Résumé :
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Communication n° 47 Unsuccessful regeneration of sensory neurons following nerve injury leads not only to ataxia but is also associated to persistent spontaneous electrical activity that plays an important role in the occurrence and maintenance of pain-related behavior. The molecular determinants of sensory neurons regeneration are not identified. We have previously shown that prior sciatic nerve injury in vivo to promote regenerative mode of growth of sensory neurons in vitro induced an up-regulation of a calcium-activated chloride current, ICl(Ca), expression in mecanoreceptors and proprioceptors neurons. This up-regulation correlated with nerve regeneration (Andre et al., 2003, J.Neurophysiol.). To date the role of ICl(Ca) in the regeneration of sensory neurons is unknown. In this study we have investigated the Ca2+-dependence of Ca2+-activated Cl- current in relation with the electrical activity of regenerating sensory neurons. Primary cultures were obtained from L4-L6 lumbar dorsal root ganglia of adult mice 5 to 10 days after sciatic nerve sectioning. The whole-cell patch-clamp technique combined with Ca2+ fluorescence measurements were used to record electrical activity or ionic currents associated with intracellular Ca2+ transients. We show that regenerating sensory neurons displayed an increase in excitability, among which 25% develop a propensity to fire repetitively. Analysis of the Ca2+-dependence of Ca2+-activated Cl- current shows that Ca2+ sensitivity of this Cl- current does not allow its activation upon one action potential but necessitates an intracellular Ca2+ load that was achieved under high frequency electrical activity. Moreover, depolarizing effects of Ca2+-dependent Cl- current activation could be observed exclusively under action potential lengthening following K+ currents inhibition. Our results suggest that repetitive activity induces primarily Cl- ion extrusion through activation of Ca2+-dependent Cl- current. The role of this current as a modulator of neuronal excitability following nerve injury is under the control of environmental factors that modulate K+ channels
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