共查询到20条相似文献,搜索用时 31 毫秒
1.
Ortega A Becker VM Alvarez R Lepock JR Gonzalez-Serratos H 《American journal of physiology. Cell physiology》2000,279(1):C166-C172
Experiments were performedto determine whether the organic Ca2+ channel blocker D-600(gallopamil), which penetrates into muscle cells, affects sarcoplasmicreticulum (SR) Ca2+ uptake by directly inhibiting the lightSR Ca2+-ATPase. We have previously shown that at 10 µM,D-600 inhibits LSR ATP-dependent Ca2+ uptake by 50% buthas no effect on ATPase activity (21). These data suggestthat the SR Ca2+-ATPase might be a potential target forD-600. The ATPase activity of the enzyme is associated with itshydrophilic cytoplasmic domain, whereas Ca2+ binding andtranslocation are associated with the transmembrane domain(18). In the present experiments, we determined which of the two domains of the ATPase is affected by D-600. Thermalinactivation experiments using the SR Ca2+-ATPasedemonstrated that D-600 decreased the thermal stability ofCa2+ transport but had no effect on the stability of ATPaseactivity. In addition, D-600 at a concentration of 160 µM did nothave any leaking effect of Ca2+ on theCa2+-loaded SR. Thermal denaturation profiles of SRmembranes revealed that D-600 interacts directly with the transmembranedomain of the Ca2+-ATPase. No evidence for interaction withthe nucleotide domain was obtained. We conclude that theCa2+ blocker D-600 inhibits the SR Ca2+ pumpspecifically by interacting with the transmembraneCa2+-binding domain of the Ca2+-ATPase. 相似文献
2.
Lactate inhibits Ca2+-activated Ca2+-channel activity from skeletal muscle sarcoplasmic reticulum 总被引:5,自引:0,他引:5
Favero Terence G.; Zable Anthony C.; Colter David; Abramson Jonathan J. 《Journal of applied physiology》1997,82(2):447-452
Favero, Terence G., Anthony C. Zable, David Colter, andJonathan J. Abramson. Lactate inhibits Ca2+-activatedCa2+-channel activity from skeletal muscle sarcoplasmicreticulum. J. Appl. Physiol. 82(2): 447-452, 1997.Sarcoplasmic reticulum (SR) Ca2+-release channelfunction is modified by ligands that are generated during about ofexercise. We have examined the effects of lactate on Ca2+-and caffeine-stimulated Ca2+ release,[3H]ryanodine binding, and singleCa2+-release channel activity of SR isolated from rabbitwhite skeletal muscle. Lactate, at concentrations from 10 to 30 mM,inhibited Ca2+- and caffeine-stimulated[3H]ryanodine binding to and inhibited Ca2+-and caffeine-stimulated Ca2+ release from SR vesicles.Lactate also inhibited caffeine activation of single-channel activityin bilayer reconstitution experiments. These findings suggest thatintense muscle activity, which generates high concentrations oflactate, will disrupt excitation-contraction coupling. This may lead todecreases in Ca2+ transients promoting a decline in tensiondevelopment and contribute to muscle fatigue. 相似文献
3.
