Transient receptor potential (TRP) ion channels in peripheral sensory neurons are functionally regulated by hydrolysis of the phosphoinositide PI(4,5)P2 and changes in the level of protein kinase mediated phosphorylation following activation of various G protein coupled receptors. We now show that the activity of TRPM3 expressed in mouse dorsal root ganglion (DRG) neurons is inhibited by agonists of the Gi-coupled µ opioid, GABA-B and NPY receptors. These agonist effects are mediated by direct inhibition of TRPM3 by Gβγ subunits, rather than by a canonical cAMP mediated mechanism. The activity of TRPM3 in DRG neurons is also negatively modulated by tonic, constitutive GPCR activity as TRPM3 responses can be potentiated by GPCR inverse agonists. GPCR regulation of TRPM3 is also seen in vivo where Gi/o GPCRs agonists inhibited and inverse agonists potentiated TRPM3 mediated nociceptive behavioural responses.DOI: http://dx.doi.org/10.7554/eLife.26138.001

Transient receptor potential melastatin 3 (TRPM3) is a nonselective cation channel that is inhibited by G␤␥ subunits liberated following activation of G␣ i/o protein-coupled receptors. Here, we demonstrate that TRPM3 channels are also inhibited by G␤␥ released from G␣ s and G␣ q. Activation of the G s-coupled adenosine 2B receptor and the G q-coupled muscarinic acetylcholine M1 receptor inhibited the activity of TRPM3 heterologously expressed in HEK293 cells. This inhibition was prevented when the G␤␥ sink ␤ARK1-ct (C terminus of ␤-adrenergic receptor kinase-1) was coexpressed with TRPM3. In neurons isolated from mouse dorsal root ganglion (DRG), native TRPM3 channels were inhibited by activating G s-coupled prostaglandin-EP2 and G q-coupled bradykinin B2 (BK2) receptors. The G i/o inhibitor pertussis toxin and inhibitors of PKA and PKC had no effect on EP2-and BK2-mediated inhibition of TRPM3, demonstrating that the receptors did not act through G␣ i/o or through the major protein kinases activated downstream of G-protein-coupled receptor (GPCR) activation. When DRG neurons were dialyzed with GRK2i, which sequesters free G␤␥ protein, TRPM3 inhibition by EP2 and BK2 was significantly reduced. Intraplantar injections of EP2 or BK2 agonists inhibited both the nocifensive response evoked by TRPM3 agonists, and the heat hypersensitivity produced by Freund's Complete Adjuvant (FCA). Furthermore, FCA-induced heat hypersensitivity was completely reversed by the selective TRPM3 antagonist ononetin in WT mice and did not develop in Trpm3 ؊/؊ mice. Our results demonstrate that TRPM3 is subject to promiscuous inhibition by G␤␥ protein in heterologous expression systems, primary neurons and in vivo, and suggest a critical role for this ion channel in inflammatory heat hypersensitivity.

Background: Existing anthrax postexposure antibiotic treatments are inadequate because they do not clear the high levels of secreted anthrax toxins. Results: Susceptible cells treated with anthrax toxin receptor-targeted siRNAs became resistant to anthrax toxin-mediated cytotoxicity. Conclusion: RNAi-targeted silencing of anthrax toxin receptors prevents toxins from entering target cells and inducing pathogenesis. Significance: Toxin receptor-targeted RNAi can be developed as a postexposure treatment against anthrax.

Transient receptor potential (TRP) ion channels in peripheral sensory neurons are functionally regulated by hydrolysis of the phosphoinositide PI(4,5)P 2 and changes in the level of protein kinase mediated phosphorylation following activation of various G protein coupled receptors. We now show that the activity of TRPM3 expressed in mouse dorsal root ganglion (DRG) neurons is inhibited by agonists of the G i -coupled m opioid, GABA-B and NPY receptors. These agonist effects are mediated by direct inhibition of TRPM3 by Gbg subunits, rather than by a canonical cAMP mediated mechanism. The activity of TRPM3 in DRG neurons is also negatively modulated by tonic, constitutive GPCR activity as TRPM3 responses can be potentiated by GPCR inverse agonists. GPCR regulation of TRPM3 is also seen in vivo where G i/o GPCRs agonists inhibited and inverse agonists potentiated TRPM3 mediated nociceptive behavioural responses.