Differential contributions of CaV2.2, GIRK, and HCN channels to the modulation of excitability by alpha-conotoxin Vc1.1 and baclofen effects in somatic and visceral sensory neurons

Abstract

Chronic visceral pain is a key symptom of irritable bowel syndrome (IBS). Modulation of voltage-dependent calcium and potassium channels by G protein-coupled receptors (GPCRs) plays a key role in dampening nociceptive transmission. Baclofen and the analgesic peptide -conotoxin Vc1.1 both activate GABAB receptors (GABABR), resulting in the inhibition of CaV2.2 and CaV2.3 calcium channels to reduce colonic nociception. Recent studies have also shown that GABABR activation potentiates GIRK1/2 potassium channels in mammalian sensory afferent neurons. In this study, we investigated the expression of these ion channel targets in rodent and human dorsal root ganglion (DRG) neurons, including those innervating the colon. We also examined how CaV2.2 and GIRK channel antagonists, as well as a GIRK channel activator, affect the passive and active electrical properties of adult mouse DRG neurons. Additionally, we assessed the effects of -conotoxin Vc1.1 on neuronal excitability in the presence of the selective CaV2.2 antagonist {omega}-conotoxin CVIE and the GIRK channel activator ML297. We further evaluated the impact of the GIRK channel antagonist Tertiapin-Q on excitability in mouse colonic DRGs and colonic afferents and explored the role of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels in regulating membrane excitability of colonic DRGs. Our findings demonstrate that both CaV2.2 inhibition and GIRK channel potentiation reduce excitability in mouse DRGs, likely mediating the analgesic effects of Vc1.1 and baclofen observed in vivo. However, our findings indicate that GIRK channel potentiation appears to play a limited role in modulating excitability in colon-innervating DRGs and colonic afferents. These findings suggest that neurons innervating different regions of the body employ distinct mechanisms to regulate neuronal excitability and nociceptive signaling. KEY POINTS SUMMARYO_LIGABABR1, CaV2.2, and GIRK1 are highly expressed in the thoracolumbar dorsal root ganglia (DRGs) of both mice and humans. C_LIO_LIIn mouse DRGs, CaV2.2 inhibition and GIRK channel potentiation contribute to reduced neuronal excitability. C_LIO_LIThe analgesic peptide, -conotoxin Vc1.1 reduces neuronal excitability by inhibiting CaV2.2 and potentiating GIRK channels. C_LIO_LIHowever, potentiation of GIRK channels does not significantly affect the excitability in colon-innervating DRG neurons or colonic afferents. C_LIO_LISensory neurons innervating different body regions utilize distinct mechanisms to regulate their excitability. C_LI