Fig. 1.

Inhibitory effect of atenolol on the uptake of probe substrates by selected drug transporters. Uptake of 6.1 μM metformin by hOCT1, hOCT2, hOCT3, hMATE1, and hMATE2-K, 2 μM para-aminohippurate by hOAT1, and 0.06 μM estrone sulfate by hOAT3 in the absence and presence of 500 μM atenolol was measured in both transporter-expressing and control HEK293 cells. Transporter-specific uptake was obtained by subtracting the uptake in control cells from the uptake in transporter-expressing cells. The uptake in the absence of atenolol (unfilled) was set as 100%. The uptake in the presence of atenolol (filled) was expressed as a percentage of the uptake in the absence of atenolol. The uptake was measured after a 2-minute incubation at 37°C. Data are presented as the mean ± S.D. Uptake in the presence of atenolol was compared with that in the absence of atenolol (**P < 0.01; ***P < 0.001).