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  • kinetics  (727)
  • Springer  (727)
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  • 1
    Electronic Resource
    Electronic Resource
    Analysis of the blocking activity of charybdotoxin homologs and iodinated derivatives against Ca2+-Activated K+ channels (1989)
    Springer
    The journal of membrane biology 109 (1989), S. 269-281 
    Details
    ISSN: 1432-1424
    Keywords: charybdotoxin ; erythrocytes ; iodination ; kinetics ; peptides ; potassium channels ; scorpions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Two charybdotoxin peptides were purified from venom of the Israeli scorpion,Leiurus quinquestriatus hebraeus. Microsequencing of the most abundant toxin, ChTX-Lq1, revealed identity with the 37-residue peptide previously sequenced by Gimenez-Gallego et al. [Gimenez-Gallego, G., et al.,Proc. Natl. Acad. Sci. USA 85:3329–3333 (1988)]. Sequence data on the minor peptide, ChTX-Lq2, showed substantial homology to ChTX-Lq1 with differences observed at eight positions. These two charybdotoxin sequences, along with that of noxiustoxin, define a distinct family of scorpion peptide toxins with activity against K+ channels. Both charybdotoxin homologs inhibited Ca2+-dependent K+ efflux from human erythrocytes with similar potency,K 0.5∼-40nm. In planar bilayer assays of single K(Ca) channels from rat muscle, ChTX-Lq1 and ChTX-Lq2 blocked with intrinsicK d's of 1.3 and 43nm, respectively, in the presence of 50mm external KCl. A new application of dwell-time histogram analysis of single-channel blocking events was used to characterize the kinetic homogeneity of toxin samples and the blocking kinetics of ChTX derivatives. The lower blocking affinity of ChTX-Lq2 was the combined result of a faster dissociation rate and a slower association rate as compared to ChTX-Lq1. The blocking activity of two mono-iodinated derivatives of ChTX-Lq1 was also analyzed. Blocked dwell-time histograms of the iodinated peptides were characterized by predominately brief (0.2–2 sec) blocking events in comparison to the native toxin (20 sec). Histogram analysis revealed that mono-iodination of ChTX-Lq1 impairs blocking activity by adverse effects on both dissociation and association rate constants. Frequency density histograms of single channel blocking events provide a sensitive assay of toxin purity suitable for quantitating structure-activity relationships of charybdotoxin derivatives.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870284
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  • 2
    Electronic Resource
    Electronic Resource
    Characteristics of manganese current and its comparison with currents carried by other divalent cations in snail soma membranes (1983)
    Springer
    The journal of membrane biology 76 (1983), S. 289-297 
    Details
    ISSN: 1432-1424
    Keywords: neuron ; internal perfusion ; Mn current ; kinetics ; Ca blocker
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Characteristics of currents carried by Mn2+ and other divalent cations were studied in the isolated identified neuron in the circumesophageal ganglia ofHelix aspersa using a suction pipette technique which allows internal perfusion of the cell body and voltage clamp. Increases in [Mn2+] 0 induced not only saturation of the peak ofI Mn but also shifts theI–V relationships along the voltage axis to the more positive potentials. Internal perfusion with F−, which blocks Ca channels, depressedI Mn. Diltiazem, an organic Ca blocker, inhibitedI Mn over the entire range of theI–V relation without shifting the threshold and peak voltage of theI–V relation. Co2+, Ni2+, Cd2+ and La3+ also suppressedI Mn. Relative maximum peak currents of the divalent cations wereI Ba=I Sr〉I Ca〉I Mn=I Zn. Time constants for activation (τ m ) and inactivation (τ h ) of these cations were voltage dependent, and both time constants were greater in the sequence ofI Mn=I Zn〉I Ba=I Sr〉I Ca over the whole voltage range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870371
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  • 3
    Electronic Resource
    Electronic Resource
    Initial steps of αand β-d-glucose binding to intact red cell membrane (1993)
    Springer
    The journal of membrane biology 132 (1993), S. 167-178 
    Details
    ISSN: 1432-1424
    Keywords: red cell ; glucose transport protein ; GLUT1 ; kinetics ; rapid reactions ; tryptophan
