THE VESTIBULAR TYPE-I HAIR-CELLS - A SELF-REGULATED SYSTEM

In this study the functional role of afferent nerve calyx surrounding the type I vestibular hair cells was investigated. Synaptic microvesic les were present at the apex of the calyx in the vestibular epithelium of human foetuses at 9 weeks from gestation. Whole cell clamped type I hair cells isolated from guinea pig epithelium presented active move ments as shortening of the neck and tilting of the cuticular plate at the cessation of the depolarising step. These movements were calcium d ependent. With the aim of establishing the kinetics of calcium influx during the cell depolarisation, intracellular free calcium rate variat ions were investigated by coupling cytofluorimetry technique with whol e cell patch clamp. An increase of intracellular calcium was only obse rved at the repolarisation of type I hair cells. Thus, a regulatory sh ort-loop is thought to exist to control adaptation phenomena at the up per part of the type I hair cell. It is suggested that this occurs thr ough the release of a neurotransmitter from the apex of the afferent c alyx.