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F Dreyer

Publications and source records attributed to F Dreyer.

At least 37 records · Page 2Linked to original sources
PubMed1990

A K+ channel in Xenopus nerve fibres selectively blocked by bee and snake toxins: binding and voltage-clamp experiments.

1. The effects of mast cell degranulating peptide (MCDP), a toxin from the honey bee, and of dendrotoxin (DTX), a toxin from the green mamba snake, were studied in voltage-clamp experiments with myelinated nerve fibres of Xenopus. 2. MCDP and DTX blocked part of the K+ current. About 20% of the K+ current, however, was resistant to the toxins even in high concentrations. In Ringer solution half-maximal block was reached with concentrations of 33 nM-MCDP and 11 nM-DTX. In high-K+ solution the potency of both toxins was lower. beta-Bungarotoxin (beta-BuTX), another snake toxin, also blocked part of the K+ current, but was less potent than MCDP and DTX. 3. Tail currents in high-K+ solution were analysed and three K+ current components were separated according to Dubois (1981 b). Both MCDP and DTX selectively blocked a fast deactivating, slowly inactivating K+ current component which steeply activates between E = -60 mV and E = -40 mV (component f1). In concentrations around 100 nM, MCDP and DTX blocked neither the slow K+ current (component s) nor the fast deactivating, rapidly inactivating K+ current which activates between E = -40 mV and E = 20 mV (component f2). Similar results could be derived from K+ outward currents in Ringer solution. In high-K+, IC50 of MCDP for component f1 was 99 nM, whereas it was 7.6 microM for f2. Corresponding values for DTX are 68 nM and 1.8 microM. 4. Binding studies with nerve fibre membranes of Xenopus reveal high-affinity binding sites for 125I-labelled DTX (KD = 22 pM in Ringer solution and 81 pM in high-K+ solution). 125I-labelled DTX can be displaced from its sites completely by unlabelled DTX, toxin I (black mamba toxin), MCDP, and partially by beta-BuTX. 5. Immunocytochemical staining demonstrates that binding sites for DTX are present in nodal and paranodal regions of the axonal membrane. 6. The axonal membrane of motor and sensory nerve fibres is equipped with three types of well-characterized K+ channels and constitutes so far the best preparation to study MCDP- and DTX-sensitive K+ channels with electrophysiological and biochemical methods.

Animals↗
PubMed1989

Actin involvement in exocytosis from PC12 cells: studies on the influence of botulinum C2 toxin on stimulated noradrenaline release.

Botulinum C2 toxin is known to ADP-ribosylate actin. The toxin effect was studied on [3H]noradrenaline secretion of PC12 cells. [3H]Noradrenaline release was stimulated five- to 15-fold by carbachol (100 microM) or K+ (50 mM) and 10-30-fold by the ionophore A23187 (5 microM). Pretreatment of PC12 cells with botulinum C2 toxin for 4-8 h at 20 degrees C, increased carbachol-, K+-, and A23187-induced, but not basal, [3H]noradrenaline release maximally 1.5-to three-fold, whereas approximately 75% of the cellular actin pool was ADP-ribosylated. Treatment of PC12 cells with botulinum C2 toxin for up to 1 h at 37 degrees C also increased stimulated [3H]noradrenaline secretion, whereas toxin treatment for greater than 1 h decreased the enhanced [3H]noradrenaline release stimulated by carbachol and K+ but not by A23187. Concomitantly with toxin-induced stimulation of secretion, 20-50% of the cellular actin was ADP-ribosylated, whereas greater than 60% of actin was modified when exocytosis was attenuated. The data indicate that ADP-ribosylation of actin by botulinum C2 toxin largely modulates stimulation of [3H]noradrenaline release. Moreover, the biphasic toxin effects suggest that distinct mechanisms are involved in the role of actin in secretion.

Actins↗
PubMed1987

Differential effects of various secretagogues on quantal transmitter release from mouse motor nerve terminals treated with botulinum A and tetanus toxin.

