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1.
The two parameters of the hyperbolic tangent equation, Pm and, were estimated from in situ vertical profiles of primary productionusing mesocosm data along a nutrient gradient. The parameters,derived from 4-h (around noon) 14C incubations, were used togetherwith the photosynthesis-light curve and hourly solar radiationdata to calculate daily primary production rates (Pd). Approximately40% of the daily production occurred in the 4 h around noon.Considering parameter uncertainty, there was no indication ofan increase in variation in production with increased nutrientloading, nor did biomass-specific P-I parameters increase. Annualproduction ranged from 82 to 901 g C m2 year1and was highest in the highest nutrient treatment tank. Dailyproductivity ranged from 0.02 to 9.1 g C m2 day1and was significantly correlated, in all treatments, with acomposite parameter BI0/k (where B is phytoplankton biomass;I0 is daily radiation and k is the extinction coefficient).Linear regressions of Pd against BI0/k indicated that much ofthe variability (86%) in productivity was explained by lightavailability and phytoplankton biomass. Two approaches for predictingproductivity were compared: (i) predicting production directlyfrom environmental variables (i.e. BI0/k) and (ii) predictingthe parameters of the P-I curve from environmental variablesand using these to calculate daily production. 相似文献
2.
Light and dark bottle experiments, carried out in three systemsin the Netherlands, were used to estimate the parameters ofmodels relating the oxygen production rate to incident lightintensity. The maximum production rate (PM) and the light saturationconstant (IS) were estimated using both gross and nett oxygenproduction data. In the latter case, the community oxygen consumptionrate (Rox was also estimated. Eight models were compared withrespect to goodness of fit, as has been accomplished previouslyby Jassby and Platt (Limnol. Oceanogr., 21, 540547, 1976)and many others. This study, however, emphasizes the problemof parameter correlation and the consequential usefulness ofthese type of experiments to identify the P/I curve parameters.The results show that at a 90% level of confidence, the modelscannot be distinguished with respect to goodness of fit. However,the models do show distinct differences in parameter correlation.Parameter correlation was shown to be related to the shape ofthe curve. P/I curves with high convexity were shown to be lesssensitive for parameter correlation. In particular, models showinglow convexity suffer from over-paraineterisation, which meansthat on the basis of the observed production rates it is difficultto discriminate between the parameters. Also, alternative modelformulations, using PM and the initial slope (), were investigated.These formulations produced less parameter correlation. However,for models with low convexity, showing high parameter correlationanyway, the reduction is limited. The use of nett oxygen productiondata does not show a significant difference in fit at a 90%confidence level. However, measured Rox from dark bottle experimentstends to be higher than the values found by estimating Rox fromnett oxygen production. 相似文献
3.
Weiss RG O'Connell KM Flucher BE Allen PD Grabner M Dirksen RT 《American journal of physiology. Cell physiology》2004,287(4):C1094-C1102
Malignant hyperthermia (MH) is an inherited pharmacogenetic disorder caused by mutations in the skeletal muscle ryanodine receptor (RyR1) and the dihydropyridine receptor (DHPR) 1S-subunit. We characterized the effects of an MH mutation in the DHPR cytoplasmic III-IV loop of 1S (R1086H) on DHPR-RyR1 coupling after reconstitution in dysgenic (1S null) myotubes. Compared with wild-type 1S, caffeine-activated Ca2+ release occurred at approximately fivefold lower concentrations in nonexpressing and R1086H-expressing myotubes. Although maximal voltage-gated Ca2+ release was similar in 1S- and R1086H-expressing myotubes, the voltage dependence of Ca2+ release was shifted 5 mV to more negative potentials in R1086H-expressing myotubes. Our results demonstrate that 1S functions as a negative allosteric modulator of release channel activation by caffeine/voltage and that the R1086H MH mutation in the intracellular III-IV linker disrupts this negative regulatory influence. Moreover, a low caffeine concentration (2 mM) caused a similar shift in voltage dependence of Ca2+ release in 1S- and R1086H-expressing myotubes. Compared with 1S-expressing myotubes, maximal L channel conductance (Gmax) was reduced in R1086H-expressing myotubes (1S 130 ± 10.2, R1086H 88 ± 6.8 nS/nF; P < 0.05). The decrease in Gmax did not result from a change in retrograde coupling with RyR1 as maximal conductance-charge movement ratio (Gmax/Qmax) was similar in 1S- and R1086H-expressing myotubes and a similar decrease in Gmax was observed for an analogous mutation engineered into the cardiac L channel (R1217H). In addition, both R1086H and R1217H DHPRs targeted normally and colocalized with RyR1 in sarcoplasmic reticulum (SR)-sarcolemmal junctions. These results indicate that the R1086H MH mutation in 1S enhances RyR1 sensitivity to activation by both endogenous (voltage sensor) and exogenous (caffeine) activators. excitation-contraction coupling; calcium channel; muscle disease 相似文献
4.