K+ supplementation increases muscle [Na+-K+-ATPase] and improves extrarenal K+ homeostasis in rats 总被引:1,自引:0,他引:1
Bundgaard Henning; Schmidt Thomas A.; Larsen Jim S.; Kjeldsen Keld 《Journal of applied physiology》1997,82(4):1136-1144
Bundgaard, Henning, Thomas A. Schmidt, Jim S. Larsen, andKeld Kjeldsen. K+supplementation increases muscle[Na+-K+-ATPase]and improves extrarenal K+homeostasis in rats. J. Appl. Physiol.82(4): 1136-1144, 1997.Effects ofK+ supplementation (~200 mmolKCl/100 g chow) on plasma K+,K+ content, andNa+-K+-adeonsinetriphosphatase(ATPase) concentration([Na+-K+-ATPase])in skeletal muscles as well as on extrarenalK+ clearance were evaluated inrats. After 2 days of K+supplementation, hyperkalemia prevailed(K+-supplemented vs.weight-matched control animals) [5.1 ± 0.2 (SE) vs. 3.2 ± 0.1 mmol/l, P < 0.05, n = 5-6], and after 4 daysa significant increase in K+content was observed in gastrocnemius muscle (104 ± 2 vs. 97 ± 1 µmol/g wet wt, P < 0.05, n = 5-6). After 7 days ofK+ supplementation, a significantincrease in[3H]ouabain bindingsite concentration (344 ± 5 vs. 239 ± 8 pmol/g wet wt,P < 0.05, n = 4) was observed in gastrocnemiusmuscle. After 2 wk, increases in plasmaK+,K+ content, and[3H]ouabain bindingsite concentration in gastrocnemius muscle amounted to 40, 8, and 68%(P < 0.05) above values observed inweight-matched control animals, respectively. The latter change wasconfirmed by K+-dependentp-nitrophenyl phosphatase activitymeasurements. Fasting for 1 day reduced plasmaK+ andK+ content in gastrocnemius musclein rats that had been K+supplemented for 2 wk by 3.1 ± 0.3 mmol/l(P < 0.05, n = 5) and 15 ± 2 µmol/g wet wt(P < 0.05, n = 5), respectively. After induction of anesthesia, arterial plasma K+was measured during intravenous KCl infusion (0.75 mmolKCl · 100 g bodywt1 · h1).The K+-supplemented fasted groupdemonstrated a 42% (P < 0.05) lower plasma K+ rise, associated with asignificantly higher increase inK+ content in gastrocnemius muscleof 7 µmol/g wet wt (P < 0.05, n = 5) compared with their controlanimals. In conclusion, K+supplementation increases plasmaK+,K+ content, and[Na+-K+-ATPase]in skeletal muscles and improves extrarenalK+ clearance capacity. 相似文献
4.
Characterization of the vacuolar-type H+-ATPase from guard cell protoplasts of Commelina 总被引:1,自引:0,他引:1
Willmer C.M.; Grammatikopoulos G.; Lascve G.; Vavasseur A. 《Journal of experimental botany》1995,46(4):383-389
Characteristics of the vacuolar-type (V-type) H+-ATPase fromguard cell protoplasts of Commelina communis L. were investigatedusing a linked enzyme assay and nitrate inhibition as a diagnosticindicator of the enzyme activity. ATPase activity was completelyinhibited by about 50 mol m3 nitrate and activity wasoptimal near pH 8.0. The temperature optimum for activity wasabout 37 C and an Arrhenius plot indicated changes in activationenergy for the ATPase at 15C and possibly at about 30 C. Theenzyme was stimulated by Cl while Ca2+ inhibited activity(l50 = 1.5 mol m3). The apparent Km (MgATP) was 0.62mol m3. Incubation of guard cell protoplasts for up to 5 h in 50 µMabscisic acid (ABA) or 25µM fusicoccin (FC) did not affectsubsequent ATPase activity. In vitro assays with FC or ABA alsodid not affect enzyme activity. Activity was not affected bylight or potassium ferricyanide, two factors which are knownto influence stomatal activity. Beticoline was a potent inhibitorof activity (l50 = 50 µM) while DCCD was less effective(l50 = 90µM). On chlorophyll, protein and protoplast bases, V-type ATPaseactivity was greater in guard cell protoplasts than mesophyllcell protoplasts by 66, 13.9 and 1.9, respectively. On atonoplast surface area basis the enzyme activity was 5.6 timeshigher in guard cell protoplasts than in mesophyll cell protoplasts Thus, although the characteristics of the V-type, H +-ATPaseof GCP are very similar to those found in other cell types,rates of activity and probably tonoplast enzyme density aremuch greater in guard cell protoplasts than mesophyll cell protoplastsof C. communis which corresponds with the large and rapid ionfluxes across the tonoplast associated with stomatal movements Key words: Guard cell protoplasts, stomata, V-type H +-ATPase 相似文献
5.
