共查询到20条相似文献,搜索用时 15 毫秒
1.
Hepple Russell T.; Agey Peter J.; Hazelwood Larnelle; Szewczak Joseph M.; MacMillen Richard E.; Mathieu-Costello Odile 《Journal of applied physiology》1998,85(5):1871-1876
An increased ratio of muscle capillary tofiber number (capillary/fiber number) at altitude has been found inonly a few investigations. The highly aerobic pectoralismuscle of finches living at 4,000-m altitude(Leucosticte arctoa; A) was recentlyshown to have a larger capillary/fiber number and greater contributionof tortuosity and branching to total capillary length than sea-levelfinches (Carpodacus mexicanus; SL) ofthe same subfamily (O. Mathieu-Costello, P. J. Agey, L. Wu, J. M. Szewczak, and R. E. MacMillen. Respir. Physiol. 111: 189-199, 1998). To evaluate the roleof muscle aerobic capacity on this trait, we examined the less-aerobicleg muscle (deep portion of anterior thigh) in the same birds. We foundthat, similar to pectoralis, the leg muscle in A finches had a greater capillary/fiber number (1.42 ± 0.06) than that in SLfinches (0.77 ± 0.05; P < 0.01),but capillary tortuosity and branching were not different. As alsofound in pectoralis, the resulting larger capillary/fiber surface in Afinches was proportional to a greater mitochondrial volume permicrometer of fiber length compared with that in SL finches. Theseobservations, in conjunction with a trend to a greater (rather thansmaller) fiber cross-sectional area in A than in SL finches (A: 484 ± 42, SL: 390 ± 26 µm2,both values at 2.5-µm sarcomere length;P = 0.093), support the notion thatchronic hypoxia is also a condition in which capillary-to-fiber structure is organized to match the size of the musclecapillary-to-fiber interface to fiber mitochondrial volume rather thanto minimize intercapillary O2diffusion distances. 相似文献
2.
Chen Qiu-Hong; Ge Ri-Li; Wang Xiao-Zhen; Chen Hui-Xin; Wu Tian-Yi; Kobayashi Toshio; Yoshimura Kazuhiko 《Journal of applied physiology》1997,83(2):661-667
Chen, Qiu-Hong, Ri-Li Ge, Xiao-Zhen Wang, Hui-Xin Chen,Tian-Yi Wu, Toshio Kobayashi, and Kazuhiko Yoshimura. Exercise performance of Tibetan and Han adolescents at altitudes of 3,417 and4,300 m. J. Appl. Physiol. 83(2):661-667, 1997.The difference was studied betweenO2 transport in lifelong Tibetanadolescents and in newcomer Han adolescents acclimatized to highaltitude. We measured minute ventilation, maximalO2 uptake, maximal cardiac output,and arterial O2 saturation duringmaximal exercise, using the incremental exercise technique, ataltitudes of 3,417 and 4,300 m. The groups were well matched for age,height, and nutritional status. The Tibetans had been living at thealtitudes for a longer period than the Hans (14.5 ± 0.2 vs. 7.8 ± 0.8 yr at 3,417 m, P < 0.01; and 14.7 ± 0.3 vs. 5.3 ± 0.7 yr at 4,300 m,P < 0.01, respectively). At rest,Tibetans had significantly greater vital capacity and maximal voluntaryventilation than the Hans at both altitudes. At maximal exercise,Tibetans compared with Hans had higher maximalO2 uptake (42.2 ± 1.7 vs. 36.7 ± 1.2 ml · min1 · kg1at 3,417 m, P < 0.01; and 36.8 ± 1.9 vs. 30.0 ± 1.4 ml · min1 · kg1at 4,300 m, P < 0.01, respectively)and greater maximal cardiac output (12.8 ± 0.3 vs. 11.4 ± 0.2 l/min at 3,417 m, P < 0.01; 11.5 ± 0.5 vs. 10.0 ± 0.5 l/min at 4,300 m,P < 0.05, respectively). Althoughthe differences in arterial O2saturation between Tibetans and Hans were not significant at rest andduring mild exercise, the differences became greater with increases inexercise workload at both altitudes. We concluded that exposure to highaltitude from birth to adolescence resulted in an efficientO2 transport and a greater aerobicexercise performance that may reflect a successful adaptation to lifeat high altitude. 相似文献
3.
