Regulation ofmu opiate receptors by endomorphin-1 and morphine in SH-SY5Y human neuroblastoma cells
Experience the future of the Tulane University Digital Library.
We invite you to visit the new Digital Collections website.
Description
The human neuroblastoma cell line, SH-SY5Y, was used to determine to examine the effects of the endogenous opioid peptides, endomorphin-1 and endomorphin-2, and the plant-derived alkaloid, morphine on mu opiate receptors. Chronic exposure to endomorphin-1, endomorphin-2 and morphine resulted in over a 50% reduction in total receptor number, without affecting the affinity of 3H-DAMGO for mu opiate receptors in SH-SY5Y cells. There was no significant difference in the reduction in receptor number between the three agonists. EM-1, EM-2 and morphine treatment for 24h at 100nM 1muM and 10muM doses resulted in a dose-dependent down-regulation in mu opiate receptors. EM-1 treatment resulted in a rapid down-regulation of mu opiate receptors, with a half-time to maximal down-regulation of 1h, compared to 2.3h for morphine. Down-regulation of mu opiate receptors by morphine and EM-1 was blocked by treatment with 0.5M sucrose, indicating that down-regulation of mu opiate receptors by these agonists was endocytosis-dependent. Cell-surface binding studies revealed that morphine was able to induce internalization of mu opiate receptors in SH-SY5Y cells. After 30 min of EM-1 or morphine treatment, over 60% and 30% of mu opiate receptors were internalized. The half-time to maximal down-regulation by EM-1 and morphine was 0.75 and 17 min. The internalization induced by each of these agonists was blocked by treatment with 0.4M sucrose. Recovery of mu opiate receptors to the cell surface after 30 min of EM-1 or morphine treatment did not require protein synthesis. Cycloheximide did not effect the recovery of cell-surface receptors, for up to an 1h after agonist removal. The half-time to recovery of receptors to control levels was 8 and 5 minutes for EM-1 and morphine. There was a significant difference in the amount of cell-surface receptors recovered after 30 min and 2.5h of EM-1 or morphine treatment. After 2.5h of EM-1 or morphine treatment, 28% and 68% of mu opiate receptors were recovered to the cell-surface during a 10 min recovery period. This study demonstrates that EM-1 induces a more rapid internalization and down-regulation of mu opiate receptors than morphine, but that after chronic treatment, there is no difference between the two agonists in the degree of mu opiate receptors down-regulated. This suggests that during the initial phases of treatment that the degree of tolerance induced by EM-1 is greater than that induced by morphine; however, after chronic treatment, the degree of tolerance induced by the two agonists is similar