Nicotinic depolarization activates calcium dependent gK in myenteric neurons.

Intracellular recordings were made from S type neurons in the myenteric plexus of the guinea-pig ileum. Acetylcholine (ACh) was applied directly onto the soma membrane by iontophoresis with visual placement of the iontophoretic pipette. Fast nicotinic depolarizations were evoked which were followed by slow muscarinic depolarizations. After application of hyoscine to block the slow muscarinic depolarization, the nicotinic depolarization was found to be followed by a hyperpolarization. This hyperpolarization was several mV in amplitude and 1-5 s in total duration. It disappeared when the preceding nicotinic depolarization was blocked by hexamethonium. The ACh induced by hyperpolarization was due to calcium entry and subsequent opening of potassium channels.