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1 School of Life Sciences, University of Sussex, Brighton, United Kingdom
2 Department of Experimental Zoology, Balaton Limnological Research Institute, Hungarian Academy of Sciences, Tihany, Hungary
3 Medical Research Council Laboratory for Molecular and Cell Biology, University College London, London, United Kingdom; School of Life Sciences, University of Sussex, Brighton, United Kingdom
* To whom correspondence should be addressed. E-mail: G.Kemenes{at}sussex.ac.uk.
We have identified a TTX-resistant low-threshold persistent inward sodium current in the cerebral giant cells (CGCs) of Lymnaea, an important state-setting modulatory cell type of molluscan feeding networks. This current has slow voltage-dependent activation and de-activation kinetics, ultra-slow inactivation kinetics and fast de-inactivation kinetics. It activates at ~ -90 mV, peaks at ~-30 mV, reverses at ~ +35 mV and does not show full voltage-dependent inactivation even at positive voltage steps. Lithium-sodium replacement experiments indicated that the persistent sodium current makes a significant contribution to the CGC membrane potential. Injection of cyclic adenosine monophosphate (cAMP) into the CGC cell body produces a large increase in the persistent sodium current which lasts for several hours. cAMP injection also leads to increased bursting, a significant decrease in the input resistance and a significant depolarization of the soma membrane, indicating that cAMP-dependent mechanisms induce prolonged neuronal plasticity in the CGCs. Our observations provide the first link between cAMP-mediated modulation of a TTX-resistant persistent sodium current and prolonged neuronal plasticity in an identified modulatory cell type that plays an important role in behavioral state setting.
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