Harmon Shona; Froemming Gabriele R.; Leisner Elmi; Pette Dirk; Ohlendieck Kay 《Journal of applied physiology》2001,90(1):371-379
After chronic, low-frequency stimulation, a rapiddecline in Ca2+ pump activity is observed during the earlystages of skeletal muscle transformation. However, thisvariation in enzymatic activity does not coincide with a drasticreduction in the amount of sarcoplasmic reticulumCa2+-ATPases. To investigate whether changes in subunitinteractions within Ca2+ pump complexes contribute to thisphenomena, we performed a chemical cross-linking analysis of 4 dayscontinuously, and 4 days discontinuously, electrostimulated fast musclefibers. The abundance of the slow and fast Ca2+-ATPaseisoforms sarco(endo)plasmic reticulum Ca2+- ATPase types1 and 2 was affected during the fast-to-slow transition process,demonstrating that, even after short-term stimulation, distinct changesin the isoform expression pattern of muscle proteins occur. However,the oligomeric status of both ion pump species did not change. Hence,chemical modifications of critical enzyme domains must be responsiblefor the rapid stimulation-induced activity changes, not variations inprotein-protein interactions within Ca2+-ATPase units.Oligomerization appears to be of central importance to the properphysiological functioning of the Ca2+-ATPase and does notundergo changes during skeletal muscle conditioning. 相似文献
6.
To investigatethe Ca2+-dependent plasticity ofsarcoplasmic reticulum (SR) function in vascular smooth muscle,transient responses to agents releasing intracellularCa2+ by either ryanodine(caffeine) orD-myo-inositol1,4,5-trisphosphate [IP3;produced in response to norepinephrine (NE),5-hydroxytryptamine (5-HT), arginine vasopressin (AVP)] receptorsin rat tail arterial rings were evaluated after 4 days of organculture. Force transients induced by all agents were increased comparedwith those induced in fresh rings. Stimulation by 10% FCSduring culture further potentiated the force andCa2+ responses to caffeine (20 mM)but not to NE (10 µM), 5-HT (10 µM), or AVP (0.1 µM). The effectwas persistent, and SR capacity was not altered after reversibledepletion of stores with cyclopiazonic acid. The effects of serum couldbe mimicked by culture in depolarizing medium (30 mMK+) and blocked by the additionof verapamil (1 µM) or EGTA (1 mM) to the medium, loweringintracellular Ca2+ concentration([Ca2+]i)during culture. These results show that modulation of SR function canoccur in vitro by a mechanism dependent on long-term levels of basal[Ca2+]iand involving ryanodine- but notIP3 receptor-mediatedCa2+release. 相似文献
7.
Codina J Cardwell J Gitomer JJ Cui Y Kone BC Dubose TD 《American journal of physiology. Cell physiology》2000,279(5):C1319-C1326
Two H+-K+-ATPase isoforms are presentin kidney: the gastric, highly sensitive to Sch-28080, and the colonic,partially sensitive to ouabain. Upregulation of Sch-28080-sensitiveH+-K+-ATPase, or "gastric"H+-K+-ATPase, has been demonstrated inhypokalemic rat inner medullary collecting duct cells (IMCDs).Nevertheless, only colonic H+-K+-ATPase mRNAand protein abundance increase in this condition. This study wasdesigned to determine whether Sch-28080 inhibits transporters otherthan the gastric H+-K+-ATPase. In the presenceof bumetanide, Sch-28080 (200 µM) and ouabain (2 mM) inhibited86Rb+ uptake (>90%). That86Rb+ uptake was almost completely abolished bySch-28080 indicates an effect of this agent on theNa+-K+-ATPase. ATPase assays in membranes, orlysed cells, demonstrated sensitivity to ouabain but not Sch-28080.Thus the inhibitory effect of Sch-28080 was dependent on cellintegrity. 86Rb+-uptake studies withoutbumetanide demonstrated that ouabain inhibited activity by only50%. Addition of Sch-28080 (200 µM) blocked all residualactivity. Intracellular ATP declined after Sch-28080 (200 µM) butrecovered after removal of this agent. In conclusion, highconcentrations of Sch-28080 inhibit K+-ATPase activity inmouse IMCD-3 (mIMCD-3) cells as a result of ATP depletion. 相似文献
8.
