Inhibition of A-Type K+ Channels by Urotensin-II Induces Sensory Neuronal Hyperexcitability Through the PKCα-ERK Pathway

Abstract

Previous studies have implicated urotensin-II in the nociception of sensory neurons. However, to date the relevant mechanisms remain unknown. In the current study we determined the role of urotensin-II in the regulation of transient outward A-type potassium currents (IA) and neuronal excitability in trigeminal ganglion (TG) neurons. We found that application of urotensin-II to small-diameter TG neurons decreased IA in a dose-dependent manner, whereas the delayed rectifier potassium current was unaffected. The IA decrease induced by urotensin-II depended on the urotensin-II receptor (UT-R) and was associated with a hyperpolarizing shift in the steady-state inactivation curve. Exposure of TG cells to urotensin-II markedly increased protein kinase C (PKC) activity, and PKC inhibition eliminated the UT-R-mediated IA decrease. Antagonism of PKCα, either pharmacologically or genetically, but not of PKCβ prevented the decrease in IA induced by urotensin-II. Analysis of phospho-extracellular signal-regulated kinase (p-ERK) revealed that urotensin-II significantly increased the expression level of p-ERK, whereas p-p38 and p-c-Jun N-terminal kinase remained unchanged. Inhibition of mitogen-activated protein kinase/ERK signaling by the kinase antagonist U0126 and PD98059 completely abolished the UT-R-mediated IA decrease. Moreover, urotensin-II significantly increased the action potential firing rate of small TG neurons; pretreatment with 4-aminopyridine prevented this effect. In summary, our findings suggest that urotensin-II selectively attenuated IA through stimulation of the PKCα-dependent ERK1/2 signaling pathway. This UT-R-dependent mechanism might contribute to neuronal hyperexcitability in TG neurons.

Electrical stimulation of the superior sagittal sinus suppresses A-type K+ currents and increases P/Q- and T-type Ca2+ currents in rat trigeminal ganglion neurons

“…4f and g). The I A in sensory neurons is thought to be mediated by Kv1.4, Kv3.4, Kv4.1, Kv4.2, and Kv4.3 channels, among which the Kv4.2 subunit is negligibly expressed [25, 41–43]. In this study, we examined the expression of Kv4 subunits (Kv4.1, Kv4.2, and Kv4.3) as well as that of Kv1.4 and Kv3.4 in rat TG tissues by RT-PCR analysis (Fig.…”

“…Previous studies have suggested the differential expression profile of Kv subunits in different classes of sensory neurons. The I A in sensory neurons is thought to be mediated by Kv1.4, Kv3.4, Kv4.1, Kv4.2, and Kv4.3 channels [25, 41, 42]. Interestingly, both strong Kv4.3 immunoreactivity in small-sized TG neurons [42] and a large number Kv1.4-positive neurons in the TGs [56] have been reported.…”

“…Immunoblot analysis was conducted as described in our previous studies [23–25]. Briefly, equal amounts of proteins (25 μg) were separated by 10% SDS–PAGE and electroblotted onto PVDF membranes (Merck Millipore).…”

“…A standard immunohistochemistry procedure was performed as described in our previous studies [25, 26]. Briefly, after tissues were sectioned (10-μm thickness) on a cryostat (CM 1950; Leica), TG and TNC sections were blocked with 5% normal goat serum in phosphate buffer saline (PBS) plus 0.15% Triton X-100 for 1 h and then incubated overnight in a primary antibody against NeuN (neuronal marker, rabbit, 1: 500, Abcam) or calcitonin gene-related peptide (CGRP) (mouse, 1: 500, Abcam).…”

Melanocortin type 4 receptor–mediated inhibition of A-type K+ current enhances sensory neuronal excitability and mechanical pain sensitivity in rats

“…I A encoded by Kv channels plays pivotal roles in modulating membrane excitability in multiple excitable cell types, including TG neurons (15,23). To determine the functional roles of the I A decrease mediated by MC4R activation, we investigated whether ␣-MSH application might affect the neuronal excitability.…”