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The kinetics of the initial phases of d-glucose binding to the glucose transport protein (GLUT1) of the human red cell can be followed by stopped-flow measurements of the time course of tryptophan (trp) fluorescence enhancement. A number of control experiments have shown that the trp fluorescence kinetics are the result of conformational changes in GLUT1. One shows that nontransportable l-glucose has no kinetic response, in contrast to d-glucose kinetics. Other controls show that d-glucose binding is inhibited by cytochalasin B and by extracellular d-maltose. A typical time course for a transportable sugar, such as d-glucose, consists of a zero-time displacement, too fast for us to measure, followed by three rapid reactions whose exponential time courses have rate constants of0.5–100 sec+−1 at 20°C. It is suggested that the zero-time displacement represents the initial bimolecular ligand/GLUT1 association. Exponential 1 appears to be located at, or near, the external membrane face where it is involved in discriminating among the sugars. Exponential 3 is apparently controlled by events at the cytosolic face. Trp kinetics distinguish the K d of the epimer, d-galactose, from the K dfor d-glucose, with results in agreement with determinations by other methods. Trp kinetics distinguish between the binding of the α- and β-d-glucose anomers. The exponential 1 activation energy of the β-anomer, 13.6 ± 1.4 kcal mol+−1, is less than that of α-d-glucose, 18.4 ± 0.8 kcal mol+−1, and the two Arrhenius lines cross at ≈23.5°C. The temperature dependence of the kinetic response following α-d-glucose binding illustrates the interplay among the exponentials and the increasing dominance of exponential 2 as the temperature increases from 22.3 to 36.6°C. The existence of these interrelations means that previously acceptable approximations in simplified reaction schemes for sugar transport will now have to be justified on a point-to-point basis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00239006
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  • 4
    Electronic Resource
    Electronic Resource
    Protonophore anion permeability of the human red cell membrane determined in the presence of valinomycin (1988)
    Springer
    The journal of membrane biology 102 (1988), S. 225-234 
    Details
    ISSN: 1432-1424
    Keywords: erythrocytes ; valinomycin ; protonophore ; CCCP ; permeability ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A transport model for translocation of the protonophore CCCP across the red cell membrane has been established and cellular CCCP binding parameters have been determined. The time course of the CCCP redistribution across the red cell membrane, following a jump in membrane potential induced by valinomycin addition, has been characterized by fitting values of preequilibrium extracellular pHvs. time to the transport model. It is demonstrated, that even in the presence of valinomycin, the CCCP-anion is “well behaved,” in that the translocation can be described by simple electrodiffusion. The translocation kinetics conform to an Eyring transport model, with a single activation energy barrier, contrary to translocation across lipid bilayers, that is reported to follow a transport model with a plateau in the activation energy barrier. The CCCP anion permeability across the red cell membrane has been calculated to be close to 2.0×10−4 cm/sec at 37°C with small variations between donors. Thus the permeability of CCCP in the human red cell membrane deviates from that found in black lipid membranes, in which the permeability is found to be a factor of 10 higher.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01925716
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of variation of ion and methylation of carrier on the rate constants of macrotetralide-mediated ion transport in lipid bilayers (1982)
    Springer
    The journal of membrane biology 68 (1982), S. 191-206 
    Details
    ISSN: 1432-1424
