Cholecystokinin type B receptor-mediated inhibition of A-type K+ channels enhances sensory neuronal excitability through the phosphatidylinositol 3-kinase and c-Src-dependent JNK pathway

Shumin Yu,Yuan Wei,Xianyang Zhao,Yufang Sun,Dongsheng Jiang,Xinghong Jiang,Jin Tao,Zhigang Chang,Yuan Zhang

doi:10.1186/s12964-019-0385-8

Abstract

BackgroundCholecystokinin (CCK) is implicated in the regulation of nociceptive sensitivity of primary afferent neurons. Nevertheless, the underlying cellular and molecular mechanisms remain unknown.MethodsUsing patch clamp recording, western blot analysis, immunofluorescent labelling, enzyme-linked immunosorbent assays, adenovirus-mediated shRNA knockdown and animal behaviour tests, we studied the effects of CCK-8 on the sensory neuronal excitability and peripheral pain sensitivity mediated by A-type K+ channels.ResultsCCK-8 reversibly and concentration-dependently decreased A-type K+ channel (IA) in small-sized dorsal root ganglion (DRG) neurons through the activation of CCK type B receptor (CCK-BR), while the sustained delayed rectifier K+ current was unaffected. The intracellular subunit of CCK-BR coimmunoprecipitated with Gαo. Blocking G-protein signaling with pertussis toxin or by the intracellular application of anti-Gβ antibody reversed the inhibitory effects of CCK-8. Antagonism of phosphatidylinositol 3-kinase (PI3K) but not of its common downstream target Akts abolished the CCK-BR-mediated IA response. CCK-8 application significantly activated JNK mitogen-activated protein kinase. Antagonism of either JNK or c-Src prevented the CCK-BR-mediated IA decrease, whereas c-Src inhibition attenuated the CCK-8-induced p-JNK activation. Application of CCK-8 enhanced the action potential firing rate of DRG neurons and elicited mechanical and thermal pain hypersensitivity in mice. These effects were mediated by CCK-BR and were occluded by IA blockade.ConclusionOur findings indicate that CCK-8 attenuated IA through CCK-BR that is coupled to the Gβγ-dependent PI3K and c-Src-mediated JNK pathways, thereby enhancing the sensory neuronal excitability in DRG neurons and peripheral pain sensitivity in mice.

Highlights

Cholecystokinin (CCK) is implicated in the regulation of nociceptive sensitivity of primary afferent neurons
Two main types of outward voltage-gated K+ channel (Kv) currents have been characterized in these nociceptive neurons — the transient A-type K+ channel currents (IA) and the sustained and delayed-rectifier K+ channel currents (IDR) [15, 16]
Using an external solution including Z941 (10 μM) to block T-type channels, we found that 100 nM CCK-8 significantly increased action potential (AP) firing in response to 1-s current injection

Summary

Introduction

Cholecystokinin (CCK) is implicated in the regulation of nociceptive sensitivity of primary afferent neurons. The underlying cellular and molecular mechanisms remain unknown. In vitro experiments have suggested that CCK might regulate the sensitivity of nociceptive sensory neurons [4], where CCK-BRs were abundantly expressed [5, 6]. It has been established that the elevated level of CCK mRNA in the dorsal root ganglia (DRG) induced by peripheral nerve injury sensitizes and excites primary afferent sensory neurons, leading to pain hypersensitivity [7], with the application of CCK inducing pronociceptive effects [8]. The mechanisms underlying the CCK-mediated hyperalgesia still remain unclear

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Conclusion