Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    ISSN: 1432-2013
    Keywords: Interleukin-2 ; Neuromodulation ; Dissociated muscle fibres ; C2 myotubes ; Extrajunctional nAChR ; Electrophysiology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effect of interleukin-2 (rIL-2) on nicotinic acetylcholine receptors (nAChR) was examined on cultured muscle fibres isolated from the flexor digitorum brevis muscle (FDB) of the rat and on aneural mouse cultured C2 myotubes. Intracellular measurement of the sensitivity to iontophoretically applied ACh demonstrated that the sensitivity of the extrajunctional nAChRs in cultured fibres showed a transient increase after application of rIL-2 (2,000–3,000 units/ml). Cell-attached patch-clamp experiments on the same fibres proved that rIL-2 (2,000 units/ml) induces a significant increase in the mean open time of the extrajunctional nAChR channel. The other channel parameters were not significantly modified. The same applied also to aneural mouse patch-clamped C2 myotubes exposed to rIL-2 (2,000 units/ml). In freshly dissociated fibres no effects on nAChR channels were observed following rIL-2 application. 125I-rIL-2 binding experiments on either 7-day cultured or freshly dissociated adult muscle fibres showed that a specific binding with a K d of 2.07±0.4 nM develops in cultured fibres but fails to occur immediately after dissociation. It is concluded that rIL-2 modulates the duration of extrajunctional nAChR channels in both myotubes and adult muscle cells, and that this effect is probably due to the activation of a second messenger system.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 1432-2013
    Keywords: Frog-neuromuscular junction ; Spontaneous transmitter release ; Effects of phorbol ester
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Spontaneous transmitter release was studied at frog neuromuscular junctions exposed to the tumor promotor 12-O-tetradecanoylphorbol-13-acetate (TPA), a specific activator of protein kinase C (PrkC). TPA at concentrations between 10−7 and 10−6 M induced a dose-dependent increase in miniature end-plate potential frequency. This frequency increase was enhanced by raising [Ca]0, diminished by lowering the temperature of the bath and virtually abolished in Ca2+-free Ringer. The TPA effect was only poorly reversible after washing. TPA was ineffective in increasing spontaneous release of transmitter at phosphatidylcholine-pretreated neuromuscular junctions. It is suggested that PrkC might play a role in neuromuscular transmission processes.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 1432-1912
    Keywords: TPA ; Protein kinase C ; Transmitter release ; Neuromuscular junction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. The effect of the phorbol ester 12-O-tetradecanoylphorpbol-13-acetate (TPA) on the stimulation-evoked neurotransmitter release has been investigated by measuring the quantal content (m) of end-plate potentials at frog neuromuscular junctions (Rana temporaria, M. sartorius). 2. After addition of TPA (0.1 up to 1 μmol/1) to the Ringer solution the m-values increased in a concentration-dependent manner up to more than 3 times the control values. 3. Inhibition of the activity of the protein kinase C through the inhibitor 1(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7) blocked this effect of TPA. 4. The TPA effect was much more conspicuous when the m-value was reduced by raising the extracellular Mg2+ concentration. Between the control m-values and the n-fold increase in the m-value enhanced by TPA a hyperbolic relation was observed. 5. It is concluded that protein kinase C stimulation affects predominantly the spontaneous release of neurotransmitter at the frog neuromuscular junction and only very poorly the stimulation-evoked one.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 4
    ISSN: 1432-1912
    Keywords: TPA ; Protein kinase C ; Neuromuscular junction ; Nicotinic acetylcholine receptors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary (1) The effect of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), a specific activator of the protein kinase C (PrkC), on the function of junctional nicotinic acetylcholine receptors (nAChR) was examined on muscle fibres isolated from the M. flexor digitorum brevis of the rat. (2) In the presence of TPA the sensitivity of the whole endplates to iontophoretically applied ACh exhibited multiphasic oscillations: an early decrease followed by a delayed increase and, at the end again, a decrease to below pretreatment levels. This effect was more pronounced as the TPA concentration was increased in the range of 0.1–1 μM and was blocked by the PrkC-inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7). (3) TPA (0.1–0.5 μM) shortly applied to patch-clamped fibres caused a slight decrease in nAChR-channel slope conductance without affecting the mean lifetime. In a patch the opening frequency increased over time, after an initial decrease. (4) It ist concluded that specific activation of the PrkC may be of regulatory significance on nAChR function.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 5
    ISSN: 1432-2013
