Co-incident signalling between µ-opioid and M3-muscarinic receptors at the level of Ca2+ release from intracellular stores: Lack of evidence for InsP3 receptor sensitisation

DSK Samways, W-H Li, Stuart John Conway, AB Holmes, MD Bootman, G Henderson

Research output: Contribution to journalArticlepeer-review

16 Citations (Scopus)

Abstract

Activation of G(i)/G(o)-coupled opioid receptors increases [Ca2+](i) (intracellular free-Ca2+ concentration), but only if there is concomitant G(q)-coupled receptor activation. This G(i)/G(o)-coupled receptor-mediated [Ca2+](i) increase does not appear to result from further production of InsP(3) [Ins(1,4,5)P-3] in SH-SY5Y cells. In the present study, fast-scanning confocal microscopy revealed that activation of mu-opioid receptors alone by I muM DAMGO ([D-Ala, NMe-Phe, Gly-ol]-enkephalin) did not stimulate the InsP(3)-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 muM carbachol. We next determined whether mu-opioid receptor activation might increase [Ca2+](i) by sensitizing the InSP3 receptor to InsP(3). DAMGO did not potentiate the amplitude of the [Ca2+](i) increase evoked by flash photolysis of the caged InsP(3) receptor agonist, caged 2,3-isopropylidene-InsP(3), whereas the InsP(3) receptor sensitizing agent, thimerosal (10 muM), 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-InsP(3). Furthermore, DAMGO did not increase [Ca2+](i) in the presence of the cell-membrane-permeable InsP(3) receptor agonist, InsP(3) hexakis(butyryloxymethyl) ester. Therefore it appears that mu-opioid receptors do not increase [Ca2+](i) through either InsP(3) receptor sensitization, enhancing the releasable pool of Ca2+ or inhibition of Ca2+ removal from the cytoplasm.

Original languageEnglish
Pages (from-to)713-750
Number of pages8
JournalBiochemical Journal
Volume375
DOIs
Publication statusPublished - 1 Nov 2003

Keywords

  • Ca2+
  • G-protein
  • InSP3
  • mu-opioid
  • INOSITOL 1,4,5-TRISPHOSPHATE RECEPTOR
  • BETA-GAMMA-SUBUNITS
  • HUMAN NEUROBLASTOMA-CELLS
  • SENSITIVE G-PROTEINS
  • PHOSPHOLIPASE-C
  • CROSS-TALK
  • HELA-CELLS
  • THIOL REAGENT
  • SH-SY5Y CELLS
  • CALCIUM

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