共查询到20条相似文献,搜索用时 15 毫秒
1.
Single water fibers of the frog glossopharyngeal nerve respondto relatively high concentrations of NaCl (>80 mM). NiCl2at 1 mM enhanced the Na+ response and reduced the thresholdconcentration for NaCl to 20 mM. CaCl2 at 0.51 mM inducedan inhibition of the Ni2+-enhanced response to Na+ ions. A quantitativeexplanations for these results is provided by the hypothesisthat Ni2+ ions secondarily affect a sodium receptor or channel(designated XNa*) that is responsible for the Na+ response andthat Ca2+ ions inhibit the Ni2+-enhanced response to Na+ ionsby competing with Na+ ions for XNa*. Double-reciprocal plotsof the experimental data indicate that the affinity of XNa*for both Na+ ions (agonist) and Ca2+ ions (competitive antagonist)in the presence of 1 mM NiCl2 was five times higher than thepreviously reported values obtained in the absence of NiCl2(Kitada, 1991). Ni2+ ions at 1 mM enhanced the maximal responseto Na+ ions by 190%. It appears that a sodium receptor (or channel)interacts with a Ni2+-binding element that is affected by Ni2+ions and, thus, Ni2+ ions can induce both an increase in theaffinity of the sodium receptor for the respective cations andan enhancement of the Na+ response. Chem Senses 21: 6573,1996. 相似文献
2.
Unitary discharges from single water fibers of the frog glossopharyngealnerve, caused by stimulation with 0.025 mM CaSO4, wererecorded from fungiform papillae with a suction electrode. NiSO4at concentrations of 0.22 mM, namely, at concentrationsthat are barely effective in producing impulses, had a dualaction on the Ca2+ response: NiSO4 caused both inhibition andenhancement of the Ca2+ response. In the present study, thisdual action of Ni2+ ions on the Ca2+ response was investigatedin detail. Single water fibers yielded a saturation type ofconcentration-response curve for CaSO4, which suggested thatsulfateions do not affect the Ca2+ response. Thus, sulfateswere used as test salts in the present study. At low concentrationsof Ca2+ ions, Ni2+ ions inhibited the Ca2+ response, but athigher concentrations of Co2+ ions they enhanced it. The resultscan be explained quantitatively by the hypothesis that Ni2+ions inhibit the Ca2+ response by competing with Ca2+ ions forthe Ca2+ receptor (Xca) that is responsible for the Ca2+ responseand that Ni2+ ions enhance the Ca2+ response by acting on amembrane element that interacts with Xca. Double-reciprocalplots of the data indicate that the enhancing action of Ni2+ions is saturated at 12 mM Ni2+ ions and that Ni2+ ionsat these concentrations increase the maximal response of theCa2+ response by 182%. Dissociation constants for the Ca-Xcacomplex and the Ni-Xca, complex were 4.2 x 105 M and7.6 x 105 M, respectively. The analysis suggests thatNi2+ ions enhance the Ca2+ response by affecting the Ca-Xcacomplex without altering the affinity of Xca, for Ca2+ ions. 相似文献
3.
Fibers of the frog glossopharyngeal nerve (water fibers) thatare sensitive to water also respond to CaCl2, MgCl2 and NaCl.In the present study, interaction among cations (Ca2+, Mg2+and Na+) on taste cell membrane in frogs was studied using transitionmetals (NiCl2, CoCl2 and MnCl2), which themselves are barelyeffective in producing neural response at concentrations below5 mM. Unitary discharges from single water fibers were recordedfrom fungiform papillae with suction electrode. Transition metalions (0.055.0 mM) had exclusively enhancing effects onthe responses to 50 mM Ca2+, 100 mM Mg2+ and 500 mM Na+. Theeffects of transition metal ions were always reversible. Therank order of effectiveness of transition metals at 1 mM inthe enhancement of the responses to 50 mM CaCl2, 100 mM MgCl2and 500 mM NaCl was NiCl2 > CoCl2 > MnCl2. The concentrationof transition metal ions effective to enhance salt responsewas almost the same among Ca2+, Mg2+ and Na+ responses. Theresults suggest that a common mechanism is involved in the enhancementof Ca2+, Mg2+ and Na+ taste responses. The enhanced Mg2+ responseand the enhanced Na+ response were greatly inhibited by theaddition of Ca2+ ions, and the enhanced Ca2+ response was inhibitedby the addition of Mg2+ or Na+ ions, suggesting that competitiveantagonism occurs between Ca2+ and Mg2+ ions and between Ca2+and Na+ ions in the presence of Ni2+ ions. Ni2+ ions had a dualeffect on the Ca2+ response induced by low concentration (0.1mM) of CaCl2: enhancement at lower concentrations (0.020.1mM) of NiCl2 and inhibition at higher concentrations (0.55mM)of NiCl2. The present results suggest that transition metalions do not affect the receptor-antagonist complex, but affectonly the receptor-agonist complex. 相似文献
4.
