Nicotine inhibits slowly inactivating K+ currents in rat cultured striatal neurons.

As shown on cultured striatal neurons recorded in whole-cell configuration, both acetylcholine (in the presence of atropine) and nicotine reduced voltage-dependent outward currents. Although, at early postnatal ages, outward currents in these cells are mainly carried by rapidly and slowly inactivating K+ channels, these inhibitions resulted from a selective and reversible effect on the slowly inactivating K+ conductance (IK+). This action was blocked by the nicotinic antagonist dihydro-beta-erythroïdine and reproduced by nicotinic agonists. When neurons were recorded under current-clamp conditions, nicotine increased reversibly their firing rate generated by step depolarizations. Therefore, in addition to its well documented muscarinic effects, acetylcholine also controls K+ currents in striatal neurons through mechanisms mediated by nicotinic receptors.