[Mechanisms of opioid receptor-induced elevation in intracellular calcium by confocal laser scanning microscopy].
OBJECTIVE
To determine the acute and chronic effects of opioid receptor agonists on the intracellular free calcium concentration ([Ca2+]i) in NG-LNCXiNOS cells, stably expressing iNOS gene, and regulation of G-protein on opioid-induced response in [Ca2+]i.


METHODS
A single cell [Ca2+]i is measured by confocal laser scanning microscopy using Ca(2+)-sensitive dye Fluo-3 as an new calcium fluorescent probe.


RESULTS
DPDPE(D-Pen2, D-Pen5-enkephalin), a delta-opioid receptor agonist, and morphine acutely induced the increase in [Ca2+]i of NG-LNCXiNOS cells. The elevation in [Ca2+]i by DPDPE could be abolished with naloxone. Pretreatment of the cells with pertussis toxin (PTX) at 100 ng/ml for 24 hours almost completely blocked morphine-evoked response. In contrast to acute effect of opioid agonists on [Ca2+]i, the cells exposed to 1 mumol/L DPDPE or 10 mumol/L morphine for 48 hours also appeared to raise [Ca2+]i. However, the elevation in [Ca2+]i was not greater than that caused by acute effect of DPDPE or morphine. After cell "withdrawal" was precipitated by the addition of 10 mumol/L naloxone, the increase in [Ca2+]i could further be intensified.


CONCLUSIONS
The opioid agonist-induced increase in [Ca2+]i is mediated by opioid receptor and regulated though PTX-sensitive G-protein. The attenuation of this response in chronically treated cells with opioid agonist is associated with receptor desensitization.
Zang
M
M
Department of Pharmacology, Institute of Basic Medical Sciences, CAMS, PUMC, Beijing 100005, China.
Shen
Q
Q
Sun
Y
Y
Wang
Q
Q
Liu
J
J
D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000502:physiology*; D007424:Intracellular Fluid / Q000378:metabolism*; D018613:Microscopy, Confocal; D009020:Morphine / Q000494:pharmacology*; D009892:Opium / Q000819:agonists; D011957:Receptors, Opioid / Q000187:drug effects / Q000502:physiology*
D011957:Receptors, Opioid; D009020:Morphine; D009892:Opium; D020881:Enkephalin, D-Penicillamine (2,5)-; D019204:GTP-Binding Proteins; D002118:Calcium