In the frog glossopharyngeal nerve, single water fibers respondto low CaCl2 (12 mM) and relatively high MgCl2 (100 mM).In the present study, it was found that stimulation by a mixtureof low CaCl2 and relatively high MgCl2 led to a small response.This suggests that the Ca+ response is inhibited by the presenceof Mg2+ and the Mg2+ response is inhibited by the presence ofCa2+. Hence, it is suggested that there are different receptorsites for divalent cations in single water fibers of the frogglossopharyngeal nerve, a calcium receptor site (XCa) responsiblefor the Ca2+ response and a magnesium receptor site (XMg) responsiblefor the Mg2+ response. It has been reported that Mg2+ inhibitsthe Ca2+ response by competing with Ca2+ for XCa (Kitada andShimada, 1980). In the present study, the inhibition of theMg2+ response by Ca2+ was examined quantitatively under theassumption that the magnitude of the neural response is proportionalto the amount of MgXMg complex minus a constant (the thresholdconcentration of the MgXMg complex). The results obtained indicatethat Ca2+ competes with Mg2+ for XMg. The apparent dissociationconstants for MgXMg complex and CaXMg complex, which were obtainedfrom the present study, were 8.0 x 102 M and 7.2 x 104M, respectively. Thus, competition between Ca+ and Mg2+ forthe distinct receptor sites involved in taste reception wasdemonstrated by the results described in this paper. Since thedivalent cations do not always bring about activation of tastereceptors, the responses to salts in the frog glossopharyngealnerve cannot be explained in terms of changes in the surfacepotential outside the taste cells. The present results suggestthat there exist multiple specific receptor sites for cationsinvolved in salt taste responses, and only the binding of eachseparate cation to its appropriate receptor sites leads to activationof the receptor and the initiation of impulses in sensory nerveendings. 相似文献
5.
NiCl2 induces a response to cboline Cl and enhances the responseto CaCl2 in water-sensitiv fibers (water fibers) of the frogglossopharyngeal nerve. The Ni2+-induced choline+ response wasinhibited by Ca2+ ions and, conversely, the enhanced Ca2+ responseby Ni2+ ions was inhibited by choline+ ions. Hence, there existsa mutual antagonism between Ca2+ and choline+ ions. In the presentstudy, the inhibition of the Ni2+-induced choline+ responseby Ca2+ ions was investigated quantitatively. The assumptionwas made that receptors for choline (XCh) exist and that bindingof a choline+ ion to XCh, brings about a neural response. Itwas further assumed that the magnitude of the neural responseis proportional to the amount of choline-XCh, complex minussome constant (the threshold concentration of the choline-XCh,complex). The results from analysis of double-reciprocal plotwere consistent with the hypothesis that Ca2+ ions compete withcholine+ ions for XCh,. The dissociation constants for the choline-XCh,complex and the CaXCh, complex were obtained to be 0.6 M and7.4 x 10-5 M, respectively. This result indicates that the affinitiesof XCh, for choline+ and Ca2+ ions are very different. Furthermore,Mg2+ ions did not affect the Ni2+-induced choline+ response,an indication that the affinity of XCh, is not charge-specific,but is chemically specific. The identification of a competitiveinhibitor of the choline+ response provide* evidence for existenceof a choline-specific receptor at the surface of taste cellsthat are innervated by the water fibers of the frog glossopharyngealnerve. Differences between the features of the response to cholineCl in the chorda tympani nerve of the rat and those in the frogglossopharyngeal nerve are discussed. 相似文献
6.
