Multiple pathways of Pb(2+) permeation in rat cerebellar granule neurones.
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 microM) 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 mM Mg(2+) or Ca(2+), but it was readily reversed by the membrane-permeant heavy metal chelator tetrakis(2-pyridylmethyl) ethylene-diamine (TPEN, 100 microM), indicating that it was due to Pb(2+) influx. The rate of rise, dR/dt, 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 omega-agatoxin IVA (200 nM), 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 microM 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 approximately 10 microM, 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.
Mazzolini
M
M
Istituto di Cibernetica and Biofisica, Consiglio Nazionale delle Ricerche, Genoa, Italy.
Traverso
S
S
Marchetti
C
C
D000818:Animals; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005456:Fluorescent Dyes; D016257:Fura-2; D018698:Glutamic Acid / Q000494:pharmacology; D007854:Lead / Q000493:pharmacokinetics*; D016202:N-Methylaspartate / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D010539:Permeability; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012996:Solutions
D005456:Fluorescent Dyes; D012996:Solutions; D007854:Lead; D018698:Glutamic Acid; D016202:N-Methylaspartate; D011189:Potassium Chloride; D016257:Fura-2