Zinc transport and metallothionein induction in primary cultures of rabbit kidney proximal cells.
Primary cultures of isolated rabbit renal proximal cells were grown on collagen-coated permeable supports. The confluent epithelia were polarized, making possible the measurement of uptakes and effluxes across the apical and the basolateral membranes. Uptakes of 65Zn were assessed under initial rate conditions, after 0.5 min incubation. The kinetic parameters of apical uptake were a Jmax of 25.1 +/- 5.3 pmol min-1 (micrograms DNA)-1, a Km of 43.3 +/- 7.3 microM and an unsaturable constant of 0.105 +/- 0.029 (n = 7) at 37 degrees C. Cadmium competitively inhibited the zinc uptake, with a Ki value of 24.5 +/- 7.3 microM. Basolateral uptake was characterized by a high capacity (Jmax = 227.9 +/- 46.6 pmol min-1 (micrograms DNA)-1) and an affinity similar to that of the apical uptake (Km = 35.4 +/- 14.2 microM). Cadmium had no effect on the basolateral zinc uptake. Effluxes across the basolateral face of the epithelium always exceeded those across the apical face. Excess zinc in the culture medium induced the synthesis of metallothionein in the epithelia, as judged by the rate of [35S]cysteine incorporation into a fraction of cytosolic proteins. Metallothionein induction did not appear to modify the kinetic parameters of the apical zinc uptake. These data suggest that separate saturable transport systems are responsible for the apical and basolateral zinc uptakes in proximal renal cells. Induction of metallothionein had no apparent effect on apical zinc uptake in this system.
Gachot
B
B
Département de Biologie Cellulaire et Moléculaire, Centre d'Etudes de Saclay, Gif sur Yvette, France.
Tauc
M
M
Wanstok
F
F
Morat
L
L
Poujeol
P
P
D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003545:Cysteine / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008668:Metallothionein / Q000096:biosynthesis*; D011817:Rabbits; D013462:Sulfur Radioisotopes; D015032:Zinc / Q000378:metabolism*; D015037:Zinc Radioisotopes
D013462:Sulfur Radioisotopes; D015037:Zinc Radioisotopes; D002104:Cadmium; D008668:Metallothionein; D015032:Zinc; D003545:Cysteine