In single water-sensitive fibers (water fibers) of the frogglossopharyngeal nerve, application of a solution of 500 mMcholine Cl to the tongue elicited responses of varying magnitude.Some water fibers (plain choline-insensitive water fibers) barelyresponded to the solution, while some water fibers (plain choline-sensitivewater fibers) exhibited a considerable response to this solution.NiCl2. which is barely effective in producing neural responseat concentrations below 5 mM, induced the response of plaincholine-insensitrve water fibers to choline+ ions. It was confirmed,in a collision test, that the Ni2+-induced responses to choline+ions were derived from water fibers. However, NiCl2 did notaffect the magnitude of me response generated by choline+ ionsin plain choline-sensitive water fibers. The concentration-responsecurve for choline Cl in the presence of 1 mM NiCl2 for plaincholine-insensitive water fibers was similar to the curves obtainedin the absence of NiCl2 for plain choline-sensitive water fibers.Other organic salts, such as tris(hydroxymethyl)arrdnomethane-HCl,triethanotamine-HCl and tetraethylammonium Cl, elicited no responseor only a very small response from water fibers, and NiCl2 didnot affect these responses. It is suggested that there existsa choline receptor for the response to choline+ ions in theapical membrane of frog taste cells and that Ni2+ ions exposethe sites of such choline receptors, which are deeply embeddedin the receptor membrane, to the outside medium. The effectof Ni2+ ions results in an increase in the number of the cholinereceptor sites available for binding of choline+ ions. The rankorder of effectiveness of transition metal ions in elicitingthe appearance or enhancement of the response to choline Clwas Ni2+ > Co2+ > Mn2+. Mg2+ ions had no effect on theresponse to choline+ ions. A similar rank order was previouslyobtained in enhancement of the responses to Ca2+, Mg2+ and Na2+ions (Kitada, 1994a). It seems likely that the mechanism forenhancement or elicitation of the response to choline+ ionsby the transition metal ions has features in common with thatfor enhancement of the responses to Ca2+, Mg2+ and Na+ ions. 相似文献
7.
Single water fibers of the frog glossopharyngeal nerve respondto low concentrations of CaCl2 (12 mM) and to relativelyhigh concentrations of NaCl(>80 mM). However, stimulationby a mixture with a low concentration of CaCl2 and relativelyhigh concentration of NaCl gives rise to only a small response,suggesting that the effects of Ca2+ and Na+ are mutually antagonistic.It has been reported that Na+ inhibits the response to Ca2+by competing with Ca2+ for a calcium receptor site (XCa; Kitadaand Shimada, 1980). In the present study, it was found tha Ca2+inhibited the response to Na+. Therefore, the sodium receptorsite (XNa) responsible for the response to Na is different fromXCa. The inhibition of the response to Na+ by Ca2+ was examinedquantitatively on the assumption that the magnitude of the neuralresponse is proportinal to the amount of NaXNa complex minusa constant (the threshold concentration of the NaXNa complex).The results obtained indicate that Ca2+ competes with Na+ forXNa. The apparent dissociation constants for the NaXNa complexand the CaXNa complex obtained from the present study were 1.0M and 1.2 x 10-3 M, respectively, XNa as proposed here, doesnot represent simply a binding site for cations since therecan be competition for XNa by an antagonistie cation. The highaffinity of XNa for Ca2+ suggests that XNa is a specific receptorsite involved in salt-taste reception. Since Mg2+ did not affectthe response to Na+, the affinity of XNa for cations is notcharge-specific but is, rather, chemically specific. The presentresults indicate that both Ca2+ and Na+ have a dual action,being involved both in excitation and in inhibition, in waterfibers of the frog glossopharyngeal nerve. 相似文献
8.
NADP malic enzyme (EC 1.1.1.40
[EC]
) from leaves of two C4 speciesof Cyperus (C. rotundus and C. brevifolius var leiolepis) exihibiteda low level of activity in an assay mixture that contained lowconcentrations of Cl. This low level of activity wasmarkedly enhanced by increases in the concentration of NaClup to 200 mM. Since the activity of NADP malic enzyme was inhibitedby Na2SO4 and stimulated by relatively high concentration ofTris-HCl (50100 mM, pH 78), the activation ofthe enzyme by NaCl appears to be due to Cl. Variationsin the concentration of Mg2+ affected the KA (the concentrationof activator giving half-maximal activation) for Cl,which decreased from 500 mM to 80 mM with increasing concentrationsof Mg2+ from 0.5 mM to 7 mM. The Km for Mg2+ was decreased from7.7 mM to 1.3 mM with increases in the concentration of NaClfrom zero to 200 mM, although the increase of Vmax was not remarkable.NADP malic enzyme from Cyperus, being similar to that from otherC4 species, was able to utilize Mn2+. The Km for Mn2+ was 5mM, a value similar to that for Mg2+. The addition of 91 mMNaCl markedly decreased the Km for Mn2+ to 20 +M. NADP malicenzyme from Setaria glauca, which contains rather less Clthan other C4 species, was inactivated by concentrations ofNaCl above 20 mM, although slight activation of the enzyme wasobserved at low concentrations of NaCl at pH7.6. (Received February 20, 1989; Accepted June 12, 1989) 相似文献
9.
