Pathways of cadmium influx in mammalian neurons.
The influx of the toxic cation Cd2+ was studied in fura 2-loaded rat cerebellar granule neurons. In cells depolarized with Ca2(+)-free, high-KCI solutions, the fluorescence emission ratio (R) increased in the presence of 100 microM Cd2(+). This increase was fully reversed by the Cd2+ chelator tetrakis(2-pyridylmethyl)ethylenediamine, indicating a cadmium influx into the cell. The rate of increase, dR/dt, was greatly reduced (67+/-5%) by 1 microM nimodipine and enhanced by 1 microM Bay K 8644. Concurrent application of nimodipine and omega-agatoxin IVA (200 nM) blocked Cd2+ permeation almost completely (88+/-5%), whereas omega-conotoxin MVIIC (2 microM) reduced dR/dt by 24+/-8%. These results indicate a primary role of voltage-dependent calcium channels in Cd2+ permeation. Stimulation with glutamate or NMDA and glycine also caused a rise of R in external Cd2+. Simultaneous application of nimodipine and omega-agatoxin IVA moderately reduced dR/dt (25+/-3%). NMDA-driven Cd2(+) entry was almost completely prevented by 1 mM Mg2+, 50 microM memantine, and 10 microM 5,7-dichlorokynurenic acid, suggesting a major contribution of NMDA-gated channels in glutamate-stimulated Cd2+ influx. Moreover, perfusion with alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate caused a slow increase of R. These results suggest that Cd2+ permeates the cell membrane mainly through the same pathways of Ca2+ influx.
Usai
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C
Istituto di Cibernetica e Biofisica, Consiglio Nazionale delle Ricerche, Genova, Italy.
Barberis
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A
Moccagatta
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L
Marchetti
C
C
D000818:Animals; D002104:Cadmium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D005456:Fluorescent Dyes; D016257:Fura-2; D018698:Glutamic Acid / Q000494:pharmacology; D008959:Models, Neurological; D009474:Neurons / Q000378:metabolism*; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley
D002121:Calcium Channel Blockers; D005456:Fluorescent Dyes; D002104:Cadmium; D018698:Glutamic Acid; D016257:Fura-2