FIG. 4.

Internalization and recycling of opioid ligand. (A) Internalization. CHO cells expressing wild type or T353A receptors or NG108-15 cells expressing endogenous receptors were incubated at 37°C with 2 nM [³H]-DPDPE for different time intervals. Cells were acid washed to remove surface-bound ligand, and the radiolabel associated with the cells was determined as described in Materials and Methods. (B) Recycling. Cells were incubated for 30 min with 2 nM [³H]-DPDPE, acid washed to remove surface-bound ligand, and incubated in buffer without radioactivity for various periods of time. The radioactivity in acid-washed cells after 30 min of incubation with radiolabeled agonist is taken as 100%. The data represent mean ± SEM of three to five experiments.