Ion Composition of the Chara Internode 总被引:2,自引:0,他引:2
Ion compositions of the cytoplasm and the vacuole of Chara australiswere analyzed according to Kishimoto and Tazawa (1964) and Kiyosawa(1979a). The ions in the cytoplasm and the vacuole analyzedwere K+, Na+, Ca2+, Mg2+, Cl, NO3 and H2PO4.Assuming that the volume of the cytoplasm Vp is 10% of thatof the whole cell V, the concentrations of K+, Na+, Ca2+, Mg2+,Cl, NO3 and H2PO4 in the cytoplasm averaged70, 15, 13, 4.6, 31, 2.2 and 16 mM, respectively. If the volumeof the cytoplasm was assumed to be 5% of that of the whole cell,their averaged concentrations were 139, 31, 25, 9.2, 62, 4.4and 33 mM, respectively. The averaged ion compositions of thecell sap were K+, 111; Na+, 47; Ca2+, 4.4; Mg2+, 8.9; Cl,91; NO3, 3.3 and H2PO4, 6.0 mM. These values,taking the concentrations and the charges of the protein (Kiyosawa1979b) and amino acids (Sakano and Tazawa 1984) into accountand assuming the presence of some uni- or oligovalent anionsand/or small nonelectrolyte molecules, could explain fairlywell both the electroneutrality and the osmotic pressure ofthe cell, except when Vp/V = 5%. (Received May 18, 1987; Accepted September 29, 1987) 相似文献
10.
Ion Content of the Halotolerant Alga Dunaliella salina 总被引:3,自引:0,他引:3
The intracellular concentration of the major ions in Dunaliellasalina cells were determined, following the removal of extracellularions by ion-exchange minicolumns. Log phase cells, grown inmedia containing 14 molar NaCl, contained 3050mM chloride and 200350 mM magnesium (5 mM in medium).Phosphorus, which is present intracellularly mostly as polyphosphate,was present in amounts of 60100 fmoles per cell, equivalentto a concentration of 6001,000 mM (0.2 mM in medium).Previous data indicated that such cells contained 2040mM Na+, 150300mM K+, 20mM SO24, and very low concentrationsof Ca2+ and charged nitrogenous compounds. Mg2+ and K+ seemto serve as the major counter ions for the intracellular negativecharge present in the massively accumulated polyphosphates.The former accounts for about 2/3 of the required positive charge.This is supported by the observation that limitation in thephosphate or K+ supply in the medium lead to a parallel decreasein the accumulation of intracellular phosphorus, Mg2+ or K+.
1Present address: Department of Vegetables, The Volcani Center,Bet-Dagan 50250, Israel. (Received June 13, 1988; Accepted August 25, 1988) 相似文献
11.
A sulfite-dependent ATPase [EC 3.6.1.3
[EC]
] of Thiobacillus thiooxidanswas activated and solubilized by treatment with trypsin [EC3.4.4.4
[EC]
], and purified 84-fold with a 32% recovery. It requiredboth Mg2+ and SO32 for full activity, and its optimumpH was found at 7.58.0. Mn2+, Co2+, and Ca2+ could partiallysubstitute for Mg2+, while SeO32 and CrO42 couldpartially substitute for SO32. The enzyme hydrolyzed ATP and deoxy-ATP most rapidly and otherphosphate esters were poorer substrates. The apparent Km valuefor ATP was 0.33 mM. The enzyme activity was strongly inhibitedby 0.2 mM NaN3 and 10 mM NaF. (Received July 27, 1977; ) 相似文献
12.
