Cloned delta -Opioid Receptors in GH3 Cells Inhibit Spontaneous Ca2+ Oscillations and Prolactin Release Through KIR Channel Activation

• Published in: Journal of neurophysiology Vol. 83; no. 5; p. 2691
• Main Authors: Piros, Elemer T, Charles, Rew C, Song, Lei, Evans, Chris J, Hales, Tim G
• Format: Journal Article
• Language: English
• Published: Am Phys Soc 01.05.2000
• ISSN: 0022-3077; 1522-1598

  1 Department of Physiology, Cornell University, New York, New York 10021;   2 Department of Neurology, University of California Los Angeles School of Medicine, Los Angeles, California 90095;   3 Department of Pharmacology, The George Washington University, Washington, DC 20037; and   4 Department of Psychiatry, University of California Los Angeles School of Medicine, Los Angeles, California 90095 Piros, Elemer T., Rew C. Charles, Lei Song, Chris J. Evans, and Tim G. Hales. Cloned -Opioid Receptors in GH 3 Cells Inhibit Spontaneous Ca 2+ Oscillations and Prolactin Release Through K IR Channel Activation. J. Neurophysiol. 83: 2691-2698, 2000. Opioid receptors can couple to K + and Ca 2+ channels, adenylyl cyclase, and phosphatidyl inositol turnover. Any of these actions may be important in the regulation of neurotransmitter and hormone release from excitable cells. GH 3 cells exhibit spontaneous oscillations of intracellular Ca 2+ concentration ([Ca 2+ ] i ) and prolactin release. Activation of cloned -opioid receptors stably expressed in GH 3 cells inhibits both spontaneous Ca 2+ signaling and basal prolactin release. The objective of this study was to examine a possible role for K + channels in these processes using the patch-clamp technique, fluorescence imaging, and a sensitive ELISA for prolactin. The selective  receptor agonist [ D -Pen 2 , D -Pen 2 ]enkephalin (DPDPE) inhibited [Ca 2+ ] i oscillations in GH 3 cells expressing both µ and  receptors (GH 3 MORDOR cells) but had no effect on control GH 3 cells or cells expressing µ receptors alone (GH 3 MOR cells). The inhibition of [Ca 2+ ] i oscillations by DPDPE was unaffected by thapsigargin pretreatment, suggesting that this effect is independent of inositol 1,4,5-triphosphate-sensitive Ca 2+ stores. DPDPE caused a concentration-dependent inhibition of prolactin release from GH 3 MORDOR cells with an IC 50 of 4 nM. DPDPE increased inward K + current recorded from GH 3 MORDOR cells but had no significant effect on K + currents recorded from control GH 3 cells or GH 3 MOR cells. The   µ receptor agonist morphine also had no effect on currents recorded from control cells but activated inward K + currents recorded from GH 3 MOR and GH 3 MORDOR cells. Somatostatin activated inward currents recorded from all three cell lines. The DPDPE-sensitive K + current was inwardly rectifying and was inhibited by Ba 2+ but not TEA. DPDPE had no effect on delayed rectifier-, Ca 2+ -, and voltage-activated or A-type K + currents, recorded from GH 3 MORDOR cells. Ba 2+ attenuated the inhibition of [Ca 2+ ] i and prolactin release by DPDPE, whereas TEA had no effect, consistent with an involvement of K IR channels in these actions of the opioid.