Activation of Gi/Go-coupled opioid receptors increases [Ca2+]i (intracellular free-Ca2+ concentration), but only if there is concomitant Gq-coupled receptor activation. This Gi/Go-coupled receptor-mediated [Ca 2+]i increase does not appear to result from further production of InsP3 [Ins(1,4,5)P3] in SH-SY5Y cells. In the present study, fast-scanning confocal microscopy revealed that activation of μ-opioid receptors alone by 1 μM DAMGO ([D-Ala, NMe-Phe, Gly-ol]-enkephalin) did not stimulate the InsP3-dependent elementary Ca2+-signalling events (Ca2+ puffs), whereas DAMGO did evoke Ca2+ puffs when applied during concomitant activation of M 3 muscarinic receptors with 1 μM carbachol. We next determined whether μ-opioid receptor activation might increase [Ca2+] i by sensitizing the InsP3 receptor to InsP3. DAMGO did not potentiate the amplitude of the [Ca2+]i increase evoked by flash photolysis of the caged InsP3 receptor agonist, caged 2,3-isopropylidene-InsP3, whereas the InsP 3 receptor sensitizing agent, thimerosal (10 μM), did potentiate this response. DAMGO also did not prolong the rate of decay of the increase in [Ca2+]i evoked by flash photolysis of caged 2,3-isopropylidene-InsP3. Furthermore, DAMGO did not increase [Ca2+], in the presence of the cell-membrane-permeable InsP 3 receptor agonist, InsP3 hexakis(butyryloxymethyl) ester. Therefore it appears that μ-opioid receptors do not increase [Ca 2+]i through either InsP3 receptor sensitization, enhancing the releasable pool of Ca2+ or inhibition of Ca2+ removal from the cytoplasm.
|Original language||English (US)|
|Number of pages||8|
|State||Published - Nov 1 2003|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology