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1.
Cervical magnetic stimulation as a method to discriminate between diaphragm and rib cage muscle fatigue 总被引:1,自引:0,他引:1
Similowski Thomas; Straus Christian; Attali Valerie; Duguet Alexandre; Derenne Jean-Philippe 《Journal of applied physiology》1998,84(5):1692-1700
Inspiratory muscle fatigue can probablydetermine hypercapnic respiratory failure. Diaphragm fatigue isdetected by electrical phrenic stimulation (ELS), but there is nosimple tool to assess rib cage muscle (RCM) fatigue. Cervical magneticstimulation (CMS) costimulates the phrenic nerves and RCM. We reasonedthat changes in transdiaphragmatic pressure twitch (Pdi,tw) with CMSand ELS should be different after selective diaphragm vs. RCM fatigue. Five volunteers performed inspiratory resistive tasks while voluntarily uncoupling diaphragm and RCM. BaselinePdi,twELS andPdi,twCMS were 28.57 ± 1.68 and 32.83 ± 2.92 cmH2O. Afterselective diaphragm loading,Pdi,twELS andPdi,twCMS were reduced by 39 and26%, with comparable decreases in gastric pressure twitch (Pga,tw).Esophageal pressure twitch (Pes,tw) was better preserved with CMS.Therefore Pes,tw/Pga,tw was lower with ELS than CMS (1.24 ± 0.16 vs. 1.73 ± 0.11, P = 0.05). After selectiveRCM loading, there was no diaphragm fatigue, butPes,twCMS was significantlyreduced (30%). These findings support the role of rib cagestiffening by CMS-related RCM contraction in the ELS-CMSdifferences and suggest that CMS can be used to assess RCM fatigue. 相似文献
2.
Ethylene action in plants contains nine articles on the roleof ethylene in plants, the primary focus being on responsesto ethylene. Four articles cover the role of ethylene as a plantgrowth regulator, including articles on the general effectsof ethylene on growth rates and cell enlargement, as well asmore specific effects of ethylene on stem gravitropic curvatureand the development of adventitious roots. Two articles coverthe role of ethylene in the ageing of plant tissues,including 相似文献
3.
Human skeletal muscle carnitine palmitoyltransferase I activity determined in isolated intact mitochondria 总被引:2,自引:0,他引:2
Berthon Phanelie M.; Howlett Richard A.; Heigenhauser George J.F.; Spriet Lawrence L. 《Journal of applied physiology》1998,85(1):148-153
This study was designed to compare theactivity of skeletal muscle carnitine palmitoyltransferase I (CPT I) intrained and inactive men (n = 14) andwomen (n = 12). CPT Iactivity was measured in intact mitochondria, isolated from needlebiopsy vastus lateralis muscle samples (~60 mg). The variability ofCPT I activity determined on two biopsy samples from the same leg onthe same day was 4.4, whereas it was 7.0% on two biopsy samples fromthe same leg on different days. The method was sensitive to the CPT Iinhibitor malonyl-CoA (88% inhibition) and therefore specific for CPTI activity. The mean CPT I activity for all 26 subjects was 141.1 ± 10.6 µmol · min1 · kgwet muscle (wm)1 and wasnot different when all men vs. all women (140.5 ± 15.7 and 142.2 ± 14.5 µmol · min1 · kgwm1, respectively) were compared. However, CPT Iactivity was significantly higher in trained vs. inactive subjects forboth men (176.2 ± 21.1 vs. 104.1 ± 13.6 µmol · min1 · kgwm1) and women (167.6 ± 14.1 vs. 91.2 ± 9.5 µmol · min1 · kgwm1). CPT I activity was also significantly correlatedwith citrate synthase activity (all subjects,r = 0.76) and maximal oxygen consumption expressed in milliliters per kilogram per minute (all subjects, r = 0.69). Theresults of this study suggest that CPT I activity can be accurately andreliably measured in intact mitochondria isolated from human musclebiopsy samples. CPT I activity was not affected by gender, and higheractivities in aerobically trained subjects appeared to be the result ofincreased mitochondrial content in both men and women. 相似文献
4.
Diffusional permeability (P) to sucrose(Psuc) andNa+(PNa+)was determined in specimens of rabbit sternal parietal pericardium,which may be obtained without stripping. Specimens were mounted in anUssing apparatus with 3H-labeledsucrose and22Na+in a luminal (L) or interstitial (I) chamber.Psuc was 2.16 ± 0.44 for LI and 2.63 ± 0.45 (SE) × 105 cm/s for IL,i.e., ~10 times smaller than that previously obtained in strippedspecimens of pleura despite the similarity of intercellular junctionsin pericardium and pleural mesothelium of various species. Thesefindings suggest that previousPsuc wasoverestimated because stripping damages the mesothelium.PNa+ (×105 cm/s) was 7.07 ± 0.71 for LI and 7.37 ± 0.69 × 105 cm/s for IL.Measurements were also done with phospholipids, which are adsorbed onthe luminal side of mesothelium in vivo. With phospholipids in L,Psuc was 0.75 ± 0.10 and 0.65 ± 0.08 andPNa+was 3.80 ± 0.32 and 3.76 ± 0.15 × 105 cm/s for LI andIL, respectively, i.e., smaller than without phospholipids.With phospholipids in I (where they are not adsorbed), Psuc (2.33 ± 0.42 × 105 cm/s) andPNa+(7.01 ± 0.45 × 105 cm/s) were similar tothose values without phospholipids. Hence, adsorbed phospholipidsdecrease P of mesothelium. If themesothelium were scraped away from the specimen,Psuc of theconnective tissue would be 13.2 ± 0.76 × 105 cm/s.Psuc of themesothelium, computed fromPsuc of theunscraped and scraped specimens, corrected for the effect of unstirredlayers (2.54 and 19.4 × 105 cm/s, respectively),was 2.92 and 0.74 × 105 cm/s without and withphospholipids, respectively. Hence, most of the resistance to diffusionof the pericardium is provided by the mesothelium. 相似文献
5.
Hogan Michael C.; Gladden L. Bruce; Grassi Bruno; Stary Creed M.; Samaja Michele 《Journal of applied physiology》1998,84(6):1882-1888
The purpose ofthis study was to examine the bioenergetics and regulation ofO2 uptake(O2) and force productionin contracting muscle when blood flow was moderately reduced during asteady-state contractile period. Canine gastrocnemius muscle(n = 5) was isolated, and 3-minstimulation periods of isometric, tetanic contractions were elicitedsequentially at rates of 0.25, 0.33, and 0.5 contractions/s (Hz)immediately followed by a reduction of blood flow [ischemic (I)condition] to 46 ± 3% of the value obtained at 0.5 Hz with normal blood flow. TheO2 of thecontracting muscle was significantly (P < 0.05) reduced during the Icondition [6.5 ± 0.8 (SE) ml · 100 g1 · min1]compared with the same stimulation frequency with normal flow (11.2 ± 1.5 ml · 100 g1 · min1),as was the tension-time index (79 ± 12 vs. 123 ± 22 N · g1 · min1,respectively). The ratio ofO2 to tension-time indexremained constant throughout all contraction periods. Musclephosphocreatine concentration, ATP concentration, and lactate effluxwere not significantly different during the I condition compared withthe 0.5-Hz condition with normal blood flow. However, at comparable rates of O2 andtension-time index, muscle phosphocreatine concentration and ATPconcentration were significantly less during the I condition comparedwith normal-flow conditions. These results demonstrate that, in thishighly oxidative muscle, the normal balance ofO2 supply to force output wasmaintained during moderate ischemia by downregulation of forceproduction. In addition,1) the minimal disruption inintracellular homeostasis after the initiation of ischemia waslikely a result of steady-state metabolic conditions having alreadybeen activated, and 2) thedifference in intracellular conditions at comparable rates ofO2 and tension-time index between the normal flow and I condition may have been due to altered intracellular O2 tension. 相似文献
6.
Journal of Plankton Research, 11, 12731295, 1989. The values of P/U0 (Table I) and fluid velocity used to calculatethe energy required for sieving (pp. 12891290) and severalequations (footnote b of Table I; p. 1290, lines 34)are incorrect. The corrected table appears below: Table I. Filter setule measurements (mean and within specimenstandard deviation) of the gnathobases for the cladocerans studiedaGnathobaseof trunklimb number. bP = 8µU0/(b(1 21nt + 1/6(t2) - 1/144(t4))), whereP = pressure drop in dyn cm2, =3.1416, U0 = fluid velocityin cm s1, b = distance between setule centres in cm,t = ( x setule diameter)/b and µ = 0.0101 dyn s1cm2. Formula from Jørgensen (1983). The text (p. 1289, line 19 to p. 1290, line 10) should read: organism. Using a similar argument, a 0.5 mm Ceriodaphnia witha filter area of 0.025 mm2 (Ganf and Shiel, 1985) and pressuredrop P = 2757 dyn cm2 (with fluid velocity of 0.07 cms1) allocates only 2171 ergs h1 to filtrationof a total energy expenditure of 104 ergs h1 [filtrationenergy (ergs h1) = area (cm2) x pressure drop (dyn cm2)x 3600 (s h1) x 1/0.2 (efficiency of conversion of biochemicalinto mechanical work); total energy (ergs h1) = respiration(0.05 µl O2 ind1 h1 consumed; Gophen, 1976)x conversion factor (2 x 105 ergs µl1 O2). Withan estimated 0.034 mm2 in filter area, fluid velocity of 0.041cm s1 and respiration of 1.8 x 104 ergs h1 (calculatedfrom Porter and McDonough, 1984), a 0.5 mm Bosmina uses <4%of its metabolism to overcome filter resistance. The velocities used in the original examples (0.4 cm s1for Ceriodaphnia, 0.2 cm s1 for Bosmina) were derivedfrom literature values of appendage beat rate and estimatesof the distance travelled by the appendages during each beatcycle. This approach unnecessarily assumes that all water movedpasses through the filter. In the new calculations, the flowacross the filter needed for food to be collected by sieving(0.07 cm s1 for Ceriodaphnia and 0.041 cm s1 forBosmina) was determined from the maximum clearance rate/filterarea. The amended energy expenditures, although higher, do notrefute the sieve model of particle collection. 相似文献
7.
