Date of Award

5-4-2007

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

First Advisor

Dr. Delon W. Barfuss - Chair

Second Advisor

Dr. Chun Jiang

Third Advisor

Dr. Deborah Baro

Abstract

The lumen-to-cell transport, cellular accumulation, and toxicity of ionic cadmium (109Cd2+) and cadmium-cysteine conjugate (Cys-S-109Cd-S-Cys) were studied in isolated perfused S2 segments of the proximal tubule of the rabbit kidney. All perfusion solutions were HEPES buffered and contained 3H-L-glucose which functioned as a volume and leak marker along with 250 nM FD & C Green dye as a vital dye. When ionic cadmium, 0.73µM Cd2+, or 0.73µM cadmium-cysteine conjugate (Cys-S-109Cd-S-Cys) containing solution was perfused through the lumen of the tubule there was no visual evidence of toxicity such as blebbing of the luminal membrane, cellular vital dye uptake, and cellular swelling. Ionic Cd2+ transport was temperature dependent (87% reduction at 22°C and 100% at 11°C) and inhibited by FeCl2 (42% reduction at 10µM) and ZnCl2 (48% reduction at 20µM), and high Ca2+ concentrations (27% reduction at 1.95mM and 69% at 2.6mM). The ionic Cd2+ transport was not affected by verapamil and diltiazem. The cadmium conjugate (Cys-S-Cd-S-Cys) transport was also temperature dependent (76% reduction at 22°C and 100% at 11°C) and inhibited by the amino acids L-cystine and L-arginine (55% and 50% respectively), stimulated by L-methionine (56%), but not affected by L-aspartate, L-glutamate and Gly-Sar. 2, 3-Dimercaptopropane-1-Sulfonate (DMPS) co-perfused with Cd2+ decreased absorption of 20µM Cd2+ (39% reduction at 30 µM and 94.6% reduction at 200 µM), while DMPS added to the bathing solution has no effect on the luminal transport of Cd2+. DMPS co-perfused with 20 µM Cys-S-Cd-S-Cys substantially reduced Cd2+ transport (62% reduction at 30 µM). We conclude that cadmium can be transported at the luminal membrane of the S2 segment of the proximal tubule by multiple mechanisms, depending on the form which it is presented to membrane. Ionic cadmium appears to be transported by iron (DCT1), zinc (ZTL1) transporters and some kind of calcium-selective channel while cadmium conjugate of L-cysteine appears to be transported by L-cystine transporters (system b0+). Dipeptide transporter is not involved in the transport of cadmium. DMPS appears to be a chelator for cadmium.

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