Differences between OK and LLC-PK1 cells: cystine handling

Cultured opossum kidney (OK) and porcine kidney (LLC-PK1) cells were compared for biochemical characteristics and cystine transport systems. The cell lines differ in amount of protein per cell, with OK cells having approximately one-half the amount found in LLC-PK1. Both cell lines contain 19 micrograms DNA/10(6) cells. As cells reach confluence, cystine uptake increases in OK and decreases in LLC-PK1 cells. Throughout the growth period, only lysine inhibits cystine uptake in OK, whereas glutamate is the inhibitor in LLC-PK1. The predominant site of cystine transport in OK cells is across the apical membrane, and the basolateral membrane is the corresponding site of transport in LLC-PK1 cells. Although the intracellular reduced glutathione pool is the same, the cysteine pool in OK cells is approximately one-fourth that found in LLC-PK1 cells. The ability of OK cells to reflect the shared cystine-dibasic amino acid transport system and LLC-PK1 to exhibit the cystine-glutamate antiporter system makes available two models for investigation of the development and structure of cystine transport systems.