ABSTRACT
Previous studies have documented slow shape changes in outer hair cells, and it was suggested that this form of motility was caused by a calcium- activated actin and myosin system like that seen in muscle. Supporting evidence for a muscle-like mechanism involved in outer hair cell motility includes: the presence of actin filaments in the cytoplasm and lateral wall; the colocalization of calcium-binding and calcium-regulatory proteins (calsequestrin, calmodulin, and calbindin) with calcium; the activation of the response by second messengers; and sensitivity of outer hair cells to the neurotransmitter acetylcholine. However, more recent results from this lab argue against such a similarity. Unlike muscle cells, outer hair cells lack: an organized contractile apparatus; caldesmon, a major regulatory protein for smooth muscle; and muscle-type myosins in the cytoplasm, although myosin has been found in the cuticular plate and along the lateral wall.
