GPR35 modulates Nav1.9 gating and sensory neuron excitability

Background and Purpose: The voltage-gated Na ⁺ channel Na _V1.9 is a determinant of excitability in sensory neurons, yet the upstream G-protein–coupled receptors (GPCRs) that regulate its activity remain poorly defined. Here, we identify GPR35 as a modulator of Na _V1.9 function in dorsal root ganglion (DRG) neurons, establishing a previously unrecognized receptor–channel signalling axis. Experimental Approach: Transcriptomics of Na _V1.9-expressing neurons, proximity ligation assays, patch-clamp electrophysiology in primary mouse DRG neurons and a genetic mouse model were combined to assess spatial and functional relationships between GPR35 and Na _V1.9. Pharmacological activation of GPR35 was examined using cromolyn disodium, whereas zaprinast and sildenafil were used to probe potential cGMP-dependent mechanisms. Key Results: GPR35 transcripts were enriched in Na _V1.9-positive neurons and proximity assays demonstrated spatial association between both proteins in DRG neurons. Activation of GPR35 with cromolyn disodium potentiated Na _V1.9 currents, accelerated channel gating and modified neuronal excitability, reflected by increased action potential overshoot and upstroke velocity. These effects were absent from GPR35-deficient DRG neurons. Zaprinast and the phosphodiesterase-5 inhibitor sildenafil also potentiated Na _V1.9 currents in a GPR35-dependent manner, indicating that cGMP-associated signalling requires GPR35 expression to influence Na _V1.9. Under inflammatory conditions induced by prostaglandin E ₂, GPR35 activation partially attenuated Na _V1.9 potentiation but did not restore normal excitability. Conclusion and Implications: These findings identify GPR35 as a regulator of Na _V1.9 and define a receptor–channel signalling module linking GPCR activation to ion channel–dependent modulation of sensory neuron excitability. This work provides a mechanistic framework for understanding GPCR–Na _V1.9 coupling.