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1.
In semicells of the unicellular green alga Closterium that areundergoing elongation, transcellular ion currents enter theelongating region of the cell and leave via the non-elongatingregion of the cell, as in the case of many other tip-growingorganisms. The density of the inwardly and outwardly directedcurrents was 142.5±63.7 nA cm–2 (n=42) and 109.3±46.5nA cm–2 (n=33), respectively, at the respective regionsof the cells. Both currents clearly decreased with decreasesin the external concentration of Ca2+ ions, and they were completelyblocked by addition of Ca2+-channel blockers, such as 20 µMLaCl3, to the external medium. Increases in pH up to 10.2 hadno effect on the currents, but a decrease in pH from 7.5 to5.7 or 4.5 resulted in an explosive increase in the currents.Removal of external K+ and Cl ions induced some increasesin the currents, but removal of external Na+ Mg2+ plus and ions had little effect on the currents. A major part of thecurrents may be carried by Ca2+ ions, while H+, K+ and Clions may play a minor role as members of the group of ions thatcarry the currents. Thus, there is a clear relationship betweenCa2+ ion currents and elongation in Closterium. (Received April 30, 1992; Accepted July 13, 1992)  相似文献   

2.
Effluxes of K+ and Ca2+ from root segments of both wheat, Triticunaestivum L. cv. Capelle and mung bean, Vigna radiata (L.) Wilczek,were measured in the presence or absence of 20 mol m–3para-fluorophenylalanine (p-FPA). The results were used to estimatethe compartment contents and transmembrane K+ and Ca2+ fluxesin root cortex cells. Using the Ussing-Teorell flux equationas the criterion, it was concluded that entry of K+ from theoutside solution to the cytoplasm, and from the cytoplasm tothe vacuole were active in both wheat and mung bean. Also, inboth species, Ca2+ entered the cytoplasm passively across theplasmalemma and was actively pumped back to the external solution.However, interpretation of the direction of active transportacross the tonoplast depends upon an assumption about Ca2+ activityin the cytoplasm. The only qualitative effect of p-FPA was to alter the drivingforce for K+ influx, across the plasmalemma in wheat, from anactive to a passive one. Quantitative effects of the analoguewere seen for K+ fluxes in both wheat and mung bean and forCa2+ fluxes in wheat. The p-FPA reduced transport of K+ in bothspecies, while transport of Ca2+ was unaffected. The implicationsof these results for the ‘two pump hypothesis’ arediscussed. Key words: Triticum aestivum, Vigna radiata, Two pump hypothesis  相似文献   

3.
A hyposmotic challenge elicited contraction of isolated canine basilar arteries. The contractile response was nearly abolished by the removal of extracellular Ca2+ and by the voltage-dependent Ca2+ channel (VDCC) blocker nicardipine, but it was unaffected by thapsigargin, which depletes intracellular Ca2+ stores. The contraction was also inhibited by Gd3+ and ruthenium red, cation channel blockers, and Cl channel blockers DIDS and niflumic acid. The reduction of extracellular Cl concentrations enhanced the hypotonically induced contraction. Patch-clamp analysis showed that a hyposmotic challenge activated outwardly rectifying whole cell currents in isolated canine basilar artery myocytes. The reversal potential of the current was shifted toward negative potentials by reductions in intracellular Cl concentration, indicating that the currents were carried by Cl. Moreover, the currents were abolished by 10 mM BAPTA in the pipette solution and by the removal of extracellular Ca2+. Taken together, these results suggest that a hyposmotic challenge activates cation channels, which presumably cause Ca2+ influx, thereby activating Ca2+-activated Cl channels. The subsequent membrane depolarization is likely to increase Ca2+ influx through VDCC and elicit contraction. stretch-activated cation channels; Ca2+-activated Cl channels; voltage-dependent Ca2+ channels; large-conductance Ca2+-activated K+ channels; gadolinium  相似文献   

4.
We examined a role of Ca2+ in the activation of the two majorion channels, i.e., Cl and K+ channels at the excitationof the characean plasmalemma. The current-voltage relation (I-Vcurve) of the Chara membrane was compared under the ramp voltageclamp condition before and after external application of 20µMof La3+ (a Ca2+ channel blocker). The transient inward currentcomponent, which is carried mainly by the efflux of Cl,disappeared almost completely in about 30 min with La3+ treatment.On the other hand, no effect was observed on the late largeoutward current, which is mainly carried by the efflux of K+in a large depolarization region (less negative than –50mV). These results suggest that the Cl channel in theChara plasmalemma is activated by Ca2+ influx, while the K+channel is simply activated by depolarization. (Received April 7, 1986; Accepted June 6, 1986)  相似文献   