Carbachol inhibits Na(+)-K(+)-ATPase activity in choroid plexus via stimulation of the NO/cGMP pathway 总被引:1,自引:0,他引:1
Ellis DZ Nathanson JA Sweadner KJ 《American journal of physiology. Cell physiology》2000,279(6):C1685-C1693
Secretion of cerebrospinal fluid by the choroid plexus canbe inhibited by its cholinergic innervation. We demonstrated that carbachol inhibits the Na+-K+-ATPase in bovinechoroid tissue slices and investigated the mechanism. Many of theactions of cholinergic agents are mediated by nitric oxide (NO), whichplays important roles in fluid homeostasis. The inhibition ofNa+-K+-ATPase was blocked by the NO synthaseinhibitor [N-nitro-L-argininemethyl ester] and was quantitatively mimicked by the NO agonistssodium nitroprusside (SNP) and diethylenetriamine NO. Inhibition by SNPcorrelated with an increase in tissue cGMP and was abolished by1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, an inhibitor of soluble guanylate cyclase. Inhibition was mimicked bythe protein kinase G activator 8-bromo-cGMP and by okadaic acid, aninhibitor of protein phosphatases 1 and 2A. cGMP-dependent proteinkinase inhibitors Rp-8-pCPT-cGMP (0.5-5 µM) and KT-5823 (2.0 µM) did not block the effects of SNP, but higher concentrations ofthe more selective inhibitor (Rp-8-pCPT-cGMP) had a pharmacological inhibitory effect on Na+-K+-ATPase. The datasuggest that cholinergic regulation of theNa+-K+-ATPase is mediated by NO and involvesactivation of guanylate cyclase and elevation of cGMP. 相似文献
9.
SYNOPSIS. Actomyosin was extracted from skeletal muscle of Coryphaenoides,a benthic fish living at 2,200 meters depth, at a temperatureof 2°C, or less, and at pressure of 3,000 psi. On SDS-ureaelectrophoresis on acrylamide gel, the actomyosin extracts yieldcomponents of apparent molecular weight 210,000 (myosin heavychains), 47,000 (actin), 35,000 (tropomyosin and/or troponinsubunits), and 13,000 (myosin light chains). The Mg2+-ATPaseof Coryphaenoides actomyosin shows a complex Arrhenius plot,with marked denaturation at temperatures above 30°C, anddiminished temperature sensitivity at temperatures below 15°C.Mg2+-ATPase is inhibited by pressure, with activation volumesof + 160 cc/mole at 25°C, and + 230 cc/mole at 2°C.Ca2+-ATPase of actomyosin exhibits the same pH, temperature,and pressure dependence as Ca2+-ATPase of myosin. The overalldata would be consistent with a positive activation volume thatis independent of temperature (to first approximation) and isrelated to the interaction of actin and myosin, and a negativeactivation volume that is temperature dependent and is relateddirectly to activation of myosin ATPase. The net effect appearsto be an adaptive mechanism whereby Mg2+-ATPase of Coryphaenoidesactomyosin is relatively insensitive to pressure and temperatureunder conditions encountered by the living fish. 相似文献
10.
Cifuentes F Vergara J Hidalgo C 《American journal of physiology. Cell physiology》2000,279(1):C89-C97
TheNa+/Ca2+ exchanger participates inCa2+ homeostasis in a variety of cells and has a key rolein cardiac muscle physiology. We studied in this work the exchanger ofamphibian skeletal muscle, using both isolated inside-out transversetubule vesicles and single muscle fibers. In vesicles, increasingextravesicular (intracellular) Na+ concentrationcooperatively stimulated Ca2+ efflux (reverse mode), withthe Hill number equal to 2.8. In contrast to the stimulation of thecardiac exchanger, increasing extravesicular (cytoplasmic)Ca2+ concentration ([Ca2+]) inhibited thisreverse activity with an IC50 of 91 nM. Exchanger-mediated currents were measured at 15°C in single fibers voltage clamped at90 mV. Photolysis of a cytoplasmic caged Ca2+ compoundactivated an inward current (forward mode) of 23 ± 10 nA(n = 3), with an average current density of 0.6 µA/µF. External Na+ withdrawal generated an outwardcurrent (reverse mode) with an average current density of 0.36 ± 0.17 µA/µF (n = 6) but produced a minimal increasein cytosolic [Ca2+]. These results suggest that, inskeletal muscle, the main function of the exchanger is to removeCa2+ from the cells after stimulation. 相似文献
11.
