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  • 1
    Digitale Medien
    Digitale Medien
    Occurrence and Properties of Phospholipases A1 of Plasma Membranes Prepared from Neuronal- and Glial-Enriched Fractions of the Rabbit Cerebral Cortex (1981)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 36 (1981), S. 0 
    Details
    ISSN: 1471-4159
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: Abstract: Exogenously added glycerophosphatides, specifically radioactively labelled either in the 1 or in the 2 position, were used to investigate the occurrence and properties of phospholipase A1 in plasma membranes prepared from neuronal- and glial-enriched fractions of rabbit brain. Phospholipase A1 activity was maximal at pH values ranging between 8.0 and 9.0 for the plasma membranes of both cell types. The enzyme activity was most abundant in the microsomal fraction, with a neurondglial ratio of about 2. The plasma membranes displayed about half the enzymic activity of the microsomal fraction, whereas only small amounts of phospholipase A1 were present in the neuronal and glial mitochondria. Investigations on the substrate specificity showed a different pattern for the enzyme of neuronal and glial origin. The release of labelled fatty acids from phosphatidylcholine by the neuronal plasma membrane phospholipase A1 decreased with increasing degree of unsaturation of the fatty acids at the 1 position. The presence of plasmalogens and plasmalogen precursors in the incubation mixture appreciably inhibited the hydrolysis of the corresponding diacyl compounds.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1471-4159.1981.tb01675.x
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  • 2
    Digitale Medien
    Digitale Medien
    The action of arginine-specific reagents on ionic and gating currents in frog myelinated nerve
    Amsterdam : Elsevier
    Biochimica et Biophysica Acta (BBA)/Biomembranes 943 (1988), S. 1-12 
    Details
    ISSN: 0005-2736
    Schlagwort(e): (Frog) ; Arginine residue ; Myelinated nerve fiber ; Potassium current ; Sodium current
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Biologie , Chemie und Pharmazie , Medizin , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1016/0005-2736(88)90340-9
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  • 3
    Digitale Medien
    Digitale Medien
    Purification and characterization of a β-toxin from the venom of the African scorpion Leiurus quinquestriatus
    Amsterdam : Elsevier
    FEBS Letters 214 (1987), S. 163-166 
    Details
    ISSN: 0014-5793
    Schlagwort(e): (Leiurus quinquestriatus, Nerve fiber, Frog node) ; Na^+ channel ; Voltage clamp ; β-Toxin
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Biologie , Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    URL: http://linkinghub.elsevier.com/retrieve/pii/0014-5793(87)80034-0
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  • 4
    Digitale Medien
    Digitale Medien
    Voltage-dependent effect of a scorpion toxin on sodium current inactivation (1984)
    Springer
    Pflügers Archiv 402 (1984), S. 24-33 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Myelinated nerve fibre ; Voltage clamp ; Scorpion toxin ; Sea anemone toxin ; KIO3
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract 1. In voltage clamped nodes of Ranvier inactivation of the sodium permeability is slowed by toxin V from the scorpionCentruroides sculpturatus, by sea anemone toxin ATX II or by internally applied KIO3. The slow decay of the Na inward current is markedly accelerated if the test pulse is preceded by a depolarizing conditioning pulse followed by a 10–500 ms pause. This phenomenon was studied in detail, using conditioning pulses of varying amplitude and up to 15 s duration. 2. In nodes treated with toxin V a 20 ms conditioning pulse to positive potentials was sufficient to produce a clear acceleration of the decay of the Na current and a reduction of the inward current remaining at the end of a 50 ms test pulse, i.e. a weakening of the toxin effect. In nodes treated with ATX II or internal KIO3 longer conditioning pulses were required. A similar effect of conditioning pulses on the decaying phase of the Na current was also observed in untreated fibres. 3. To study the phenomenon quantitatively we fitted the decaying phase of the inward Na current with the equationI Na=A exp(-t/τ1)+B exp(-t/τ2)+C The effect of depolarizing conditioning pulses could be described as an increase of A, a decrease of B and C and a reduction of the time constants τ1 and τ1. 