Jean K Bernatchez G Klein H Garneau L Sauvé R Parent L 《American journal of physiology. Cell physiology》2002,282(4):C665-C672
The Ca2+ affinity andpermeation of the epithelial Ca2+ channel (ECaC1) wereinvestigated after expression in Xenopus oocytes. ECaC1displayed anomalous mole-fraction effects. Extracellular Ca2+ and Mg2+ reversibly inhibited ECaC1 wholecell Li+ currents: IC50 = 2.2 ± 0.4 µM (n = 9) and 235 ± 35 µM (n = 10), respectively. These values compare well with theCa2+ affinity of the L-type voltage-gated Ca2+(CaV1.2) channel measured under the same conditions,suggesting that high-affinity Ca2+ binding is awell-conserved feature of epithelial and voltage-gated Ca2+channels. Neutralization of D550 and E535 in the pore region had nosignificant effect on Ca2+ and Mg2+ affinities.In contrast, neutralization of D542 significantly decreasedCa2+ affinity (IC50 = 1.1 ± 0.2 mM,n = 6) and Mg2+ affinity(IC50 > 25 ± 3 mM, n = 4).Despite a 1,000-fold decrease in Ca2+ affinity in D542N,Ca2+ permeation properties and theCa2+-to-Ba2+ conductance ratio remainedcomparable to values for wild-type ECaC1. Together, our observationssuggest that D542 plays a critical role in Ca2+ affinitybut not in Ca2+ permeation in ECaC1. 相似文献
4.
Balog Edward M.; Gallant Esther M. 《American journal of physiology. Cell physiology》1999,276(1):C128
Modulation of the L-type current by sarcoplasmicreticulum (SR) Ca2+ release hasbeen examined in patch-clamped mouse myotubes. Inhibition of SRCa2+ release by inclusion ofryanodine in the internal solution shifted the half-activating voltage(V0.5) of theL-type current from 1.1 ± 2.1 to 7.7 ± 1.7 mV. Rutheniumred in the internal solution shiftedV0.5 from 5.4 ± 1.9 to 3.2 ± 4.1 mV. Chelation of myoplasmic Ca2+ with1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraaceticacid perfusion shiftedV0.5 from 4.4 ± 1.7 to 3.5 ± 3.3 mV and increased the peak current.Extracellular caffeine (1 mM), which should enhance SRCa2+ release, significantlydecreased the peak Ca2+ current.In low (0.1 mM) internal EGTA, myotube contraction was abolished byinternal perfusion with ryanodine or ruthenium red, whereas addition ofcaffeine to the extracellular solution lowered the contractilethreshold, indicating that these modulators of SRCa2+ release had the expectedeffects on contraction. Therefore, SR Ca2+ release appears to modulatethe sarcolemmal L-type current, suggesting a retrograde communicationfrom the SR to the sarcolemmal L-type channels inexcitation-contraction coupling. 相似文献
5.
Gomora Juan Carlos; Enyeart John J. 《American journal of physiology. Cell physiology》1998,275(6):C1526
Bovine adrenalzona fasciculata cells (AZF) express a noninactivatingK+ current(IAC) whoseinhibition by adrenocorticotropic hormone and ANG II may be coupled tomembrane depolarization andCa2+-dependentcortisol secretion. We studiedIACinhibition byCa2+ and theCa2+ionophore ionomycin in whole cell and single-channel patch-clamp recordings of AZF. In whole cell recordings with intracellular (pipette)Ca2+concentration([Ca2+]i)buffered to 0.02 µM,IAC reachedmaximum current density of 25.0 ± 5.1 pA/pF(n = 16); raising[Ca2+]ito 2.0 µM reduced it 76%. In inside-out patches, elevated[Ca2+]idramatically reducedIAC channelactivity. Ionomycin inhibited IAC by 88 ± 4% (n = 14) without altering rapidlyinactivating A-type K+ current.Inhibition of IACby ionomycin was unaltered by adding calmodulin inhibitory peptide tothe pipette or replacing ATP with its nonhydrolyzable analog5'-adenylylimidodiphosphate.IAC inhibition byionomycin was associated with membrane depolarization. When[Ca2+]iwas buffered to 0.02 µM with 2 and 11 mM1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), ionomycin inhibitedIAC by 89.6 ± 3.5 and 25.6 ± 14.6% and depolarized the same AZF by 47 ± 8 and 8 ± 3 mV, respectively (n = 4). ANG II inhibitedIAC significantlymore effectively when pipette BAPTA was reduced from 11 to 2 mM. Raising[Ca2+]iinhibits IACthrough a mechanism not requiring calmodulin or protein kinases,suggesting direct interaction withIAC channels. ANGII may inhibitIAC anddepolarize AZF by activating parallel signaling pathways, one of whichuses Ca2+ asa mediator. 相似文献
6.
