Table 1.

Average fold-increase values for HEK293 cells expressing P-gp, MRP1 or ABCG2 as measured by flow cytometer or cell counter.

Transporter	Fold-increase
	Cell counter	Flow cytometer	p
P-gp	10.0±5.0	27.5±9.0	0.0085
MRP1	3.7±1.5	4.1±0.9	0.61
ABCG2	2.3±0.9	3.1±0.8	0.22

Fold-increase was determined by dividing intracellular fluorescence determined in cells incubated with substrate in the presence of inhibitor alone by intracellular fluorescence determined in the presence of substrate alone. Substrate/inhibitor pairs were rhodamine/valspodar, calcein AM/MK571, and BODIPY-prazosin/FTC for P-gp, MRP1, and ABCG2, respectively. Mean ± standard deviation is shown; p values were determined by Students t-test between average fold-increase values measured by flow cytometer or cell counter. p < 0.05 was considered significant.