Abstract

The voltage-activated T-type calcium channel (Ca_V3.2) and the G protein-coupled neurokinin 1 (NK1) receptor are expressed in peripheral tissues and in central neurons, in which they participate in diverse physiological processes, including neurogenic inflammation and nociception. In the present report, we demonstrate that recombinant Ca_V3.2 channels are reversibly inhibited by NK1 receptors when both proteins are transiently coexpressed in human embryonic kidney 293 cells. We found that the voltage-dependent macroscopic properties of Ca_V3.2 currents were unaffected during NK1 receptor-mediated inhibition. However, inhibition was attenuated in cells coexpressing either the dominant-negative Gα_q Q209L/D277N or the regulator of G protein signaling (RGS) proteins 2 (RGS2) and 3T (RGS3T), which are effective antagonists of Gα_q/11. By contrast, inhibition was unaffected in cells coexpressing human rod transducin (Gα_t), which buffers Gβγ. Channel inhibition was blocked by 1-[6-[[17β-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione (U73122) and bisindolylmaleimide I, selective inhibitors of phospholipase Cβ and protein kinase C (PKC), respectively. Inhibition was occluded by application of the PKC activator phorbol-12-myristate-13-acetate. Altogether, these data indicate that NK1 receptors inhibit Ca_V3.2 channels through a voltage-independent signaling pathway that involves Gα_q/11, phospholipase Cβ, and PKC. Our results provide novel evidence regarding the mechanisms underlying T-type calcium channel modulation by G protein-coupled receptors. Functional coupling between Ca_V3.2 channels and NK1 receptors may be relevant in neurogenic inflammation, neuronal rhythmogenesis, nociception, and other physiological processes.