5.
Using the whole cell patch clamp technique, we measured changesin outward K+ currents of gerbil taste cells in response todifferent kinds of sweeteners. Outward K+ currents of the tastecell induced by depolarizing pulses were suppressed by sweetstimuli such as 10 mM Na-saccharin. The membrane-permeable analogof cAMP, cpt-cAMP, also decreased outward K+ currents. On theother hand, the K+ currents were enhanced by amino acid sweetenerssuch as 10 mM D-tryptophan. The outward K+ current was enhancedby external application of Ca2+-transporting ionophore, 5 µMionomycin, and intracellular application of 5 µM inositol-1,4,5-trisphosphate(IP3). The outward K+ currents were no longer suppressed by10 mM Na-saccharin containing 20 µM gurmarin, but werestill enhanced by 10 mM D-tryptophan containing 20 µMgurmarin. These results suggest that sweet taste transductionfor one group of sweeteners such as Na-saccharin in gerbilsis concerned with an increase of the intracellular cAMP level,and that the transduction for the other group of sweetenerssuch as D-tryptophan is concerned with an increase of the intracellularIP3 level which releases Ca2+ from the internal stores. Chem.Senses 22: 163–169, 1997.  相似文献   

6.
We have reported that ryanodine receptor (RyR) channels display three different responses to cytoplasmic free Ca2+ concentration ([Ca2+]) depending on their redox state (Marengo JJ, Hidalgo C, and Bull R. Biophys J 74: 1263–1277, 1998), with low, moderate, and high maximal fractional open times (Po). Activation by ATP of single RyR channels from rat brain cortex was tested in planar lipid bilayers with 10 or 0.1 µM cytoplasmic [Ca2+]. At 10 µM [Ca2+], low-Po channels presented lower apparent affinity to activation by ATP [[ATP] for half-maximal activation (KaATP) = 422 µM] than moderate-Po channels (KaATP = 82 µM). Oxidation of low-Po channels with thimerosal or 2,2'-dithiodipyridine (DTDP) gave rise to moderate-Po channels and decreased KaATP from 422 to 82 µM. At 0.1 µM cytoplasmic [Ca2+], ATP induced an almost negligible activation of low-Po channels. After oxidation to high-Po behavior, activation by ATP was markedly increased. Noise analysis of single-channel fluctuations of low-Po channels at 10 µM [Ca2+] plus ATP revealed the presence of subconductance states, suggesting a conduction mechanism that involves four independent subchannels. On oxidation the subchannels opened and closed in a concerted mode. subconductance states; calcium ion release channels; calcium ion regulation; thimerosal; 2,2'-dithiodipyridine  相似文献   

7.
Darkening after illumination induces a transient hyperpolarizationof the plasma membrane of the unicellular green alga Eremosphaeraviridis de Bary. With electro-physiological methods, in particularthe two electrode voltage-clamp technique, we investigated theion fluxes involved in this transient potential change (TP).The question was whether other ion currents besides those carriedby the known Ca2+-dependent K+ channel take part in this actionpotential-like, but hyperpolarizing, response. At maximum hyperpolarizationvoltage-clamp measurements resulted in ‘N-shaped’I/V curves, known from other botanical systems. The differentinstantaneous current components of the N-shaped I/V curvesoccurred at different times during a single transient potentialchange (TP). Substitution of alkali metal cations in the bathingsolution by NMG/NO3 showed that the inward currents in the I/Vcurves were not carried by an influx of K+ into the cytoplasm.The voltage amplitude of the TP not only depended on the externalK+ concentration, but also on the Mg2+ concentration in thebathing solution. Increasing Mg2+ concentrations shifted themembrane potential in the top of the TP in the direction ofthe Nernst potential of Mg2+ and resulted in an increased inwardcurrent component of the N-shaped I/V curves. Another currentcomponent was found to be carried not by cations but by an effluxof anions. It was a voltage-dependent component with a maximumcurrent amplitude at voltages of about –220 to –240mV, and was blocked by the anion channel inhibitors anthracen-9-carboxylicacid (A9C), (5-nitro-2-3-phenylpropylamino) benzoic acid (NPPB)and ZnCI2. Based on these data a model is proposed which explainsthe N-shape of the I/V curves observed during the transientpotential change of the alga E. viridis by the combination ofan inward cation current with an inward anion current and theoutward cation current carried by the Ca2+-dependent K+ channels. Key words: Anion current, cation current, Eremosphaera viridis, potassium channel, voltage-clamp  相似文献   

