An investigation into the desensitization of neurotransmitter gated ion channels — functional relevance, impact on ganglionic receptor function, and structural insights

The desensitized state of neurotransmitter-gated ion channels (NGICs) remains poorly understand, both in terms of its functional role and its structure. Although the state was historically thought to have limited functional relevance, recent results have demonstrated that the state is indeed likely to play a role in shaping receptor responses to normal physiological stimulation. To determine the generality of this role, we subjected all types of NGICs known to exist in the human body to high-frequency stimulation and quantified the impact of the desensitized state on their responses. Our results, presented in Chapter II, show that the desensitized state is likely to be visited by all of these receptors in response to synaptic-like stimulation. Furthermore, our findings indicate that the desensitized state can enable receptors to act as low-pass filters, a behavior that had been observed to occur in synapses, but which had not been attributed to receptors. In Chapter III, we investigate the unusual desensitization properties of the α3β4 AChRs, receptors that are the primary mediators of fast-synaptic transmission in the autonomic ganglia. Previously, it had been proposed that oxidation of an intracellular cysteine is fundamentally critical in the mechanism of this unusual desensitization; in the work presented in Chapter III, we found that this cysteine oxidation hypothesis cannot explain our results, implying that the mechanism must be more complex than was previously proposed. In the work presented in Chapter IV, we used scanning mutagenesis to investigate whether the M1-M2 linker of pentameric ligand-gated ion channels is likely to undergo structural rearrangement during open-closed and open-desensitized transitions. We found that this region is unlikely to be important during these kinetic transitions, implying that the hinge point to accommodate the tilting of the pore-lining M2 helix is likely to be near the intracellular edge of the pore. We also investigated the structure-function relationship underlying the variability in desensitization kinetics and found that, at least in glycine receptors, post-translational modification of the M3-M4 loop cannot account for the large variability in behavior seen from cell to cell. Overall, the results presented in this dissertation shine light on the functional role of the desensitized state and give novel insight into the structure and regulation of this conformation.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Neuroscience

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2013

Author dc:creator

• Papke, David

Contributors dc:contributor

• Grosman, Claudio F.
• Cox, Charles L.
• Chung, Hee Jung
• Brieher, William M.
• Steinbach, Joe Henry

• ion channels
• molecular neuroscience
• biophysics

Statement dc:rights

• Copyright 2013 David Papke

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/44766

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/44766