Abstract
Activation of δ-opioid receptors in NG108-15 cells releases Ca2+ from an intracellular store through activation of a pertussis toxin-sensitive G protein. We tested the hypothesis that activation of δ-opioid receptors mobilizes inositol 1,4,5-trisphosphate (IP3)-sensitive Ca2+stores via liberation of Gβγ. Fura-2-based digital imaging was used to study the mechanism of opioid-induced increases in [Ca2+]i in NG108-15 cells. Exposure tod-Ala2-d-Leu5enkephalin (100 nM) for 90 s induced increases in [Ca2+]i that were blocked by microinjection of the IP3 receptor antagonist heparin (pipette concentration = 100 mg/ml) but not by sham injection. Microinjection of a peptide that binds Gβγ (QEHA, 1 mM) decreased the d-Ala2-d-Leu5enkephalin-evoked response. Microinjection of an inactive peptide (SKEE, 1 mM) that does not bind to Gβγ failed to inhibit the opioid-induced increase in [Ca2+]i. Microinjection of a peptide (QLKK, 15 mM) that binds to free Gαq blocked the increase evoked by 3 nM bradykinin, but microinjection of an inactive peptide (ADRK, 15 mM) did not. Microinjection of QLKK did not significantly affect the opioid-induced increase in [Ca2+]i. Collectively, these data demonstrate that activation of δ-opioid receptors induces the release of Ca2+ from IP3-sensitive stores in NG108-15 cells through activation of the βγ subunits of inhibitory G proteins.
Footnotes
- Received May 18, 1999.
- Accepted August 5, 1999.
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Send reprint requests to: Stanley A. Thayer, Ph.D., Dept. of Pharmacology, University of Minnesota, 3-249 Millard Hall, 435 Delaware St. SE, Minneapolis, MN 55455. E-mail: thayer{at}med.umn.edu
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This work was supported by grants from the National Institute on Drug Abuse (DA07304, DA09293, DA11806) and the National Science Foundation (IBN9723796).
- The American Society for Pharmacology and Experimental Therapeutics
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