Examining The Effects Of Gallein On Opioid Induced GIRK Currents

Abstract

Opioids are powerful analgesics, but carry a risk of overdose that has become a pressing issue to public health in the United States. Overdose deaths are caused by the opioid-induced shutdown of neuronal circuits that operate unconscious breathing cycles, leading to respiratory depression. Respiratory depression, alongside antinociception, is mediated by the activation of μ-opioid receptors, which are coupled to inhibitory heterotrimeric G proteins. Recent studies have shown that gallein, a Gβγ subunit inhibitor, amplifies the antinociceptive effects of opioids through Gq-phospholipase C (PLC) mediated mechanisms, while either attenuating or having no effect on respiratory depression. The molecular mechanisms of gallein effects on respiratory depression are unclear. Based on the binding interface, gallein is predicted to inhibit Gβγ binding to phospholipase C, but not G protein inwardly rectifying potassium channels (GIRK). The goal of this study is to examine the effects of gallein on opioid-induced GIRK currents, with or without Gq subunit activation, in mouse locus coeruleus (LC) neurons. The LC is an area of particular interest due its involvement in respiratory circuits, and activation of Gq-coupled pathways decreases the amplitude of opioid-mediated GIRK currents in LC neurons. We hypothesized that gallein would have no effect on opioid mediated GIRK currents without Gq activation, but would prevent Gq-mediated inhibition of GIRK. We tested this hypothesis using whole-cell voltage-clamp recordings of LC neurons contained in brain slices from adult male and female mice. The endogenous opioid agonist Met-enkephalin induced outward GIRK currents that were not significantly altered by gallein. The Gq-coupled receptor agonist oxotremorine-M reduced the amplitude of Met-enkephalin mediated GIRK currents, as expected. Preliminary data suggests no effect of gallein on GIRK currents in the presence of Gq activation, contrary to our hypothesis. These results will increase our understanding of the role of PLC in Gq-mediated inhibition of GIRK currents at the cellular level and provide insight regarding the potential respiratory related impacts associated with using gallein derived compounds in combination with opioids to increase opioid antinociception and reduce the doses of opioids needed to treat pain. This research is supported by NIH Grant R01DA047978-05 to ESL. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.