Selective sensitization of C-fiber nociceptors by hydrogen sulfide.

We examined the effects of intraplantar (i.pl.) administration of NaHS, an H2S donor, known to cause T-type Ca(2+) channel (T-channel)-dependent mechanical hyperalgesia, on responsiveness to electric stimulation with 5, 250 and 2000 Hz sine waves (SW) that selectively excites C, Aδ and Aß fibers, respectively. NaHS, given i.pl., caused behavioral hypersensitivity to SW stimulation at 5 Hz, but not 250 or 2000 Hz, in rats. NaHS also enhanced phosphorylation of spinal ERK following 5 Hz SW stimulation. Three distinct T-channel blockers abolished the NaHS-induced behavioral hypersensitivity to 5 Hz SW stimulation. Thus, H2S selectively sensitizes C-fiber nociceptors via T-channels.

AKAP-dependent sensitization of Ca(v) 3.2 channels via the EP(4) receptor/cAMP pathway mediates PGE(2) -induced mechanical hyperalgesia.

BACKGROUND AND PURPOSE: The Ca(v) 3.2 isoform of T-type Ca(2+) channels (T channels) is sensitized by hydrogen sulfide, a pro-nociceptive gasotransmitter, and also by PKA that mediates PGE(2) -induced hyperalgesia. Here we examined and analysed Ca(v) 3.2 sensitization via the PGE(2) /cAMP pathway in NG108-15 cells that express Ca(v) 3.2 and produce cAMP in response to PGE(2) , and its impact on mechanical nociceptive processing in rats. EXPERIMENTAL APPROACH: In NG108-15 cells and rat dorsal root ganglion (DRG) neurons, T-channel-dependent currents (T currents) were measured with the whole-cell patch-clamp technique. The molecular interaction of Ca(v) 3.2 with A-kinase anchoring protein 150 (AKAP150) and its phosphorylation were analysed by immunoprecipitation/immunoblotting in NG108-15 cells. Mechanical nociceptive threshold was determined by the paw pressure test in rats. KEY RESULTS: In NG108-15 cells and/or rat DRG neurons, dibutyryl cAMP (db-cAMP) or PGE(2) increased T currents, an effect blocked by AKAP St-Ht31 inhibitor peptide (AKAPI) or KT5720, a PKA inhibitor. The effect of PGE(2) was abolished by RQ-00015986-00, an EP(4) receptor antagonist. AKAP150 was co-immunoprecipitated with Ca(v) 3.2, regardless of stimulation with db-cAMP, and Ca(v) 3.2 was phosphorylated by db-cAMP or PGE(2) . In rats, intraplantar (i.pl.) administration of db-cAMP or PGE(2) caused mechanical hyperalgesia, an effect suppressed by AKAPI, two distinct T-channel blockers, NNC 55-0396 and ethosuximide, or ZnCl(2) , known to inhibit Ca(v) 3.2 among T channels. Oral administration of RQ-00015986-00 suppressed the PGE(2) -induced mechanical hyperalgesia. CONCLUSION AND IMPLICATIONS: Our findings suggest that PGE(2) causes AKAP-dependent phosphorylation and sensitization of Ca(v) 3.2 through the EP(4) receptor/cAMP/PKA pathway, leading to mechanical hyperalgesia in rats.