Title

 

Authors

P. Ambrosino¹, M.V. Soldovieri¹, D. Presutti¹, M. Taglialatela<sup>1,2

1</sup>Department of Health Sciences, University of Molise, Campobasso, Italy; ²Division of Pharmacology, Department of Neuroscience, University of Naples “Federico II”, Naples, Italy

 

Abstract

Kv7.2-5 potassium channels are the molecular basis of the M-current, a repolarizing current playing a pivotal role in the regulation on neuronal excitability in central and peripheral neurons. Kv7 channels are currently regarded as attractive targets for pharmacological therapy against hyperexcitability diseases such as inflammatory and neuropathic pain (Barrese et al., 2010). In fact, Kv7 channels expression has been detected in nociceptive neurons of the ganglia and of the spinal cord; drug-induced activation of Kv7 channels inhibited C and Adelta fiber-mediated responses of dorsal horn neurons evoked by natural or electrical afferent stimulation (Passmore et al., 2003). Moreover, Kv7 channels are present on axons of unmyelinated, including nociceptive, peripheral human nerve fibers: activation of these channels reduced the ectopic generation of action potentials in neuropathic pain (Lang et al., 2008). In addition, the partial inhibition of Kv7 channels in sensory neurons mediates a significant part of the nociceptive effects of inflammatory and pain-inducing mediators such as exogenous proteases and bradykinin (Linley et al., 2008; Liu et al., 2010). Recently, a decreased expression of Kv7 channels has been shown to contribute to neuropathic hyperalgesia following partial sciatic nerve ligation (Rose et al., 2011). In the present study we have investigated whether the activation of Kv7 channels could affect the changes in intracellular Ca²⁺ concentrations ([Ca²⁺]_i) prompted by pain-inducing stimuli such as bradykinin (BK) or capsaicin (CPS) in sensory neurons. To this aim, Ca²⁺-imaging experiments in differentiated mouse neuroblastoma/rat dorsal root ganglionic hybrid neurons (F11 cells), a widely used cellular model for nociceptive responses, were performed. Moreover, compounds displaying a certain degree of selectivity against distinct Kv7 subunits were used to attempt to distinguish their potential contribution. A 20 sec exposure of F11 cells to BK (250 nM) induced a transient increase in [Ca²⁺]_i of about 400% over basal levels. This [Ca²⁺]_i increase appeared to depend mostly on extracellular Ca²⁺ influx, since the removal of Ca²⁺ ions from the extracellular solution reduced the BK-induced Ca²⁺ response by about 80%. BK-induced [Ca²⁺]_i increase was significantly reduced by all Kv7 openers tested: retigabine (a pan-Kv7 opener), ICA-27243 (a relatively selective Kv7.2/3 opener), and S1 (a relatively selective Kv7.4/5 opener) reduced the BK-induced [Ca²⁺]_i response by about 60%, 57% and 36%, respectively. These effects were completely reversed by co-exposure with the Kv7 blocker XE991 (10 µM). Similarly, when F11 cells were exposed to 50 µM CPS, a stronger increase in the [Ca²⁺]_i was measured (500% of the basal levels), which was largely reversed by the selective TRPV1 antagonist capsazepine. Co-application with 10 µM Retigabine, ICA-27243 or S1 reduced CPS-induced [Ca²⁺]_i response by about 65%, 60% and 32%, respectively. Collectively, these results confirm that drug-induced activation of Kv7 channels can significantly inhibit cellular responses underlying pain sensation, confirming their pivotal role as targets for novel pain treatment strategies.
 
Barrese et al. (2010) Clinical Pharmacology: Advances and Applications 2:225–236.
Passmore et al. (2003) J Neurosci 23(18):7227-7236.
Lang et al. (2008)Neuropharmacology 54(8):1271-1278.
Linley et al. (2008) J Neurosci 28:11240-11249.
Liu et al. (2010) J Clin Invest 120(4):1240-1252.
Rose et al. Pain 2011.in press.