Possible role of Ca ions in the vestibular system

The Ca++ messenger system is nearly universally present in the control of cell functions by extracellular messengers. It elicits different kinds of responses: either brief, as in neurotransmission and in skeletal muscle contraction, or sustained, as in smooth muscle contraction and in the regulation of transepithelial transport systems. In this latter function the Ca++ messenger system interacts with other cellular modulation systems such as cAMP production and arachidonic acid cascade. In the vestibular apparatus, the Ca++ messenger system is involved in the transduction processes in that it controls both the release of neurotransmitter at the basal pole of the hair cell and the electrical resonance of the cell. It also figures in the contractile properties of cochlear outer hair cells. The Ca++ messenger system as well as adenylate cyclase and prostaglandins may play an important role in the modulation of endolymph secretion.