Zinc permeates mouse muscle ACh receptor channels expressed in BOSC 23 cells and affects channel function.
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 (tau op) by 50%. No obvious increment of tau op was observed following exposure of inside-out patches to Zn2+. 6. The possible physiological relevance of zinc-induced modulation of AChR channels is discussed.
Ragozzino
D
D
Istituto Pasteur-Fondazione Cenci Bolognetti and Dipartimento di Fisiologia Umana e Farmacologia, Universita 'La Sapienza', Rome, Italy.
Giovannelli
A
A
Degasperi
V
V
Eusebi
F
F
Grassi
F
F
D000818:Animals; D002460:Cell Line; D004558:Electric Stimulation; D004594:Electrophysiology; D007473:Ion Channels / Q000378:metabolism* / Q000648:ultrastructure; D051379:Mice; D018613:Microscopy, Confocal; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000648:ultrastructure; D009538:Nicotine / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010539:Permeability; D011950:Receptors, Cholinergic / Q000378:metabolism* / Q000648:ultrastructure; D013050:Spectrometry, Fluorescence; D015032:Zinc / Q000378:metabolism*
D007473:Ion Channels; D018722:Nicotinic Agonists; D011950:Receptors, Cholinergic; D009538:Nicotine; D015032:Zinc