8.
Light-dependent potassium uptake by Pisum sativum leaf fragments   总被引:1,自引:0,他引:1  
A net K+ influx into chopped pea leaves bathed in 5 mM KCl,0.26 M sucrose and illuminated with 4000 lux amounted to about7.5 µmoles/g fresh weight-hr, while essentially no netflux occurred in the dark. This light-dependent K+ uptake waslinear with time for nearly 2 hr and continuously increasedas the light intensity was raised to 9000 lux. Over half ofthe K+ uptake was balanced by H+ release into the bathing solution,possibly by a mechanism in which bicarbonate was the anion accompanyingK+. The replacement of Cl by HCO3 increased thelight-dependent K+ uptake to 56 µmoles/g fresh weight-hr.About 23% of the light-dependent K+ uptake in 5 mM KCl was accompaniedby a Cl uptake. This net Cl influx was less sensitiveto the uncoupler tri-Fl-CCP and more sensitive to DCMU in thebathing solution than was the K+ uptake. The remaining net K+influx into pea leaf fragments was balanced by effluxes of sodium(accounting for 5%), magnesium (8%) and calcium (1%). (Received March 31, 1969; )  相似文献   

9.
The uptake of K+ by plant roots is matched to the demand forK+ for growth. The growing shoot must communicate its K+ requirementto the root. It has been suggested that this might be effectedby varying the amount of K+ retranslocated from the shoot tothe root via the phloem. It is predicted that less K+ is returnedto the roots in K+-deficient plants and that this promotes compensatoryK+ uptake from the external medium. These experiments addressthis hypothesis. Rye (Secale cereale L.) was grown hydroponically in completenutrient solutions containing either 100 aM or 400 µMK+. Plant development, shoot fresh weight (FW) and plant drymatter accumulation did not differ between seedlings grown atthese K+ concentrations. However, root FW was lower in seedlingsgrown in solutions containing 100 µM K+, which resultedin a greater shoot/root FW ratio. Seedlings from both treatmentshad similar shoot K+ concentrations, but the root K+ concentrationof seedlings grown In solutions containing 100 µM K+ wasless than their counterparts grown at 400 µM K+. When assayed at the same K+ concentration, unidirectional K+(86Rb+) influx into 14-d-old seedlings grown with 100 µMK+ in the nutrient solution was greater than that into seedlingsgrown with 400 µM K+ in the nutrient solution, indicatingan increased K+ influx capacity in the former. Furthermore,K+ (86Rb+) influx into seedlings grown and assayed at 100 µMK+ was greater than that into seedlings grown and assayed at400 µM K+. Since net K+ uptake was lower in the seedlingsgrown at 100 µM K+, this indicates a greater unidirectionalK+ efflux from roots in solutions containing 100 µM K+. An empirical model, based on the immobility of calcium in thephloem, was used to describe quantitatively K+ fluxes in seedlings14 d after sowing. As primary data, the composition of xylemsap and the accumulation of elements in root and shoot tissueswere determined. Xylem sap was collected either as root-pressureexudate or from excised roots immersed in nutrient solutionand subjected to a pneumatic pressure of 0.4 MPa. The K:Ca ratioin these saps differed, and led to contrasting conclusions concerningthe effect of K+ nutrition on the recirculation of K+. Basedon the K:Ca ratio in the sap obtained following the applicationof pneumatic pressure, which is thought to resemble that ofintact transpiring plants, it was calculated that the K+ fluxfrom the shoot to the root was higher in seedlings maintainedin solutions containing higher K+ concentrations. This suggeststhat a negative feedback mechanism based on K+ recirculationfrom the shoot to the root via the phloem could be a primarysignal decreasing K+ influx. Key words: K+ influx, K+ recirculation, regulation, root, rye, Secale cereale L  相似文献   

