Figure 1. Internalization of ¹²⁵I-UII by the wild-type UT receptor in transiently transfected COS-7 cells.

Cells expressing the wild-type UT receptor were incubated with ¹²⁵I-UII (0.2 nM) at 37 °C for different periods of time (A). The effect of 0.45 M sucrose on receptor internalization was evaluated after 90 min (B). Internalization was stopped by washing the cells three times with ice-cold PBS. Acid-resistant binding was evaluated as indicated in the Experimental section. Data are expressed as a percentage of total binding for each time point, and represent means± S.D. of triplicate values. Internalization was calculated from the ratio of acid-resistant binding to total binding (acid-resistant plus acid-released). Non-specific binding was measured in the presence of 1 μM unlabelled UII. These results are representative of three independent experiments.