Two-photon molecular excitation imaging of Ca2+ transients in Langendorff-perfused mouse hearts 总被引:1,自引:0,他引:1
Rubart M Wang E Dunn KW Field LJ 《American journal of physiology. Cell physiology》2003,284(6):C1654-C1668
The ability to image calciumsignals at subcellular levels within the intact depolarizing heartcould provide valuable information toward a more integratedunderstanding of cardiac function. Accordingly, a system combiningtwo-photon excitation with laser-scanning microscopy was developed tomonitor electrically evoked [Ca2+]itransients in individual cardiomyocytes within noncontracting Langendorff-perfused mouse hearts. [Ca2+]itransients were recorded at depths 100 µm from the epicardial surface with the fluorescent indicators rhod-2 or fura-2 in the presence of the excitation-contraction uncoupler cytochalasin D. Evoked[Ca2+]i transients were highly synchronizedamong neighboring cardiomyocytes. At 1 Hz, the times from 90 to 50%(t90-50%) and from 50 to 10%(t50-10%) of the peak[Ca2+]i were (means ± SE) 73 ± 4 and 126 ± 10 ms, respectively, and at 2 Hz, 62 ± 3 and94 ± 6 ms (n = 19, P < 0.05 vs.1 Hz) in rhod-2-loaded cardiomyocytes.[Ca2+]i decay was markedly slower infura-2-loaded hearts (t90-50% at 1 Hz,128 ± 9 ms and at 2 Hz, 88 ± 5 ms;t50-10% at 1 Hz, 214 ± 18 ms and at2 Hz, 163 ± 7 ms; n = 19, P < 0.05 vs. rhod-2). Fura-2-induced deceleration of[Ca2+]i decline resulted from increasedcytosolic Ca2+ buffering, because the kinetics of rhod-2decay resembled those obtained with fura-2 after incorporation of theCa2+ chelator BAPTA. Propagating calcium waves and[Ca2+]i amplitude alternans were readilydetected in paced hearts. This approach should be of general utility tomonitor the consequences of genetic and/or functional heterogeneity incellular calcium signaling within whole mouse hearts at tissue depthsthat have been inaccessible to single-photon imaging. 相似文献
7.
Roberts A. C.; Butterfield G. E.; Cymerman A.; Reeves J. T.; Wolfel E. E.; Brooks G. A. 《Journal of applied physiology》1996,81(4):1762-1771
Roberts, A. C., G. E. Butterfield, A. Cymerman, J. T. Reeves, E. E. Wolfel, and G. A. Brooks. Acclimatization to 4,300-m altitude decreases reliance on fat as a substrate. J. Appl. Physiol. 81(4): 1762-1771, 1996.We testedthe hypothesis that exposure to altitude decreases reliance on freefatty acids (FFA) as substrates and increases dependency on bloodglucose. Therefore, the effects of exercise, hypobaric hypoxia, andaltitude acclimatization on FFA, glycerol and net glucose uptake andrelease [ = 2(leg blood flow)(arteriovenous concentration)]and on fatty acid (FA) consumption by the legs (= 3 × glycerolrelease + FFA uptake) were measured. Because sympathetic responses havebeen implicated, we utilized nonspecific -blockade and observedresponses to exercise, altitude, and altitude acclimatization. Westudied six healthy -blocked men () and five matched controls (C)during rest and cycle ergometry exercise (88 W) at 49% of sea-level(SL) peak O2 uptake at the sameabsolute power output on acute altitude exposure (A1; barometric pressure = 430 Torr) and after 3 wk of chronic altitude exposure to4,300 m (A2). During exercise at SL, FA consumption rates increased (P < 0.05). On arrival at 4,300 m,resting leg FFA uptake and FA consumption rates were not significantlydifferent from those at SL. However, after acclimatization to altitude,at rest leg FA consumption decreased to essentially zero in both C and groups. During exercise at altitude after acclimatization, leg FAconsumption increased significantly, but values were less than at SL orA1 (P < 0.05), whereas glucoseuptake increased relative to SL values. Furthermore, -blockadesignificantly increased glucose uptake relative to control. We concludethat 1) chronic altitude exposure decreases leg FA consumption during rest and exercise;2) relative to SL, FFA uptakedecreases while glucose uptake increases during exercise at altitude;and 3) -blockade potentiatesthese effects. 相似文献
8.
