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Pflügers Archiv

, Volume 429, Issue 6, pp 781–788 | Cite as

GABAergic inhibition of crayfish deep extensor abdominal muscle exhibits a steep dose-response relationship and a high degree of cooperativity

  • Nicolas von Beckerath
  • Helmuth Adelsberger
  • Franz Parzefall
  • Christian Franke
  • Josef Dudel
Original Article Neurophysiology, Muscle and Sensory Organs

Abstract

A patch-clamp study was done to characterize the recently found GABAergic (i.e. γ-aminobutyric acid) inhibitory synaptic channels of crayfish deep extensor abdominal muscle. Outside-out patches were rapidly activated by GABA to measure the dose/ response curves for the open probability of the channels, Po, and the rise time, tr, (time from Po=0.1 to Po=0.9). In some of the patches the GABA-activated currents decayed due to desensitization and such patches were not studied further. Rare channel openings were elicited with 0.1 mM GABA. The Po at this low concentration of GABA was 0.0005 to 0.01. Application of 10 mM GABA was necessary to reach the maximal Po of 0.9. The slope of the dose/response relationship in the double logarithmic plot was 5.4±1.1 (mean±SD; n=9) between 0.1 mM and 0.2 mM GABA. The plot of tr versus GABA concentration had a peculiar shape, recently found to be characteristic for positive cooperativity of the binding sites. tr increased from a minimum at 10 mM GABA with declining concentrations of GABA and reached a peak at 0.4 mM GABA. Below 0.4 mM GABA, tr decreased again. With 0.2 mM GABA tr was 0.40±0.1 (mean±SD; n=4) of the peak value measured at 0.4 mM GABA. Simulations were compared with the experimental results and a linear reaction scheme with five binding sites for GABA was established to describe the dose/response curves for Po and tr.

Key words

GABA Inhibition Crayfish muscle Hill coefficient Cooperativity Allosteric proteins Desensitization Patch-clamp 

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Copyright information

© Springer-Verlag 1995

Authors and Affiliations

  • Nicolas von Beckerath
    • 1
  • Helmuth Adelsberger
    • 1
  • Franz Parzefall
    • 1
  • Christian Franke
    • 2
  • Josef Dudel
    • 1
  1. 1.Physiologisches Institut der Technischen Universität MünchenMunichGermany
  2. 2.Neurologische Klinik der Technischen Universität MünchenMunichGermany

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