4. I 50/I peak, the normalised inward current remaining at the end of a 50 ms test pulse, decreased exponentially with increasing duration of the conditioning pulse to a steady-state value. The time constant τ and the steady-state value depended on the potential during the conditioning pulse. For nodes treated with toxin V, τ was 0.24 s at 0 mV and 12° C and half inhibition occurred at −42 mV. The time constant τ was larger for nodes treated with ATX II or internal KIO3. At positive potentials, I50 was reduced to 20% of the control value in toxin V-treated nodes, but only to 70% in KIO3-treated nodes. 5. Recovery from the effect of the conditioning pulse was studied by varying the pause between conditioning pulse and test pulse; recovery was 66–100% complete after 500 ms. 6. The results are interpreted by assuming that a sepolarizing conditioning pulse (a) accelerates inactivation of the sodium permeability and (b) causes dissociation of the toxin-receptor complex or transition into an inactive state. The latter effect occurs in toxin V-treated fibres but not in those treated with ATX II or KIO3.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00584827
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  • 5
    Digitale Medien
    Digitale Medien
    Kinetics of sodium current and gating current in the frog node of Ranvier (1986)
    Springer
    Pflügers Archiv 407 (1986), S. 18-26 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Myelinated nerve fibre ; Voltage clamp ; Gating currents ; Chloramine-T
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract 1. The experiments were done on voltage-clamped nodes of Ranvier of the frog. The aim was to study the kinetics of sodium currentI Na and gating currentI gat over a large potential range (−92 to −12 mV) and to compare the time constants for the turning-on ofI Na orI gat with those for the turning-off measured at the same potential. 2. Sodium tail currents were recorded at different postpulse potentials. Inactivation was inhibited by a few min treatment with 0.5 mM chloramine-T (Wang 1984). The sodium permeability was activated by a 0.4 ms pulse from holding potential (−92 mV) to about 0 mV. At the peak ofI Na the membrane was repolarized to postpulse potentials between −92 and −12 mV. AtE〉 −60 mV the tail currents decayed with two time constants, τ1 and τ2, reflecting presumably the turning-off and the inactivation of the sodium permeability. The relation between τ1 and postpulse potential was bellshaped with a maximum at −32 mV. 3. The tail currents could also be fitted by the Hodgkin-Huxley equation with the sodium activation variablem raised to the second or third power. AtE〈−50 mV τm off was equal to 2 τ1 or 3 τ1, respectively, whereas atE〉−25 mV τm off was equal to τ1. 4. In addition, the time constant of the turning-on of sodium activationm (τm on) was determined, assumingI Na ∼m 2 (with a small initial delay) orI Na ∼m 3 (without an initial delay). At −22 mV and −12 mV the ratio τm off/τm on was close to 1. At −42 mV and −32 mV it was larger than 1 (1.22 and 1.65 for them 2 andm 3 fit, respectively, at −32 mV). 5. A similar pulse program was used to measure the turning-on and turning-off ofI gat in the presence of 300 nM TTX. In the potential range −52 to −22 mV, no significant difference between τoff and τon (measured at the same potential) was found. This is in conflict with the findings of Dubois and Schneider (1982) who reported an inequality τoff 〈 τon. 6. Comparison between τoff of charge movement and τ1 of the tail current yielded τoff/τ1 = 2.8 at −92 mV. This agrees with previous measurements of Neumcke et al. (1976).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00580715
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  • 6
    Digitale Medien
    Digitale Medien
    A quantitative study of the action ofCentruroides sculpturatus toxins III and IV on the Na currents of the node of Ranvier (1983)
    Springer
