G-Protein Beta-Gamma Subunits Inhibit the Heat-Sensitive TRPM3 Ion Channels

Abstract

Transient Receptor Potential Melastatin 3 (TRPM3) is a heat-activated non-selective, Ca2+ permeable cation channel also stimulated by chemical agents such as pregnenolone sulphate and CIM0216. Here we show that activation of Gi-coupled cell surface receptors inhibits TRPM3 currents in a mammalian expression system, which was alleviated by co-expression of proteins that bind βγ subunits of heterotrimeric G-proteins (Gβγ). Co-expression of Gβ1γ2, Gβ3γ2, Gβ4γ2, but not Gβ5γ2 or constitutively active mutants of Gαo or Gαi, inhibited pregnenolone sulphate-induced TRPM3 currents. Purified Gβγ proteins applied to excised inside out patches also inhibited TRPM3 activity, indicating a direct effect. Baclofen, somatostatin, and DAMGO, agonists of Gi coupled receptors, inhibited Ca2+ signals induced by pregnenolone sulphate and CIM0216 in dorsal root ganglion (DRG) neurons. The GABAB receptor agonist baclofen also inhibited CIM0216-induced currents in DRG neurons, and nocifensive responses elicited by this TRPM3 agonist in vivo. Our data show that Gβγ inhibits TRPM3 channels upon Gi-coupled receptor activation.