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. 1990 Sep;428:155–174. doi: 10.1113/jphysiol.1990.sp018205

The actions of suxamethonium (succinyldicholine) as an agonist and channel blocker at the nicotinic receptor of frog muscle.

C G Marshall 1, D C Ogden 1, D Colquhoun 1
PMCID: PMC1181640  PMID: 2133043

Abstract

1. Patch clamp methods were used to study the equilibrium and kinetic properties of the acetylcholine analogue, succinyldicholine (suxamethonium), which is used clinically as a neuromuscular blocking agent. 2. The equilibrium concentration-response curve, corrected for desensitization was estimated by measuring as the response the probability of being open of single ion channels during clusters of activity that occur between long desensitized periods. Suxamethonium (Sux) was about 7.6-fold less potent than acetylcholine (ACh) (at low concentrations), partly because of 2.9-fold lower affinity for the resting receptor, and partly because of a lower ability to activate the receptor once bound. 3. Sux was a more potent blocker of the open ion channel than ACh (equilibrium constant about 200 microM); this limited the maximum open probability to about 0.36 (at 12 degrees C and -120 mV). Individual channel blockages lasted about 65 microseconds on average. They appeared to get longer at high agonist concentration; however, a simulation method was used to show that this effect could be accounted for by the fact that at higher concentrations there are more openings that are too brief to be detected. Over the concentration range tested the effects were described by a simple open channel block mechanism. 4. No component of brief shut times could be detected other than those resulting from channel blockages. However, the results suggest that multiple channel openings (the nachschlag phenomenon) should be rare, so this is not inconsistent with previous results with other agonists. 5. Sux differed from ACh and carbachol in that it had a somewhat lower efficacy and a greater channel blocking action. However, in clinical practice channel block is unlikely to contribute to neuromuscular block to any significant extent; the main mechanism of paralysis, at least in the early stages, is probably a result of prolonged depolarization of the region of membrane surrounding the motor endplate leading to inactivation of the sodium channels therein.

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Selected References

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  1. BURNS B. D., PATON W. D. M. Depolarization of the motor end-plate by decamethonium and acetylcholine. J Physiol. 1951 Sep;115(1):41–73. doi: 10.1113/jphysiol.1951.sp004652. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Betz W., Sakmann B. Effects of proteolytic enzymes on function and structure of frog neuromuscular junctions. J Physiol. 1973 May;230(3):673–688. doi: 10.1113/jphysiol.1973.sp010211. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Blatz A. L., Magleby K. L. Correcting single channel data for missed events. Biophys J. 1986 May;49(5):967–980. doi: 10.1016/S0006-3495(86)83725-0. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Colquhoun D., Ogden D. C. Activation of ion channels in the frog end-plate by high concentrations of acetylcholine. J Physiol. 1988 Jan;395:131–159. doi: 10.1113/jphysiol.1988.sp016912. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Colquhoun D., Sakmann B. Fast events in single-channel currents activated by acetylcholine and its analogues at the frog muscle end-plate. J Physiol. 1985 Dec;369:501–557. doi: 10.1113/jphysiol.1985.sp015912. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Hamill O. P., Marty A., Neher E., Sakmann B., Sigworth F. J. Improved patch-clamp techniques for high-resolution current recording from cells and cell-free membrane patches. Pflugers Arch. 1981 Aug;391(2):85–100. doi: 10.1007/BF00656997. [DOI] [PubMed] [Google Scholar]
  7. KATZ B., THESLEFF S. A study of the desensitization produced by acetylcholine at the motor end-plate. J Physiol. 1957 Aug 29;138(1):63–80. doi: 10.1113/jphysiol.1957.sp005838. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Neher E., Steinbach J. H. Local anaesthetics transiently block currents through single acetylcholine-receptor channels. J Physiol. 1978 Apr;277:153–176. doi: 10.1113/jphysiol.1978.sp012267. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Neher E. The charge carried by single-channel currents of rat cultured muscle cells in the presence of local anaesthetics. J Physiol. 1983 Jun;339:663–678. doi: 10.1113/jphysiol.1983.sp014741. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Ogden D. C., Colquhoun D. Ion channel block by acetylcholine, carbachol and suberyldicholine at the frog neuromuscular junction. Proc R Soc Lond B Biol Sci. 1985 Sep 23;225(1240):329–355. doi: 10.1098/rspb.1985.0065. [DOI] [PubMed] [Google Scholar]
  11. Ogden D. C., Colquhoun D. The efficacy of agonists at the frog neuromuscular junction studied with single channel recording. Pflugers Arch. 1983 Nov;399(3):246–248. doi: 10.1007/BF00656725. [DOI] [PubMed] [Google Scholar]
  12. Sakmann B., Patlak J., Neher E. Single acetylcholine-activated channels show burst-kinetics in presence of desensitizing concentrations of agonist. Nature. 1980 Jul 3;286(5768):71–73. doi: 10.1038/286071a0. [DOI] [PubMed] [Google Scholar]
  13. Sine S. M., Steinbach J. H. Activation of acetylcholine receptors on clonal mammalian BC3H-1 cells by high concentrations of agonist. J Physiol. 1987 Apr;385:325–359. doi: 10.1113/jphysiol.1987.sp016496. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Sine S. M., Steinbach J. H. Agonists block currents through acetylcholine receptor channels. Biophys J. 1984 Aug;46(2):277–283. doi: 10.1016/S0006-3495(84)84022-9. [DOI] [PMC free article] [PubMed] [Google Scholar]

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