Inflammation alters cation chloride cotransporter expression in sensory neurons.

Cation chloride cotransporters have been proposed to play a role in the modulation of neuronal responses to gamma-aminobutyric acid (GABA). In conditions of neuronal damage, where neuronal excitability is increased, the expression of the KCC2 transporter is decreased. This is also seen in spinal cord in models of neuropathic pain. We have investigated the expression of the Na-K-Cl, and K-Cl cotransporters NKCC1 and KCC2, in dorsal root ganglion (DRG) and spinal sensory neurons during arthritis, a condition in which neuronal excitability is also increased. NKCC1 was expressed in control DRG neurons, and its expression was decreased in arthritis. Both NKCC1 and KCC2 were expressed in sensory neurons in the spinal cord. In acute arthritis, both NKCC1 and KCC2 mRNA increased in superficial but not deep dorsal horn, and this was accompanied by an increase in protein expression. In chronic arthritis, NKCC1 expression remained raised, but KCC2 mRNA and protein expression returned to control levels. Altered KCC2 and NKCC1 expression in arthritis may contribute to the control of spinal cord excitability and may represent novel therapeutic targets in the treatment of inflammatory pain.