Conditions | IC50 | nH | |
---|---|---|---|
Total (Li+) | 394 ± 42 μM | 0.99 ± 0.10 | |
NBMPR-resistant (Li+) | 543 ± 31 μM | 1.08 ± 0.09 | |
NBMPR-resistant (Na+) | A | 17 ± 5 nM4-a | |
B | 415 ± 126 μM | 0.29 ± 0.044-b |
IC50 values and pseudo Hill coefficients (nH) were calculated from sigmoid curves fitted to data plotted as shown in figure 7. Cells (± Na+) were exposed concurrently to 10 μM [3H]formycin B and a range of concentrations of gemcitabine in the presence (“NBMPR-resistant”) and absence (“Total”) of 100 nM NBMPR. Each value represents the mean ± S.E. from five experiments.
↵4-a Data from individual experiments conducted in the presence of NBMPR and Na+ fit best to a biphasic inhibition curve (F test, P < .02) allowing the calculation of IC50 values for each of the two components (A and B). The component with highest affinity for gemcitabine (A) represented 47 ± 3% of the total transporter-mediated [3H]formycin B uptake.
↵4-b Calculated from the averaged data shown in figure 7.