Electrophysiological and electron microscopic techniques were used to investigate the actions of potassium depolarization, black widow venom (BWSV), Ca2+-ionophore A 23187 and hyperosmotic solution on mouse hemidiaphragms poisoned in vitro with botulinum A toxin (BoTx) and tetanus toxin (TeTx). These neurotoxins reduced the frequency of miniature endplate potentials (m.e.p.ps) from 5/s of the control to 2/min and 21/min, respectively. High potassium (25 mmol/l) increased the m.e.p.p.-frequency at BoTx- and TeTx-poisoned endplates to 30/min and 50/s, respectively. The ultrastructure of endplates showed no obvious changes. BWSV (0.04 glands/ml) was just as effective in promoting transmitter release from BoTx-treated endplates as in control preparations. Electron micrographs revealed depletion of vesicles as well as swollen and disrupted mitochondria. When preparations were pretreated with TeTx, BWSV only moderately increased transmitter release and no alterations of the ultrastructure could be observed. At TeTx- or BoTx-poisoned endplates Ca2+-ionophore A 23187 usually produced an extreme reduction of m.e.p.p.-frequency (0.005/s), sometimes preceded by a short burst-like release. The ultrastructure of these endplates was not obviously affected. Application of hyperosmotic solution to BoTx- or TeTx-poisoned preparations further reduced the already low m.e.p.p.-frequency. These results further demonstrate that TeTx and BoTx act at different sites in the transmitter releasing process.

Animals↗
PubMed1987

Distinct sites of action of clostridial neurotoxins revealed by double-poisoning of mouse motor nerve terminals.

(1) We investigated the effects of single- and double-poisoning with tetanus toxin (TeTx), botulinum neurotoxin type A (BoTx A) and botulinum neurotoxin type B (BoTx B) on spontaneous and nerve-evoked quantal transmitter release at motor endplates of the triangularis sterni preparation of the mouse. (2) Inhibitory effects of TeTx and BoTx B on spontaneous and nerve-evoked transmitter release were very similar, except that the action of BoTx B required 500-fold lower concentrations and was less dependent on temperature. BoTx A caused stronger inhibition of quantal release than TeTx or BoTx B, but was comparatively much easier counteracted by 4-aminopyridine (4-AP). (3) In contrast to BoTx A, with TeTx or BoTx B the increase of transmitter release following onset of 50 Hz nerve stimulation was delayed for a few seconds and synaptic latencies of quanta showed large variations. This release pattern was also evident in all double-poisoning experiments, regardless of intoxication sequence. (4) Inhibition of evoked release was found to be slightly stronger with TeTx than with BoTx B, so the amount of nerve-evoked quanta released after double-poisoning with any sequence of these toxins always approached that of TeTx. In no case supra-additive actions were observed. (5) A strong reduction of evoked quanta was observed when BoTx A was applied in addition to either of the two other toxins. With reversed poisoning sequences (BoTx A - TeTx or BoTx A - BoTx B) the resulting values remained at the extremely low level of BoTx A. (6) In the presence of 4-AP double-poisoning with any combination between BoTx A and TeTx or BoTx B (regardless of intoxication sequence) revealed supra-additive effects, since the number of quanta released was considerably lower than that obtained with any of the toxins alone (in the presence of 4-AP). (7) Our results indicate that tetanus toxin and botulinum toxin type B have a common site of action which is different and independent from that of botulinum toxin type A.

Animals↗
PubMed1987

The actions of presynaptic snake toxins on membrane currents of mouse motor nerve terminals.

1. The m. triangularis sterni of the mouse was used to investigate the actions of dendrotoxin, beta-bungarotoxin, crotoxin, taipoxin, bee venom phospholipase A2, aprotinin and apamin on presynaptic currents which flow inside the perineural sheath of nerve bundles upon nerve stimulation. 2. Neither the fast K+ current (IK,f) nor the Ca2+-dependent K+ current IK(Ca) (unmasked after blockade of IK,f by 3,4-diaminopyridine) was affected by the neurotoxins and drugs mentioned. 3. Inhibition of both IK,f and IK(Ca) by tetraethylammonium (30 mM) prolonged presynaptic depolarization owing to Ca2+ influx through fast and slow Ca2+ channels. Additional application of dendrotoxin, beta-bungarotoxin, crotoxin or taipoxin in the nanomolar range caused further prolongation of Ca2+ influx, presumably due to blockade of slowly activating K+ current (IK,s). Onset of toxin effects was immediate and could not be reversed by washing for 60 min. 4. Similar prolongation of slow Ca2+ current was effected by 3,4-diaminopyridine, whereas addition of apamin, aprotinin or phospholipase A2 left the signals unchanged. 5. These data indicate that facilitatory actions of dendrotoxin, beta-bungarotoxin, taipoxin and crotoxin are mediated by an increase of Ca2+ entry into nerve terminals. The actions of these toxins are discussed in terms of a blockade of presynaptic K+ channels with slow activation kinetics.

