Down-regulation | Desensitization | |||||
---|---|---|---|---|---|---|
Internalization | Protease inhibitor present | |||||
t = 5 min | t = 90 min | No | Yes | No | Yes | |
% | ||||||
GRP-R-Low | 39 ± 3 | 78 ± 2 | 84 ± 2 | 92 ± 23-a | 82 ± 2 | 88 ± 23-b |
GRP-R-Med | 52 ± 6 | 82 ± 2 | 67 ± 3 | 78 ± 33-a | 44 ± 3 | 71 ± 33-b |
GRP-R-High | 31 ± 7 | 77 ± 1 | 46 ± 9 | 74 ± 23-a | 21 ± 3 | 75 ± 33-b |
Internalization was determined as described in the legend to Fig. 3 and was expressed as the percentage of the total saturably bound ligand at 90 min that was not acid-strippable. Down-regulation was determined as described in the legend to Fig. 4 and was expresses as the percentage decrease in B max of the bombesin-treated cells compare with the untreated control cells processed in parallel. Chronic desensitization was determined as described in the legend to Fig. 5, with the data expresses as the percentage decrease in the maximal increase in [3H]IP caused by 1 μm bombesin in the cells after 24-hr treatment with 6 nm bombesin compare with control cells processed in parallel but untreated. Values are expresses as mean ± standard error of at least four experiments.