    Keywords: Neuromuscular junction ; Sarin ; Obidoxime chloride ; AChR ; AChE ; AChE reactivation ; Frog
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract 1. The effect of the oxime reactivator obidoxime chloride (obidoxime) on single frog neuromuscular junctions has been studied in order to clarify its action on the acetylcholine receptor (AChR) and on the acetylcholine esterase (AChE), both before and after blocking its enzymatic activity with the organophosphorus compound sarin. 2. Experiments with iontophoretic application of obidoxime to end-plates demonstrated that it has a weak direct depolarizing effect. Furtheron, the drug is shown to possess a potentiating effect on the ACh-induced depolarization. After the AChE activity had been inhibited with sarin, obidoxime on the contrary decreases the depolarization induced by ACh. Both effects are fully reversible. 3. It is concluded that obidoxime acts as an inhibitor of the AChE and as a partial antagonist of the AChR. The antagonistic effect on the receptor is usually masked by the predominating anticholinesterase effect. 4. The effect of obidoxime on miniature end-plate potentials in long-time experiments on sarin-poisoned muscles, showed only weak signs of recovery from the action of the AChE inhibitor. Only focally higher concentration of the drug produced a more marked but short term recovery of the mepps, which is, however, supposed to be dependent on the AChR antagonism. 5. It is still unclear how much of the varying therapeutic usefulness of obidoxime in clinical cases is due to its AChE reactivation and how much to the antagonistic effect on the AChR.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 6
    ISSN: 1432-1912
    Keywords: p-Nitrophenyl diazonium fluoroborate ; Cholinergic neurons ; Acetylcholine receptor ; Acetylcholinesterase ; Affinity labelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Electrophysiological experiments were done to investigate the effect of p-nitrophenyl diazonium fluoroborate (p-NPD) on motor endplates of the frog's m. cutaneus pectoris. The compound has no direct depolarizing effect on the postsynaptic membrane and stabilizes it irreversibly when added to the bath. Longtime iontophoretical applications of p-NPD produce a biphasic effect: initially a potentiation of the depolarizations due to acetylcholine (ACh) (both iontophoretically applied and presynaptically liberated), and subsequently an inhibition of the response to ACh. When the acetylcholinesterase (AChE) is inactivated previously, only the inhibiting effect of the compound is demonstrable. The association constant of p-NPD to purified AChE and to membrane fragments of electroplax was determined by biochemical methods. The compound's affinity to the AChE was found to be about 20 times greater than to the acetylcholine receptor (AChR). Iontophoretical application of p-NPD to cholinergic neurons in the hippocampal cortex of the cat also produced the characteristic biphasic effect on ACh-induced activity of these investigated neurons. The results suggest that the biphasic effect depends on the capacity of p-NPD to combine with both the AChE and the AChR. The AChE is first inhibited with low concentrations thereby potentiating the ACh response. At higher concentrations the AChR's are progressively inhibited too, thereby diminishing the excitability of the postsynaptic membrane up to a complete block.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 7
    ISSN: 1432-1912
    Keywords: 14C-Toxiferine ; Nicotinic acetylcholine receptor ; Motor endplate ; Endplate potential ; Autoradiography ; Saturation of drug binding sites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. To study the quantitative correlation between the stabilizing effect of toxiferine on the postsynaptic membrane and the number of drug binding sites at the motor endplate, experiments were performed on isolated mouse hemidiaphragms using combined electrophysiological and autoradiographic techniques. 2. The membrane stabilizing effect of 14C-toxiferine was investigated over a wide range of concentrations, in order to obtain not only muscle paralysis but the complete abolition of the endplate response to nerve stimulation. 3. Motor endplate activity was recorded intracellularly. For each concentration of the drug the percentage of endplates reacting to nerve stimulation with action potentials (a.p.), or with subliminal endplate potentials (e.p.p.), or being completely blocked, was determined. The mean amplitude of the e.p.p.'s was also calculated. 4. Reduction of the e.p.p. to an undetectable level required a concentration of 14C-toxiferine about 3 times greater than that which induced complete paralysis. 5. Correlation of these data with autoradiographic measurements demonstrated that decreasing e.p.p. amplitude corresponded to increasing values for the number of drug binding sites per endplate. Saturation was reached by that concentration which completely blocked the postsynaptic sensitivity to ACh. 6. It is concluded that at this concentration all the specific drug binding sites are occupied.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...