Smith, J. R., Walker, N. A. and Smith, F. A. 1987. Potassiumtransport across the membranes of Chara. III. Effects of pH,inhibitors and illumination.J. exp. Bot. 38: 778787. The effects of several treatments, normally used to inhibitelectrogenic proton transport, upon the potassium permeability(Pk) of the membranes of Chara were examined by means of simultaneousmeasurements of the 42K influx (inK) and the membrane electricalconductance (Gm). inK, PK and Gmwere found to be substantiallyunaffected when the external pH (pH?) was varied over the range5?0 to 85. However, when pH? was increased to 11 it was foundthat, although Gm increased considerably, both Pk and inK decreasedtypically by an order of magnitude. When cells were placed intotal darkness, PK decreased substantially only after one dayhad elapsed. For the particular experimental conditions used,the inhibitors DES, NaN3, and La3+ were found to alter PK, whereasDCCD left PK substantially unaffected. These results suggestthat care must be taken with some common procedures used toexamine the electrical properties of the electrogenic protonpump. Key words: Potassium, pH, illumination, inhibitors 相似文献
5.
cAMP-independent phosphorylation activation of CFTR by G proteins in native human sweat duct 总被引:3,自引:0,他引:3
It is generally believed thatcAMP-dependent phosphorylation is the principle mechanism foractivating cystic fibrosis transmembrane conductance regulator (CFTR)Cl channels. However, we showed that activating Gproteins in the sweat duct stimulated CFTR Cl conductance(GCl) in the presence of ATP alone without cAMP. The objective of this study was to test whether the G protein stimulation of CFTR GCl is independent ofprotein kinase A. We activated G proteins and monitored CFTRGCl in basolaterally permeabilized sweat duct.Activating G proteins with guanosine5'-O-(3-thiotriphosphate) (10-100 µM) stimulated CFTRGCl in the presence of 5 mM ATP alone withoutcAMP. G protein activation of CFTR GCl requiredMg2+ and ATP hydrolysis (5'-adenylylimidodiphosphate couldnot substitute for ATP). G protein activation of CFTRGCl was 1) sensitive to inhibition bythe kinase inhibitor staurosporine (1 µM), indicating that theactivation process requires phosphorylation; 2) insensitive to the adenylate cyclase (AC) inhibitors 2',5'-dideoxyadenosine (1 mM)and SQ-22536 (100 µM); and 3) independent ofCa2+, suggesting that Ca2+-dependent proteinkinase C and Ca2+/calmodulin-dependent kinase(s) are notinvolved in the activation process. Activating AC with106 M forskolin plus 106 M IBMX (in thepresence of 5 mM ATP) did not activate CFTR, indicating that cAMPcannot accumulate sufficiently to activate CFTR in permeabilized cells.We concluded that heterotrimeric G proteins activate CFTR GCl endogenously via a cAMP-independent pathwayin this native absorptive epithelium. 相似文献
6.
Ferris, Daniel P., and Claire T. Farley. Interaction ofleg stiffness and surface stiffness during human hopping.J. Appl.Physiol. 82(1): 15-22, 1997.When mammals run,the overall musculoskeletal system behaves as a single linear "legspring." We used force platform and kinematic measurements todetermine whether leg spring stiffness(kleg) isadjusted to accommodate changes in surface stiffness(ksurf) whenhumans hop in place, a good experimental model for examiningadjustments tokleg in bouncinggaits. We found thatkleg was greatlyincreased to accommodate surfaces of lower stiffnesses. The seriescombination ofkleg andksurf[total stiffness(ktot)]was independent ofksurf at a givenhopping frequency. For example, when humans hopped at a frequency of 2 Hz, they tripled theirkleg on the leaststiff surface(ksurf = 26.1 kN/m; kleg = 53.3 kN/m) compared with the most stiff surface(ksurf = 35,000 kN/m; kleg = 17.8 kN/m). Values forktot were notsignificantly different on the least stiff surface (16.7 kN/m) and themost stiff surface (17.8 kN/m). Because of thekleg adjustment,many aspects of the hopping mechanics (e.g., ground-contact time andcenter of mass vertical displacement) remained remarkably similardespite a >1,000-fold change inksurf. This studyprovides insight into howkleg adjustmentscan allow similar locomotion mechanics on the variety of terrainsencountered by runners in the natural world. 相似文献
7.
