Figure 4. Effects of C-terminal truncations on UT receptor internalization.

COS-7 cells expressing wild-type UT receptor (◆), UTΔ363 (□), UTΔ350 (Δ) or UTΔ336 (○) (A), and COS-7 cells expressing wild-type UT receptor (◆), UTΔ367 (○), UTΔ363 (□) or Mut4S (Δ) (B), were incubated with ¹²⁵I-UII (0.2 nM) at 37 °C for different periods of time. (C) The effects of 0.45 M sucrose (suc) on internalization of the wild-type receptor and UTΔ363 were evaluated after 90 min. Internalization was stopped by washing the cells three times with ice-cold PBS. Acid-resistant binding was evaluated as indicated in the Experimental section. Values 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.