Thermal and metabolic responses to cold-water immersion at knee, hip, and shoulder levels 总被引:1,自引:0,他引:1
Lee Dae T.; Toner Michael M.; McArdle William D.; Vrabas Ioannis S.; Pandolf Kent B. 《Journal of applied physiology》1997,82(5):1523-1530
Lee, Dae T., Michael M. Toner, William D. McArdle, IoannisS. Vrabas, and Kent B. Pandolf. Thermal and metabolic responses tocold-water immersion at knee, hip, and shoulder levels.J. Appl. Physiol. 82(5):1523-1530, 1997.To examine the effect of cold-water immersion atdifferent depths on thermal and metabolic responses, eight men (25 yrold, 16% body fat) attempted 12 tests: immersed to the knee (K), hip(H), and shoulder (Sh) in 15 and 25°C water during both rest (R) orleg cycling [35% peak oxygen uptake; (E)] for up to 135 min. At 15°C, rectal (Tre)and esophageal temperatures(Tes) between R and E were notdifferent in Sh and H groups (P > 0.05), whereas both in K group were higher during E than R(P < 0.05). At 25°C,Tre was higher(P < 0.05) during E than R at alldepths, whereas Tes during E washigher than during R in H and K groups.Tre remained at control levels inK-E at 15°C, K-E at 25°C, and in H-E groups at 25°C,whereas Tes remained unchanged inK-E at 15°C, in K-R at 15°C, and in all 25°C conditions (P > 0.05). During R and E, themagnitude of Tre change wasgreater (P < 0.05) than themagnitude of Tes change in Sh andH groups, whereas it was not different in the K group(P > 0.05). Total heat flow wasprogressive with water depth. During R at 15 and 25°C, heatproduction was not increased in K and H groups from control level(P > 0.05) but it did increase in Shgroup (P < 0.05). The increase inheat production during E compared with R was smaller(P < 0.05) in Sh (121 ± 7 W/m2 at 15°C and 97 ± 6 W/m2 at 25°C) than in H (156 ± 6 and 126 ± 5 W/m2,respectively) and K groups (155 ± 4 and 165 ± 6 W/m2, respectively). These datasuggest that Tre andTes respond differently duringpartial cold-water immersion. In addition, water levels above knee in15°C and above hip in 25°C cause depression of internal temperatures mainly due to insufficient heat production offsetting heatloss even during light exercise. 相似文献
9.
Peronnet F.; Burelle Y.; Massicotte D.; Lavoie C.; Hillaire-Marcel C. 《Journal of applied physiology》1997,82(2):440-446
Péronnet, F., Y. Burelle, D. Massicotte, C. Lavoie,and C. Hillaire-Marcel. Respective oxidation of13C-labeled lactate and glucoseingested simultaneously during exercise. J. Appl.Physiol. 82(2): 440-446, 1997.The purpose ofthis experiment was to measure, by using13C labeling, the oxidation rateof exogenous lactate (25 g, as Na+,K+,Ca2+, andMg2+ salts) and glucose (75 g)ingested simultaneously (in 1,000 ml of water) during prolongedexercise (120 min, 65 ± 3% maximum oxygen uptake in 6 male subjects). The percentage of exogenous glucose and lactateoxidized were similar (48 ± 3 vs. 45 ± 5%, respectively). However, because of the small amount of oral lactate that could be tolerated without gastrointestinal discomfort, the amountof exogenous lactate oxidized was much smaller than that of exogenousglucose (11.1 ± 0.5 vs. 36.3 ± 1.3 g, respectively) andcontributed to only 2.6 ± 0.4% of the energy yield(vs. 8.4 ± 1.9% for exogenous glucose). The cumulative amount ofexogenous glucose and lactate oxidized was similar to that observedwhen 100 g of[13C]glucose wereingested (47.3 ± 1.8 vs. 50.9 ± 1.2 g, respectively). When[13C]glucose wasingested, changes in the plasma glucose13C/12Cratio indicated that between 39 and 61% of plasma glucose derived fromexogenous glucose. On the other hand, the plasma glucose 13C/12Cratio remained unchanged when[13C]lactate wasingested, suggesting no prior conversion into glucose before oxidation. 相似文献
10.
