MECHANICALLY INDUCED CALCIUM INCREASES IN ISOLATED VESTIBULAR HAIR-CELLS OF THE GUINEA-PIG

Intracellular Ca2+([Ca2+](i)) is elevated by depolarization or mechani cal stimulation in some hair cell systems. It is not clear whether bot h these stimuli promote Ca2+ entry in mammalian vestibular hair cells. We monitored [Ca2+](i) with the indicator fluo-3 in isolated type I v estibular hair cells of the guinea pig maintained in Hanks' balanced s alt solution (HBSS). Mechanical stimulation by bolus application of HB SS led to an immediate rise of [Ca2+](i). The effect depended upon the presence of extracellular Ca2+ ([Ca2+](0),) and no increase occurred in calcium-free HBSS supplemented with calcium-chelators. When the cel ls were depolarized by bolus application of KCl (final concentration, 100 mM KCI in modified HBSS), the increase in [Ca2+](i) was similar to that elicited by HBSS. In the absence of [Ca2+](0), the application o f KCl/HBSS led to a slow sustained increase in the fluorescence of the cells suggesting release of calcium from intracellular stores. Finall y, treatment of cells with BAPTA prior to mechanical stimulation preve nted the rise in [Ca2+](i) indicating the need for intact stereociliar y tip-links. The results are consistent with the hypothesis that mecha nical stimulation elevates [Ca2+](i) in isolated vestibular hair cells via calcium influx through mechanotransduction channels.