Ca2+ mediates the effect of inhibition of Na+-K+-ATPase on the basolateral K+ channels in the rat CCD 总被引:1,自引:0,他引:1
We investigated the effect ofinhibiting Na+-K+-ATPase on the basolateral18-pS K+ channel in the cortical collecting duct (CCD) ofthe rat kidney. Inhibiting Na+-K+-ATPase withstrophanthidin decreased the activity of the 18-pS K+channel and increased the intracellular Ca2+ to 420 nM.Removal of extracellular Ca2+ abolished the effect ofstrophanthidin. When intracellular Ca2+ was raised with 5 µM ionomycin or A-23187 to 300, 400, and 500 nM, the activity of the18-pS K+ channel in cell-attached patches fell by 40, 85, and 96%, respectively. To explore the mechanism ofCa2+-induced inhibition, the effect of 400 nMCa2+ on channel activity was studied in the presence ofcalphostin C, an inhibitor of protein kinase C, or KN-93 and KN-62,inhibitors of calmodulin-dependent kinase II. Addition of calphostin Cor KN-93 or KN-62 failed to block the inhibitory effect of highconcentrations of Ca2+. This suggested that the inhibitoryeffect of high concentrations of Ca2+ was not mediated byprotein kinase C or calmodulin-dependent kinase II pathways. To examinethe possibility that the inhibitory effect of high concentrations ofCa2+ was mediated by the interaction of nitric oxide withsuperoxide, we investigated the effect of 400 nM Ca2+ onchannel activity in the presence of 4,5-dihydroxy-1,3-benzenedisulfonic acid (Tiron) orN-nitro-L-arginine methyl ester.Pretreatment of the tubules with 4,5-dihydroxy-1,3-benzenedisulfonicacid or N-nitro-L-arginine methylester completely abolished the inhibitory effect of 400 nMCa2+ on channel activity. Moreover, application of4,5-dihydroxy-1,3-benzenedisulfonic acid reversed the inhibitory effectof strophanthidin. We conclude that the effect of inhibitingNa+-K+-ATPase is mediated by intracellularCa2+ and the inhibitory effect of high concentrations ofCa2+ is the result of interaction of nitric oxide with superoxide. 相似文献
12.
Zhong Juming; Hume Joseph R.; Keef Kathleen D. 《American journal of physiology. Cell physiology》1999,277(4):C840
Stimulation of cardiac L-typeCa2+ channels by cAMP-dependentprotein kinase (PKA) requires anchoring of PKA to a specificsubcellular environment by A-kinase anchoring proteins (AKAP). Thisstudy evaluated the possible requirement of AKAP in PKA-dependentregulation of L-type Ca2+ channelsin vascular smooth muscle cells using the conventional whole cellpatch-clamp technique. Peak Ba2+current in freshly isolated rabbit portal vein myocytes wassignificantly increased by superfusion with either 0.5 µM isoproterenol (131 ± 3% of the control value,n = 11) or 10 µM 8-bromoadenosine3',5'-cyclic monophosphate (8-BrcAMP; 114 ± 1%,n = 8). The PKA-induced stimulatory effects ofboth isoproterenol and 8-BrcAMP were completely abolished by a specificPKA inhibitor KT-5720 (0.2 µM) or by dialyzing cells with Ht 31 (100 µM), a peptide that inhibits the binding of PKA to AKAP. In contrast,Ht 31 did not block the excitatory effect of the catalytic subunit ofPKA when dialyzed into the cells. These data suggest that stimulationof Ca2+ channels in vascularmyocytes by endogenous PKA requires localization of PKA through bindingto AKAP. 相似文献
13.