Effects of ions on the orientation of cortical micro-lubules(MTs) in Spirogyra cells were studied. After depo-lymerizalionwith amiprophos-methyl (APM), MTs were allowed to reorganizein NaCI solutions of various concentrations. As the concentrationof NaCI increased, the frequency of cells that had oblique MTsincreased. When cells in NaCI solution were transferred intoartificial pond water (APW) and incubated for 6 h, all the MTschanged to become transverse to the longitudinal axis of thecell. KC1 and MgCl2 also had effects on the orientation of MTs.However, NH4Cl, CaCl2;, CoCl2, and Co(NO3)2 did not show anyeffect. These results suggest that Na+, K+, and Mg2+have effectson MT orientation and that NH+4, Ca2+, Co2+, Cl, andNO3 have little effect. When MTs were reorganized ineither NaCl or KCl solutions, all the oblique MTs were organizedinto an S-helix. In contrast, some of the oblique MTs were foundas a Z-helix in the cells incubated in MgCl2 or mannitol solutions.These results suggest that effects of Na+ and K+ on the orientationof MTs are not the same as those of Mg2+ and mannitol. Theseresults provide the first evidence that ions are involved inthe orientation of MTs in algae. (Received January 27, 1998; Accepted August 10, 1998) 相似文献
13.
Movement of Ions and Electrogenesis in Higher Plant Cells 总被引:2,自引:0,他引:2
During the past 10 years considerable information has accumulatedon the electrochemical relationships of higher plant cells duringtransport of mineral ions. Using the Nernst equation as a criterion,none of eight ions (K+, Na+, Ca++, Mg++, NO3, Cl,H2PO4, and SO4) is in a passive equilibrium. Na+,Ca++, and Mg++ are subject to an exclusion mechanism, and allof the anions appear to be pumped inwardly. K+ apparently approachesan electrochemical balance under certain conditions but probablyis actively accumulated. Compartmental analyses giving estimatesof amounts in the cytoplasm and vacuole and of unidirectionalfluxes permit application of the Ussing flux-ratio equation.The criterion in oat coleoptile cells suggests that at the plasmalemmaNa+ is pumped out while K+ and Cl are pumped in. K+ andCl appear to be coupled in active transport across thetonoplast into the vacuole. Good evidence has been found thatthe cell's electropotential arises from an electrogenic pump:CN (cyanide) and DNP (dinitrophenol) reversibly blockthe potential and ionic transport; cell potentials are higherthan can be accounted for by diffusion; the responses of respirationand potential to the concentration of CN are nearly parallel;and CN inhibited tissue approaches a fit to the Goldmanconstant field equation. Future objectives should be identificationof the ion, or ions, subject to the electrogenic pump and discoveryof the immediate energy source. 相似文献
14.
Sink-limited conditions, defined as treatment with continuousillumination, cause a reduction in the rate of photosyntheticfixation of CO2 in single-rooted leaves of soybean (Glycinemax. Merr. cv. Turunoko). We suggested previously that thisreduction is due to a deactivation of ribulose-1,5-bisphosphatecarboxylase (RuBPcase, E.C. 4.1.1.39
[EC]
) that is caused by a decreasein the level of Pi in the leaves [Sawada et al. (1989) PlantCell Physiol. 30: 691, Sawada et al. (1990) Plant Cell Physiol.31: 697]. In the present study, the mechanism of regulationof RuBPcase activity by Pi was examined. The activity of RuBPcasein the sink-limited leaves, exposed for 6 or 7 d to continuousillumination to alter the source/sink balance, was enhancedwith increasing concentrations of Pi, in a CO2-free preincubationmedium in the presence of 5 mM MgCl2 The maximum value [6.3µmole CO2 (mg Chl)1 min1] was obtained atapproximately 5 mM Pi after a 5 min incubation, being 3 timesof the activity without the preincubation. The activity of acrude preparation of RuBPcase that had been deactivated by removalof CO2 and Mg2+ ions by the gel filtration was 5.29.3nmole CO2 (mg protein)1 min1 and was also enhancedby Pi plus Mg2+ ions. The maximum value [147151 nmoleCO2 (mg protein)1 min1] was attained at 5 mM Piafter a 5 min incubation. The cycle of activation and inactivationof deactivated crude RuBPcase was perfectly reversible by additionof Pi to the enzyme and removal of Pi from the enzyme. Levelsof free Pi and of esterified phosphate in the sink-limited leaveswere 69% and 31% of the total phosphate, respectively. By contrast,in the control leaves, these values were 87% and 13%, respectively.These results support our previously stated hypothesis and indicatean important role for free Pi in the regulation of RuBPcaseactivity, in particular in sink-limited plants. (Received February 21, 1992; Accepted July 23, 1992) 相似文献
15.