10.
The processes of NO3 uptake and transport and the effectsof NH4+ or L-glutamate on these processes were investigatedwith excised non-mycorrhizal beech (Fagus sylvatica L.) roots.NO3 net uptake followed uniphasic Michaelis-Menten kineticsin a concentration range of 10µM to 1 mM with an apparentKm of 9.2 µM and a Vmax of 366 nmol g–1 FW h–1.NH4+, when present in excess to NO3, or 10 mM L-glutamateinhibited the net uptake of NO3 Apparently, part of NO3taken up was loaded into the xylem. Relative xylem loading ofNO3 ranged from 3.21.6 to 6.45.1% of NO3 netuptake. It was not affected by treatment with NH4+ or L-glutamate.16N/13N double labelling experiments showed that NO3efflux from roots increased with increasing influx of NO3and, therefore, declined if influx was reduced by NH4+ or L-glutamateexposure. From these results it is concluded that NO3net uptake by non-mycorrhizal beech roots is reduced by NH4+or L-glutamate at the level of influx and not at the level ofefflux. Key words: Nitrate transport, net uptake, influx, efflux, ammonium, Fagus, Fagaceae  相似文献   

11.
A depolarization-activated outwardly-rectifying channel (OR),most likely involved in the passive release of K+ from the rootsymplasm into the stelar apoplast (for subsequent transportto the shoot via the xylem vessels), has been characterizedin the plasma membrane of maize root stelar cells (Roberts andTester, 1995). In the present study, the selectivity of thischannel was further characterized using single channel current-voltagecurves generated using a voltage ramp protocol. This protocolpermitted the accurate and unambiguous measurement of the reversalpotentials of currents resulting from single channel openings.Using the voltage ramp protocol, it was shown that the OR allowsboth K+ efflux and Ca2+ influx at potentials positive of EKand negative of ECa. The OR had a PCa/PK of 1.72–0.21decreasing as extracellular Ca2+ was increased. The permeabilityof the OR for monovalent cations other than K+ was also investigated.In biionic conditions, a relative permeability sequence of was determined (i.e. Eisenman sequenceIV). The physiological implications of the selectivity of theOR are discussed. Key words: Maize roots, K+ channel selectivity, Ca2+ permeation  相似文献   

12.
The aim of the present study was to investigate the properties and role of capacitative Ca2+ entry (CCE) in interstitial cells (IC) isolated from the rabbit urethra. Ca2+ entry in IC was larger in cells with depleted intracellular Ca2+ stores compared with controls, consistent with influx via a CCE pathway. The nonselective Ca2+ entry blockers Gd3+ (10 µM), La3+ (10 µM), and Ni2+ (100 µM) reduced CCE by 67% (n = 14), 65% (n = 11), and 55% (n = 9), respectively. These agents did not inhibit Ca2+ entry when stores were not depleted. Conversely, CCE in IC was resistant to SKF-96365 (10 µM), wortmannin (10 µM), and nifedipine (1 µM). Spontaneous transient inward currents were recorded from IC voltage-clamped at –60 mV. These events were not significantly affected by Gd3+ (10 µM) or La3+ (10 µM) and were only slightly decreased in amplitude by 100 µM Ni2+. The results from this study demonstrate that freshly dispersed IC from the rabbit urethra possess a CCE pathway. However, influx via this pathway does not appear to contribute to spontaneous activity in these cells. smooth muscle; patch clamp; spontaneous transient inward currents  相似文献   

13.
Apoplastic potassium activities (ak) in leaves of Commelinacommunis L., Vicia faba L. and Pisum sativum L. var. argenteumwere recorded with neutral-carrier-based, potassium-sensitivemicro-electrodes. Measurements were carried out in 0.3–1.4nl volumes contiguous with the extracellular space of attachedleaves and were held for periods of 7–68 min. Mean steady-stateaK values recorded from all three species were below 50 µM.Similar potassium activities were attained, regardless of theinitial values obtained after washing with distilled water orpotassium additions, and the activities recorded showed onlyminimal dependence on the relative vapour pressure difference.Tissue capacity for K+ absorption was increased 15–30-foldin the presence of added Ca2+. By contrast, cyanide reducedboth the initial rate of potassium absorption by the tissuesand their apparent capacity for the cation. These observationsindicate that the free potassium pool in the leaf apoplast issignificantly smaller than has previously been assumed. Theresults contradict the notion that high concentrations of potassiumaccumulate locally as a result of transpiration, and may indicatethe presence in the leaf tissues of potassium transport activitysensitive to Ca2+ and dependent on metabolism. Key words: Apoplastic potassium activity, Transpiration/K+ transport, Guard cells  相似文献   

