Effects of nicotine on K+ currents and nicotinic receptors in astrocytes of the hippocampal CA1 region.

Nicotine, the main addictive substance in tobacco, interacts with muscle and neuronal nicotinic acetylcholine receptors (nAChRs) that are also localized in astrocytes. We studied electrical effects elicited by nicotine in cultured astrocytes from the CA1 area of the rat hippocampus. Nicotine elicited different types of responses: sustained inward currents, decaying inward currents, and biphasic responses (an outward, followed by an inward current). Nicotine showed two opposite effects, an increase or a decrease of astrocyte membrane conductance, when voltage ramps were applied during sustained inward currents. The former was isolated by blocking K+ currents with Cs+ and was inhibited by mecamylamine. The latter was mimicked by tetraethylammonium ion, and was obtained in the presence of nAChR antagonists (mecamylamine, methyllycaconitine plus dihydro-beta-erythroidine). Thus, these results indicate that nicotine activates nAChRs and directly inhibits K+ currents in cultured astrocytes from the CA1 region of the rat hippocampus.