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Multiple pathways of Pb 2+ permeation in rat cerebellar granule neurones
Author(s) -
Mazzolini Monica,
Traverso Sonia,
Marchetti Carla
Publication year - 2001
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.2001.00557.x
Subject(s) - chemistry , biophysics , cerebellum , calcium , nmda receptor , depolarization , intracellular , granule (geology) , glutamate receptor , membrane potential , permeation , biochemistry , membrane , endocrinology , biology , paleontology , receptor , organic chemistry
The pathways of lead (Pb 2+ ) uptake were studied in fura‐2‐loaded cerebellar granule cells from 8‐day‐old rats. In a nominal Ca‐free external bath, Pb 2+ (5–50 µ m ) determined an increase of the fluorescence emission ratio ( R = E 340 / E 380 ) even in the absence of any specific stimulus. This rise was dose‐dependent, was not significantly affected by m m Mg 2+ or Ca 2+ , but it was readily reversed by the membrane‐permeant heavy metal chelator tetrakis(2‐pyridylmethyl) ethylene‐diamine (TPEN, 100 µ m ), indicating that it was due to Pb 2+ influx. The rate of rise, d R /d t , was increased up to a factor of 5 by depolarizing high‐KCl solution, indicating a sizeable permeation through voltage‐dependent channels. This effect was neither antagonized by nimodipine, nor enhanced by BayK8644, but it was slackened by ω‐agatoxin IVA (200 n m ), suggesting an involvement of non‐L‐type calcium channels. Pb 2+ influx was also stimulated by glutamic acid or NMDA in the presence of 10–30 µ m glycine, but only in Mg‐free solution, suggesting that glutamate channels of the NMDA type are an additional pathway of Pb 2+ uptake. Pb 2+ caused a time‐, dose‐ and stimulus‐dependent saturation of the dye, whose intracellular concentration is ∼ 10 µ m , indicating that intracellular Pb 2+ can readily reach a concentration in the micromolar range. These results indicate that the particular vulnerability of neurones to Pb 2+ poisoning is linked to the presence of specific transport systems, which mediate the rapid uptake of Pb 2+ into the neurone.