CYSTINE UPTAKE BY CULTURED HUMAN RENAL CORTEX CELLS

Abstract

In vitro studies of human renal transport have been limited in part because of the difficulty in obtaining adequate tissue. Cell culturing techniques afford the opportunity to perform such studies with limited amounts of tissue. Starting with small samples of normal human cortex obtained at nephrectomy for cancer, we were able to culture renal cortex epithelial cells that were free of fibroblast contamination by using a hormonally defined, serum-free medium. These cells proliferated and formed a monolayer, adhering to the surface of the culture flask. The cells could be passed for up to 5-6 times. The cell membrane facing the media had microvilli. There were connections between the cells resembling the tight junctions observed in vivo between renal tubule cells. When they were nearly confluent, "dome" formation, the lifting of the monolayer off the supporting structure, occurred suggesting active sodium and water movement. Dome formation became more evident with the addition of fetal calf serum to the medium. The cultured cells had alkaline phosphatase activity on the plasma membrane suggesting a proximal tubule origin. Because of this proximal tubule characteristic, we examined the ability of these cultured cells to transport the amino acid cystine. The monolayer progressively transported 35S-cystine for up to 60 min. of incubation. Lysine inhibited cystine uptake by these cells. This is the first in vitro evidence for the interaction between cystine transport and lysine which has been observed in vivo in the human kidney. Cultured renal cortex cells offer a new approach to the study of renal transport in humans.