Antinociceptive effect of selective G protein-gated inwardly rectifying K+ channel agonist ML297 in the rat spinal cord

Abstract

The G protein-gated inwardly rectifying K + (GIRK) channels play important signaling roles in the central and peripheral nervous systems. However, the role of GIRK channel activation in pain signaling remains unknown mainly due to the lack of potent and selective GIRK channel activators until recently. The present study was designed to determine the effects and mechanisms of ML297, a selective GIRK1/2 activator, on nociception in the spinal cord by using behavioral studies and whole-cell patch-clamp recordings from substantia gelatinosa (SG) neurons. Rats were prepared for chronic lumber catheterization and intrathecal administration of ML297. The nociceptive flexion reflex was tested using an analgesy-meter, and the influence on motor performance was assessed using an accelerating rotarod. We also investigated pre- and post-synaptic actions of ML297 in spinal cord preparations by whole-cell patch-clamp recordings. Intrathecal administration of ML297 increased the mechanical nociceptive threshold without impairing motor function. In voltage-clamp mode of patch-clamp recordings, bath application of ML297 induced outward currents in a dose-dependent manner. The ML297-induced currents demonstrated specific equilibrium potential like other families of potassium channels. At high concentration, ML297 depressed miniature excitatory postsynaptic currents (mEPSCs) but not their amplitude. The ML297-induced outward currents and suppression of mEPSCs were not inhibited by naloxone, a μ-opioid receptor antagonist. These results demonstrated that intrathecal ML297 showed the antinociceptive effect, which was mediated through direct activation of pre- and post-synaptic GIRK channels. Selective GIRK channel activation is a promising strategy for the development of new agents against chronic pain and opioid tolerance.

Next-generation inward rectifier potassium channel modulators: discovery and molecular pharmacology

“…Since its discovery, ML297 and other more recently discovered GIRK activators have been used by a number of groups to probe the function of GIRK channels in isolated cells, tissues, and in vivo. These studies include demonstration that pharmacologically increasing the activity of GIRK channels can produce efficacy rodent models of numerous disorders: anti-seizure (88,94,95), anxiolytic (90,96), anti-nociceptive (97,98), facilitation of conditioned fear extinction (93), promotion of non-REM sleep (99), and rescue of amyloid-b-evoked deficits in hippocampal function (100,101). These tools have also been used extensively to probe GIRK's role in wide variety of systems (102)(103)(104)(105)(106)(107)(108)(109)(110)(111).…”

GABA excitatory actions in cerebrospinal-fluid contacting neurones of adult mouse spinal cord

“…We further investigated the mechanisms underlying the lack of GABA B receptors-dependent K + currents, assuming that GIRK channels are not expressed in spinal CSF-cNs. To test this hypothesis, we applied on spinal CSF-cNs ML297, a direct and selective activator of GIRK1/2 channels, the most abundant neuronal GIRK channels (Gonzalez et al ., 2018; Kimura et al ., 2020; Luo et al ., 2022). However, ML297 failed to elicit an increase in the holding currents in CSF-cNs ( Fig.…”

“…6B ; n = 11). In contrast and in agreement with previous reports (Kangrga et al ., 1991; Kimura et al ., 2020), bath application of baclofen (100 μM) or ML297 (100 μM) induced an outward K + currents in DH VGAT + neurones with amplitudes of respectively 38.8 ± 22.2 pA (n = 12) and 34.8 ± 21.2 pA (n = 7) ( Fig. 6Ca and Cb ), which confirms the potent modulator effect of ML297 on GIRK channels.…”

Exploring the Painless Nature and Potential Mechanisms of Asymptomatic Irreversible Pulpitis: A Narrative Review

“…GIRK are G protein-activated effector ion channels [83] that participate in opioid-mediated antinociception in the CNS and PNS via hyperpolarization of the neuronal membrane, which in turn inhibits the propagation of action potentials [84][85][86][87][88][89][90]. At the spinal cord level, these receptors contribute to the analgesic effects of MOR and DOR but not those of KOR [88].…”