Zn2+ current is mediated by voltage-gated Ca2+ channels and enhanced by extracellular acidity in mouse cortical neurones.
1. Mammalian neuronal voltage-gated Ca2+ channels have been implicated as potential mediators of membrane permeability to Zn2+. We tested directly whether voltage-gated Ca2+ channels can flux Zn2+ in whole-cell voltage-clamp recordings from cultured murine cortical neurones. 2. In the presence of extracellular Zn2+ and no Na+, K+, or other divalent cations, a small, non-inactivating, voltage-gated inward current was observed exhibiting a current-voltage relationship characteristic of high-voltage activated (HVA) Ca2+ channels. Inward current was detectable at Zn2+ levels as low as 50 microM, and both the amplitude and voltage sensitivity of the current depended upon Zn2+ concentration. This Zn2+ current was sensitive to blockade by Gd3+ and nimodipine and, to a lesser extent, by omega-conotoxin GVIA. 3. Zn2+ could permeate Ca2+ channels in the presence of Ca2+ and other physiological cations. Inward currents recorded with 2 mM Ca2+ were attenuated by Zn2+ (IC50 = 210 microM), and currents recorded with Zn2+ were unaffected by up to equimolar Ca2+ concentrations. Furthermore, the Zn2+-selective fluorescent dye Newport Green revealed a depolarisation-activated, nimodipine-sensitive Zn2+ influx into cortical neurones that were bathed in a physiological extracellular solution plus 300 microM ZnCl2. 4. Surprisingly, while lowering extracellular pH suppressed HVA Ca2+ currents, Zn2+ current amplitude was affected oppositely, varying inversely with pH with an apparent pK of 7.4. The acidity-induced enhancement of Zn2+ current was associated with a positive shift in reversal potential but no change in the kinetics or voltage sensitivity of channel activation. 5. These results provide evidence that L- and N-type voltage-gated Ca2+ channels can mediate Zn2+ entry into cortical neurones and that this entry may be enhanced by extracellular acidity.
Kerchner
G A
GA
Center for the Study of Nervous System Injury and Department of Neurology, Washington University School of Medicine, 660 S. Euclid Avenue, St Louis, MO 63110, USA.
Canzoniero
L M
LM
Yu
S P
SP
Ling
C
C
Choi
D W
DW
D000143:Acids / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism*; D005456:Fluorescent Dyes; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D017136:Ion Transport / Q000187:drug effects; D051379:Mice; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D015032:Zinc / Q000378:metabolism* / Q000494:pharmacology
D000143:Acids; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D005456:Fluorescent Dyes; D015032:Zinc; D002118:Calcium