    Pflügers Archiv 397 (1983), S. 90-99 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Myelinated nerve fibre ; Voltage clamp ; Scorpion toxin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract 1. In nodes of Ranvier treated with toxin III or IV from the scorptionCentruroides sculpturatus Ewing a strong positive pulse is followed by a transient shift of the descending branch of theI Na(E) curve to more negative values of membrane potential (cf. Meves et al. 1982). This effect was studied in more detail, using toxin concentrations between 0.8 and 3.3 μg/ml. 2. The change of theI Na(E) curve was accompanied by a shift of the kinetic parameters of both activation (time to peak, time constant τm) and inactivation (time constant τh1). The τm curve was shifted by the same amount as the descending branch of theI Na(E) curve while the shift of τh1 was somewhat smaller. The curve relating Na permeability to membrane potential became less steep and its lower part was shifted to more negative values of membrane potential. 3. The change of theI Na(E) curve was also accompanied by a change in the turning-on kinetics of the Na current. The normal signoidal time course was replaced by first-order kinetics. A strong hyperpolarizing prepulse restored the sigmoidal time course without abolishing the shift of the descending branch of theI Na(E) curve. 4. The transient change of theI Na(E) curve was not accompanied by a marked change in the ion selectivity of the Na channels: the equilibrium potential decreased only by 4–8 mV. 5. Ca slightly reduced the shift of the descending branch of theI Na(E) curve. The long-lasting inward Na current which follows a strong positive pulse in nodes treated with toxin III or IV was reduced by 7.8 mM Ca to 41% of the value measured in normal *1.8 mM) Ca. Mg was slightly less effective than Ca. 6. From the change of the Na permeability curve the percentage of Na channels transiently modified by a strong positive pulse was estimated as about 50%.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00582045
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  • 7
    Digitale Medien
    Digitale Medien
    Gating current experiments on frog nodes of Ranvier treated withCentruroides sculpturatus toxins or aconitine (1987)
    Springer
    Pflügers Archiv 409 (1987), S. 381-393 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Myelinated nerve fibre ; Voltage clamp ; Gating currents ; Scorpion toxins ; Aconitine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract (1) Gating currents were recorded from frog nodes of Ranvier treated either with toxins III or IV from the venom of the scorpionCentruroides sculpturatus or with the alkaloid toxin aconitine. (2) Toxins III or IV fromCentruroides sculpturatus (which drastically reduce the sodium permeabilityP Na and slightly shift its voltage dependence in the depolarizing direction) caused a small depolarizing shift of the relation between charge (Q on) and membrane potential (E) without affecting the maximum chargeQ on max. (3) On nodes treated with toxins III or IV fromCentruroides sculpturatus, a depolarizing conditioning pulse (which transiently shifts the descending branch of theI Na(E) curve by up to 60 mV in the hyperpolarizing direction) shifted the midpoint potential (Emid) of theQ on(E) curve by −17 mV and slightly increased the slope of the curve; it also decreasedQ on max markedly but had little effect onQ on measured with small depolarizing pulses. By contrast, massive treatment with aconitine (which irreversibly shifts sodium activation in the hyperpolarizing direction) irreversibly shifted the midpoint potential of theQ on(E) curve from −28.5 to −69 mV and significantly increasedQ on andQ off measured with small depolarizing pulses; concomitantly, the voltage dependence of the on time constant of the charge movement [τon(E)] was shifted by −44 mV. (4) The sodium currentI Na was exponential both in nodes treated with toxins III or IV ofCentruroides sculpturatus and subjected to a depolarizing conditioning pulse and in aconitine-treated nodes; in the latter,I Na started after a delay of 30–40 μs. The time constant of the sodium current, τon Na, was larger than the time constant of the charge movement, τon Q; the ratio τon Q/τon Na was 0.61 and 0.73 in the experiments withCentruroides sculpturatus toxins and aconitine, respectively. (5) The off time constant of the sodium current (τoff Na) was slightly increased in nodes treated withCentruroides sculpturatus toxins and subjected to a depolarizing conditioning pulse, whereas it was markedly increased in aconitine-treated nodes. With the former treatment, the off time constant of the charge movement (τoff Q) was unaffected but with aconitine treatment it was considerably increased although it remained smaller than τoff Na. Consequently, the ratio τoff Q/τoff Na (which is ≥1 in untreated nodes) became smaller than one, reaching values as low as 0.58 and 0.44 in the experiments withCentruroides sculpturatus toxins and aconitine, respectively. The small τoff Q/τoff Na ratio suggests that the channels remain open for an appreciable time after most of the gating charges have returned to their resting position. (6) The results obtained with aconitine resemble the findings on batrachotoxin-treated nodes (Dubois and Schneider 1985), except that in the latter the time constants τon Na and τoff Na of the sodium current are smaller than the corresponding time constants τon Q and τoff Q of the charge movement.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00583792
