Muscarine affects calcium-currents in rat hippocampal pyramidal cells in vitro.

Ca2+-currents were recorded from single CA3 pyramidal cells in hippocampal slice cultures, voltage-clamped through a single Cs+ - or K+-filled microelectrode and perfused with Hanks' balanced salt solution containing 1 microM tetrodotoxin and 10 mM tetraethylammonium. The Ca2+-current was reversibly reduced by bath-perfused muscarine (10-100 microM). This effect was inhibited by pirenzepine (10 microM) or atropine (1 microM). In K+-filled cells, inhibition was preceded by a phase of inward current enhancement; this was considered to be secondary to rapid outward current inhibition induced it by muscarine since it was reduced when outward currents were previously inhibited with Ba2+. In partially clamped or unclamped cells inhibition of Ca2+-current leads to a shortening of the Ca2+-spike plateau.