Regulation of the spontaneous augmentation of Na(V)1.9 in mouse dorsal root ganglion neurons: effect of PKA and PKC pathways.

Sensory neurons in the dorsal root ganglion express two kinds of tetrodotoxin resistant (TTX-R) isoforms of voltage-gated sodium channels, Na(V)1.8 and Na(V)1.9. These isoforms play key roles in the pathophysiology of chronic pain. Of special interest is Na(V)1.9: our previous studies revealed a unique property of the Na(V)1.9 current, i.e., the Na(V)1.9 current shows a gradual and notable up-regulation of the peak amplitude during recording ("spontaneous augmentation of Na(V)1.9"). However, the mechanism underlying the spontaneous augmentation of Na(V)1.9 is still unclear. In this study, we examined the effects of protein kinases A and C (PKA and PKC), on the spontaneous augmentation of Na(V)1.9. The spontaneous augmentation of the Na(V)1.9 current was significantly suppressed by activation of PKA, whereas activation of PKA did not affect the voltage dependence of inactivation for the Na(V)1.9 current. On the contrary, the finding that activation of PKC can affect the voltage dependence of inactivation for Na(V)1.9 in the perforated patch recordings, where the augmentation does not occur, suggests that the effects of PMA are independent of the augmentation process. These results indicate that the spontaneous augmentation of Na(V)1.9 was regulated directly by PKA, and indirectly by PKC.