    Keywords: ion transport ; carriers ; lipid bilayers ; kinetics ; nonactin ; methylation ; macrotetralides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The effects of methylation on the rate constants of carrier-mediated ion transport have been studied on monooleindecane bilayers with K+, Rb+, NH 4 + , and TI+ ions, using the series of homologue carriers, nonactin, monactin, dinactin, trinactin, and tetranactin, each member of the series differing from the previous one by only one methyl group. Measurements of the amplitude and time constant of the current relaxation after a voltage jump over a large domain of voltage and permeant ion concentration, together with a computer curve-fitting procedure, have allowed us, without the help of steady-state current-voltage data, to deduce and compare the values of the various rate constants for ion transport: formation (k Ri) and dissociation (k Di) of the ion-carrier complex at the interface, translocation across the membrane interior of the carrier (k s) and the complex (k is). With the additional information from steady-state low-voltage conductance measurements, we have obtained the value of the aqueous phase-membrane and torus-membrane partition coefficient of the carrier ({ie191-1} and {ie191-2}). From nonactin to tetranactin with the NH 4 + ion,k is, and {ie191-3} are found to increase by factors of 5 and 3, respectively,k Di and {ie191-4} to decrease respectively by factors 8 and 2, whilek Ri andk s are practically invariant. Nearly identical results are found for K+, Rb+, and Tl+ ions.k Ri,k s andk is are quite invariant from one ion to the other except for Tl+ wherek Ri is about five times larger. On the other hand,k Di depends strongly on the ion, indicating that dissociation is the determining step of the ionic selectivity of a given carrier. The systematic variations in the values of the rate constants with increasing methylation are interpreted in terms of modifications of energy barriers induced by the carrier increasing size. Within this framework, we have been able to establish and verify a fundamental relationship between the variations ofk is andk Di with methylation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01872264
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  • 6
    Electronic Resource
    Electronic Resource
    Pressure dependence of the potassium currents of squid giant axon (1982)
    Springer
    The journal of membrane biology 69 (1982), S. 35-40 
    Details
    ISSN: 1432-1424
    Keywords: axon ; hydrostatic pressure ; K currents ; kinetics ; activation volume
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The effect of pressure upon the delayed, K, voltage-clamp currents of giant axons from the squidLoligo vulgaris was studied in axons treated with 300nm TTX to block the early, Na, currents. The effect of TTX remained unaltered by pressure. The major change produced by pressures up to 62 MPa is a slowing down of the rising phase of the K currents by a time scaling factor which depends on pressure according to an apparent activation volume, ΔV∓, of 31 cm3/mole at 15°C; ΔV∓ increased to about 42 cm3/mole at 5°C. Pressure slightly increased the magnitude, but did not produce any obvious major change in the voltage dependence, of the steady-state K conductance estimated from the current jump at the end of step depolarizations of small amplitude (to membrane potentials,E, ≦20 mV) and relatively short duration. At higher depolarizations, pressure produced a more substantial increase of the late membrane conductance, associated with an apparent enhancement of a slow component of the K conductance which could not be described within the framework of the Hodgkin-Huxley (HH)n 4 kinetic scheme. The apparent ΔV∓ values that characterize the pressure dependence of the early component of the K conductance are very close to those that describe the effect of pressure on Na activation kinetics, and it is conceivable that they are related to activation volumes involved in the isomerization of the normal K channels. The enhancement of the slow component of membrane conductance by pressure implies either a large increase in the conductance of the ionic channels that are responsible for it or a strong relative hastening of their turn-on kinetics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871239
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  • 7
    Electronic Resource
    Electronic Resource
    Na+, Li+ and Cl− transport by brush border membranes from rabbit jejunum (1983)
    Springer
    The journal of membrane biology 74 (1983), S. 85-94 
    Details
    ISSN: 1432-1424
