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J Physiol Volume 529, Number 1, 83-91, November 15, 2000
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Journal of Physiology (2000), 529.1, pp.83-91
© Copyright 2000 The Physiological Society

Zinc permeates mouse muscle ACh receptor channels expressed in BOSC 23 cells and affects channel function


Davide Ragozzino, Aldo Giovannelli*, Valentina Degasperi, Fabrizio Eusebi and Francesca Grassi


Istituto Pasteur-Fondazione Cenci Bolognetti and Dipartimento di Fisiologia Umana e Farmacologia, Universitá 'La Sapienza', Rome and *Dipartimento di Medicina Sperimentale, Universitá de L'Aquila, Italy

  1. The influx of Zn2+ through the channels of fetal and adult mouse muscle nicotinic acetylcholine receptors (gamma- and epsilon-AChRs) and its effects on receptor function were studied in transiently transfected human BOSC 23 cells, by combining patch-clamp recordings with digital fluorescence microscopy.

  2. ACh-induced whole-cell currents were reversibly reduced by external ZnCl2, with half-maximal inhibitory concentrations of 3 and 1 mM for gamma- and epsilon-AChRs, respectively.

  3. Both gamma- and epsilon-AChR channels were permeable to Zn2+, as shown by fluorescence measurements using Zn2+-sensitive dyes. The fractional current carried by Zn2+ (Pf,Zn; 0.5 mM Zn2+ in Ca2+- and Mg2+-free medium) through gamma- and epsilon-AChR channels was 1.7 and 4 %, respectively.

  4. Pf,Zn increased with the concentration of ZnCl2, but was little affected by physiological concentrations of Ca2+ and Mg2+ in the external medium.

  5. The conductance of ACh-evoked unitary events, measured by cell-attached or outside-out recordings, decreased when the patched membrane was exposed to ZnCl2 (1 or 3 mM). Simultaneous application of ACh and Zn2+ to the extra-patch membrane lengthened channel open duration (tauop) by 50%. No obvious increment of tauop was observed following exposure of inside-out patches to Zn2+.

  6. The possible physiological relevance of zinc-induced modulation of AChR channels is discussed.




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