Recovery of free ADP, Pi, and free energy of ATP hydrolysis in human skeletal muscle 总被引:1,自引:0,他引:1
Wackerhage Henning; Hoffmann Uwe; Essfeld Dieter; Leyk Dieter; Mueller Klaus; Zange Jochen 《Journal of applied physiology》1998,85(6):2140-2145
We measuredsignificant undershoots of the concentrations of free ADP([ADP]) and Pi([Pi]) and the freeenergy of ATP hydrolysis (GATP) belowinitial resting levels during recovery from severe ischemic exercisewith 31P-nuclear magneticresonance spectroscopy in 11 healthy sports students. Undershoots ofthe rate of oxidative phosphorylation would be predicted if the rate ofoxidative phosphorylation would depend solely on free[ADP],[Pi], orGATP. However,undershoots of the rate of oxidative phosphorylation have not beenreported in the literature. Furthermore, undershoots of the rate ofoxidative phosphorylation are unlikely because there is evidence that a balance between ATP production and consumption cannot be achieved if anundershoot of the rate of oxidative phosphorylation actually occurs.Therefore, oxidative phosphorylation seems to depend not only on free[ADP],[Pi], orGATP. Anexplanation is that acidosis-related or other factors control oxidativephosphorylation additionally, at least under some conditions. 相似文献
8.
Fan H Zingarelli B Peck OM Teti G Tempel GE Halushka PV Spicher K Boulay G Birnbaumer L Cook JA 《American journal of physiology. Cell physiology》2005,289(2):C293-C301
Heterotrimeric Gi proteins may play a role in lipopolysaccharide (LPS)-activated signaling through Toll-like receptor 4 (TLR4), leading to inflammatory mediator production. Although LPS is a TLR4 ligand, the gram-positive bacterium Staphylococcus aureus (SA) is a TLR2 ligand, and group B streptococci (GBS) are neither TLR2 nor TLR4 ligands but are MyD88 dependent. We hypothesized that genetic deletion of Gi proteins would alter mediator production induced by LPS and gram-positive bacterial stimulation. We examined genetic deletion of Gi2 or Gi1/3 protein in Gi2-knockout (Gi2/) or Gi1/3-knockout (Gi1/3/) mice. LPS-, heat-killed SA-, or GBS-induced mediator production in splenocytes or peritoneal macrophages (M) was investigated. There were significant increases in LPS-, SA-, and GBS-induced production of TNF- and IFN- in splenocytes from Gi2/ mice compared with wild-type (WT) mice. Also, LPS-induced TNF- was increased in splenocytes from Gi1/3/ mice. In contrast to splenocytes, LPS-, SA-, and GBS-induced TNF-, IL-10, and thromboxane B2 (TxB2) production was decreased in M harvested from Gi2/ mice. Also, LPS-induced production of IL-10 and TxB2 was decreased in M from Gi1/3/ mice. In subsequent in vivo studies, TNF- levels after LPS challenge were significantly greater in Gi2/ mice than in WT mice. Also, myeloperoxidase activity, a marker of tissue neutrophil infiltration, was significantly increased in the gut and lung of LPS-treated Gi2/ mice compared with WT mice. These data suggest that Gi proteins differentially regulate murine TLR-mediated inflammatory cytokine production in a cell-specific manner in response to both LPS and gram-positive microbial stimuli. Gi protein-deficient mice; endotoxin; group B streptococci; Staphylococcus aureus; Toll-like receptors 相似文献
9.