14.
In springwater (25.5 mol m–3 Cl, 20.4 mol m–3Na+, 0.14 mol m–3 K+) Enteromorpha intestinalis couldnot survive for more than a few weeks unless provided with 0.5mol m–3 K+ in the medium or alternatively exposed to seawaterfor 1 day per week. Maintenance of a cytoplasmic K+ level ofabout 200 mol m–3 is critical for the maintenance of normalmetabolic activity. Net gains of intracellular K+ occurred whenthe plants were transferred from low-salinity to seawater; converselylarge net losses occurred when plants were transferred fromseawater to springwater. These two processes were not simplythe reverse of one another; net gain of K+ involved a largeincrease in the tracer flux both into and out of the cell butnet loss of K+ virtually halted the tracer flux into the cell.Any injury incurred by rapid salinity changes was short-lived;plants were rapidly able to adjust intracellular [K1.K+). K+(orto some extent Rb+) was found to be necessary in the effluxmedium for 42K+ exchange to occur. The osmotic concentrationof the medium was also important but extracellular Na+ and Clconcentrationswere not critical. K+ influx and efflux in both springwaterand seawater were largely independent of light and were sensitivein varying degrees to a range of common metabolic inhibitorsand uncouplers. The results are best explained by the presenceof an active K+ influx, generated by an ATP-dependent K+ pumpat the plasmalemma. Key words: Enteromorpha, Potassium transport, Salinity changes, Uncouplers, Inhibitors  相似文献   

15.
Mechanism of Postinhibitory Rebound in Molluscan Neurons   总被引:1,自引:1,他引:0  
Postinhibitory rebound (PIR) is an intrinsic property of manyneurons but the underlying mechanism is not well understood.We studied PIR and its relationship to spike adaptation in B-cellsisolated from the buccal ganglia of Aplysia. These neurons exhibitPIR following inhibitory synaptic input and following directmembrane hyperpolarization. Hyperpolarizing and depolarizingvoltage clamp pulses from the resting potential evoke slow changesin membrane current that persist in the form of tail currentsfollowing the pulses. A subtraction method was used to isolateslow tail currents for study. Current-voltage measurements indicatethat slow outward tail currents following depolarizing pulsesresult from increases in membrane conductance, while inwardtail currents following hyperpolarizations to –50 and–60 mV result from conductance decreases. The reversalpotential of both outward and inward tail current is between–60 and –70 mV. Tail currents activated by pulsesmore positive than –60 mV are sensitive to the externalK+ concentration and blocked by injection of Cs+ and TEA. WhenCa2+ influx is prevented by bathing cells in Ca2+ free salineor by adding Co2+ or Ni2+, the tail currents are reduced buta significant fraction of the current is insensitive to thesetreatments. More negative conditioning pulses activate a secondcomponent of inward tail current that is weakly sensitive toK+ but more strongly effected by substitution of N-methyl glucamineor Li+ for external Na+. We conclude that both PIR and adaptationresult from slow changes in a voltage dependent, non-inactivatingK+ conductance that is active at voltages near the resting potentialand is not tightly coupled to Ca2+ influx. In addition, a secondinward current is activated by large hyperpolarizing pulsesthat results from an increase in Na+ and K+ conductance. Thissecond process is likely to contribute to PIR under particularcircumstances.  相似文献   

16.
The Ionic Relations of Acetabularia mediterranea   总被引:3,自引:0,他引:3  
The concentrations of K+, Na+, and Cl in the cytoplasmand the vacuole of Acetabularia mediterranea have been measured,as have the vacuolar concentrations of SO4–– andoxalate. The electrical potential difference between externalsolution, and vacuole and cytoplasm has been measured. The resultsindicate that Cl and SO4–– are probably transportedactively into the cell, and that active transport of Na+ isoutwards. The results for K+ are equivocal. The fluxes of K+,Na+, Cl, and S04–– into the cell and theeffluxes of Na+ and Cl have been determined. The Clfluxes are extremely large. In all cases the plasmalemma isthe rate-limiting membrane for ion movement. A technique isdescribed for the preparation of large, completely viable cellfragments containing only cytoplasm, with no vacuole.  相似文献   

17.
The influences of Ca2+-free solutions and increasing K+ concentrationson the H14CO3 influx capacity of Chara corallina wereinvestigated. It was found that contact with Ca2–freesolutions resulted in a gradual reduction in the H14CO3influx capacity of these cells. Recovery of this influx capacity,following the return of Ca2+ to the experimental solution, followeda ‘mirror-image’ of the time course of decay. Potassium concentrations above a certain critical value (2 mM)induced a rapid reduction in H14CO3 influx capacity.Normal activity was recovered within 60–90 min followingthe return to 0.2 mMK+ solutions. It was also shown that 10mM K+ can be used to determine the relative contribution of14C supplied by diffusion of 14CO2 and transport of H14CO3.The Ca2+ and K+ results are discussed in relation to the effectsof these treatments on the electrical properties of the plasmalemma.  相似文献   

