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Investigation of Competitive Antagonist Binding to the Nicotinic Acetylcholine Receptor Using Voltage-Jump and Light-Flash Techniques

Citation

Krouse, Mauri Eugene (1984) Investigation of Competitive Antagonist Binding to the Nicotinic Acetylcholine Receptor Using Voltage-Jump and Light-Flash Techniques. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/wb48-ph26. https://resolver.caltech.edu/CaltechTHESIS:05282015-161004818

Abstract

1. The effect of 2,2’-bis-[α-(trimethylammonium)methyl]azobenzene (2BQ), a photoisomerizable competitive antagonist, was studied at the nicotinic acetycholine receptor of Electrophorus electroplaques using voltage-jump and light-flash techniques.

2. 2BQ, at concentrations below 3 μΜ, reduced the amplitude of voltage-jump relaxations but had little effect on the voltage-jump relaxation time constants under all experimental conditions. At higher concentrations and voltages more negative than -150 mV, 2BQ caused significant open channel blockade.

3. Dose-ratio studies showed that the cis and trans isomers of 2BQ have equilibrium binding constants (Ki) of .33 and 1.0 μΜ, respectively. The binding constants determined for both isomers are independent of temperature, voltage, agonist concentration, and the nature of the agonist.

4. In a solution of predominantly cis-2BQ, visible-light flashes led to a net cis→trans isomerization and caused an increase in the agonist-induced current. This increase had at least two exponential components; the larger amplitude component had the same time constant as a subsequent voltage-jump relaxation; the smaller amplitude component was investigated using ultraviolet light flashes.

5. In a solution of predominantly trans-2BQ, UV-light flashes led to a net trans→cis isomerization and caused a net decrease in the agonist-induced current. This effect had at least two exponential components. The smaller and faster component was an increase in agonist-induced current and had a similar time constant to the voltage-jump relaxation. The larger component was a slow decrease in the agonist-induced current with rate constant approximately an order of magnitude less than that of the voltage-jump relaxation. This slow component provided a measure of the rate constant for dissociation of cis-2BQ (k_ = 60/s at 20°C). Simple modelling of the slope of the dose-rate curves yields an association rate constant of 1.6 x 108/M/s. This agrees with the association rate constant of 1.8 x 108/M/s estimated from the binding constant (Ki). The Q10 of the dissociation rate constant of cis-2BQ was 3.3 between 6° and 20°C. The rate constants for association and dissociation of cis-28Q at receptors are independent of voltage, agonist concentration, and the nature of the agonist.

6. We have measured the molecular rate constants of a competitive antagonist which has roughly the same Ki as d-tubocurarine but interacts more slowly with the receptor. This leads to the conclusion that curare itself has an association rate constant of 4 x 109/M/s or roughly as fast as possible for an encounter-limited reaction.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Neurobiology
Degree Grantor:California Institute of Technology
Division:Biology
Major Option:Neurobiology
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Lester, Henry A.
Thesis Committee:
  • Lester, Henry A. (chair)
  • Pine, Jerome
  • Chan, Sunney I.
  • Berg, Howard C.
  • Van Essen, David
Defense Date:5 May 1984
Funders:
Funding AgencyGrant Number
NIHUNSPECIFIED
NIHNS 11756
Jean Weigle Memorial FundUNSPECIFIED
Record Number:CaltechTHESIS:05282015-161004818
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:05282015-161004818
DOI:10.7907/wb48-ph26
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8905
Collection:CaltechTHESIS
Deposited By: Leslie Granillo
Deposited On:02 Jun 2015 17:34
Last Modified:16 Apr 2021 23:23

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