Orexins Activates Protein Kinase C-Mediated Ca^sup 2+^ Signaling in Isolated Rat Primary Sensory Neurons

Previous results have suggested that orexins causes a rise of intracellular free calcium ([Ca^sup 2+^]^sub i^) in cultured rat dorsal root ganglion (DRG) neurons, implicating a role in nociception, but the underlying mechanism is unknown. Hence, the aim of the present study was to investigate whether the orexins-mediated signaling involves the PKC pathways in these sensory neurons. Cultured DRG neurons were loaded with 1 µmol Fura-2 AM and [Ca^sup 2+^]^sub i^ responses were quantified by the changes in 340/380 ratio using fluorescence imaging system. The orexin-1 receptor antagonist SB-334867-A (1 µM) inhibited the calcium responses to orexin-A and orexin-B (59.1±5.1 % vs. 200 nM orexin-A, n=8, and 67±3.8 % vs. 200 nM orexin-B, n=12, respectively). The PKC inhibitor chelerythrine (10 and 100 µM) significantly decreased the orexin-A (200 nM)-induced [Ca^sup 2+^]^sub i^ increase (59.4±4.8 % P