4-Aminopyridine↗
PubMed1986

Beta-bungarotoxin inhibits a non-inactivating potassium current in guinea pig dorsal root ganglion neurones.

beta-Bungarotoxin (beta-BuTx), at concentrations of 0.45-45 nmol/l, selectively reduced a portion of the noninactivating potassium current (IsK) in dorsal root ganglion neurones of the guinea pig, measured by voltage clamp of internally perfused cells. The average reduction of IsK obtainable with beta-BuTx was 34% and usually not completed within 20 min, but irreversible upon washing for 20 min. The I/V-characteristic of the current blocked by beta-BuTx was almost linear. It is suggested that beta-BuTx selectively blocks a noninactivating subtype of potassium channel.

Animals↗
PubMed1986

Two different presynaptic calcium currents in mouse motor nerve terminals.

Extracellular recordings of potential changes under the perineural sheath of nerve bundles close to some of the nerve terminals were performed using the M. triangularis sterni of the mouse. The nerve signals consisted of a predominant double-peaked negativity which was often preceded by a small positive deflection. While the first negative peak is related to the propagating nerve action potential, the second negative deflection can be attributed to a potassium conductance since it was selectively blocked by tetraethylammonium (TEA) or 3,4-diaminopyridine (3,4-DAP). Combined application of TEA and 3,4-DAP gave rise to a prolonged positive-going wave which was blocked by Cd2+, thus, indicating its underlying cause to be a Ca current. Ionophoretic application of TEA and Cd2+ to the endplates affected potassium and calcium components of the subendothelial signals, respectively, thus indicating their presynaptic origin. This finding is supported by the decrease of the amplitude of these components with increasing distance from the endplate region. Maximal effects on K conductance attainable with 3,4-DAP could still be potentiated by TEA, indicating the presence of at least two distinct sets of K channels. The prolonged positive potential induced by TEA and 3,4-DAP consisted of a fast and slow component, both of which can be attributed to Ca conductances with different characteristics. The fast positive signal component is attributed to the voltage-dependent Ca channel, responsible for the initiation of transmitter release. Its amplitude and duration depend on extracellular Ca2+ -concentration. The fast component is still present when Ca2+ is substituted by Sr2+ or Ba2+.(ABSTRACT TRUNCATED AT 250 WORDS)

4-Aminopyridine↗
PubMed1986

Dendrotoxin: a selective blocker of a non-inactivating potassium current in guinea-pig dorsal root ganglion neurones.

The voltage clamp technique was used to study the effects of dendrotoxin (DTX) on outward potassium currents in internally perfused dorsal root ganglion neurones of guinea-pig. Sodium currents were eliminated by tetrodotoxin (TTX, 2 mumol/l), calcium currents and calcium-activated potassium conductances were abolished by intracellular perfusion of cells with KF. Depolarizing voltage shifts from a holding potential of -90 mV yielded a fast transient outward current (IfK) and a delayed non-inactivating outward current (IsK). These currents could be separated by shifting the membrane potential to -50 mV, where IfK was almost completely inactivated. DTX, at concentrations of 0.14-1.4 nmol/l selectively reduced a portion of the non-inactivating potassium current, leaving the transient outward current unaffected. Once manifested, the action of DTX could not be reversed by washing. The I-V characteristic of the current blocked by DTX is almost linear and quite different from the one of the 'DTX-resistant' portion of IsK, which shows a non-linear I-V curve. Tetraethylammonium (TEA, 30 mmol/l) strongly reduced IfK and IsK. However, subsequent application of DTX was still able to further reduce IsK. 3,4-diaminopyridine (3,4-DAP, 500 mumol/l) unselectively reduced IfK and a portion of IsK. The remainder of the latter could not further be reduced by DTX, suggesting a similar action of the two blockers on non-inactivating potassium currents. From the results presented, it is suggested that dendrotoxin selectively blocks a non-inactivating subtype of potassium channel.

