Figure 7.

Multi-drug resistance proteins, MDR1 and MRP1, do not affect C₆-NBD-lipid arrival at the PM domains. In A, cells were preincubated with PSC 833 (5 μg/ml) at 37°C for 30 min before step 1 (see Fig. 1). In the presence of the drug, the cells were then labeled with lipid analogues at 37°C for 30 min. The cells were subsequently subjected to a back exchange (step 2 of Fig. 1) and the percentage of NBD-positive BC was determined (white bars). Alternatively, cells were subsequently treated with 30 mM dithionite and the percentage of NBD-positive BC was determined (hatched bars). In B, cells were incubated with either lipid analogue at 37°C for 30 min and back exchanged at 4°C twice for 30 min. Then, cells were rewarmed to 37°C and incubated for 1 h in back exchange medium. Lipids were extracted from the back exchange media and cell fractions to determine the percentage back exchangeable C₆-NBD-lipid. Data are expressed as mean ± SEM of at least two independent experiments.