Gonzalez Antonio; Pfeiffer Fatima; Schmid Andreas; Schulz Irene 《American journal of physiology. Cell physiology》1998,275(3):C810
We have used fluo3-loaded mouse pancreatic acinar cells to investigate the relationshipbetween Ca2+ mobilization andintracellular pH (pHi). TheCa2+-mobilizing agonist ACh (500 nM) induced a Ca2+ release in theluminal cell pole followed by spreading of the Ca2+ signal toward the basolateralside with a mean speed of 16.1 ± 0.3 µm/s. In the presence of anacidic pHi, achieved by blockade of theNa+/H+exchanger or by incubation of the cells in aNa+-free buffer, a slowerspreading of ACh-evoked Ca2+ waveswas observed (7.2 ± 0.6 µm/s and 7.5 ± 0.3 µm/s,respectively). The effects of cytosolic acidification on thepropagation rate of ACh-evokedCa2+ waves were largely reversibleand were not dependent on the presence of extracellularCa2+. A reduction in the spreadingspeed of Ca2+ waves could also beobserved by inhibition of the vacuolarH+-ATPase with bafilomycinA1 (11.1 ± 0.6 µm/s), whichdid not lead to cytosolic acidification. In contrast, inhibition of theendoplasmic reticulum Ca2+-ATPaseby 2,5-di-tert-butylhydroquinone ledto faster spreading of the ACh-evokedCa2+ signals (25.6 ± 1.8 µm/s), which was also reduced by cytosolic acidification or treatmentof the cells with bafilomycin A1.Cytosolic alkalinization had no effect on the spreading speed of theCa2+ signals. The data suggestthat the propagation rate of ACh-induced Ca2+ waves is decreased byinhibition of Ca2+ release fromintracellular stores due to cytosolic acidification or toCa2+ pool alkalinizationand/or to a decrease in the proton gradient directed from theinositol 1,4,5-trisphosphate-sensitiveCa2+ pool to the cytosol. 相似文献
11.
We hypothesized that highextracellular K+ concentration([K+]o)-mediated stimulation ofNa+-K+-Cl cotransporter isoform 1 (NKCC1) may result in a net gain of K+ and Cland thus lead to high-[K+]o-induced swellingand glutamate release. In the current study, relative cell volumechanges were determined in astrocytes. Under 75 mM[K+]o, astrocytes swelled by 20.2 ± 4.9%. This high-[K+]o-mediated swelling wasabolished by the NKCC1 inhibitor bumetanide (10 µM, 1.0 ± 3.1%; P < 0.05). Intracellular36Cl accumulation was increased from acontrol value of 0.39 ± 0.06 to 0.68 ± 0.05 µmol/mgprotein in response to 75 mM [K+]o. Thisincrease was significantly reduced by bumetanide (P < 0.05). Basal intracellular Na+ concentration([Na+]i) was reduced from 19.1 ± 0.8 to16.8 ± 1.9 mM by bumetanide (P < 0.05).[Na+]i decreased to 8.4 ± 1.0 mM under75 mM [K+]o and was further reduced to5.2 ± 1.7 mM by bumetanide. In addition, the recovery rate of[Na+]i on return to 5.8 mM[K+]o was decreased by 40% in the presenceof bumetanide (P < 0.05). Bumetanide inhibitedhigh-[K+]o-induced 14C-labeledD-aspartate release by ~50% (P < 0.05).These results suggest that NKCC1 contributes tohigh-[K+]o-induced astrocyte swelling andglutamate release. 相似文献
12.
Multiple targets of chemosensitive signaling in locus coeruleus neurons: role of K+ and Ca2+ channels 总被引:3,自引:0,他引:3
Westudied chemosensitive signaling in locus coeruleus (LC) neurons usingboth perforated and whole cell patch techniques. Upon inhibition offast Na+ spikes by tetrodotoxin (TTX), hypercapnic acidosis[HA; 15% CO2, extracellular pH (pHo) 6.8]induced small, slow spikes. These spikes were inhibited byCo2+ or nifedipine and were attributed to activation ofL-type Ca2+ channels by HA. Upon inhibition of bothNa+ and Ca2+ spikes, HA resulted in a membranedepolarization of 3.52 ± 0.61 mV (n = 17) thatwas reduced by tetraethylammonium (TEA) (1.49 ± 0.70 mV,n = 7; P < 0.05) and absent(0.97 ± 0.73 mV, n = 7; P < 0.001) upon exposure to isohydric hypercapnia (IH; 15%CO2, 77 mM HCO , pHo 7.45).Either HA or IH, but not 50 mM Na-propionate, activatedCa2+ channels. Inhibition of L-type Ca2+channels by nifedipine reduced HA-induced increased firing rate andeliminated IH-induced increased firing rate. We conclude that chemosensitive signals (e.g., HA or IH) have multiple targets in LCneurons, including TEA-sensitive K+ channels andTWIK-related acid-sensitive K+ (TASK) channels.Furthermore, HA and IH activate L-type Ca2+ channels, andthis activation is part of chemosensitive signaling in LC neurons. 相似文献
13.