Kawanabe Y Hashimoto N Masaki T 《American journal of physiology. Cell physiology》2004,286(3):C596-C600
We demonstrated recently that norepinephrine activates Ca2+-permeable nonselective cation channels (NSCCs) in Chinese hamster ovary cells stably expressing 1A-adrenergic receptors (CHO-1A). Moreover, extracellular Ca2+ through NSCCs plays essential roles in norepinephrine-induced arachidonic acid release. The purpose of the present study was to identify the G proteins involved in the activation of NSCCs and arachidonic acid release by norepinephrine. For these purposes, we used U73122, an inhibitor of phospholipase C (PLC), and dominant negative mutants of G12 and G13 (G12G228A and G13G225A, respectively). U73122 failed to inhibit NSCCs activation by norepinephrine. The magnitudes of norepinephrine-induced extracellular Ca2+ influx in CHO-1A microinjected with G13G225A were smaller than those in CHO-1A. In contrast, the magnitudes of norepinephrine-induced extracellular Ca2+ influx in CHO-1A microinjected with G12G228A were similar to those in CHO-1A. In addition, neither a Rho-associated kinase (ROCK) inhibitor nor a phosphoinositide 3-kinase inhibitor affected norepinephrine-induced extracellular Ca2+ influx. G13G225A, but not G12G228A, also inhibited arachidonic acid release partially. These results demonstrate that 1) the Gq/PLC-pathway is not involved in NSCCs activation by norepinephrine, 2) G13 couples with CHO-1A and plays important roles for norepinephrine-induced NSCCs activation, 3) neither ROCK- nor PI3K-dependent cascade is involved in NSCCs activation, and 4) G13 is involved in norepinephrine-induced arachidonic acid release in CHO-1A. norepinephrine; 1A-adrenergic receptor; nonselective cation channel; G13 protein; arachidonic acid release 相似文献
10.
Reddy M. M.; Kopito Ron R.; Quinton P. M. 《American journal of physiology. Cell physiology》1998,275(4):C1040
Our objective inthis study was to determine the effect of changes in luminal andcytoplasmic pH on cystic fibrosis transmembrane regulator (CFTR)Cl conductance(GCl). Wemonitored CFTRGCl in the apicalmembranes of sweat ducts as reflected byCl diffusion potentials(VCl) andtransepithelial conductance(GCl). We foundthat luminal pH (5.0-8.5) had little effect on thecAMP/ATP-activated CFTRGCl, showing thatCFTR GCl ismaintained over a broad range of extracellular pH in which it functionsphysiologically. However, we found that phosphorylation activation ofCFTR GCl issensitive to intracellular pH. That is, in the presence of cAMP and ATP [adenosine5'-O-(3-thiotriphosphate)],CFTR could be phosphorylated at physiological pH (6.8) but not at lowpH (~5.5). On the other hand, basic pH prevented endogenousphosphatase(s) from dephosphorylating CFTR.After phosphorylationof CFTR with cAMP and ATP, CFTRGCl is normallydeactivated within 1 min after cAMP is removed, even in the presence of5 mM ATP. This deactivation was due to an increase in endogenousphosphatase activity relative to kinase activity, since it was reversedby the reapplication of ATP and cAMP. However, increasing cytoplasmicpH significantly delayed the deactivation of CFTRGCl in adose-dependent manner, indicating inhibition of dephosphorylation. Weconclude that CFTRGCl may beregulated via shifts in cytoplasmic pH that mediate reciprocal controlof endogenous kinase and phosphatase activities. Luminal pH probably has little direct effect on these mechanisms. This regulation of CFTRmay be important in shifting electrolyte transport in the duct fromconductive to nonconductive modes. 相似文献
11.
Bumetanide blocks CFTR GCl in the native sweat duct 总被引:1,自引:0,他引:1
Bumetanide is wellknown for its ability to inhibit the nonconductiveNa+-K+-2Clcotransporter. We were surprised in preliminary studies to find thatbumetanide in the contraluminal bath also inhibited NaCl absorption inthe human sweat duct, which is apparently poor in cotransporteractivity. Inhibition was accompanied by a marked decrease in thetransepithelial electrical conductance. Because the cystic fibrosistransmembrane conductance regulator (CFTR) Cl channel is richlyexpressed in the sweat duct, we asked whether bumetanide acts byblocking this anion channel. We found that bumetanide1) significantly increased wholecell input impedance, 2)hyperpolarized transepithelial and basolateral membrane potentials, 3) depolarized apical membranepotential, 4) increased the ratio ofapical-to-basolateral membrane resistance, and5) decreased transepithelialCl conductance(GCl).These results indicate that bumetanide inhibits CFTRGClin both cell membranes of this epithelium. We excluded bumetanideinterference with the protein kinase A phosphorylation activationprocess by "irreversibly" phosphorylating CFTR [by usingadenosine5'-O-(3-thiotriphosphate) in thepresence of a phosphatase inhibition cocktail] before bumetanideapplication. We then activated CFTRGClby adding 5 mM ATP. Bumetanide in the cytoplasmic bath(103 M) inhibited ~71%of this ATP-activated CFTRGCl,indicating possible direct inhibition of CFTRGCl.We conclude that bumetanide inhibits CFTRGClin apical and basolateral membranes independent of phosphorylation. Theresults also suggest that>105 M bumetanide cannotbe used to specifically block theNa+-K+-2Cl cotransporter. 相似文献
12.
