Epac and Nociceptor Sensitization

Primary sensory neurons are responsible for transmitting sensory information from the peripheral to the central nervous system. Their responses to incoming stimulation become greatly enhanced and prolonged following inflammation, giving rise to exaggerated nociceptive responses and chronic pain. The inflammatory mediator, prostaglandin E2 (PGE2), released from the inflamed tissue surrounding the terminals of sensory neurons contributes to the abnormal pain responses. PGE2 acts on G-protein coupled EP receptors to activate adenylyl cyclase (AC), which catalyzes the conversion of adenosine triphosphate (ATP) to cyclic adenosine 3',5'-monophosphate (cAMP). Under normal conditions, cAMP activates primarily protein kinase A (PKA). After inflammation, cAMP also activates the exchange proteins activated by cAMP (Epacs) to produce exaggerated PGE2-mediated hyperalgesia. The role of cAMP-Epac signaling in the generation of hypersensitivity is the topic of this review.