生长激素瘤（GH(3)）细胞中克隆的δ阿片受体通过激活内向整流钾（K(IR)）通道抑制自发性钙（Ca(2+)）振荡和催乳素释放。

Piros E T, Charles R C, Song L, Evans C J, Hales T G

Department of Physiology, Cornell University, New York, NY 10021, USA.

J Neurophysiol. 2000 May;83(5):2691-8. doi: 10.1152/jn.2000.83.5.2691.

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+)) and prolactin release. Activation of cloned delta-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 delta receptor agonist [D-Pen(2), D-Pen(2)]enkephalin (DPDPE) inhibited Ca(2+) oscillations in GH(3) cells expressing both mu and delta receptors (GH(3)MORDOR cells) but had no effect on control GH(3) cells or cells expressing mu receptors alone (GH(3)MOR cells). The inhibition of Ca(2+) 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 mu 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+) and prolactin release by DPDPE, whereas TEA had no effect, consistent with an involvement of K(IR) channels in these actions of the opioid.

阿片受体可与钾离子（K⁺）通道、钙离子（Ca²⁺）通道、腺苷酸环化酶以及磷脂酰肌醇代谢相偶联。这些作用中的任何一种在调节可兴奋细胞释放神经递质和激素方面可能都很重要。GH₃细胞表现出细胞内钙离子浓度（[Ca²⁺]i）的自发振荡以及催乳素释放。在GH₃细胞中稳定表达的克隆δ-阿片受体的激活可抑制自发的Ca²⁺信号传导和基础催乳素释放。本研究的目的是使用膜片钳技术、荧光成像以及一种灵敏的催乳素酶联免疫吸附测定法来研究K⁺通道在这些过程中可能发挥的作用。选择性δ受体激动剂[D-青霉胺²，D-青霉胺²]脑啡肽（DPDPE）抑制了同时表达μ和δ受体的GH₃细胞（GH₃MORDOR细胞）中的[Ca²⁺]i振荡，但对对照GH₃细胞或仅表达μ受体的细胞（GH₃MOR细胞）没有影响。DPDPE对[Ca²⁺]i振荡的抑制作用不受毒胡萝卜素预处理的影响，这表明该作用独立于肌醇1,4,5-三磷酸敏感的Ca²⁺储存。DPDPE对GH₃MORDOR细胞催乳素释放产生浓度依赖性抑制，IC₅₀为4 nM。DPDPE增加了从GH₃MORDOR细胞记录到的内向K⁺电流，但对从对照GH₃细胞或GH₃MOR细胞记录到的K⁺电流没有显著影响。μ受体激动剂吗啡对从对照细胞记录到的电流也没有影响，但激活了从GH₃MOR和GH₃MORDOR细胞记录到的内向K⁺电流。生长抑素激活了从所有三种细胞系记录到的内向电流。对DPDPE敏感的K⁺电流是内向整流的，并且被Ba²⁺抑制但不被四乙铵（TEA）抑制。DPDPE对从GH₃MORDOR细胞记录到的延迟整流钾电流、Ca²⁺电流、电压激活钾电流或A型K⁺电流没有影响。Ba²⁺减弱了DPDPE对[Ca²⁺]i和催乳素释放的抑制作用，而TEA没有影响，这与内向整流钾（KIR）通道参与阿片类药物的这些作用一致。