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  • 8
    Digitale Medien
    Digitale Medien
    Effect of toxins isolated from the venom of the scorpionCentruroides sculpturatus on the Na currents of the node of ranvier (1982)
    Springer
    Pflügers Archiv 393 (1982), S. 56-62 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Myelinated nerve fibre ; Voltage clamp ; Scorpion toxin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract 1. The effect of various toxin fractions isolated by Watt et al. (1978) from the venom of the scorpionCentruroides sculpturatus Ewing on the Na currents of the node of Ranvier has been studied with the voltage clamp method. 2. The toxin fractions were applied externally. The most potent fractions were toxins III, IV and V which were effective in concentrations of 0.33–3.33 μg/ml. The effect of toxins III and IV was quite different from that of toxin V. 3. In toxin III or IV — treated nodes a strong depolarizing pulse was followed by a transient shift of the negative resistance branch of theI Na (E) curve to more negative potentials. The amount of shift varied between −10 and −60 mV. A 500ms depolarizing pulse of small amplitude produced a slowly developing Na inward current which slowly decayed after the end of the pulse. Inactivation was incomplete, even with 500 ms pulses to 0 mV. 4. The transient shift of theI Na (E) curve was not seen in nodes treated with toxin V. This toxin merely caused slow and incomplete Na inactivation. The effect of toxin IV was not suppressed by a four times higher concentration of toxin V, suggesting that the two toxins act on different receptors. 5. Toxin I acted like toxin IV but was about 10 times less potent. The effect of high concentrations of variants 1, 2, 3, 5, 6 resembled that of toxin V. 6. All effects observed with toxin III or IV were also seen with the whole venom (cf. Cahalan 1975).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00582392
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  • 9
    Digitale Medien
    Digitale Medien
    Effects of reagents modifying carboxyl groups on the gating current of the myelinated nerve fiber (1987)
    Springer
    The journal of membrane biology 100 (1987), S. 63-72 
    Details
    ISSN: 1432-1424
    Schlagwort(e): voltage clamp ; node of Ranvier ; gating current ; chemical modification ; carboxyl groups
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Summary The effect of the carboxyl group activating reagent N-ethoxy-carbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) on the gating current of the frog node of Ranvier was investigated. A 10-min treatment with 2mm EEDQ (in the presence or absence of 10mm ethylenediamine) irreversibly reduced the slope of the on charge-voltage relationQ on(E), shifted its midpoint potentialE mid in the positive direction and reduced the maximum chargeQ on max measured with strong depolarizing pulses. In six experiments, 2mm EEDQ + 10mm ethylenediamine increased the factork (a reciprocal measure of the slope of theQ on(E) curve) from 16 to 22 mV. In five experiments, 2mm EEDQ alone increasedk from 16 to 23 mV. In a single experiment, 5mm EEDQ + 10mm ethylene diamine increasedk from 17 to 31 mV. The reduction in slope suggests that EEDQ decreases the valence of the gating particles or reduces the fraction of the membrane field that they traverse. In addition, EEDQ (which inhibits inactivation of the sodium current.see M. Rack and K.H. Woll,J. Membrane Biol. 82:41–48, 1984) caused a small increase of the off chargeQ off, and a marked increase of theQ off/Q on ratio, i.e. inhibited charge immobilization. Since the effects of EEDQ occurred regardless of the presence or absence of ethylenediamine, they are probably due to crosslinking reactions. The effects of EEDQ were compared with those of the water-soluble carbodiimide EDC. Treatment with 10 or 50mm EDC (plus 10 or 50mm ethylenediamine) caused a smaller increase ofk than treatment with 2mm EEDQ but reducedQ on max by the same amount.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02209141
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