Effects of growth regulator applications on the flowering of5-years-grafted mature scions of Picea sitchensis (Bong.) Carr.were assessed. Growth regulators were applied to the bud surfacein droplets of ethanol during July, August and September ina polythene house or glasshouse. A mixture of gibberellins A4and A7 applied alone, and in combination with gibberellins A3and A5, significantly increased numbers by up to seven timesfor male and by up to eight times for female strobili, gibberellinA, gave relatively the strongest response, and gibberellin A4was inactive. Phosphon D and abscisic acid each reversed thepromotion of flowering by gibberellins, whilst kinetin and N,N-diphenylureahad no effect. The number of female strobili was negativelycorrelated with vegetative shoot length in the year after treatment. Under field conditions hormones were applied in July and Augustunder flaps of bark on the branches of 10-years-grafted maturescions. Gibberellin applications caused a 5-fold increase inflowering and N6-benzyladenine further increased the response.Naphth-lyl-acetic acid reduced female and increased male flowering.Bark removal near the base of the branch further enhanced hormone-inducedstrobilus production. The usefulness of these findings for thebreeding of Picea sitchensis is discussed. 相似文献
13.
Scintillation autoradiography was utilized to demonstrate thevariable duration of G2 in Vicia faba root meristems. The ratioof the longest (max G) to the shortest (min ) duration was 5.4,with min being approximately 2.5 h. 相似文献
14.
Comparative Potency of Nine Gibberellins 总被引:1,自引:0,他引:1
Gibberellins A1 to A9 have been compared, each at several doselevels, in bioassays based on extension of stems of dwarf gardenpea (Pisum sativum), dwarf bean (Phaseolus vulgaris) and Lunariaannua, of hypocotyls of cucumber (Cucumis sativus) and lettuce(Lactuca sativa), and of leaf sheaths of three dwarf mutants(d1, d3, d5) of maize (Zea mays). GibberellinsA3 (gibberellic acid) and A7 are of high potency in most bioassays.A8 is of negligible potency in all and is probably not a functionalhormone. The other gibberellins show a more or less marked tendencyto specificity. The plants used as bioassay material also differin the specificity of their response. Some, for example, maizedwarfs d3 and d5 and lettuce, respond well tomost gibberellins; others, for example, cucumber, respond onlyto a few; extreme specificity is shown by Lunaria annua which,in the unvernalized condition, responds by stem elongation onlyto gibberellin A7. Dose/response curves of the various gibberellinsare usually parallel, but certain exceptions to this have beenfound. Possible explanations of specificity are discussed inrelation to the results obtained, and it is concluded that insufficientevidence is available to make it possible to draw any validconclusions. Current definitions of gibberellins, whether basedon chemical structure or biological activity, are unsatisfactory. 相似文献
15.
A model for phosphocreatine resynthesis 总被引:1,自引:0,他引:1
Nevill Alan M.; Jones David A.; McIntyre David; Bogdanis Gregory C.; Nevill Mary E. 《Journal of applied physiology》1997,82(1):329-335
Nevill, Alan M., David A. Jones, David McIntyre, Gregory C. Bogdanis, and Mary E. Nevill. A model forphosphocreatine resynthesis. J. Appl.Physiol. 82(1): 329-335, 1997.A model for phosphocreatine (PCr) resynthesis is proposed based on a simple electric circuit, where the PCr store in muscle is likened to thestored charge on the capacitor. The solution to the second-order differential equation that describes the potential around the circuitsuggests the model for PCr resynthesis is given byPCr(t) = R [d1 · exp(k1 · t) ± d2 · exp(k2 · t)],where R is PCr concentration at rest,d1,d2, k1, andk2 are constants, andt is time. By using nonlinear leastsquares regression, this double-exponential model was shown to fit thePCr recovery data taken from two studies involving maximal exerciseaccurately. In study 1, when themuscle was electrically stimulated while occluded, PCr concentrations rose during the recovery phase to a level above that observed at rest.In study 2, after intensive dynamicexercise, PCr recovered monotonically to resting concentrations. Thesecond exponential term in the double-exponential model was found tomake a significant additional contribution to the quality of fit inboth study 1 (P < 0.05) andstudy 2 (P < 0.01). 相似文献
16.
