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Acta Physiologica 2012; Volume 204, Supplement 689
91st Annual Meeting of The German Physiological Society
3/22/2012-3/25/2012
Dresden, Germany
-ACH-BINDING SITE CONTRIBUTION IN OPENING NICOTINIC RECEPTOR CHANNELS
Abstract number: O84
Heckmann1 *M., Stock1 P., Dudel2 J.
1Physiologie, Neurophysiologie, Wrzburg, Germany
2Technical University Munich, Friedrich-Schiedel-Institute for Neuroscience, Munich, Germany
Agonists bind at interfaces of a- and neighbouring g- or d/e-subunits in muscle type nicotinic receptor/channels (nAChRs) (1) but distinct opening contributions of ag- & ad- binding sites remain elusive. We compared high-resolution patch-clamp currents evoked by epibatidine (Ebd), carbamylcholine (CCh) & acetylcholine (ACh). Ebd, an analgesic skin alkaloid of Ecuadorian poison dart frogs (2), binds with 75-fold higher affinity at ag- than ad-binding sites (3) whereas CCh & ACh slightly prefer ad-sites. Short (tO1), intermediate (tO2) and long (tO3) types of openings were observed with all three agonists, consistent with earlier work (4 & 5). At Ebd concentrations below 10 nM preferentially tO2 openings occurred from ag-binding sites. Vice versa, tO1 openings appear to be generated at ad-binding sites. In addition two types of bursts could be distinguished: Short bursts (tB1) and long bursts (tB2). Closings within bursts were agonist independent, as recently reported (6 & 7). However, the duration of openings within long bursts were agonist dependent, but with further improved time resolution may approach tO2. In this case nAChRs would operate with only two open states, longer openings (tO2) occurring as single openings and also within bursts and single short openings (tO1). Aside from associating tO2 and tO1 with ag- & ad-binding sites, we propose that short bursts arise from nAChRs with a single agonist molecule at ag- binding sites.
References
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2. Daly JW. (1995) The chemistry of poisons in amphibian skin. Proc Natl Acad Sci U S A. 92:9–13
3. Prince RJ, Sine SM. (1998) Epibatidine activates muscle acetylcholine receptors with unique site selectivity. Biophys J. 75:1817–27
4. Parzefall F, Wilhelm R, Heckmann M, Dudel J. (1998) Single channel currents at six microsecond resolution elicited by acetylcholine in mouse myoballs. J Physiol. 512:181–8
5. Hallermann S, Heckmann S, Dudel J, Heckmann M. (2005) Short openings in high resolution single channel recordings of mouse nicotinic receptors. J Physiol. 563:645–62
6. Purohit P, Mitra A, Auerbach A. (2007) A stepwise mechanism for acetylcholine receptor channel gating. Nature. 446:930–3
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Supported by DFG grants to MH (HE 2621/4-2 & B27/SFB 581)
To cite this abstract, please use the following information:
Acta Physiologica 2012; Volume 204, Supplement 689 :O84