Pseudomonas aeruginosa induces changes in fluid transport across airway surface epithelia 总被引:3,自引:0,他引:3
Evans D. J.; Matsumoto P. S.; Widdicombe J. H.; Li-Yun C.; Maminishkis A. A.; Miller S. S. 《American journal of physiology. Cell physiology》1998,275(5):C1284
Fluid transport across cultures of bovine tracheal epitheliumwas measured with a capacitance probe technique. Baseline fluid absorption (Jv)across bovine cells of 3.2 µl · cm2 · h1was inhibited by ~78% after 1 h of exposure to suspensions of Pseudomonas aeruginosa, with aconcomitant decrease in transepithelial potential (TEP) and increase intransepithelial resistance(Rt). Effectsof P. aeruginosa were blocked byamiloride, which decreased Jv by 112% frombaseline of 2.35 ± 1.25 µl · cm2 · h1,increased Rt by101% from baseline of 610 ± 257 · cm2, anddecreased TEP by 91% from baseline of 55 ± 18.5 mV.Microelectrode studies suggested that effects of P. aeruginosa on amiloride-sensitive Na absorption weredue in part to a block of basolateral membrane K channels. In thepresence of Cl transport inhibitors[5-nitro-2-(3-phenylpropylamino)-benzoic acid,H2-DIDS, and bumetanide],P. aeruginosa induced a fluid secretion of ~2.5 ± 0.4 µl · cm2 · h1and decreased Rtwithout changing TEP. However, these changes were abolished when thetransport inhibitors were used in a medium in which Cl was replaced byan impermeant organic anion. Filtrates of P. aeruginosa suspensions had no effect onJv, TEP, orRt. Mutantslacking exotoxin A or rhamnolipids or with defective lipopolysaccharide still inhibited fluid absorption and altered bioelectrical properties. By contrast, mutations in the rpoN gene encodinga factor of RNA polymerase abolished actions of P. aeruginosa. In vivo, changes in transepithelial saltand water transport induced by P. aeruginosa may alter viscosity and ionic composition ofairway secretions so as to foster further bacterial colonization. 相似文献
8.
Devor DC Bridges RJ Pilewski JM 《American journal of physiology. Cell physiology》2000,279(2):C461-C479
Forskolin,UTP, 1-ethyl-2-benzimidazolinone (1-EBIO), NS004, 8-methoxypsoralen(Methoxsalen; 8-MOP), and genistein were evaluated for theireffects on ion transport across primary cultures of human bronchialepithelium (HBE) expressing wild-type (wt HBE) and F508(F-HBE) cystic fibrosis transmembrane conductance regulator. In wtHBE, the baseline short-circuit current (Isc)averaged 27.0 ± 0.6 µA/cm2 (n = 350). Amiloride reduced this Isc by 13.5 ± 0.5 µA/cm2 (n = 317). In F-HBE,baseline Isc was 33.8 ± 1.2 µA/cm2 (n = 200), and amiloride reducedthis by 29.6 ± 1.5 µA/cm2 (n = 116), demonstrating the characteristic hyperabsorption of Na+ associated with cystic fibrosis (CF). In wt HBE,subsequent to amiloride, forskolin induced a sustained,bumetanide-sensitive Isc(Isc = 8.4 ± 0.8 µA/cm2; n = 119). Addition ofacetazolamide, 5-(N-ethyl-N-isopropyl)-amiloride, and serosal 4,4'-dinitrostilben-2,2'-disulfonic acid further reduced Isc, suggesting forskolin also stimulatesHCO3 secretion. This was confirmed by ionsubstitution studies. The forskolin-induced Iscwas inhibited by 293B, Ba2+, clofilium, and quinine,whereas charybdotoxin was without effect. In F-HBE the forskolinIsc response was reduced to 1.2 ± 0.3 µA/cm2 (n = 30). In wt HBE, mucosal UTPinduced a transient increase in Isc ( Isc = 15.5 ± 1.1 µA/cm2;n = 44) followed by a sustained plateau, whereas inF-HBE the increase in Isc was reduced to5.8 ± 0.7 µA/cm2 (n = 13). In wtHBE, 1-EBIO, NS004, 8-MOP, and genistein increased Isc by 11.6 ± 0.9 (n = 20), 10.8 ± 1.7 (n = 18), 10.0 ± 1.6 (n = 5), and 7.9 ± 0.8 µA/cm2(n = 17), respectively. In F-HBE, 1-EBIO, NS004, and8-MOP failed to stimulate Cl secretion. However, additionof NS004 subsequent to forskolin induced a sustained Clsecretory response (2.1 ± 0.3 µA/cm2,n = 21). In F-HBE, genistein alone stimulatedCl secretion (2.5 ± 0.5 µA/cm2,n = 11). After incubation of F-HBE at 26°C for24 h, the responses to 1-EBIO, NS004, and genistein were allpotentiated. 1-EBIO and genistein increased Na+ absorptionacross F-HBE, whereas NS004 and 8-MOP had no effect. Finally,Ca2+-, but not cAMP-mediated agonists, stimulatedK+ secretion across both wt HBE and F-HBE in aglibenclamide-dependent fashion. Our results demonstrate thatpharmacological agents directed at both basolateral K+ andapical Cl conductances directly modulate Clsecretion across HBE, indicating they may be useful in ameliorating theion transport defect associated with CF. 相似文献
