Table 1

DAMGO stimulation of [GTPγ35S] binding in membranes from agonist-pretreated cells

TreatmentEC50Maximal stimulation
nm % over control
Control28  ± 6367  ± 21
DAMGO209  ± 14149  ± 10
Morphine103  ± 10286  ± 16
Butorphanol58  ± 18325  ± 9
Etorphine>60058  ± 7
β-Endorphin240  ± 12205  ± 9

Confluent cells in medium were incubated with 10 μm of each agonist for 24 hr; then, cells were washed with PBS and collected, and membranes were prepared as described in Experimental Procedures. [GTPγ35S] binding to membranes was measured in the presence of DAMGO (1 nm to 10 μm) at 25° for 30 min. Data are expressed as percentage stimulation over that obtained in the absence of added DAMGO.

    • Values are mean ± standard error from four or five experiments.