Mechanically induced calcium increases in isolated vestibular hair cells of the guinea pig.

Intracellular Ca2+([Ca2+]i) is elevated by depolarization or mechanical stimulation in some hair cell systems. It is not clear whether both these stimuli promote Ca2+ entry in mammalian vestibular hair cells. We monitored [Ca2+]i with the indicator fluo-3 in isolated type I vestibular hair cells of the guinea pig maintained in Hanks' balanced salt solution (HBSS). Mechanical stimulation by bolus application of HBSS led to an immediate rise of [Ca2+]i. The effect depended upon the presence of extracellular Ca2+([Ca2+]o) and no increase occurred in calcium-free HBSS supplemented with calcium-chelators. When the cells were depolarized by bolus application of KCl (final concentration, 100 mM KCl in modified HBSS), the increase in [Ca2+]i was similar to that elicited by HBSS. In the absence of [Ca2+]o, the application of KCI/HBSS led to a slow sustained increase in the fluorescence of the cells suggesting release of calcium from intracellular stores. Finally, treatment of cells with BAPTA prior to mechanical stimulation prevented the rise in [Ca2+]i indicating the need for intact stereociliary tip-links. The results are consistent with the hypothesis that mechanical stimulation elevates [Ca2+]i in isolated vestibular hair cells via calcium influx through mechanotransduction channels.