    Keywords: sodium ; lithium ; chloride ; pH ; transport ; kinetics ; ion permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Na+, Li+, K+, Rb+, Br−, Cl− and SO 4 2− transport were studied in brush border membrane vesicles isolated from rabbit jejunum., Li+ uptakes were measured by flameless atomic absorption spectroscopy, and all others were measured using isotopic flux and liquid scintillation counting. All uptakes were performed with a rapid filtration procedure. A method is presented for separating various components of ion uptake: 1) passive diffusion, 2) mediated transport and 3) binding. It was concluded that a Na+/H+ exchange mechanism exists in the jejunal brush border. The exchanger was inhibited with 300 μm amiloride or harmaline. The kinetic parameters for sodium transport by this mechanism depend on the pH of the intravesicular solution. The application of a pH gradient (pHin=5.5, pHout=7.5) causes an increase inJ max (50 to 125 pmol/mg protein·sec) with no change inK t (≈4.5mm). Competition experiments show that other monovalent cations, e.g. Li+ and NH 4 + , share the Na+/H+ exchanger. This was confirmed with direct measurements of Li+ uptakes. Saturable uptake mechanisms were also observed for K+, Rb+ and SO 4 2− , but not for Br−. TheJ max for K+ and Rb+ are similar to theJ max for Na+, suggesting that they may share a transporter. The SO 4 2− system appears to be a Na+/SO 4 2− cotransport system. There does not appear to be either a Cl−/OH− transport mechanism of the type observed in ileum or a specific Na+/Cl− symporter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870497
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  • 8
    Electronic Resource
    Electronic Resource
    Characterization of sodium and pyruvate interactions of the two carrier systems specific of mono- and di- or tricarboxylic acids by renal brush-border membrane vesicles (1989)
    Springer
    The journal of membrane biology 108 (1989), S. 197-205 
    Details
    ISSN: 1432-1424
    Keywords: sodium ; pyruvate ; transport ; proximal tubule ; kinetics ; kidney
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The experiments reported in this paper aim at characterizing the carboxylic acid transport, the interactions of pyruvate and citrate with their transport sites and specificity. The study of these carriers was performed using isotopic solutes for the influx measurements in brush-border membrane vesicles under zerotrans conditions where the membrane potential was abolished with KCl preloading with valinomycin or equilibrium exchange conditions and Δψ=0. Under zerotrans condition and Δψ=0, the influence of pyruvate concentrations on its initial rates of transport revealed the existence of two families of pyruvate transport sites, one with a high affinity for pyruvate (K t =88 μm) and a low affinity for sodium (K t =57.7mm) (site I), the second one with a low affinity for pyruvate (K t =6.1mm) and a high affinity for sodium (K t =23.9mm) (site II). The coupling factor [Na]/[pyruvate] stoichiometry were determined at 0.25mm and 8mm pyruvate and estimated at 1.8 for site I, and 3 when the first and the second sites transport simultaneously. Under chemical equilibrium (Δψ≅0) single isotopic labeling, transport kinetics of pyruvate carrier systems have shown a double interaction of pyruvate with the transporter; the sodium/pyruvate stoichiometry also expressed according to a Hill plot representation wasn=1.7. The direct method of measuring Na+/pyruvate stoichiometry from double labeling kinetics and isotopic exchange, for a time course, gives an=1.67. Studies of transport specificity, indicate that the absence of inhibition of lactate transport by citrate and the existence of competitive inhibition of lactate and citrate transports by pyruvate leads to the conclusion that the low pyruvate affinity site can be attributed to the citrate carrier (tricarboxylate) and the high pyruvate affinity site to the lactate carrier (monocarboxylate).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871734
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  • 9
    Electronic Resource
    Electronic Resource
    Kinetic response of H+-coupled transport to extracellular pH: Critical role of cytosolic pH as a regulator (1989)
    Springer
    The journal of membrane biology 108 (1989), S. 253-261 
    Details
    ISSN: 1432-1424
