Outer hair cells (OHCs) are synapsed with efferent cholinergic medial olivocochlear fibers (reviewed in Fritzsch and Elliott 2017, Fuchs and Lauer 2019). Acetylcholine released at the synapse binds an unusual, nicotine-antagonized, nicotinic receptor comprising CHRNA9 and CHRNA10. Upon binding acetylcholine, CHRNA9:CHRNA10 transports calcium ions into the OHC. The calcium activates nearby SK2 potassium channels (KCNN2, small potassium current channels) and BK potassium channels (KCNMA1:KCNMB1, big potassium current channels) which extrude potassium ions, hyperpolarize the OHC, and inhibit activation of the OHC.
The overall effects of acetylcholine on OHCs are complex. OHCs exhibit fast motility caused by voltage effect on SLC26A5 and slow motility caused by cytoskeleton organization.