Bull R Finkelstein JP Humeres A Behrens MI Hidalgo C 《American journal of physiology. Cell physiology》2007,293(1):C162-C171
Despite their relevance for neuronal Ca2+-induced Ca2+ release (CICR), activation by Ca2+ of ryanodine receptor (RyR) channels of brain endoplasmic reticulum at the [ATP], [Mg2+], and redox conditions present in neurons has not been reported. Here, we studied the effects of varying cis-(cytoplasmic) free ATP concentration ([ATP]), [Mg2+], and RyR redox state on the Ca2+ dependence of endoplasmic reticulum RyR channels from rat brain cortex. At pCa 4.9 and 0.5 mM adenylylimidodiphosphate (AMP-PNP), increasing free [Mg2+] up to 1 mM inhibited vesicular [3H]ryanodine binding; incubation with thimerosal or dithiothreitol decreased or enhanced Mg2+ inhibition, respectively. Single RyR channels incorporated into lipid bilayers displayed three different Ca2+ dependencies, defined by low, moderate, or high maximal fractional open time (Po), that depend on RyR redox state, as we have previously reported. In all cases, cis-ATP addition (3 mM) decreased threshold [Ca2+] for activation, increased maximal Po, and shifted channel inhibition to higher [Ca2+]. Conversely, at pCa 4.5 and 3 mM ATP, increasing cis-[Mg2+] up to 1 mM inhibited low activity channels more than moderate activity channels but barely modified high activity channels. Addition of 0.5 mM free [ATP] plus 0.8 mM free [Mg2+] induced a right shift in Ca2+ dependence for all channels so that [Ca2+] <30 µM activated only high activity channels. These results strongly suggest that channel redox state determines RyR activation by Ca2+ at physiological [ATP] and [Mg2+]. If RyR behave similarly in living neurons, cellular redox state should affect RyR-mediated CICR. Ca2+-induced Ca2+ release; Ca2+ release channels; endoplasmic reticulum; thimerosal; 2,4-dithiothreitol; ryanodine receptor 相似文献
16.
RNA interference targeted to multiple P2X receptor subtypes attenuates zinc-induced calcium entry 总被引:2,自引:0,他引:2
Liang L Zsembery A Schwiebert EM 《American journal of physiology. Cell physiology》2005,289(2):C388-C396
A postulated therapeutic avenue in cystic fibrosis (CF) is activation of Ca2+-dependent Cl channels via stimulation of Ca2+ entry from extracellular solutions independent of CFTR functional status. We have shown that extracellular zinc and ATP induce a sustained increase in cytosolic Ca2+ in human airway epithelial cells that translates into stimulation of sustained secretory Cl transport in non-CF and CF human and mouse airway epithelial cells, cell monolayers, and nasal mucosa. On the basis of these studies, the Ca2+ entry channels most likely involved were P2X purinergic receptor channels. In the present study, molecular and biochemical data show coexpression of P2X4, P2X5, and P2X6 subtypes in non-CF (16HBE14o) and CF (IB3-1) human bronchial epithelial cells. Other P2X receptor Ca2+ entry channel subtypes are expressed rarely or not at all in airway epithelia, epithelial cell models from other CF-relevant tissues, or vascular endothelia. Novel transient lipid transfection-mediated delivery of small interference RNA fragments specific to P2X4 and P2X6 (but not P2X5) into IB3-1 CF human airway epithelial cells inhibited extracellular zinc- and ATP-induced Ca2+ entry markedly in fura-2 Ca2+ measurements and "knocked down" protein by >65%. These data suggest that multiple P2X receptor Ca2+ entry channel subtypes are expressed in airway epithelia. P2X4 and P2X6 may coassemble on the airway surface as targets for possible therapeutics for CF independent of CFTR genotype. purinergic receptors; zinc receptors; airway epithelia; cystic fibrosis; therapy 相似文献
17.
