Opiate modulation of dynorphin conversion in primary cultures of rat cerebral cortex.
Rat brain cortical cells in primary culture were used to investigate long-term effects of opiates on endopeptidases acting on dynorphin peptides. Enzyme activity in the soluble fraction of the cells converted dynorphin B to Leu-enkephalin-Arg6 and to a lesser extent to Leu-enkephalin. Five day treatment with 10 microM morphine increased the conversion to Leu-enkephalin-Arg6 by 370%. This effect was prevented by the presence of naloxone in the culture medium. The opiate-inducible activity was directed to the Arg-Arg bond in dynorphins with preference for dynorphin B > alpha-neoendorphin > > dynorphin A. The Km for the generation of Leu-enkephalin-Arg6 from dynorphin B was 40 microM. Enzyme activity was inhibited by dynorphin fragments, in the following order of potency: dynorphin A(1-13) > A(2-13) > A(1-17) > A(2-17) and by SH-reagents, suggesting the presence of a cysteine-protease. The opiate-stimulated dynorphin-converting enzyme (DCE)-activity affects the balance between dynorphin peptides (selective for kappa-opioid receptors) and enkephalin peptides (selective for delta-opioid receptors). Since both types of opioid peptides can influence the development of opiate tolerance, the change in the extent of this transformation may be functionally important.
Vlaskovska
M
M
Department of Clinical Neuroscience, Karolinska Institute, Stockholm, Sweden.
Nylander
I
I
Schramm
M
M
Hahne
S
S
Kasakov
L
L
Silberring
J
J
Terenius
L
L
D000818:Animals; D002478:Cells, Cultured / Q000187:drug effects; D002540:Cerebral Cortex / Q000187:drug effects* / Q000378:metabolism; D004399:Dynorphins / Q000378:metabolism*; D007150:Immunohistochemistry; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology*; D009294:Narcotics / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D009294:Narcotics; D009270:Naloxone; D004399:Dynorphins; D009020:Morphine