    Keywords: Chara ; Cl− ; cotransport ; reaction kinetic model ; pH ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary H+-coupled transport in plant and fungal cells is relatively insensitive to external pH (pH o ). H+-coupled Cl− transport at the plasma membrane ofChara corallina was studied to explore the phenomena responsible for this insensitivity. Raising pH o from a control value of 7.5 to 9.0 results in a modest (2.5-fold) decline inJ max and increase inK m . Further increase in pH o results in a selective increase inJ max, in accordance with predictions from a reaction kinetic model of the transport system (Sanders, D., Hansen, U.-P., 1981.J. Membrane Biol. 58:139–153). Increase in cytosolic Cl− concentration ([Cl−] c ) also results in a selective decrease inJ max at pH o =7.5. Quantitative kinetic modeling of the results is not possible if it is assumed that the sole effect of pH o isvia mass action on the binding of external H+ to a transport site. If, instead, the dependence of cytosolic pH (pH c ) on pH o (Smith, F.A., 1984,J. Exp. Bot. 35:1525–1536) is taken into account along with the dependence of Cl− influx on pH c (Sanders, D., 1980,J. Membrane Biol. 53:129–141), then the observed modest changes in Michaelis parameters can be accommodated by a reaction kinetic model. The quantitative parameters of the model yield respective pK a s of the internal and external H+-binding sites=7.85 and 7.2, respective dissociation constants of the internal and external Cl−-binding sites=160 and 40 μm, and an additional, kinetically transparent, H+-binding site with a pK a 〉8.0. The quantitative model independently predicts the response ofJ max andK m to acidic conditions. The results are discussed in terms of the general physiological requirement that fluxes through H+-coupled transport systems are relatively insensitive to environmental variation in pH o . It is proposed that (i) the weak (but finite) dependence of pH c on pH o , coupled with (ii) the strong dependence of H+-coupled transport on pH c are instrumental in endowing H+-coupled transport systems with a relative insensitivity to variation in pH o . This hypothesis might also explain why pH c in plants and fungi is not acutely controlled with respect to variation of pH o .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871740
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  • 10
    Electronic Resource
    Electronic Resource
    Pre-steady-state analysis of the turn-on and turn-off of water permeability in the kidney collecting tubule (1989)
    Springer
    The journal of membrane biology 110 (1989), S. 57-65 
    Details
    ISSN: 1432-1424
    Keywords: fluorescence ; water transport ; vasopressin ; kidney collecting tubule ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Water transport across the mammalian collecting tubule is regulated by vasopressin-dependent water channel insertion into and retrieval from the cell apical membrane. The time course of osmotic water permeability (P f ) following addition and removal of vasopressin (VP) and 8-Br-cAMP was measured continuously by quantitative fluorescence microscopy using an impermeant fluorophore perfused in the lumen. Cortical collecting tubules were subjected to a 120 mOsm bath-to-lumen osmotic gradient at 37°C with 10–15 nl/min lumen perfusion and 10–20 ml/min bath exchange rate. With addition of VP (250 μU/ml), there was a 23±3 sec (sem,n=16) lag in whichP f did not change, followed by a rise inP f (initial rate 1.4±0.2×10−4 cm/sec2) to a maximum of 265±10×10−4 cm/sec. With addition of 8-Br-cAMP (0.01–1mm) there was an 11±2 sec lag. For [8-Br-cAMP]=0.01, 0.1 and 1mm, the initial rate ofP f increase following the lag was (units 10−4 cm/sec2): 1.1±0.1, 1.2±0.1 and 1.7±0.3. MaximumP f was (units 10−4 cm/sec): 64±4, 199±9 and 285±11. With removal of VP,P f decreased to baseline (12×10−4 cm/sec) with aT 1/2 of 18 min; removal of 0.1 and 1mm 8-Br-cAMP gaveT 1/2 of 4 and 8.5 min. These results demonstrate (i) a brief lag in theP f response, longer for stimulation by VP than by 8-Br-cAMP, representing the transient build-up of biochemical intermediates proximal to the water channel insertion step, (ii) similar initialdP f /dt (water channel insertion) over a wide range of [8-Br-cAMP] and steady-stateP f values, and (iii) more rapidP f decrease with removal of 8-Br-cAMP than with VP. These pre-steady-state results define the detailed kinetics of the turn-on and turn-off of tubuleP f and provide kinetic evidence that the rate-limiting step for turn-on ofP f is not the step at which VP regulates steady-stateP f . If water channel insertion is assumed to be the rate-limiting step in the turn-on ofP f , these results raise the possibility that water channels must be activated following insertion into the apical membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870993
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