Jung Dennis W.; Brierley Gerald P. 《American journal of physiology. Cell physiology》1999,277(6):C1194
Mitochondria must maintain volume homeostasis inorder to carry out oxidative phosphorylation. It has been postulatedthat the concentration of freeMg2+([Mg2+]) serves as thesensor of matrix volume and regulates aK+-extrudingK+/H+antiport (K. D. Garlid. J. Biol. Chem.255: 11273-11279, 1980). To test this hypothesis, the fluorescentprobe furaptra was used to monitor[Mg2+] and freeCa2+ concentration ([Ca2+]) in the matrix ofisolated beef heart mitochondria, andK+/H+antiport activity was measured by passive swelling in potassium acetate. Concentrations that result in 50% inhibition of maximum activity of 92 µM matrix [Mg2+] and 2.2 µM[Ca2+] were determined for theK+/H+ antiport. Untreated mitochondria average670 µM matrix [Mg2+], a value that would permit <1%of maximumK+/H+antiport activity. Hypotonic swelling results in large decreases inmatrix [Mg2+], butswelling due to accumulation of acetate salts does not alter[Mg2+]. Swelling inphosphate salts decreases matrix[Mg2+], but not tolevels that permit appreciable antiport activity. We conclude that1) it is unlikely that matrix[Mg2+] serves as themitochondrial volume sensor, 2) ifK+/H+antiport functions as a volume control transporter, it is probably regulated by factors other than[Mg2+], and3) alternative mechanisms formitochondrial volume control should be considered. 相似文献
14.
Changes in intracellular Ca2+ concentration induced by L-type Ca2+ channel current in guinea pig gastric myocytes 总被引:1,自引:0,他引:1
Kim Sung Joon; Ahn Seung Cheol; Kim Jin Kyung; Kim Young Chul; So Insuk; Kim Ki Whan 《American journal of physiology. Cell physiology》1997,273(6):C1947
We investigatedthe relationship between voltage-operatedCa2+ channel current and thecorresponding intracellular Ca2+concentration([Ca2+]i)change (Ca2+ transient) in guineapig gastric myocytes. Fluorescence microspectroscopy was combined withconventional whole cell patch-clamp technique, and fura 2 (80 µM) wasadded to CsCl-rich pipette solution. Step depolarization to 0 mVinduced inward Ca2+ current(ICa) andconcomitantly raised[Ca2+]i.Both responses were suppressed by nicardipine, an L-typeCa2+ channel blocker, and thevoltage dependence of Ca2+transient was similar to the current-voltage relation ofICa. When pulseduration was increased by up to 900 ms, peakCa2+ transient increased andreached a steady state when stimulation was for longer. The calculatedfast Ca2+ buffering capacity(B value), determined as the ratio ofthe time integral ofICa divided bythe amplitude of Ca2+ transient,was not significantly increased after depletion of Ca2+ stores by the cyclicapplication of caffeine (10 mM) in the presence of ryanodine (4 µM).The addition of cyclopiazonic acid (CPA, 10 µM), a sarco(endo)plasmicreticulum Ca2+-ATPase inhibitor,decreased B value by ~20% in areversible manner. When KCl pipette solution was used,Ca2+-activatedK+ current[IK(Ca)]was also recorded during step depolarization. CPA sensitivelysuppressed the initial peak and oscillations of IK(Ca) withirregular effects on Ca2+transients. The above results suggest that, in guinea pig gastric myocyte, Ca2+ transient is tightlycoupled to ICaduring depolarization, and global[Ca2+]iis not significantly affected byCa2+-inducedCa2+ release from sarcoplasmicreticulum during depolarization. 相似文献
15.