Pyruvate and citric acid cycle carbon requirements in isolated skeletal muscle mitochondria 总被引:1,自引:0,他引:1
Messer JI Jackman MR Willis WT 《American journal of physiology. Cell physiology》2004,286(3):C565-C572
Carbohydrate depletion precipitates fatigue in skeletal muscle, but, because pyruvate provides both acetyl-CoA for mainline oxidation and anaplerotic carbon to the citric acid cycle (CAC), the mechanism remains obscure. Thus pyruvate and CAC kinetic parameters were independently quantified in mitochondria isolated from rat mixed skeletal muscle. Mitochondrial oxygen consumption rate (Jo) was measured polarographically while either pyruvate or malate was added stepwise in the presence of a saturating concentration of the other substrate. These substrate titrations were carried out across a physiological range of fixed extramitochondrial ATP free energy states (GP), established with a creatine kinase energy clamp, and also at saturating [ADP]. The apparent Km,malate for mitochondrial Jo ranged from 21 to 32 µM, and the apparent Km,pyruvate ranged from 12 to 26 µM, with both substrate Km values increasing as GP declined. Vmax for both substrates also increased as GP fell, reflecting thermodynamic control of Jo. Reported in vivo skeletal muscle [malate] are >10-fold greater than the Km,malate determined in this study. In marked contrast, the Km,pyruvate determined is near the [pyruvate] reported in muscle approaching exhaustion associated with glycogen depletion. When data were evaluated in the context of a linear thermodynamic force-flow (GP-Jo) relationship, the GP-Jo slope was essentially insensitive to changes in [malate] in the range observed in vivo but decreased markedly with declining [pyruvate] across the physiological range. Mitochondrial respiration is particularly sensitive to variations in [pyruvate] in the physiological range. In contrast, physiological [malate] exerts very little, if any, influence on mitochondrial pyruvate oxidation measured in vitro. bioenergetics; fatigue; anaplerosis; Krebs cycle; fuel limitation; metabolic control analysis 相似文献
17.
Primary production was measured for 7 years, using the in situ14C-method in hypertrophic Hartbeespoort Dam, South Africa,to examine the influence of light and water temperature on theupper limit of Microcystis aeruginosa production. Water temperaturesvaried from 11 to >25°C and chlorophyll concentrationsreached 6500 mg m3. The maximum volumetric rate of production(Amax) was 12->8800 mg C m3 h1 with areal productions(A) of 69->3300 mg C m2 h1 for euphotic zonedepths of <0.58.4 m. The intrinsic parameters of phytoplanktonproduction (, Amax/B, Ik) indicated that the phytoplankton populationwas adapted to high light levels. Both Amax/B and Ik were correlatedwith temperature. Under optimal conditions, , the theoreticalupper limit of A, was calculated to be 2.8 g Cm2 h1,while the measured rate was 2.5 g Cm2 h1. Measuredareal rates exceeding were overestimated due to methodologicalproblems when working with Microcystis scums. Light and watertemperature interacted to yield high production rates: watertemperature through its direct effect on photosynthetic ratesand indirectly in the formation of diurnal mixed layers; lightindirectly through water temperature and directly through itsattenuation and induction of light-adapted physiology in Microcystis. 相似文献
18.
