Orexins Activates Protein Kinase C-Mediated Ca2+ Signaling in Isolated Rat Primary Sensory Neurons

Previous results have suggested that orexins causes a rise ofintracellular free calcium ([Ca2+]i) in cultured rat dorsal rootganglion (DRG) neurons, implicating a role in nociception, but theunderlying mechanism is unknown. Hence, the aim of the presentstudy was to investigate whether the orexins-mediated signalinginvolves the PKC pathways in these sensory neurons. CulturedDRG neurons were loaded with 1 μmol Fura-2 AM and [Ca2+]iresponses were quantified by the changes in 340/380 ratio usingfluorescence imaging system. The orexin-1 receptor antagonistSB-334867-A (1 µM) inhibited the calcium responses to orexin-Aand orexin-B (59.1±5.1 % vs. 200 nM orexin-A, n=8, and67±3.8 % vs. 200 nM orexin-B, n=12, respectively). The PKCinhibitor chelerythrine (10 and 100 µM) significantly decreasedthe orexin-A (200 nM)-induced [Ca2+]i increase (59.4±4.8 %P<0.01, n=10 and 4.9±1.6 %, P<0.01, n=9) versus response toorexin-A). It was also found that chelerythrine dose-dependentlyinhibited the [Ca2+]i response to 200 nM orexin-B. In conclusion,our results suggest that orexins activate intracellular calciumsignaling in cultured rat sensory neurons through PKC-dependentpathway, which may have important implications for nociceptivemodulation and pain.