Effects of Ions and Membrane Potential on the Elongation of the Unicellular Green Alga Closterium 总被引:1,自引:0,他引:1
Cells of the unicellular green alga Closterium ehrenbergii elongatedexclusively at septa and for 45 hours after cell division.Cell elongation was strongly inhibited by a decrease in eitherthe external concentration of Ca2+ or pH, and was also inhibitedby several competitive Ca2+ channel blockers. Changes in concentrationsof other external ions had no effect on the elongation. Theaverage concentrations of ions in the intracellular fluid ofthe interphase cell before cell division was as follows (inmM): K+=56.5, Na+=4.8, Ca2+=2.4, Mg2+=1.3, Cl=59.5; thepH was 7.4. The levels of K+, Na+ and Cl ions decreasedsignificantly with cell elongation, suggesting that this process,which proceeds with water uptake, surpasses ion absorption.The plasma membrane potential (Vm) in both the interphase cellsand in the elongating cells was in the range of 90 to105 mV (interior negative). The Vm was entirely determinedby the simple diffusion of K+. A decrease in the external concentrationof Ca2+ caused depolarization, probably by an indirect effectof low Ca2+. Changes in the extracellular level of H+ and othercations barely affected Vm. Thus, external Ca2+ and H+ are concludedto affect cell elongation but not via a change in the Vm acrossthe plasma membrane. (Received February 29, 1988; Accepted June 8, 1988) 相似文献
18.
This paper describes the first experimental evidence that theinhibition of nitrate reductase by Mg2+ or Ca2+ is related tothe hysteretic properties of the enzyme. The low activity formof nitrate reductase, i.e. the form of nitrate reductase showinghysteretic behaviour, was inhibited 7090% by 5 mM Ca2+or Mg2+. However, no inhibition by Ca2+ or Mg2+ was seen afterthe enzyme was converted to its high activity form by preincubationwith substrates. Addition of thiol compounds or certain aminoacids to the assay mixture also prevented the Mg2+ or Ca2+ inhibition. (Received June 28, 1993; Accepted August 11, 1993) 相似文献
19.
A P2X7 receptor stimulates plasma membrane trafficking in the FRTL rat thyrocyte cell line 总被引:1,自引:0,他引:1
Thyroid cells express a variety of P2Y and P2X purinergic receptor subtypes. G protein-coupled P2Y receptors influence a wide variety of thyrocyte-specific functions; however, functional P2X receptor-gated channels have not been observed. In this study, we used whole cell patch-clamp recording and fluorescence imaging of the plasma membrane marker FM1-43 to examine the effects of extracellular ATP on membrane permeability and trafficking in the Fisher rat thyroid cell line FRTL. We found a cation-selective current that was gated by ATP and 2',3'-O-(4-benzoylbenzoyl)-ATP but not by UTP. The ATP-evoked currents were inhibited by pyridoxal phosphate 6-azophenyl-2',4'-disulfonic acid, adenosine 5'-triphosphate-2',3'-dialdehyde, 100 µM Zn2+, and 50 µM Cu2+. Fluorescence imaging revealed pronounced, temperature-sensitive stimulation of exocytosis and membrane internalization by ATP with the same pharmacological profile as observed for activation of current. The EC50 for ATP stimulation of internalization was 440 µM in saline containing 2 mM Ca2+ and 2 mM Mg2+, and 33 µM in low-Mg2+, nominally Ca2+-free saline. Overall, the results are most consistent with activation of a P2X7 receptor by ATP4. However, low permeability to N-methyl-D-glucamine+ and the propidium cation YO-PRO-1 indicates absence of the cytolytic pore that often accompanies P2X7 receptor activation. ATP stimulation of internalization occurs in Na+-free, Ca2+-free, or low-Mg2+ saline and therefore does not depend on cation influx through the ATP-gated channel. We conclude that ATP activation of a P2X7 receptor stimulates membrane internalization in FRTL cells via a transduction pathway that does not depend on cation influx. purinergic receptor; internalization; patch clamp 相似文献
20.
With slight modifications, conventional assay procedures forK+, Na+, Ca2+, Mg2+, Cl, NO3, H2PO4, fructoseand fructose-yielding saccharides, and glucose were applicableto the extract of Phaseolus pulvini. About 10 ml of a hot-waterextract from about 30 mg fresh weight of the pulvini was sufficientfor separate measurement of the ions and saccharides named above. (Received August 7, 1979; ) 相似文献