Force generation,but not myosin ATPase activity,declines with age in rat muscle fibers 总被引:2,自引:0,他引:2
Lowe DA Thomas DD Thompson LV 《American journal of physiology. Cell physiology》2002,283(1):C187-C192
We tested the hypothesis thatage-associated decline in muscle function is related to a change inmyosin ATPase activity. Single, glycerinated semimembranosus fibersfrom young (8-12 mo) and aged (32-37 mo) Fischer 344 × Brown Norway male rats were analyzed simultaneously for force andmyosin ATPase activity over a range of Ca2+ concentrations.Maximal force generation was ~20% lower in fibers from aged animals(P = 0.02), but myosin ATPase activity was not different between fibers from young and aged rats: 686 ± 46 (n = 30) and 697 ± 46 µM/s (n = 33) (P = 0.89). The apparent rate constant for thedissociation of strong-binding myosin from actin was calculated to be~30% greater in fibers from aged animals (P = 0.03),indicating that the lower force produced by fibers from aged animals isdue to a greater flux of myosin heads from the strong-binding state tothe weak-binding state during contraction. This is in agreement withour previous electron paramagnetic resonance experiments that showed areduced fraction of myosin heads in the strong-binding state during amaximal isometric contraction in fibers from older rats. 相似文献
16.
The effects of blue light (B) pretreatments on internode extensiongrowth and their possible interaction with phytochrome mediatedresponses were examined in Sinapis alba seedlings grown for11 d under 280 µmol m2 s1 of continuousblue-deficient light from low pressure sodium lamps (SOX). SupplementaryB (16 µmol m2 s1) caused no detectable inhibitionof the first internode growth rate under continuous SOX, butgrowth rate was inhibited after transfer to darkness. This effect,and the growth promotion caused by far-red bend-of-day' lightpulses were additive. The addition of B at 16 µmol m2s1 during 11 d, or only during the first 9 or 10 d orthe latest 0.75, 1 or 2 d of the SOX pretreatment caused approximatelythe same extent of inhibition after the transition to darkness.A single hour of supplementary B before darkness caused morethan 50% of the maximum inhibition. However, 24 h of lower fluencerates of B (4 or 7 µmol m2 s1) were ineffective.Covering the internode during the supplementary B period didnot prevent the response to B after the transition to darkness.Far-red light given simultaneously with B (instead of the SOXbackground) reduced the inhibitory effect of B. Above a given threshold fluence rate, B perceived mainly inthe leaves inhibits extension growth in subsequent darkness,provided that high phytochrome photo-equilibria are presentduring the irradiation with B. Once triggered, this effect doesnot interact significantly with the end-of-dayphytochrome effect. Key words: Blue light, extension growth, phytochrome 相似文献
17.
Role of plasma membrane Ca2+-ATPase in contraction-relaxation processes of the bladder: evidence from PMCA gene-ablated mice 总被引:1,自引:0,他引:1
Liu L Ishida Y Okunade G Shull GE Paul RJ 《American journal of physiology. Cell physiology》2006,290(4):C1239-C1247
We investigated the roles and relationships of plasma membrane Ca2+-ATPase (PMCA), sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA)2, and Na+/Ca2+ exchanger (NCX) in bladder smooth muscle contractility in Pmca-ablated mice: Pmca4-null mutant (Pmca4/) and heterozygous Pmca1 and homozygous Pmca4 double gene-targeted (Pmca1+/Pmca4/) mice. Gene manipulation did not alter the amounts of PMCA1, SERCA2, and NCX. To study the role of each Ca2+ transport system, contraction of circular ring preparations was elicited with KCl (80 mM) plus atropine, and then the muscle was relaxed with Ca2+-free physiological salt solution containing EGTA. We measured the contributions of Ca2+ clearance components by inhibiting SERCA2 (with 10 µM cyclopiazonic acid) and/or NCX (by replacing NaCl with N-methyl-D-glucamine/HCl plus 10 µM KB-R7943). Contraction half-time (time to 50% of maximum tension) was prolonged in the gene-targeted muscles but marginally shortened when SERCA2 or NCX was inhibited. The inhibition of NCX significantly inhibited this prolongation, suggesting that NCX activity might be augmented to compensate for PMCA4 function in the gene-targeted muscles under nonstimulated conditions. Inhibition of SERCA2 and NCX as well as gene targeting all prolonged the relaxation half-time. The contribution of PMCA to relaxation was calculated to be 2530%, with that of SERCA2 being 20% and that of NCX being 70%. PMCA and SERCA2 appeared to function additively, but the function of NCX might overlap with those of other components. In summary, gene manipulation of PMCA indicates that PMCA, in addition to SERCA2 and NCX, plays a significant role in both excitation-contraction coupling and the Ca2+ extrusion-relaxation relationship, i.e., Ca2+ homeostasis, of bladder smooth muscle. ATP2B; sarco(endo)plasmic reticulum Ca2+-ATPase 2; Na+/Ca2+ exchanger; homeostasis 相似文献
18.