To find whether cytoplasmic streaming in Acetabularia is controlledby Ca2+, a tonoplast-permeabilized cell model was prepared usinga vacuolar perfusion technique. The cytoplasmic streaming remainedalmost normal after perfusion with EGTA medium (10 mM EGTA,40 mM PIPES, 5mM MgCl2 and 800 mM sorbitol, pH 6.9), but stoppedwithin 10 min when saponin medium (EGTA medium plus 50 µg/mlsaponin, 50 µg/ml hexokinase and 5 mM glucose) was perfused.This model system was reactivated with a solution containing0.5 mM ATP and different concentrations of Ca2+ (reactivationmedium). With the reactivation medium at pCa 65, theresumed streaming lasted for about 10 min before the cytoplasmaggregated. At pCa 43, the streaming was observed onlyfor a few minutes because the cytoplasm aggregated quickly.At pCa 7, no reactivated movement was observed. Reactivationwas not induced in an ATP- or Mg2+-deficient medium even inthe presence of an adequate concentration of Ca2+, and was inhibitedby 50 µg/ml cytochalasin B or 1 mM N-ethylmaleimide. We concluded from these observations that the cytoplasmic streamingin Acetabularia is very likely to be driven by the actomyosinsystem in the presence of Mg-ATP and Ca2+ at pCa 65. (Received October 31, 1984; Accepted April 1, 1985) 相似文献
14.
Microdialysis ethanol removal reflects probe recovery rather than local blood flow in skeletal muscle 总被引:2,自引:0,他引:2
Radegran G.; Pilegaard H.; Nielsen J. J.; Bangsbo J. 《Journal of applied physiology》1998,85(2):751-757
The present study compared the microdialysis ethanoloutflow-inflow technique for estimating blood flow (BF) in skeletalmuscle of humans with measurements by Doppler ultrasound of femoralartery inflow to the limb(BFFA). The microdialysis probeswere inserted in the vastus lateralis muscle and perfused with a Ringeracetate solution containing ethanol,[2-3H]adenosine (Ado),andD-[14C(U)]glucose.BFFA at rest increased from0.16 ± 0.02 to 1.80 ± 0.26 and 4.86 ± 0.53 l/minwith femoral artery infusion of Ado (AdoFA,i) at 125 and 1,000 µg · min1 · l1thigh volume (low dose and high dose, respectively;P < 0.05) and to 3.79 ± 0.37 and6.13 ± 0.65 l/min during one-legged, dynamic, thigh muscle exercisewithout and with high AdoFA,i,respectively (P < 0.05). The ethanoloutflow-to-inflow ratio (38.3 ± 2.3%) and the probe recoveries(PR) for [2-3H]Ado(35.4 ± 1.6%) and forD-[14C(U)]glucose(15.9 ± 1.1%) did not change withAdoFA,i at rest (P = not significant). During exercisewithout and with AdoFA,i, theethanol outflow-to-inflow ratio decreased(P < 0.05) to a similar level of17.5 ± 3.4 and 20.6 ± 3.2%, respectively(P = not significant), respectively,while the PR increased (P < 0.05) toa similar level (P = not significant)of 55.8 ± 2.8 and 61.2 ± 2.5% for[2-3H]Ado and to 42.8 ± 3.9 and 45.2 ± 5.1% forD-[14C(U)]glucose.Whereas the ethanol outflow-to-inflow ratio and PR correlated inverselyand positively, respectively, to the changes in BF during muscularcontractions, neither of the ratio nor PR correlated tothe AdoFA,i-induced BF increase.Thus the ethanol outflow-to-inflow ratio does not represent skeletalmuscle BF but rather contraction-induced changes in molecular transport in the interstitium or over the microdialysis membrane. 相似文献
15.
Larsson-Nyrén G Pakhtusova N Sehlin J 《American journal of physiology. Cell physiology》2002,282(6):C1199-C1204
The length of the silent lag time beforeelevation of the cytosolic free Ca2+ concentration([Ca2+]i) differs between individualpancreatic -cells. One important question is whether thesedifferences reflect a random phenomenon or whether the length of lagtime is inherent in the individual -cell. We compared the lag times,initial dips, and initial peak heights for[Ca2+]i from two consecutive glucosestimulations (with either 10 or 20 mM glucose) in individualob/ob mouse -cells with the fura 2 technique in amicrofluorimetric system. There was a strong correlation between thelengths of the lag times in each -cell (10 mM glucose:r = 0.94, P < 0.001; 20 mM glucose:r = 0.96, P < 0.001) as well as between theinitial dips in [Ca2+]i (10 mM glucose:r = 0.93, P < 0.001; 20 mM glucose:r = 0.79, P < 0.001) and between theinitial peak heights (10 mM glucose: r = 0.51, P < 0.01; 20 mM glucose: r = 0.77, P < 0.001). These data provide evidence that theresponse pattern, including both the length of the lag time and thedynamics of the subsequent [Ca2+]i, isspecific for the individual -cell. 相似文献
16.