9.
Bundgaard H 《American journal of physiology. Cell physiology》2004,287(1):C135-C141
Potassium depletion (KD) is a very common clinical entity often associated with adverse cardiac effects. KD is generally considered to reduce muscular Na-K-ATPase density and secondarily reduce K uptake capacity. In KD rats we evaluated myocardial Na-K-ATPase density, ion content, and myocardial K reuptake. KD for 2 wk reduced plasma K to 1.8 ± 0.1 vs. 3.5 ± 0.2 mM in controls (P < 0.01, n = 7), myocardial K to 80 ± 1 vs. 86 ± 1 µmol/g wet wt (P < 0.05, n = 7), increased Mg, and induced a tendency to increased Na. Myocardial Na-K-ATPase 2-subunit abundance was reduced by 30%, whereas increases in 1- and K-dependent pNPPase activity of 24% (n = 6) and 13% (n = 6), respectively, were seen. This indicates an overall upregulation of the myocardial Na-K pump pool. KD rats tolerated a higher intravenous KCl dose. KCl infusion until animals died increased myocardial K by 34% in KD rats and 18% in controls (P < 0.05, n = 6 for both) but did not induce different net K uptake rates between groups. However, clamping plasma K at 5.5 mM by KCl infusion caused a higher net K uptake rate in KD rats (0.22 ± 0.04 vs. 0.10 ± 0.03 µmol·g wet wt1·min1; P < 0.05, n = 8). In conclusion, a minor KD-induced decrease in myocardial K increased Na-K pump density and in vivo increased K tolerance and net myocardial K uptake rate during K repletion. Thus the heart is protected from major K losses and accumulates considerable amounts of K during exposure to high plasma K. This is of clinical interest, because a therapeutically induced rise in myocardial K may affect contractility and impulse generation-propagation and may attenuate increased myocardial Na, the hallmark of heart failure. Na-K-ATPase; ion homeostasis; heart failure; iatrogenic potassium depletion 相似文献
10.
Determinants of diastolic myocardial tissue Doppler velocities: influences of relaxation and preload 总被引:10,自引:0,他引:10
Firstenberg Michael S.; Greenberg Neil L.; Main Michael L.; Drinko Jeanne K.; Odabashian Jill A.; Thomas James D.; Garcia Mario J. 《Journal of applied physiology》2001,90(1):299-307
Myocardial tissueDoppler echocardiography (TDE) has been proposed as a tool for theassessment of diastolic function. Controversy exists regarding whetherTDE measurements are influenced by preload. In this study, leftventricular volume and high-fidelity pressures were obtained ineight closed-chest dogs during intermittent caval occlusion. The timeconstant of isovolumic ventricular relaxation () was alteredwith varying doses of dobutamine and esmolol. Peak early diastolicmyocardial (Em) and transmitral (E)velocities were measured before and after preload reduction. Therelative effects of changes in preload and relaxation were determinedfor Em and compared with their effects onE. The following results were observed: caval occlusionsignificantly decreased E (E = 16.4 ± 3.3 cm/s, 36.6 ± 13.7%, P < 0.01) andEm (Em = 1.3 ± 0.4 cm/s, 32.5 ± 26.1%, P < 0.01) underbaseline conditions. However, preload reduction was similar forE under all lusitropic conditions (P = notsignificant), but these effects on Em decreasedwith worsening relaxation. At < 50 ms, changes inEm with preload reduction were significantlygreater (Em = 2.8 ± 0.6 cm/s) than at = 50-65 ms (Em = 1.2 ± 0.2 cm/s) and at >65 ms(Em = 0.5 ± 0.1 cm/s,P < 0.05). We concluded that TDEEm is preload dependent. However, this effectdecreases with worsening relaxation. 相似文献
11.
