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Murine splenocytes express a naloxone-insensitive binding site for beta-endorphin
N A Shahabi1, K M Linner, B M Sharp
1Endocrine-Neuroscience Research Laboratory, Minneapolis Medical Research Foundation, Minnesota.
Endocrinology
|March 1, 1990
Summary
Normal mouse splenocytes can develop naloxone-insensitive beta-endorphin binding sites after culture. These sites exhibit unique characteristics distinct from brain opioid receptors, suggesting a potential functional role for N-acetyl-beta-endorphin.
Area of Science:
- Immunology
- Neuroendocrinology
- Cell Biology
Background:
- Naloxone-resistant binding sites for beta-endorphin were previously identified on transformed immune cells.
- These sites may mediate naloxone-insensitive immunomodulatory effects of beta-endorphin.
Purpose of the Study:
- To investigate the presence of these binding sites on normal murine splenocytes.
- To characterize the nature and properties of these beta-endorphin binding sites.
Main Methods:
- Radioligand binding assay using [125I]beta-endorphin on cultured murine splenocytes.
- Scatchard analysis to determine binding parameters.
- Competition studies with various beta-endorphin fragments and opioid ligands.
- Covalent cross-linking followed by gel electrophoresis.
Main Results:
- High-affinity, saturable binding sites for beta-endorphin were inducible on cultured normal splenocytes.
- Scatchard analysis revealed a single binding site with a Kd of 4.1 X 10(-9) M.
- N-acetyl-beta-endorphin was equipotent to beta-endorphin, while certain fragments and naloxone were ineffective.
- Covalent cross-linking identified protein bands at 66K and 57K.
Conclusions:
- Normal mouse splenocytes can develop inducible, high-affinity, naloxone-insensitive beta-endorphin binding sites.
- These sites display distinct competition characteristics compared to brain opioid receptors.
- N-acetyl-beta-endorphin may be biologically active at these novel sites.