Duneclift, S., U. Wells, and J. Widdicombe. Estimationof thickness of airway surface liquid in ferret trachea in vitro. J. Appl. Physiol. 83(3): 761-767, 1997.The tracheae of ferrets and rabbits were mounted in vitro inorgan baths. While the tracheae were liquid filled, the permeabilitycoefficient ( P) was determined, and then while thetracheae were air filled, the percent clearance for99mTc-labeleddiethylenetriaminepentaacetic acid (DTPA) was determined. The thicknessof airway surface liquid (ASL) was estimated by three methods.1) The initial concentration of99mTc-DTPA and the total amount of99mTc-DTPA (the sum of thatentering the outside medium, that draining from the trachea, and thatwashed out at the end of 40 min) gave the initial volume of ASL andthus its thickness. Mean values were 45.7 µm for the ferret and 41.9 µm for the rabbit. 2) Estimates ofASL thickness at the end of the 40-min period, based on the final99mTc-DTPA concentration and theamount in the washout, were 42.9 µm for ferret and 45.4 µm forrabbit. 3) The ratio of Pto percent clearance gave mean ASL thickness values of 49.2 µm forthe ferret and 40.3 µm for the rabbit. Thus three separate methodsfor determining ASL thickness give very similar results, with means inthe range 40-49 µm. Administration of methacholine or atropineto ferret tracheae did not significantly change ASL thickness. 相似文献
19.
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
20.
Gallagher Dympna; Visser Marjolein; De Meersman Ronald E.; Sepulveda Dennis; Baumgartner Richard N.; Pierson Richard N.; Harris Tamara; Heymsfield Steven B. 《Journal of applied physiology》1997,83(1):229-239
Gallagher, Dympna, Marjolein Visser, Ronald E. De Meersman,Dennis Sepúlveda, Richard N. Baumgartner, Richard N. Pierson, Tamara Harris, and Steven B. Heymsfield. Appendicular skeletal muscle mass: effects of age, gender, and ethnicity. J. Appl. Physiol. 83(1): 229-239, 1997.This studytested the hypothesis that skeletal muscle mass is reduced in elderlywomen and men after adjustment first for stature and body weight. Thehypothesis was evaluated by estimating appendicular skeletal musclemass with dual-energy X-ray absorptiometry in a healthy adult cohort. Asecond purpose was to test the hypothesis that whole body40K counting-derived total bodypotassium (TBK) is a reliable indirect measure of skeletal muscle mass.The independent effects on both appendicular skeletal muscle and TBK ofgender (n = 148 women and 136 men) andethnicity (n = 152 African-Americans and 132 Caucasians) were also explored. Main findingswere 1) for both appendicularskeletal muscle mass (total, leg, and arm) and TBK, age was anindependent determinant after adjustment first by stepwise multipleregression for stature and weight (multiple regression modelr2 = ~0.60);absolute decrease with greater age in men was almost double that inwomen; significantly larger absolute amounts were observed in men andAfrican-Americans after adjustment first for stature, weight, and age;and >80% of within-gender or -ethnic group between-individualcomponent variation was explained by stature, weight, age, gender, andethnicity differences; and 2) mostof between-individual TBK variation could be explained by totalappendicular skeletal muscle(r2 = 0.865),whereas age, gender, and ethnicity were small but significant additional covariates (totalr2 = 0.903). Ourstudy supports the hypotheses that skeletal muscle is reduced in theelderly and that TBK provides a reasonable indirect assessment ofskeletal muscle mass. These findings provide a foundation forinvestigating skeletal muscle mass in a wide range of health-related conditions. 相似文献