Run-down of neuromuscular transmission during repetitive nerve activity by nicotinic antagonists is not due to desensitization of the postsynaptic receptor

Content Provider	Scilit
Author	Hong, S. J. Chang, C. C.
Copyright Year	1991
Description	Journal: British Journal of Pharmacology 1 Whether the function of the postsynaptic acetylcholine receptor is use-dependently affected by repetitive nerve stimulation in the presence of competitive antagonists was studied in the mouse phrenic nerve-hemidiaphragm preparation. 2 For electrophysiological experiments, the preparation was immobilized by synthetic μ-conotoxin, which preferentially blocks muscular Na-channels causing neither depolarization of the membrane potential, inhibition of quantal transmitter release, nor depression of nicotinic receptor function. 3 High concentrations of cobratoxin depressed indirect twitches and endplate potentials (e.p.ps) without inducing waning of contractilities or run-down of trains of e.p.ps evoked at 10–100 Hz. However, waning and run-down were accelerated after washout of the toxin despite diminished postsynaptic receptor blockade. Once the run-down of e.p.ps was produced by washout or low concentrations of cobratoxin, further depression of e.p.p. amplitude with high concentrations of cobratoxin did not attenuate the e.p.p. rundown. 4 The degrees of waning of tetanus and trains of e.p.ps produced by a very high concentration of tubocurarine (20 μm) were also less than that caused at a 100 fold lower concentration, albeit the amplitudes of twitches and the first e.p.p. were depressed more rapidly and markedly. 5 Tubocurarine, like cobratoxin, depressed the amplitude of miniature endplate potentials (m.e.p.ps) more than e.p.ps. 6 In contrast to the steepened run-down of successive e.p.ps in the presence of low concentrations of either nicotinic antagonists, the amplitude of m.e.p.ps observed during repetitive stimulation was uniform and was not different from that before stimulation. 7 The results suggest that the e.p.p. run-down and tetanic fade induced by nicotinic antagonists are due to a slow kinetic blockade of presynaptic receptors and confirm that the e.p.p. run-down is not produced by a use-dependent failure of postsynaptic nicotinic receptors. The roles of the presynaptic nicotinic receptor in positive or negative feedback modulations of transmitter release are discussed.
Related Links	http://europepmc.org/articles/pmc1917973?pdf=render https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1476-5381.1991.tb12258.x
Ending Page	822
Page Count	6
Starting Page	817
e-ISSN	14765381
DOI	10.1111/j.1476-5381.1991.tb12258.x
Journal	British Journal of Pharmacology
Issue Number	4
Volume Number	102
Language	English
Publisher	Wiley-Blackwell
Publisher Date	1991-04-01
Access Restriction	Open
Subject Keyword	Journal: British Journal of Pharmacology Acetylcholine Release Endplate Potential Nicotinic Receptor
Content Type	Text
Resource Type	Article