Direct effects of carbachol on membrane potential and ion activities in leech glial cells

Ion-selective double-barreled microelectrodes were used to measure the activities of intracellular K+ and Na+ (aKi, aNai) and the membrane potential (Em) in neuropile glial cells as well as extracellular K+ (aKe) in the neuropile of segmental ganglia in the leech, Hirudo medicinalis. Bath-application of carbachol resulted in a prominent membrane depolarization. This depolarization was accompanied by transient increases of aNai and aKe, whereas aKi decreased. It is suggested that the carbachol-induced depolarization and the underlying ion activity changes are due to activation of an acetylcholine receptor-coupled cation channel in the membrane of the neuropile glial cells.