Mak Don-On Daniel; Foskett J. Kevin 《American journal of physiology. Cell physiology》1998,275(1):C179
The effects ofMg2+ andBa2+ on single-channel propertiesof the inositol 1,4,5-trisphosphate receptor(IP3R) were studied by patch clampof isolated nuclei from Xenopusoocytes. In 140 mM K+ theIP3R channel kinetics and presenceof conductance substates were similar over a range (0-9.5 mM) offree Mg2+. In 0 mMMg2+ the channel current-voltage(I-V) relation was linear withconductance of ~320 pS. Conductance varied slowly and continuouslyover a wide range (SD 60 pS) and sometimes fluctuated during single openings. The presence of Mg2+ oneither or both sides of the channel reduced the current (blocking constant ~0.6 mM in symmetricalMg2+), as well as the range ofconductances observed, and made the I-V relation nonlinear (slopeconductance ~120 pS near 0 mV and ~360 pS at ±70 mV insymmetrical 2.5 mM Mg2+).Ba2+ exhibited similar effects onchannel conductance. Mg2+ andBa2+ permeated the channel with aratio of permeability of Ba2+ toMg2+ toK+ of 3.5:2.6:1. These resultsindicate that divalent cations induce nonlinearity in theI-V relation and reduce current by amechanism involving permeation block of theIP3R due to strong binding to site(s) in the conduction pathway. Furthermore, stabilization ofconductance by divalent cations reveals a novel interaction between thecations and the IP3R. 相似文献
17.
Obara K Nobe K Nobe H Kolodney MS De Lanerolle P Paul RJ 《American journal of physiology. Cell physiology》2000,279(3):C785-C796
We used a reconstituted fiber formed when 3T3fibroblasts are grown in collagen to characterize nonmusclecontractility and Ca2+ signaling. Calf serum (CS) andthrombin elicited reversible contractures repeatable for >8 h. CSelicited dose-dependent increases in isometric force; 30% produced thelargest forces of 106 ± 12 µN (n = 30), whichis estimated to be 0.5 mN/mm2 cell cross-sectionalarea. Half times for contraction and relaxation were 4.7 ± 0.3 and 3.1 ± 0.3 min at 37°C. With imposition of constant shortening velocities, force declined with time, yieldingtime-dependent force-velocity relations. Forces at 5 s fit thehyperbolic Hill equation; maximum velocity(Vmax) was 0.035 ± 0.002 Lo/s.Compliance averaged 0.0076 ± 0.0006 Lo/Fo. Disruption of microtubules with nocodazole in a CS-contracted fiber had no net effects on force, Vmax, or stiffness; force increased in 8, butdecreased in 13, fibers. Nocodazole did not affect baselineintracellular Ca2+ concentration([Ca2+]i) but reduced (~30%) the[Ca2+]i response to CS. The force afternocodazole treatment was the primary determinant of stiffness andVmax, suggesting that microtubules were not amajor component of fiber internal mechanical resistance. Cytochalasin Dhad major inhibitory effects on all contractile parameters measured butlittle effect on [Ca2+]i. 相似文献
18.
di Wu Qiong; Wang Jiang Huai; Fennessy Fiona; Redmond H. Paul; Bouchier-Hayes David 《American journal of physiology. Cell physiology》1999,277(6):C1229
Elevated blood glucose in uncontrolled diabetes is causallycorrelated with diabetic microangiopathy. Hyperglycemia-triggered accelerated endothelial cell apoptosis is a critical event in theprocess of diabetes-associated microvascular disease. The conditionallysemiessential amino acid taurine has been previously shown to protectagainst human endothelial cell apoptosis. Therefore, this study wasdesigned to investigate the role of taurine in the prevention ofhigh-glucose-mediated cell apoptosis in human umbilical veinendothelial cells (HUVEC) and the mechanisms involved. Exposure ofHUVEC to 30 mM glucose for 48 h (short-term) and 14 days (long-term)resulted in a significant increase in apoptosis, compared with normalglucose (5.5 mM; P < 0.05).High-glucose-induced DNA fragmentation preferentially occurred in the Sphase cells. Mannitol (as osmotic control) at 30 mM failed to induceHUVEC apoptosis. Taurine prevented high-glucose-induced HUVECapoptosis, which correlates with taurine attenuation ofhigh-glucose-mediated increased intracellular reactive oxygen species(ROS) formation and elevated intracellularCa2+ concentration([Ca2+]i)level. Antioxidants, DMSO, N-acetylcysteine, and glutathione, only partly attenuated high-glucose-inducedHUVEC apoptosis. Glucose at 30 mM did not cause HUVEC necrosis.However, both glucose and mannitol at 60 mM caused HUVEC necrosis asrepresented by increased lactate dehydrogenase release and cell lysis.Taurine failed to prevent hyperosmolarity-induced cell necrosis. Theseresults demonstrate that taurine attenuates hyperglycemia-induced HUVECapoptosis through ROS inhibition and[Ca2+]istabilization and suggest that taurine may exert a beneficial effect inpreventing diabetes-associated microangiopathy. 相似文献
19.
