Ion imaging in the cochlear hair cells

Regulation of important cellular functions via signaling pathways is a fundamental property of the cell. Intracellular Ca²⁺ is probably a best known second messenger in cell biology. In mechanosensory cells of the inner ear, the hair cells, intracellular Ca²⁺ participates in a variety of functions including mechano-electrical transduction, synaptic transmission, and efferent regulation of the outer hair cells, one of two types of hair cells in the mammalian cochlea. The outer hair cells are responsible for the amplification of sound-induced vibrations within the cochlea, which determines the sensitivity of mammalian hearing. Besides Ca²⁺, another intracellular ion, Cl^- may have very specific function in the same outer hair cells. Intracellular Cl^- is required for the motor function of prestin, a unique plasma membrane molecular motor of these cells. The goal of this article is to review practical aspects of the techniques suitable for imaging of Ca²⁺ and Cl^- in live mammalian cochlear hair cells.