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Cloned δ-Opioid Receptors in GH 3 Cells Inhibit Spontaneous Ca 2+ Oscillations and Prolactin Release Through K IR Channel Activation

2000; American Physiological Society; Volume: 83; Issue: 5 Linguagem: Inglês

10.1152/jn.2000.83.5.2691

1522-1598

Elemer T. Piros, Andrew Charles, Lei Song, C. J. Evans, Tim G. Hales,

Ion channel regulation and function

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 δ-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 δ receptor agonist [d-Pen 2 ,d-Pen 2 ]enkephalin (DPDPE) inhibited [Ca 2+ ] i oscillations in GH 3 cells expressing both μ and δ 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.