• KCNQ1-4 potassium channels were expressed in mammalian Chinese hamster ovary (CHO) cells stably transfected with M1 muscarinic acetylcholine receptors and currents were recorded using the whole-cell perforated patch technique and cell-attached patch recording.

  • Stimulation of M1 receptors by 10 μm oxotremorine-M (Oxo-M) strongly reduced (to 0–10%) currents produced by KCNQ1-4 subunits expressed individually and also those produced by KCNQ2+KCNQ3 and KCNQ1+KCNE1 heteromers, which are thought to generate neuronal M-currents (IK,M) and cardiac slow delayed rectifier currents (IK,s), respectively.

  • The activity of KCNQ2+KCNQ3, KCNQ2 and KCNQ3 channels recorded with cell-attached pipettes was strongly and reversibly reduced by Oxo-M applied to the extra-patch membrane.

  • It is concluded that M1 receptors couple to all known KCNQ subunits and that inhibition of KCNQ2+KCNQ3 channels, like that of native M-channels, requires a diffusible second messenger.