Effects of glucose, glucose plus branched-chain amino acids, or placebo on bike performance over 100km 总被引:1,自引:0,他引:1
Madsen Klavs; Maclean Dave A.; Kiens Bente; Christensen Dirk 《Journal of applied physiology》1996,81(6):2644-2650
Madsen, Klavs, Dave A. MacLean, Bente Kiens, and DirkChristensen. Effects of glucose, glucose plus branched-chain aminoacids, or placebo on bike performance over 100 km. J. Appl. Physiol. 81(6): 2644-2650, 1996.This studywas undertaken to determine the effects of ingesting either glucose(trial G) or glucose plusbranched-chain amino acids (BCAA; trialB), compared with placebo (trialP), during prolonged exercise. Nine well-trained cyclists with a maximal oxygen uptake of 63.1 ± 1.5 mlO2 · min1 · kg1performed three laboratory trials consisting of 100 km of cycling separated by 7 days between each trial. During these trials, the subjects were encouraged to complete the 100 km as fast as possible ontheir own bicycles connected to a magnetic brake. No differences inperformance times were observed between the three trials (160.1 ± 4.1, 157.2 ± 4.5, and 159.8 ± 3.7 min, respectively). Intrial B, plasma BCAA levels increased from339 ± 28 µM at rest to 1,026 ± 62 µM after exercise(P < 0.01). Plasma ammoniaconcentrations increased during the entire exercise period for allthree trials and were significantly higher intrial B compared withtrials G andP (P < 0.05). The respiratory exchange ratio was similar in the threetrials during the first 90 min of exercise; thereafter, it tended todrop more in trial P than intrials G andB. These data suggest that neitherglucose nor glucose plus BCAA ingestion during 100 km of cyclingenhance performance in well-trained cyclists. 相似文献
20.
A method for isolating adult and neonatal airway smooth muscle cells and measuring shortening velocity 总被引:2,自引:0,他引:2
Driska S. P.; Laudadio R. E.; Wolfson M. R.; Shaffer T. H. 《Journal of applied physiology》1999,86(1):427-435
Methods are described for isolating smooth muscle cells from thetracheae of adult and neonatal sheep and measuring the single-cell shortening velocity. Isolated cells were elongated,Ca2+ tolerant, and contractedrapidly and substantially when exposed to cholinergic agonists, KCl,serotonin, or caffeine. Adult cells were longer and widerthan preterm cells. Mean cell length in 1.6 mMCaCl2 was 194 ± 57 (SD) µm(n = 66) for adult cells and 93 ± 32 µm (n = 20) for preterm cells(P < 0.05). Mean cell width at thewidest point of the adult cells was 8.2 ± 1.8 µm(n = 66) and 5.2 ± 1.5 µm(n = 20) for preterm cells(P < 0.05). Cells were loaded into aperfusion dish maintained at 35°C and exposed to agonists, andcontractions were videotaped. Cell lengths were measured from 30 videoframes and plotted as a function of time. Nonlinear fitting of celllength to an exponential model gave shortening velocities faster thanmost of those reported for airway smooth muscle tissues. For a sampleof 10 adult and 10 preterm cells stimulated with 100 µM carbachol,mean (± SD) shortening velocity of the preterm cells was notdifferent from that of the adult cells (0.64 ± 0.30 vs. 0.54 ± 0.27 s1, respectively), butpreterm cells shortened more than adult cells (68 ± 12 vs. 55 ± 11% of starting length, respectively;P < 0.05). The preparative andanalytic methods described here are widely applicable to other smoothmuscles and will allow contraction to be studied quantitatively at thesingle-cell level. 相似文献