Verbanck S.; Schuermans D.; Van Muylem A.; Paiva M.; Noppen M.; Vincken W. 《Journal of applied physiology》1997,83(6):1907-1916
Verbanck, S., D. Schuermans, A. Van Muylem, M. Paiva, M. Noppen, and W. Vincken. Ventilation distribution during histamine provocation. J. Appl. Physiol. 83(6):1907-1916, 1997.We investigated ventilation inhomogeneity duringprovocation with inhaled histamine in 20 asymptomatic nonsmokingsubjects. We used N2multiple-breath washout (MBW) to deriveparameters Scondand Sacin as ameasurement of ventilation inhomogeneity in conductive and acinar zonesof the lungs, respectively. A 20% decrease of forced expiratory volume in 1 s (FEV1) was used todistinguish responders from nonresponders. In the responder group,average FEV1 decreased by 26%,whereas Scondincreased by 390% with no significant change inSacin. In thenonresponder group, FEV1 decreasedby 11%, whereasScond increased by 198% with no significantSacin change.Despite the absence of change inSacin duringprovocation, baselineSacin wassignificantly larger in the responder vs. the nonresponder group. Themain findings of our study are that during provocation largeventilation inhomogeneities occur, that the small airways affected bythe provocation process are situated proximal to the acinar zone wherethe diffusion front stands, and that, in addition to overall decreasein airway caliber, there is inhomogeneous narrowing of parallelairways. 相似文献
19.
Distinct K+ conductive pathways are required for Cl- and K+ secretion across distal colonic epithelium 总被引:1,自引:0,他引:1
Secretion of Cl and K+ in the colonic epithelium operates through a cellular mechanism requiring K+ channels in the basolateral and apical membranes. Transepithelial current [short-circuit current (Isc)] and conductance (Gt) were measured for isolated distal colonic mucosa during secretory activation by epinephrine (Epi) or PGE2 and synergistically by PGE2 and carbachol (PGE2 + CCh). TRAM-34 at 0.5 µM, an inhibitor of KCa3.1 (IK, Kcnn4) K+ channels (H. Wulff, M. J. Miller, W. Hänsel, S. Grissmer, M. D. Cahalan, and K. G. Chandy. Proc Natl Acad Sci USA 97: 81518156, 2000), did not alter secretory Isc or Gt in guinea pig or rat colon. The presence of KCa3.1 in the mucosa was confirmed by immunoblot and immunofluorescence detection. At 100 µM, TRAM-34 inhibited Isc and Gt activated by Epi (4%), PGE2 (30%) and PGE2 + CCh (60%). The IC50 of 4.0 µM implicated involvement of K+ channels other than KCa3.1. The secretory responses augmented by the K+ channel opener 1-EBIO were inhibited only at a high concentration of TRAM-34, suggesting further that KCa3.1 was not involved. Sensitivity of the synergistic response (PGE2 + CCh) to a high concentration TRAM-34 supported a requirement for multiple K+ conductive pathways in secretion. Clofilium (100 µM), a quaternary ammonium, inhibited Cl secretory Isc and Gt activated by PGE2 (20%) but not K+ secretion activated by Epi. Thus Cl secretion activated by physiological secretagogues occurred without apparent activity of KCa3.1 channels but was dependent on other types of K+ channels sensitive to high concentrations of TRAM-34 and/or clofilium. epinephrine; prostaglandin E2; cholinergic; Kcnn4; TRAM-34; clofilium 相似文献
20.
Analysis and Significance of Gravity-induced Asymmetric Growth in the Grass Leaf-sheath Pulvinus 总被引:1,自引:0,他引:1
The negative gravitropic response in the grass leaf-sheath pulvinusis a consequence of cell elongation involving all cells exceptthose of the uppermost region of the upper flank of an horizontallyoriented pulvinus. The lowermost layer of cells elongate maximally,and the regions in between elongate to intermediate extents.The resulting curvatures of a responding pulvinus can be expressedmathematically by relating the angle of curvature () to theoriginal length (L0) and the maximal length of the lower surface(L1) and the diameter of the organ (D), using the equation, = (L1L0)/D, where is in radians. The elongation response(S) of any individual cell within the pulvinus can be expressedby the equation, S = 0.5-r cos, where r is the radius of thepulvinus and is in degrees. Microscopic measurement of celllengths in different regions of the pulvinus supports the mathematicalpredictions. Indirect support is also obtained from the useof colchicine, coumarin, dichloro-benzonitrile (DCBN) and isopropylN-chlorophenyl carbamate which exaggerate the inherent asymmetryduring gravitropic response. Coumarin and DCBN also induce thickeningsin the radial walls which appear first in the statenchyma, andlater, in cells located towards the outer periphery of the pulvinus.The distribution patterns of these thickenings suggest thatthe asymmetric growth response of the pulvinus may be due toa differential and radial, centrifugal transport of growth promotorsfrom the central statenchyma region. Gravity perception, grass pulvinus 相似文献