Opioid inhibition of nicotine-induced 45Ca2(+)-uptake into cultured bovine adrenal medullary cells.
The ability of a number of opioid agonists and antagonists to affect nicotine-induced 45Ca2(+)-uptake into cultured bovine adrenal medullary cells has been investigated. High (10 microM) concentrations of the opioid agonist bremazocine produced a significant inhibition of nicotine-induced 45Ca2(+)-uptake throughout the 15 min time course examined. The opioid subtype-selectivity of this inhibition was investigated; mu and delta selective agonists produced only minor effects whereas the kappa selective agonist U50-488H and the endogenous opioid peptides dynorphin(1-13) and metorphamide almost abolished nicotine-induced 45Ca2(+)-uptake. The U50-488H inhibition was significant at 10 nM concentrations with an IC50 of approximately 1 microM. U50-488H inhibition could not be reversed or reduced by the opioid antagonists naxolone, diprenophine or Mr2266. Furthermore, Mr2266 and its optical isomer Mr2267 also produced marked inhibition of 45Ca2(+)-uptake. The inhibition was specific to nicotine-induced 45Ca2(+)-uptake in that a similar level of uptake evoked by potassium depolarization was unaffected by high concentrations of U50-488H. These data indicate that opioid inhibition of nicotine-induced 45Ca2(+)-uptake does not involve classical, stereospecific opioid receptors and suggests the involvement of a pharmacologically distinct opioid recognition site. It is speculated that this may be associated with the nicotine receptor-ionophore complex.
Bunn
S J
SJ
Neuroscience Group, Faculty of Medicine, University of Newcastle, NSW, Australia.
Dunkley
P R
PR
D000313:Adrenal Medulla / Q000187:drug effects*; D000818:Animals; D001575:Benzomorphans / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D002838:Chromaffin System / Q000187:drug effects; D004399:Dynorphins / Q000494:pharmacology; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004743:Enkephalin, Leucine / Q000031:analogs & derivatives*; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives / Q000494:pharmacology; D004745:Enkephalins / Q000494:pharmacology; D009538:Nicotine / Q000037:antagonists & inhibitors*; D009842:Oligopeptides / Q000494:pharmacology
D001575:Benzomorphans; D004745:Enkephalins; D009842:Oligopeptides; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004744:Enkephalin, Methionine; D004743:Enkephalin, Leucine; D009538:Nicotine; D004399:Dynorphins; C034318:enkephalin, Ser(2), Leu(5), Thr(6)-; C039700:adrenorphin; C027248:bremazocine; D002118:Calcium