Muscarinic (m2/m4) receptors reduce N- and P-type Ca2+ currents in rat neostriatal cholinergic interneurons through a fast, membrane-delimited, G-protein pathway

The signaling pathways mediating the muscarinic modulation of Ca2+ currents in neostriatal cholinergic interneurons were studied by combined patch-clamp recording and single-cell reverse transcription-PCR. Cholinergic interneurons were identified by the presence of choline acetyltransferase mRNA. These neurons expressed Q-, N-, L-, P-, and R-type Ca2+ currents and the mRNA for the alpha 1 subunits believed to form the channels underlying these currents (classes A, B, C, D, and E). Of the interneurons tested, nearly all expressed M2-class (m2, m4) receptor mRNAs, whereas m1 receptor mRNA was found in only a subset (similar to 30%) of the sample. The muscarinic agonist oxotremorine methiodide produced a dose-dependent reduction of N- and P-type Ba2+ currents through Ca2+ channels that was antagonized by atropine. N-ethylmaleimide eliminated the modulation, as did preincubation with pertussis toxin. The onset and offset of the modulation were rapid and dose-dependent. The modulation was also attenuated by strong depolarizing prepulses and was not observed in cell-attached membrane patches. Taken together, our results suggest that activation of M2-class muscarinic receptors in cholinergic interneurons reduces N- and P-type Ca2+ currents through a membrane-delimited pathway using a G(i/o)-class G-protein. This signaling pathway provides a cellular mechanism for hetero- and homosynaptic control of interneuronal activity and acetylcholine release in the striatum.