Responses of Soybean Leaf Angle, Photosynthesis and Stomatal Conductance to Leaf and Soil Water Potential 总被引:2,自引:0,他引:2
The hypothesis that soil water potential (s) is better correlatedto heliotropic leaf orientation, photosaturated photosyntheticCO2 assimilation and stomatal conductance during periods oflimited water availability than is bulk leaf water potential(1) was examined in greenhouse-grown soybean (Glycine max) plants,submitted to a progressive drought. Paired plants were exposedto either 1000 or 100 µmol m2 s1 photonflux densities (PFD) for 4560 mins. The higher irradianceinduced short-term decreases in 1, due to increased transpiration,while l in the plant exposed to low PFD did not decrease. Thesechanges in 1 occurred independently of changes in soil waterstatus. Concurrent to the light treatments, a single attachedleaf from each of the two plants was isolated from the restof the plant by shading, and the pulvinus of its terminal leafletwas exposed to a perpendicular PFD of 500 µmol m2S1. Leaf movement of this leaflet was recorded in responseto this light, until a stable leaflet angle was achieved. Valuesof s and l (before and after light treatment), and photosaturatedrates of photosynthesis and stomatal conductance, were thenmeasured on these leaves. Leaflet angle and gas exchange werebetter correlated with s (r2 = 0.50, 0.50 and 0.57 for angle,photosynthesis and conductance, respectively) than with l especiallywhen l was the result of short-term, high-light induced changesin leaf water status (r2 = 0.36, 0.32 and 0.49, for the sameparameters). Leaflet angle was also correlated with stomatalconductance (r2 = 0.61) and photosynthetic rate (r2 = 0.60),suggesting a close association between leaf orientation, leafmetabolism and soil water availability. Glycine max (L.) Merr. cv. Essex, soybean, heliotropism, water potential, photosynthesis, stomatal conductance, solar tracking 相似文献
12.
Crawford Paul; Good Peter A.; Gutierrez Eric; Feinberg Joshua H.; Boehmer John P.; Silber David H.; Sinoway Lawrence I. 《Journal of applied physiology》1997,82(5):1601-1606
Crawford, Paul, Peter A. Good, Eric Gutierrez, Joshua H. Feinberg, John P. Boehmer, David H. Silber, and Lawrence I. Sinoway. Effects of supplemental oxygen on forearm vasodilation in humans.J. Appl. Physiol. 82(5):1601-1606, 1997.Supplemental O2 reduces cardiac output andraises systemic vascular resistance in congestive heart failure. Inthis study, 100% O2 was given tonormal subjects and peak forearm flow was measured. Inexperiment 1, 100%O2 reduced blood flow andincreased resistance after 10 min of forearm ischemia (flow 56.7 ± 7.9 vs. 47.8 ± 6.7 ml · min1 · 100 ml1;P < 0.02; vascular resistance 1.7 ± 0.2 vs. 2.4 ± 0.4 mmHg · min · 100 ml · ml1;P < 0.03). Inexperiment 2, lower body negativepressure (LBNP; 30 mmHg) and venous congestion (VC) simulatedthe high sympathetic tone and edema of congestive heart failure.Postischemic forearm flow and resistance were measured under fourconditions: room air breathing (RA); LBNP+RA; RA+LBNP+VC; and 100%O2+LBNP+VC. LBNP and VC did notlower peak flow. However, O2raised minimal resistance (2.3 ± 0.4 RA; 2.8 ± 0.5 O2+LBNP+VC,P < 0.04). When O2 alone(experiment 1) was compared withO2+LBNP+VC(experiment 2), no effect of LBNP+VCon peak flow or minimum resistance was noted, although the return rateof flow and resistance toward baseline was increased.O2 reduces peak forearm flow evenin the presence of LBNP and VC. 相似文献
13.
