Loss of SUR1 subtype KATP channels alters antinociception and locomotor activity after opioid administration

BackgroundOpioid signaling can occur through several downstream mediators and influence analgesia as well as reward mechanisms in the nervous system. KATP channels are downstream targets of the μ opioid receptor and contribute to morphine-induced antinociception.AimsThe aim of the present work was to assess the role of SUR1-subtype KATP channels in antinocicpetion and hyperlocomotion of synthetic and semi-synthetic opioids.MethodsAdult male and female mice wild-type (WT) and SUR1 deficient (KO) mice were assessed for mechanical and thermal antinociception after administration of either buprenorphine, fentanyl, or DAMGO. Potassium flux was assessed in the dorsal root ganglia and superficial dorsal horn cells in WT and KO mice. Hyperlocomotion was also assessed in WT and KO animals after buprenorphine, fentanyl, or DAMGO administration.ResultsSUR1 KO mice had attenuated mechanical antinociception after systemic administration of buprenorphine, fentanyl, and DAMGO. Potassium flux was also attenuated in the dorsal root ganglia and spinal cord cells after acute administration of buprenorphine and fentanyl. Hyperlocomotion after administration of morphine and buprenorphine was potentiated in SUR1 KO mice, but was not seen after administration of fentanyl or DAMGO.ConclusionsThese results suggest SUR1-subtype KATP channels mediate the antinociceptive response of several classes of opioids (alkaloid and synthetic/semi-synthetic), but may not contribute to the “drug-seeking” behaviors of all classes of opioids.

TMIC-18. ELECTRICAL CIRCUIT INTEGRATION OF GLIOMA THROUGH NEURON-GLIOMA SYNAPSES AND POTASSIUM CURRENTS

High-grade gliomas are a lethal group of cancers whose progression is robustly regulated by neuronal activity. Activity-regulated release of growth factors into the tumor microenvironment represents part of the mechanism by which neuronal activity influences glioma growth, but this alone is insufficient to explain the magnitude of the effect that activity exerts on glioma progression. Here, we report that neuron-glioma interactions include electrochemical communication through both bona fide synapses and activity-dependent potassium flux. Single cell transcriptomic analyses revealed unambiguous expression of synaptic genes by malignant glioma cells, and neuron to glioma synaptic structures were evident by electron microscopy. Whole cell patch clamp electrophysiology demonstrated AMPAR-mediated excitatory neurotransmission between pre-synaptic neurons and post-synaptic glioma cells. Millisecond timescale excitatory post-synaptic currents (EPSCs) were found in a subpopulation of glioma cells, reminiscent of the axon-glial synapses between neurons and normal oligodendrocyte precursor cells (OPCs). Neuronal activity also evokes a second, non-synaptic electrophysiological response characterized by a prolonged (>1 sec) depolarization in a subpopulation of glioma cells. These longer duration currents are blocked by tetrodotoxin or barium and induced by potassium, indicating neuronal activity-dependent potassium flux reminiscent of astrocyte currents. The amplitude of the prolonged currents is reduced by gap junction inhibitors, supporting the concept that gap junction-mediated tumor interconnections can function to amplify evoked potassium currents in an electrically coupled network. As membrane depolarization of normal neural precursor cells can regulate proliferation, differentiation and survival, and glioma cells exhibit two distinct mechanisms of neuronal activity-evoked membrane depolarization, we tested the hypothesis that membrane depolarization promotes glioma growth. Using in vivooptogenetic techniques to depolarize xenografted glioma cells, we found that glioma membrane depolarization robustly promoted proliferation, while pharmacologically or genetically blocking electrochemical signaling inhibited glioma xenograft growth and extended mouse survival. Together, these findings indicate that electrical circuit integration promotes glioma progression.

Epigenetic regulation of Kcna3-encoding Kv1.3 potassium channel by cereblon contributes to regulation of CD4+ T-cell activation

The role of cereblon (CRBN) in T cells is not well understood. We generated mice with a deletion in Crbn and found cereblon to be an important antagonist of T-cell activation. In mice lacking CRBN, CD4+ T cells show increased activation and IL-2 production on T-cell receptor stimulation, ultimately resulting in increased potassium flux and calcium-mediated signaling. CRBN restricts T-cell activation via epigenetic modification of Kcna3, which encodes the Kv1.3 potassium channel required for robust calcium influx in T cells. CRBN binds directly to conserved DNA elements adjacent to Kcna3 via a previously uncharacterized DNA-binding motif. Consequently, in the absence of CRBN, the expression of Kv1.3 is derepressed, resulting in increased Kv1.3 expression, potassium flux, and CD4+ T-cell hyperactivation. In addition, experimental autoimmune encephalomyelitis in T-cell–specific Crbn-deficient mice was exacerbated by increased T-cell activation via Kv1.3. Thus, CRBN limits CD4+ T-cell activation via epigenetic regulation of Kv1.3 expression.