4-Aminopyridine↗
PubMed1986

Botulinum A neurotoxin unlike tetanus toxin acts via a neuraminidase sensitive structure.

The binding and effects of tetanus and botulinum A neurotoxins were studied on mouse spinal cord cultures treated with neuraminidase. In untreated cultures both neurotoxins blocked synaptic transmission. Treatment of the cell cultures with neuraminidase, 25 mU/ml for 24 hr, decreased the potency of botulinum A neurotoxin. At 7 X 10(-11) M no toxin effect on inhibitory or excitatory synapses was observed, whereas at higher concentrations of the toxin the concentration-response curve was shifted to the right by a factor of about 30. Surprisingly, the action of tetanus toxin over a large concentration range was unaffected by pretreatment of the neurones with the enzyme. Accordingly, neurones treated with neuraminidase failed to bind 125I-botulinum A neurotoxin, whereas labelled tetanus toxin was still fixed by cell bodies, as well as by neurites, as shown by histoautoradiography. Chromatographic extraction of gangliosides from cultures prelabelled with 14C-glucosamine showed a dramatic loss in the contents of polysialogangliosides following treatment with neuraminidase. Our results indicate that neuraminidase-sensitive structures might be important for the action of botulinum A neurotoxin. The effect of tetanus toxin appears to be mediated by a different site which is insensitive to neuraminidase.

Action Potentials↗
PubMed1985

Botulinum A neurotoxin inhibits non-cholinergic synaptic transmission in mouse spinal cord neurons in culture.

The effects of botulinum A neurotoxin and tetanus toxin were studied in cultured mouse spinal cord neurons. In approximately 60% of the neurons (n = 150), botulinum A neurotoxin caused paroxysmal depolarizing events. In two cells hyperpolarizing shifts were observed. The pattern of the burst-like activity varied in shape and frequency in individual cells. Between the paroxysmal events, ongoing synaptic activity could be recorded. The other 40% of the treated neurons did not develop a characteristic pattern of bursts, but there was a decrease in frequency of synaptically generated events. In contrast to botulinum A neurotoxin, tetanus toxin invariably produced well organized paroxysmal events without any synaptic activity between them. At later stages botulinum A neurotoxin and tetanus toxin blocked inhibitory and excitatory postsynaptic potentials in all neurons studied. These results have demonstrated, for the first time using electrophysiological techniques, that botulinum A neurotoxin blocks both excitatory and inhibitory synaptic transmission in the mammalian central nervous system. There are however differences between these effects of botulinum A neurotoxin and the actions of tetanus toxin on these cells. It is suggested that at the femtomolar range tetanus toxin blocks selectively central inhibitory systems and botulinum A neurotoxin the motor endplate. At the picomolar range both toxins affect many if not all, transmitter systems.

Animals↗
PubMed1985

Electrophysiological and neurobiochemical evidence for the blockade of a potassium channel by dendrotoxin.

The effects of dendrotoxin (DTX), a toxic peptide from Dendroaspis angusticeps venom, were studied electrophysiologically on peripheral frog nerve fibres, and biochemically on large synaptosomes from rat brain. On nerve fibres, DTX reduced the amplitude and prolonged the duration of the action potential; even at 0.1 nmol/l DTX produced significant effects. Maximum block of potassium currents occurred at about 30 nmol/l. Turning on of the remaining current was slowed. Reversibility was incomplete. The reduction of potassium currents was between 31% and 85% at 85 nmol/l DTX (n = 8). The remainder appeared to be resistant to DTX. Sodium channels were not affected. On large synaptosomes DTX (above 1 nmol/l) produced a slight depolarization, indicated by an outward shift of the lipophilic cation tetraphenylphosphonium, and promoted the release of radioactivity after preloading with [3H] GABA. DTX had similar potency but lower efficacy in this respect than sea anemone toxin II (ATX II). In contrast to the effects of ATX II, those due to DTX were only partially inhibited by tetrodotoxin. The actions of 4-aminopyridine resembled those of DTX, but the latter was about 500 times more potent. The electrophysiological data provide direct evidence for blockade of a potassium channel by DTX. This action is sufficient to explain the biochemical observations, although additional effects on synaptosomes cannot be excluded.