Gozal Evelyne; Roussel Anisha L.; Holt Gregory A.; Gozal Lyad; Gozal Yair M.; Torres Jose E.; Gozal David 《Journal of applied physiology》1998,84(6):1982-1990
This study aimedto determine the role of protein kinase C (PKC) in signal transductionmechanisms underlying ventilatory regulation in the nucleus tractussolitarii (NTS). Microinjection of phorbol 12-myristate 13-acetate intothe commissural NTS of nine chronically instrumented, unrestrained ratselicited significant cardiorespiratory enhancements that lasted for atleast 4 h, whereas administration of vehicle(n = 15) or the inactive phorbol ester 4-phorbol 12,13-didecanoate (n = 7)did not elicit minute ventilation (E)changes. Peak hypoxic Eresponses (10% O2-balanceN2) were measured in 19 additional animals after NTS microinjection of bisindolylmaleimide(BIM) I, a selective PKC inhibitor (n = 12), BIM V (inactive analog; n = 7),or vehicle (Con; n = 19). In Con,E increased from 139 ± 9 to 285 ± 26 ml/min in room air and hypoxia, respectively, and similarresponses occurred after BIM V. BIM I did not affect room airE but markedly attenuated hypoxia-induced E increases (128 ± 12 to 167 ± 18 ml/min; P < 0.02 vs. Con and BIM V). When BIM I was microinjected into the cerebellum(n = 4), cortex(n = 4), or spinal cord(n = 4),E responses were similar to Con.Western blots of subcellular fractions of dorsocaudal brain stemlysates revealed translocation of PKC, , , , , and isoenzymes during acute hypoxia, and enhanced overall PKC activity wasconfirmed in the particulate fraction of dorsocaudal brain stem lysatesharvested after acute hypoxia. These studies suggest that, in the adultrat, PKC activation in the NTS mediates essential components of theacute hypoxic ventilatory response. 相似文献
14.
Li Yansui; Kuang Kunyan; Yerxa Benjamin; Wen Quan; Rosskothen Heinz; Fischbarg Jorge 《American journal of physiology. Cell physiology》2001,281(2):C595
Rabbit conjunctival epithelium exhibits UTP-dependentCl secretion into the tears. We investigated whetherfluid secretion also takes place. Short-circuit current(Isc) was 14.9 ± 1.4 µA/cm2(n = 16). Four P2Y2 purinergic receptoragonists [UTP and the novel compounds INS365, INS306, and INS440(Inspire Pharmaceuticals)] added apically (10 µM) resulted intemporary (~30 min) Isc increases (88%, 66%,57%, and 28%, respectively; n = 4 each). Importantly, the conjunctiva transported fluid from serosa to mucosa at a rate of6.5 ± 0.7 µl · h1 · cm2 (range2.1-15.3, n = 20). Fluid transport was stimulatedby mucosal additions of 10 µM: 1) UTP, from 7.4 ± 2.3 to 10.7 ± 3.3 µl · h1 · cm2,n = 5; and 2) INS365, from 6.3 ± 1.0 to 9.8 ± 2.5 µl · h1 · cm2,n = 5. Fluid transport was abolished by 1 mMouabain (n = 5) and was drastically inhibited by 300 µM quinidine (from 6.4 ± 1.2 to 3.6 ± 1.0 µl · h1 · cm2,n = 4). We conclude that this epithelium secretes fluidactively and that P2Y2 agonists stimulate bothCl and fluid secretions. 相似文献
15.
Allometric modeling does not determine a dimensionless power function ratio for maximal muscular function 总被引:2,自引:0,他引:2
Batterham, Alan M., and Keith P. George. Allometricmodeling does not determine a dimensionless power function ratio formaximal muscular function. J. Appl.Physiol. 83(6): 2158-2166, 1997.In the exercise sciences, simple allometry(y = axb) israpidly becoming the method of choice for scaling physiological andhuman performance data for differences in body size. The purpose ofthis study is to detail the specific regression diagnostics required tovalidate such models. The sum (T, in kg) of the "snatch" and"clean-and-jerk" lifts of the medalists from the 1995 Men's andWomen's World Weightlifting Championships was modeled as a function ofbody mass (M, in kg). A log-linearized allometric model (ln T = lna + bln M) yielded a common mass exponent(b) of 0.47 (95% confidenceinterval = 0.43-0.51, P < 0.01). However, size-related patterned deviations in the residuals wereevident, indicating that the allometric model was poorly specified and that the mass exponent was not size independent. Model respecification revealed that second-order polynomials provided the best fit, supporting previous modeling of weightlifting data (R. G. Sinclair. Can. J. Appl. Sport Sci. 10:94-98, 1985). The model parameters (means ± SE) were T = (21.48 ± 16.55) + (6.119 ± 0.359)M (0.022 ± 0.002)M2(R2 = 0.97) for men and T = (20.73 ± 24.14) + (5.662 ± 0.722)M (0.031 ± 0.005)M2(R2 = 0.92) for women. We conclude that allometric scaling should beapplied only when all underlying model assumptions have been rigorouslyevaluated. 相似文献
16.
