TRANSIENT INCREASE IN CYTOSOLIC-FREE CALCIUM EVOKED BY REPOLARIZATIONIN TYPE-I VESTIBULAR HAIR-CELLS OF RATS

Simultaneous whole-cell patch clamp and Fura-2 microfluorimetric recor dings of membrane currents and intracellular free calcium concentratio n ([Ca2+](i)) were made from type I vestibular hair cells isolated fro m cristae ampullares of adult rats. Cells held between -110 or -70 mV and depolarized up to -20 mV did not evoke any [Ca2+](i) changes for a ny duration of the membrane depolarization (up to 3 s), Returning the membrane to repolarizing potential induced a transient [Ca2+](i) incre ase. At the pulse break, an inward current was evoked. The [Ca2+](i) i ncrease and inward current amplitude were dependent on the duration an d the amplitude of the previous depolarization. A liminar value of mem brane depolarization of -55 +/- 3 mV (mean resting potential -62 +/- 7 my) had to be applied to induce [Ca2+](i) increase upon subsequent re polarization. [Ca2+](i) response and inward current could not be evoke d in calcium-free solution. Both responses were restored when calcium was added to the medium.