FIGURE 4.

Phosphorylation blockage enables agonists to use PKCϵ for receptor desensitization. HEKOPRM1 and HEK3A were treated with DMSO or 50 μm PKCϵi for 3 h and were then pretreated with 100 nm morphine (A), 1 nm etorphine (B), 1 nm fentanyl (C), and 100 nm DAMGO (D) for the times indicated on the x axis. ADP was added after agonist pretreatment. The percentage decrease in the agonist-induced potentiation on the ADP-induced [Ca²⁺]_i release was used to indicate the receptor desensitization. The decreases were calculated by using the formula: 100% − potentiation on ADP-induced [Ca²⁺]_i release with pretreatment/potentiation on ADP-induced [Ca²⁺]_i release without pretreatment.