Competition for Light in a Plant Monoculture Modelled as a Spatial Stochastic Process 总被引:7,自引:1,他引:6
In a glasshouse experiment closely spaced plants were regularlysub-irrigated with nutrient solution and it was assumed thatcompetition between individuals was for light. Interaction betweenneighbours is modelled as a spatial process in relation to differencesin plant height. The influence one plant has on another is calculatedas the ratio of the angle ß between their apices,and an angle which represents the intensity of competitionin the population as a whole. When ß < suppressionis considered to occur, i.e. tall plants suppress short plantsbut not vice versa, competition is one-sided. The status ofeach plant within the population is calculated by multiplicationof its individual plant neighbour interaction terms where ß< . This need not be restricted to nearest neighbours. Plantswith status = 1 are free from competition, those with status= 0 are totally suppressed. It is acknowledged that other processes than that modelled ascompetition may result in variation in relative growth rates.To account for this plant status is used to modify a relativegrowth rate drawn from a population of mean µ and standarddeviation . Plants for which status µ is less than anestimated are considered to die. Parameter values were estimatedfor a sequence of fortnightly harvests of glasshouse grown Tagetespatula. There was a decrease in µ and , increased andplants came to compete with their second nearest neighboursas well as their nearest as the community developed. The greatest was at an intermediate stage, suggesting that more frequentassessments of the competition process are required at somestages than at others. Model parameters fitted to one data setwere used in a Monte Carlo testing procedure with a second,independent data set. The importance of this technique is stressedbecause plants in a single community are not independent realizationof the competition process. Simulations with the model reproducedboth bimodality in the frequency distributions of plant sizeand an even spatial distribution of large or surviving plants,features which have been observed in a range of plant monocultures.To achieve these features it was essential that plant interactionbe modelled as a one-sided process. Tagetes patula L., competition, light, monoculture, growth model 相似文献
17.
两种麦蚜取食诱导小麦抗性品种后对后来取食蚜生物学特性的影响 总被引:4,自引:1,他引:4
刺吸式昆虫在刺吸作物韧皮部取食后会影响作物的正常生长发育,随着作物抗性及昆虫种类的不同,作物反过来也会对昆虫造成或正或反的影响,然而一种刺吸式昆虫取食后对后来者有什么样的影响目前尚不确定。本研究通过严谨的实验方法,即选定3个不同国家的小麦抗性品种98-10-30、Amigo和Batis,在所有条件严格统一的人工智能控制温室内,通过各处理在同一植株上先后不同的接蚜方式,分别测定了麦二叉蚜Schizaphis graminum (Rondani)和麦长管蚜Sitobion avenae Fab.在前期被蚜虫危害的抗虫品种98-10-30、Amigo和Batis上的发育历期、体重差及相对日均体重增长率(mean relative growth rate MRGR)等生物学参数。结果表明:品种不同,蚜虫在不同处理条件下取食作物时受到的影响也不同,即在品种98-10-30上,通过与前期不接虫的对照及前期接不同麦蚜的相关处理比较,麦长管蚜对后期取食的麦二叉蚜(MRGR=0.0974±0.0071)具有抑制作用,而麦二叉蚜对后期取食的麦长管蚜(MRGR=0.1614±0.0048)却有促进作用;在品种Amigo上,前期麦蚜的危害对麦长管蚜的取食具有促进作用,而在品种Batis上前期危害对麦二叉蚜的取食具有促进作用。同时明确了3个品种对两种蚜虫的抗性状况,即在前期无蚜虫危害时,品种98-10-30和Batis对两种麦蚜的抗性相当;在前期有麦蚜危害时,品种98-10-30对麦二叉蚜的抗性较好,而品种Batis对麦长管蚜的抗性较好;品种Amigo无论在任何处理下均对麦二叉蚜的抗性较好。 相似文献
18.
