Reciprocal inhibition of Cd and Pb sulfocomplexes for uptake in Caco-2 cells.
Cadmium-lead interactions for uptake were studied in the TC7 clone of human enterocytic-like Caco-2 cells as a function of inorganic metal speciation. We have previously shown that Cd uptake in these cells involves both the free cation Cd2+ and chlorocomplex (CdCln(2-n)) species. Here we show 1.9 times higher uptake levels for 109CdCln(2-n) compared to 210PbCln(2-n). Reciprocal inhibitions of chlorocomplexes were observed with a much higher inhibitory effect of Cd compared to Pb. Replacing Cl- by NO3- increased both the level of aquo ion 109Cd2+ and 109Cd accumulation. In contrast, higher levels of 210Pb2+ did not favor 210Pb uptake. For both metals, higher uptake data were recorded in the presence of SO4(2-), leading to sulfocomplex formation, compared with Cl-. Reciprocal inhibitions were minimal at high-cation levels but were significant and comparable in the presence of sulfo-complexes. We conclude that, in addition to Cd2+ (but not Pb2+), sulfocomplexes of both metals would preferentially be taken up compared to chlorocomplexes. NRAMP2 is not involved in Pb2+ uptake, and the NRAMP2-mediated Cd2+ uptake is insensitive to Pb. Uptake of Pb chlorocomplexes could involve specific mechanisms but of very low affinity, whereas uptake of Pb sulfocomplexes occurs with high affinity.
Aduayom
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I
Département de Chimie, Université du Québec à Montréal, C.P. 8888, Succ. centre-ville, Montréal, Québec, Canada H3C 3P8.
Jumarie
C
C
D001692:Biological Transport / Q000187:drug effects; D018938:Caco-2 Cells; D019256:Cadmium Chloride / Q000494:pharmacology*; D027682:Cation Transport Proteins / Q000378:metabolism*; D004336:Drug Antagonism; D015386:Hazardous Substances / Q000494:pharmacology*; D006801:Humans; D033862:Iron-Binding Proteins / Q000378:metabolism*; D007854:Lead / Q000494:pharmacology*; D009566:Nitrates / Q000494:pharmacology*; D013431:Sulfates / Q000494:pharmacology*; D000099236:Solute Carrier Family 11, Member 2
D019256:Cadmium Chloride; D027682:Cation Transport Proteins; D015386:Hazardous Substances; D033862:Iron-Binding Proteins; D007854:Lead; D009566:Nitrates; D013431:Sulfates; D000099236:Solute Carrier Family 11, Member 2; C017461:lead nitrate