Gγ7 proteins contribute to coupling of nociceptin/orphanin FQ peptide (NOP) opioid receptors and voltage-gated Ca2+ channels in rat stellate ganglion neurons

Abstract

The nociceptin/orphanin FQ peptide (NOP) opioid receptors regulate neurotransmitter release via inhibition of voltage-gated Ca2+ channels (CaV2.2) in sympathetic and sensory neurons. Stimulation of NOP receptors by its endogenous agonist, nociception (Noc), leads to membrane-delimited, voltage-dependent (VD) block of CaV2.2 channel currents mediated by Gβγ protein subunits. Previously we reported that the pertussis toxin-sensitive Gαi1 and Gβ2/β4 isoforms mediate the functional coupling of NOP opioid receptors with CaV channels in rat stellate ganglion (SG) sympathetic neurons. In the present report we extended our studies by identifying the Gγ subunit that forms the heterotrimer within this signaling pathway. Small interference RNA (or siRNA) was employed to silence the expression of the natively expressed Gγ subunits. Initial PCR assays indicated that SG neurons expressed seven Gγ subunits. Silencing Gγ3 subunits did not alter signaling between NOP receptors and Ca2+ channels. However, after Gγ7 isoforms were silenced, the Noc-mediated inhibition of CaV channels was significantly decreased when compared to SG neurons transfected with scrambled siRNA. We observed that Gγ10 and Gγ11 mRNA levels increased 2.5- and 2.7-fold, respectively, after Gγ7 subunits were silenced. However, this compensatory increase in mRNA expression did not appear to fully rescue the NOP receptor coupling efficiency. Additionally, both Gγ2 and Gγ5 levels increased 50 and 75%, respectively, while Gγ3 and Gγ4 expression levels remained relatively unchanged. Taken together, our findings suggest that the Gαi1/Gβ2(β4)/Gγ7 heterotrimeric G protein complex determines the NOP receptor-mediated modulation of CaV channels in SG neurons.

Gγ identity dictates efficacy of Gβγ signaling and macrophage migration

“…Heterotrimers with specific Gγ types have been shown to possess higher affinities towards certain GPCRs (20,43). However, an exchange of the CT of slow translocating Gγ3 and moderate translocating Gγ12 with the CT of Gγ9 resulted in fast translocating mutants, comparable to Gγ9.…”

Betulinic acid, derived from the desert lavender Hyptis emoryi, attenuates paclitaxel-, HIV-, and nerve injury–associated peripheral sensory neuropathy via block of N- and T-type calcium channels

“…Mechanistically, betulinic acid offers a departure from opioid mechanisms in that first, it lacks perceivable binding to opioid receptors, and second, it targets T-type Ca 2+ channels. While N-type calcium channels have been shown to associate with opioid receptors, there are no reports on specifically linking T-type Ca 2+ channels to opioid signaling pathways [49]. Between 1981 and 2014, 21% (n=326) of all drugs approved by the FDA (n=1562) were natural products and an additional 20% (n=320) were derivatives from natural products [60].…”