Guanine nucleotide transport by atractyloside-sensitive and -insensitive carriers in isolated heart mitochondria 总被引:2,自引:0,他引:2
McKee EE Bentley AT Smith RM Kraas JR Ciaccio CE 《American journal of physiology. Cell physiology》2000,279(6):C1870-C1879
Inprevious work (McKee EE, Bentley AT, Smith RM Jr, and Ciaccio CE,Biochem Biophys Res Commun 257: 466-472, 1999), the transport of guanine nucleotides into the matrix of intact isolated heart mitochondria was demonstrated. In this study, the time course andmechanisms of guanine nucleotide transport are characterized. Twodistinct mechanisms of transport were found to be capable of movingguanine nucleotides across the inner membrane. The first carrier wassaturable, displayed temperature dependence, preferred GDP to GTP, anddid not transport GMP or IMP. When incubated in the absence ofexogenous ATP, this carrier had a Vmax of946 ± 53 pmol · mg1 · min1 with aKm of 2.9 ± 0.3 mM for GDP. However,transport of GTP and GDP on this carrier was completely inhibited byphysiological concentrations of ATP, suggesting that this carrier wasnot involved with guanine nucleotide transport in vivo. Becausetransport on this carrier was also inhibited by atractyloside, thiscarrier was consistent with the well-characterized ATP/ADP translocase. The second mechanism of guanine nucleotide uptake was insensitive toatractyloside, displayed temperature dependence, and was capable oftransporting GMP, GDP, and GTP at approximately equal rates but did nottransport IMP, guanine, or guanosine. GTP transport via this mechanismwas slow, with a Vmax of 48.7 ± 1.4 pmol · mg1 · min1 and aKm = 4.4 ± 0.4 mM. However, becausethe requirement for guanine nucleotide transport is low in nondividingtissues such as the heart, this transport process is neverthelesssufficient to account for the matrix uptake of guanine nucleotides andmay represent the physiological mechanism of transport. 相似文献
19.
We have used the recombinantNH2-terminalmyc-tagged rabbitNa+-glucose transporter (SGLT1) tostudy the regulation of this carrier expressed in COS-7 cells.Treatment of cells with a protein kinase C (PKC) agonist, phorbol12-myristate 13-acetate (PMA), caused a significant decrease (38.03 ± 0.05%) in methyl-D-glucopyranoside transportactivity that could not be emulated by 4-phorbol 12,13-didecanoate. The decrease in sugar uptake stimulated by PMA was reversed by the PKCinhibitor bisindolylmaleimide I. The maximal rate ofNa+-glucose cotransport activity(Vmax) wasdecreased from 1.29 ± 0.09 to 0.85 ± 0.04 nmol · min1 · mgprotein1 after PMAexposure. However, measurement of high-affinityNa+-dependent phloridzin bindingrevealed that there was no difference in the number of cell surfacetransporters after PMA treatment; maximal binding capacities were 1.54 ± 0.34 and 1.64 ± 0.21 pmol/mg protein for untreated andtreated cells, respectively. The apparent sugar binding affinity(Michaelis-Menten constant) and phloridzin binding affinity(dissociation constant) were not affected by PMA. Because PKC reducedVmax withoutaffecting the number of cell surface SGLT1 transporters, we concludethat PKC has a direct effect on the carrier, resulting in a lowering ofthe transporter turnover rate by a factor of two. 相似文献
20.
Ethylene accumulation in waterlogged Rumex plants promotes formation of adventitious roots 总被引:8,自引:0,他引:8
Visser Eric J.W.; Bgemann Gerard M.; Blom Cornelis W.P.M.; Voesenek Laurentius A.C.J. 《Journal of experimental botany》1996,47(3):403-410
Accumulation of the gaseous plant hormone ethylene is very importantfor the induction of several responses of plants to flooding.However, little is known about the role of this gas in the formationof flooding-induced adventitious roots. Formation of adventitiousroots in Rumex species is an adaptation of these plants to floodedsoil conditions. The large air-spaces in these roots enablesdiffusion of gases between shoot and roots. Application of ethylene to non-flooded Rumex plants resultedin the formation of adventitious roots. In R. palustris Sm.shoot elongation and epinasty were also observed. The numberof roots in R. thyrsiflorus Fingerh. was much lower than inR. palustris, which corresponds with the inherent differencein root forming capacity between these two species. Ethyleneconcentrations of 1.52µI I 1 induced a maximumnumber of roots in both species. Quantification of ethylene escaping from root systems of Rumexplants that were de-submerged after a 24 h submergence periodshowed that average ethylene concentrations in submerged rootsreached 1.8 and 9.1 µl I1 in R. palustris and R.thyrsiflorus, respectively. Inhibition of ethylene productionin R. palustris by L--(2-aminoethoxyvinyl)-glycine (AVG) or-aminobutyric acid (AIB) decreased the number of adventitiousroots induced by flooding, indicating that high ethylene concentrationsmay be a prerequisite for the flooding-induced formation ofadventitious roots in Rumex species. Key words: Adventitious roots, epinasty, ethylene, flooding, Rumex, shoot elongation 相似文献