly 3 x 10^–4 mho cm^–1 and the electro-kineticcross coefficient is roughly 4x10^–5 A cm^–2 (J cm^–3)^–1cm.     

Acute effects of 17beta-estradiol on myocardial pH, Na+, and Ca2+ and ischemia-reperfusion injury

Evidence suggests that 1) ischemia-reperfusion injury is due largely to cytosolic Ca²⁺ accumulation resulting from functional coupling of Na⁺/Ca²⁺ exchange (NCE) with stimulated Na⁺/H⁺ exchange (NHE1) and 2) 17-estradiol (E2) stimulates release of NO, which inhibits NHE1. Thus we tested the hypothesis that acute E2 limits myocardial Na⁺ and therefore Ca²⁺ accumulation, thereby limiting ischemia-reperfusion injury. NMR was used to measure cytosolic pH (pH_i), Na⁺ (Na), and calcium concentration ([Ca²⁺]_i) in Krebs-Henseleit (KH)-perfused hearts from ovariectomized rats (OVX). Left ventricular developed pressure (LVDP) and lactate dehydrogenase (LDH) release were also measured. Control ischemia-reperfusion was 20 min of baseline perfusion, 40 min of global ischemia, and 40 min of reperfusion. The E2 protocol was identical, except that 1 nM E2 was included in the perfusate before ischemia and during reperfusion. E2 significantly limited the changes in pH_i, Na and [Ca²⁺]_i during ischemia (P < 0.05). In control OVX vs. OVX+E2, pH_i fell from 6.93 ± 0.03 to 5.98 ± 0.04 vs. 6.96 ± 0.04 to 6.68 ± 0.07; Na rose from 25 ± 6 to 109 ± 14 meq/kg dry wt vs. 25 ± 1 to 76 ± 3; [Ca²⁺]_i changed from 365 ± 69 to 1,248 ± 180 nM vs. 293 ± 66 to 202 ± 64 nM. E2 also improved recovery of LVDP and diminished release of LDH during reperfusion. Effects of E2 were diminished by 1 µM N-nitro-L-arginine methyl ester. Thus the data are consistent with the hypothesis. However, E2 limitation of increases in [Ca²⁺]_i is greater than can be accounted for by the thermodynamic effect of reduced Na accumulation on NCE. myocardial ischemia; Na⁺/H⁺ exchange; Na⁺/Ca²⁺ exchange; nuclear magnetic resonance; ischemic biology; ion channels/membrane transport; transplantation     

Moderation of skeletal muscle reperfusion injury by a sLe(x)-glycosylated complement inhibitory protein

Therole of the sialyl Lewis^x (sLe^x)-decoratedversion of soluble complement receptor type 1 (sCR1) in moderatingskeletal muscle reperfusion injury, by antagonizing neutrophilendothelial selectin interaction and complement activation, isexamined. Mice underwent 2 h of hindlimb ischemia and3 h of reperfusion. Permeability index (PI) was assessed byextravasation of ¹²⁵I-labeled albumin. Neutrophil depletionand complement inhibition with sCR1 reduced permeability by 72% (PI0.81 ± 0.10) compared with a 42% decrease (PI 1.53 ± 0.08)observed in neutropenic mice, indicating that part of thecomplement-mediated injury is neutrophil independent.sCR1sLe^x treatment reduced PI by 70% (PI 0.86 ± 0.06), an additional 20% decrease compared with sCR1 treatment (PI1.32 ± 0.08). Treatment with sCR1sLe^x 0.5 and 1 h after reperfusion reduced permeability by 63% (PI 0.09 ± 0.07)and 52% (PI 1.24 ± 0.09), respectively, compared with therespective decreases of 41% (PI 1.41 ± 0.10) and 32% (PI1.61 ± 0.07) after sCR1 treatment. Muscle immunohistochemistry stained for sCR1 only on the vascular endothelium ofsCR1sLe^x-treated mice. In conclusion, sCR1sLe^xis more effective than sCR1 in moderating skeletal muscle reperfusion injury.

     

Effect of complete protein 4.1R deficiency on ion transport properties of murine erythrocytes

