RT Journal Article SR Electronic T1 Calcineurin dysregulation underlies spinal cord injury-induced K+ channel dysfunction in DRG neurons JF The Journal of Neuroscience JO J. Neurosci. FD Society for Neuroscience SP 0434-17 DO 10.1523/JNEUROSCI.0434-17.2017 A1 Benjamin M Zemel A1 Tanziyah Muqeem A1 Eric V Brown A1 Miguel Goulão A1 Mark W Urban A1 Stephen R Tymanskyj A1 Angelo C Lepore A1 Manuel Covarrubias YR 2017 UL http://www.jneurosci.org/content/early/2017/07/27/JNEUROSCI.0434-17.2017.abstract AB Dysfunction of the fast-inactivating Kv3.4 potassium current in dorsal root ganglion (DRG) neurons contributes to the hyperexcitability associated with persistent pain induced by spinal cord injury (SCI). However, the underlying mechanism is not known. In light of our previous work demonstrating modulation of the Kv3.4 channel by phosphorylation, we investigated the role of the phosphatase calcineurin (CaN) using electrophysiological, molecular and imaging approaches in adult Sprague-Dawley female rats. Pharmacological inhibition of CaN in small-diameter DRG neurons slows repolarization of the somatic action potential (AP) and attenuates the Kv3.4 current. Attenuated Kv3.4 currents additionally exhibit slowed inactivation. We observed similar effects on the recombinant Kv3.4 channel heterologously expressed in CHO cells, supporting our findings in DRG neurons. Elucidating the molecular basis of these effects, mutation of four previously characterized serines within the Kv3.4 N-terminal inactivation domain eliminated the effects of CaN inhibition on the Kv3.4 current. SCI similarly induces concurrent Kv3.4 current attenuation and slowing of inactivation. Although there is little change in CaN expression and localization after injury, SCI induces upregulation of the native regulator of CaN 1 (RCAN1) in the DRG at the transcript and protein levels. Consistent with CaN inhibition resulting from RCAN1 upregulation, overexpression of RCAN1 in naïve DRG neurons recapitulates the effects of pharmacological CaN inhibition on the Kv3.4 current and the AP. Overall, these results demonstrate a novel regulatory pathway that links CaN, RCAN1 and Kv3.4 in DRG neurons. Dysregulation of this pathway might underlie a peripheral mechanism of pain sensitization induced by SCI.SIGNIFICANCE STATEMENTPain sensitization associated with spinal cord injury (SCI) involves poorly understood maladaptive modulation of neuronal excitability. Although central mechanisms have received significant attention, recent studies have identified peripheral nerve hyperexcitability as a driver of persistent pain signaling following SCI. However, the ion channels and signaling molecules responsible for this change in primary sensory neuron excitability are still not well defined. To tackle this problem, this study employed complementary electrophysiological and molecular methods to determine how Kv3.4, a voltage-gated K+ channel robustly expressed in dorsal root ganglion neurons, becomes dysfunctional upon calcineurin (CaN) inhibition. The results strongly suggest that CaN inhibition underlies SCI-induced dysfunction of Kv3.4 and the associated excitability changes through upregulation of the native regulator of CaN 1 (RCAN1).