Action Potentials↗
PubMed1984

Action of botulinum A toxin and tetanus toxin on synaptic transmission.

Intracellular recordings of the spontaneous activity from mammalian spinal cord neurons in culture demonstrated different sensitivities of excitatory and inhibitory synaptic transmission for the action of tetanus toxin (Tetx) and botulinum toxin type A (Botx). The effects of Tetx and Botx on spontaneous and nerve-evoked transmitter release were compared under identical experimental conditions in experiments on in vitro poisoned mouse diaphragms. At 37 degrees C completely paralyzed endplates are characterized by a very low frequency of spontaneous miniature endplate potentials (m.e.p.p.s) and by a 100% failure to evoke endplate potentials (e.p.p.s) in response to single nerve stimuli. Striking differences in the action of both toxins have been observed when the very low transmitter release probabilities of paralyzed nerve-muscle preparations were increased by tetanic nerve stimulation and/or application of potent K+-channel blockers and/or by reduction of temperature to 25 degrees C. While Botx did not change the short latency between nerve impulse and postsynaptic response, Tetx produced a temporal dispersion of the quantal release suggesting that the toxins act at different sites in the chain of events that result in transmitter release. To find further evidence to support the different actions of the toxins the spontaneous transmitter release was studied in more detail. Tetx blocked preferentially the release of so-called large mode m.e.p.p.s without affecting the frequency of the small mode ones. In contrast, Botx strongly inhibited both the small and large mode m.e.p.p.s.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1983

Botulinum A toxin and tetanus toxin do not affect presynaptic membrane currents in mammalian motor nerve endings.

The hypothesis according to which BoTx and TeTx block neuromuscular transmission by impairing Ca2+ influx was tested by recording presynaptic membrane currents at motor endplates of the mouse by means of external electrodes. The use of K-channel blockers allowed us to observe inward Ca current which was unaffected by bath application of BoTx or TeTx at doses which block neuromuscular transmission.

Animals↗
PubMed1983

Transmitter release in tetanus and botulinum A toxin-poisoned mammalian motor endplates and its dependence on nerve stimulation and temperature.

The effects of tetanus toxin (TeTx) and botulinum A toxin (BoTx) on spontaneous and nerve-evoked transmitter release have been compared in mouse hemidiaphragms poisoned in vitro. At 37 degrees C endplates poisoned with either of these agents were characterized by (1) a decrease of miniature endplate potential (m.e.p.p.)-frequency to less than 30/min for TeTx and 3/min for BoTx, (2) reduced mean m.e.p.p.-amplitude and (3) 100% failure to show endplate potentials (e.p.p.s) in response to single nerve stimuli. In addition (4) tetanic nerve stimulation and/or reduction of temperature to about 20 degrees C caused a remarkable increase in the nerve-evoked transmitter release, but did not affect the low frequency of spontaneous m.e.p.p.s. However, several important differences exist between the effects of both toxins. (1) At room temperature even single nerve stimuli could elicit e.p.p.s in BoTx-muscles the failure rate being about 80%. For TeTx the failure was 100%. However, if the nerve was stimulated with higher frequencies (greater than 5 Hz), the probability of quantal release increased, the delay for release from the onset of stimulation being several seconds and similar to that observed at 37 degrees C. (2) TeTx distorted the synchronous release of quanta increasing the distribution of their synaptic delays. BoTx did not influence the time course of the phasic secretion process in response to nerve action potentials. (3) TeTx preferentially blocked the release of spontaneous m.e.p.p.s of large amplitude without affecting the frequency of the small amplitude ones, while BoTx inhibited both the small and large amplitude m.e.p.p.s. The distribution of the amplitudes of the nerve-evoked m.e.p.p.s were similar to those of spontaneous m.e.p.p.s before the blockade with the toxins.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