Fig. 5.

Haptoglobin inhibits hemoglobin uptake and restores albumin endocytosis by OK cells. A: OK cells were incubated with 2 µM Alexa Fluor 568-OxyHb for 1 h at 37°C in the presence or absence of 10 µM haptoglobin, then washed, fixed, and processed for immunofluorescence to visualize cell-associated Hb. Scale bar, 25 µm. B: filter-grown OK cells were incubated with 40 µg/ml Alexa Fluor 647-albumin in the presence of OxyHb (7.5 µM) and/or 7.5 µM haptoglobin (Hpt) as indicated. After extensive washing, cells were solubilized and fluorescent cell-associated albumin was quantified. Data (means ± SD) from two independent experiments each performed in triplicate are shown.