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Depolarization drives neuronal plasticity. However, whether depolarization drives sensitization of peripheral nociceptive neurons remains elusive. By high-content screening (HCS) microscopy, we revealed that depolarization of cultured sensory neurons rapidly activates protein kinase A type II (PKA-II) in nociceptors by calcium influx through CaV1.2 channels. This effect was modulated by calpains but insensitive to inhibitors of cAMP formation, including opioids. In turn, PKA-II phosphorylated Ser1928 in the distal C terminus of CaV1.2, thereby increasing channel gating, whereas dephosphorylation of Ser1928 involved the phosphatase calcineurin. Patch-clamp and behavioral experiments confirmed that depolarization leads to calcium- and PKA-dependent sensitization of calcium currents ex vivo and local peripheral hyperalgesia in the skin in vivo. Our data suggest a local activity-driven feed-forward mechanism that selectively translates strong depolarization into further activity and thereby facilitates hypersensitivity of nociceptor terminals by a mechanism inaccessible to opioids.

Hyperalgesic priming is characterized by enhanced nociceptor sensitization by pronociceptive mediators, prototypically PGE2. Priming has gained interest as a mechanism underlying the transition to chronic pain. Which stimuli induce priming and what cellular mechanisms are employed remains incompletely understood. In adult male rats, we present the cytokine Oncostatin M (OSM), a member of the IL‐6 family, as an inducer of priming by a novel mechanism. We used a high content microscopy based approach to quantify the activation of endogenous PKA‐II and ERK of thousands sensory neurons in culture. Incubation with OSM increased and prolonged ERK activation by agents that increase cAMP production such as PGE2, forskolin, and cAMP analogs. These changes were specific to IB4/CaMKIIα positive neurons, required protein translation, and increased cAMP‐to‐ERK signaling. In both, control and OSM‐treated neurons, cAMP/ERK signaling involved RapGEF2 and PKA but not Epac. Similar enhancement of cAMP‐to‐ERK signaling could be induced by GDNF, which acts mostly on IB4/CaMKIIα‐positive neurons, but not by NGF, which acts mostly on IB4/CaMKIIα‐negative neurons. In vitro, OSM pretreatment rendered baseline TTX‐R currents ERK‐dependent and switched forskolin‐increased currents from partial to full ERK‐dependence in small/medium sized neurons. In summary, priming induced by OSM uses a novel mechanism to enhance and prolong coupling of cAMP/PKA to ERK1/2 signaling without changing the overall pathway structure. [ABSTRACT FROM AUTHOR]