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Opiate receptor mediated internalization of 125I-beta-endorphin in human polymorphonuclear leucocytes
Abstract:
The early events in the interaction of (125I)-Tyr27-beta-endorphin with human polymorphonuclear leucocytes were investigated. Using ultrastructural autoradiography we found that the labeled peptide specifically bound to the plasma membrane and was internalized within two minutes of incubation at 37 degrees C. Both processes could be inhibited by unlabeled beta-endorphin or by the opiate antagonist diprenorphine. This finding was confirmed by radioreceptorassays. With longer incubation times the specific association of the labeled beta-endorphin with the cells decreased. About 10% of the tracer was degraded within 10 min of incubation as shown by gel chromatography. The morphological changes induced by 125I-beta-endorphin in the granulocytes were investigated under the microscope. The labeled peptide had the same biological effect as unlabeled beta-endorphin.
Insights
Human polymorphonuclear leucocytes rapidly bind and internalize beta-endorphin at their plasma membrane. This interaction, crucial for cellular response, is blocked by opiate antagonists and unlabeled beta-endorphin.
Area of Science:
- Immunology
- Neuroendocrinology
- Cell Biology
Background:
- Beta-endorphin, a key endogenous opioid peptide, plays roles beyond analgesia, including immune modulation.
- Human polymorphonuclear leucocytes (PMNs) are critical immune cells involved in inflammatory responses.
Purpose of the Study:
- To investigate the early molecular and cellular events of beta-endorphin interaction with human PMNs.
- To characterize the binding, internalization, and biological effects of beta-endorphin on PMNs.
Main Methods:
- Ultrastructural autoradiography to visualize peptide binding and internalization.
- Radioreceptorassays to confirm binding specificity.
- Gel chromatography to assess peptide degradation.
- Microscopic examination to observe morphological changes.
Main Results:
- Labeled beta-endorphin specifically bound to the PMN plasma membrane within minutes.
- Peptide internalization into PMNs was observed.
- Binding and internalization were inhibited by unlabeled beta-endorphin and diprenorphine.
- Approximately 10% of the peptide was degraded within 10 minutes.
- Beta-endorphin induced morphological changes in PMNs, similar to unlabeled peptide.
Conclusions:
- Human PMNs possess specific binding sites for beta-endorphin on their plasma membrane.
- Beta-endorphin is rapidly internalized by PMNs, suggesting a role in cellular signaling.
- The interaction of beta-endorphin with PMNs elicits biological responses, highlighting its immunomodulatory potential.