18.
Effects of Cations on the Cytoplasmic pH of Chara corallina   总被引:1,自引:0,他引:1  
Smith, F. A. and Gibson, J.–L. 1985. Effects of cationson the cytoplasmic pH of Chara corallina.—J.exp. Bot.36: 1331–1340 Removal of external Ca2+ from cells of Chara corallina lowersthe cytoplasmic pH, as determined by the intracellular distributionof the weak acid 5,5–dimethyloxazolidine2–,4–dione(DM0), when the external pH is below about 60. This effect isreversed, at least partially, by addition of the following cationsto Ca2+-free solutions: tetraethylammonium (TEA+) and Na+ at5 or 10 mol m-3, Li+ and Cs+ (10 mol m-3), or Mg2+, Mn2+ andLa3+ (02 or 05 mol m-3). Under the same conditions, increasesin pH sometimes, but not always, occur in the presence of 10mol m-3 K+ or Rb+ The results are discussed in relation to the major transportprocesses that determine pH and the electric potential differenceacross the plasma membrane, namely fluxes of H+ and of K+. Thesimplest explanation of the effects of the various cations testedin this study is that they primarily affect pHic via changesin influx of H+ but direct effects on the H+ pump or on K+ fluxesmay also be involved Key words: Chara corallina, cytoplasmic pH, cations, H+transport  相似文献   

19.
The role of cytoplasmic calcium activity in activation of K+-channelsin the unicellular green alga Eremosphaera viridis has beenstudied. As reported previously, after a ‘light off’signal a voltage independent opening of K+-channels in the plasmalemmais observed. This effect is indicated by a transient polarization(TP) with a simultaneous increase of the membrane conductance.TPs can also be triggered by different treatments, which allowinvestigations within a ‘short-circuited’ signalchain. (i) After incubation with EGTA a single extended TP canbe released by a sudden increase of the external calcium concentration.The Ca2+-channel inhibitors nifedipine (10 –2 mol m–3)and verapamil (5 ? 10–2 mol m–3) suppress the releaseof this TP. (ii) In the presence of external calcium the additionof the ionophore A23187 [GenBank] (10–3 mol m–3) causes anextremely prolonged TP. (iii) Low external concentrations ofbarium (10–2 mol m–3) induce repetitive TPs in thepresence of external calcium. In this case the Ca2+-channelinhibitors are less effective. (iv) Strontium (0.1–1.0mol m–3) is able to trigger repetitive TPs even withoutexternal calcium. Whereas barium may stimulate a calcium influx,strontium can serve as a substitute for calcium to induce anopening of K+-channels. These results indicate strongly a Ca2+-dependentand voltage-independent activation of K+-channels in the plasmalemmaof Eremosphaera. The participation of cytoplasmic calcium inthe signal transduction chain after a ‘light off’signal is discussed. Key words: Ca2+-dependent K+-channels, Ca2+-channel effectors, A23187, transient membrane potential, Eremosphaera  相似文献   

20.
Membrane Potentials in Excitable Cells of Aldrovanda vesiculosa Trap-Lobes   总被引:1,自引:0,他引:1  
The resting membrane potential in excitable cells of Aldrovandatrap-lobes is composed of diffusion and electrogenic potentials.The diffusion potential, about –100 mV in artificial pondwater, was determined from the external K+ and Na+ concentrations.The permeability ratio, PNa/PK of the membrane was estimatedto be about 0.3. The electrogenic potential hyperpolarized themembrane to about –140 mV. The peak value of the actionpotential increased by +26 mV with a tenfold increase in theexternal Ca2+ concentration. The action potential was blockedby an application of the Ca2+ chelater or the Ca channel blocker,LaCl3. Cells showed additional Ca2+ influx (7.8 pmole/cm2 impulse)during membrane excitation. These facts suggest that the transientincrease in Ca2+ influx causes the action potential presentin cells of Aldrovanda trap-lobes. 1 Present address: Jerry Lewis Neuromuscular Research Center,School of Medicine, University of California Los Angeles, LosAngeles, CA90024, U.S.A. 2 Present address: Biological Laboratory, Kyoritsu Women's University,Hachioji 193, Japan. (Received September 21, 1983; Accepted September 7, 1984)  相似文献   

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