Moderate hemolytic anemia, abnormal erythrocyte morphology (spherocytosis), and decreased membrane stability are observed in mice with complete deficiency of all erythroid protein 4.1 protein isoforms (4.1^–/–; Shi TS et al. J Clin Invest 103: 331, 1999). We have examined the effects of erythroid protein 4.1 (4.1R) deficiency on erythrocyte cation transport and volume regulation. 4.1^–/– mice exhibited erythrocyte dehydration that was associated with reduced cellular K and increased Na content. Increased Na permeability was observed in these mice, mostly mediated by Na/H exchange with normal Na-K pump and Na-K-2Cl cotransport activities. The Na/H exchange of 4.1^–/– erythrocytes was markedly activated by exposure to hypertonic conditions (18.2 ± 3.2 in 4.1^–/– vs. 9.8 ± 1.3 mmol/10¹³ cell x h in control mice), with an abnormal dependence on osmolality (EC₅₀ = 417 ± 42 in 4.1^–/– vs. 460 ± 35 mosmol/kgH₂O in control mice), suggestive of an upregulated functional state. While the affinity for internal protons was not altered (K_0.5 = 489.7 ± 0.7 vs. 537.0 ± 0.56 nM in control mice), the V_max of the H-induced Na/H exchange activity was markedly elevated in 4.1^–/– erythrocytes (V_max 91.47 ± 7.2 compared with 46.52 ± 5.4 mmol/10¹³ cell x h in control mice). Na/H exchange activation by okadaic acid was absent in 4.1^–/– erythrocytes. Altogether, these results suggest that erythroid protein 4.1 plays a major role in volume regulation and physiologically downregulates Na/H exchange in mouse erythrocytes. Upregulation of the Na/H exchange is an important contributor to the elevated cell Na content of 4.1^–/– erythrocytes. spherocytosis; cell Na; Na/H exchange     

Muscle fiber hypertrophy, hyperplasia, and capillary density in college men after resistance training

McCall, G. E., W. C. Byrnes, A. Dickinson, P. M. Pattany,and S. J. Fleck. Muscle fiber hypertrophy, hyperplasia, and capillary density in college men after resistance training.J. Appl. Physiol. 81(5):2004-2012, 1996.Twelve male subjects with recreationalresistance training backgrounds completed 12 wk of intensifiedresistance training (3 sessions/wk; 8 exercises/session; 3 sets/exercise; 10 repetitions maximum/set). All major muscle groupswere trained, with four exercises emphasizing the forearm flexors.After training, strength (1-repetition maximum preacher curl) increasedby 25% (P < 0.05). Magneticresonance imaging scans revealed an increase in the biceps brachiimuscle cross-sectional area (CSA) (from 11.8 ± 2.7 to 13.3 ± 2.6 cm²;n = 8;P < 0.05). Muscle biopsies of thebiceps brachii revealed increases(P < 0.05) in fiber areas for type I(from 4,196 ± 859 to 4,617 ± 1,116 µm²;n = 11) and II fibers (from 6,378 ± 1,552 to 7,474 ± 2,017 µm²;n = 11). Fiber number estimated fromthe above measurements did not change after training (293.2 ± 61.5 × 10³ pretraining; 297.5 ± 69.5 × 10³ posttraining;n = 8). However, the magnitude ofmuscle fiber hypertrophy may influence this response because thosesubjects with less relative muscle fiber hypertrophy, but similarincreases in muscle CSA, showed evidence of an increase in fibernumber. Capillaries per fiber increased significantly(P < 0.05) for both type I(from 4.9 ± 0.6 to 5.5 ± 0.7;n = 10) and II fibers (from 5.1 ± 0.8 to 6.2 ± 0.7; n = 10). Nochanges occurred in capillaries per fiber area or muscle area. Inconclusion, resistance training resulted in hypertrophy of the totalmuscle CSA and fiber areas with no change in estimated fiber number,whereas capillary changes were proportional to muscle fiber growth.

     

Pulmonary fluid extraction and osmotic conductance, sigma K, measured in vivo

The change in aortic blood density in an in vivo rabbitpreparation was measured to assess fluid movement at the pulmonary capillaries caused by infusion of hypertonic solution (NaCl, urea, glucose, sucrose, or raffinose in isotonic saline) into the vena cavaover 20 s. The hypertonic disturbance increased the plasma osmoticpressure by 30 mosmol/l. The density change indicates that the fluidextraction from the lung tissue was completed within 10 s. It wasfollowed by a fluid filtration into the lung tissue and then anextraction and filtration from peripheral organs. An exchange modelwith flow dispersion yields two equations to estimate the osmoticconductance (K; where is the reflection coefficient of the test solute andK is the filtration coefficient including the total capillary surface area), and the tissue fluid volume from the area and first moment of the measured density changeover the extraction phase. The values ofK are 1.40 ± 0.11, 1.00 ± 0.10, 1.71 ± 0.10, 2.60 ± 0.23, and 3.73 ± 0.34 (SE) ml · h¹ · mosmol¹ · l · g¹for NaCl, urea, glucose, sucrose, and raffinose, respectively. Consistent with the model prediction, the tissue fluid volume (0.28 ± 0.04 ml/g wet lung tissue) was independent of the solute used.This value suggests that all fluid spaces in the alveolar septaparticipate in the process of fluid extraction due to an increase inplasma osmotic pressure.