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Ethanol increases agonist affinity for nicotinic receptors from Torpedo
S A Forman1, D L Righi, K W Miller
1Committee on Higher Degrees in Biophysics, Harvard University, Cambridge, MA.
Biochimica Et Biophysica Acta
|December 11, 1989
Summary
Ethanol significantly enhances acetylcholine receptor function by increasing apparent affinity for agonists and accelerating desensitization. This suggests ethanol modulates nicotinic acetylcholine receptor activity through complex mechanisms impacting both flux and desensitization rates.
Area of Science:
- Biochemistry
- Neuroscience
- Pharmacology
Background:
- Nicotinic acetylcholine receptors (nAChRs) are crucial for neurotransmission.
- Ethanol is known to affect central nervous system function, but its precise molecular targets and mechanisms remain under investigation.
- Understanding how ethanol interacts with nAChRs is vital for comprehending alcohol's neurological effects.
Purpose of the Study:
- To investigate the effects of ethanol on the function of Torpedo nicotinic acetylcholine receptors.
- To determine how ethanol influences agonist-induced cation flux and receptor desensitization.
- To elucidate the concentration-dependent and time-independent actions of ethanol on receptor activity.
Main Methods:
- Utilized Torpedo nicotinic acetylcholine receptor-rich vesicles.
- Measured 86Rb+ flux in response to acetylcholine and carbamylcholine at 4°C.
- Employed quenched-flow assays to assess flux and desensitization rates.
- Varied ethanol concentrations (up to 3.0 M) and agonist concentrations.
Main Results:
- Ethanol increased the apparent affinity of acetylcholine and carbamylcholine for the receptor in a concentration-dependent manner, up to 200-fold.
- Ethanol enhanced agonist-induced flux by 15-35% at submaximal agonist concentrations but did not affect maximum flux.
- Ethanol increased the apparent affinity for fast desensitization and accelerated the maximum rate of fast desensitization by 50% at 0.5 M.
- Effects on flux and desensitization were independent of agonist type and measurement time (5 ms to 10 s).
Conclusions:
- Ethanol potentiates Torpedo nAChR activity by increasing apparent agonist affinity and significantly accelerating fast desensitization.
- Ethanol's actions occur prior to agonist-induced desensitization, suggesting a direct interaction with the receptor.
- The pronounced effect on fast desensitization is a novel finding that warrants further investigation into ethanol's allosteric modulation of nAChRs.