内耳機能とカルシウム

Abstract

It has been generally accepted that Ca2 + plays a significant role in various cellular functions, for example, the release of neurotransmitter. Also in inner ear research, many investigations have been done to clarify the role of intracellular free calcium ([Ca2+]i) on both inner and outer hair cells by recording the intracellular potential using a patch-clamp electrode or measuring [Ca2+]i with microspectrofluorometry with fura-2. From these data, the mechanoreceptive mechanism of hair cells is postulated to be as follows: when the hair bundle is deflected, the transducing K+ channel opens, K+ flows into the cell through the cuticular plate and depolarization occurs. This depolarization leads to an opening of the Ca2+ channels present over the entire plasma membrane and Ca2+ enters the cell from the extracellular space. The increase in [Ca2+]i leads to vesicular fusion and release neurotransmitters. These transmitters excite the neuron, and a message is transmitted to the brain.The relationship between [Ca2+]i and the motile responses of outer hair cells and the role of endolymphatic Ca2+ on the whole cochlear function are also discussed.