Abstract
Simultaneous whole-cell patch clamp and Fura-2 microfluorimetric recordings of membrane currents and intracellular free calcium concentration ([Ca 2+] i) were made from type I vestibular hair cells isolated from cristae ampullares of adult rats. Cells held between −110 or −70 mV and depolarized up to −20 mV did not evoke any [Ca 2+] i changes for any duration of the membrane depolarization (up to 3 s). Returning the membrane to repolarizing potential induced a transient [Ca 2+] i increase. At the pulse break, an inward current was evoked. The [Ca 2+] i increase and inward current amplitude were dependent on the duration and the amplitude of the previous depolarization. A liminar value of membrane depolarization of −55 ± 3 mV (mean resting potential −62 ± 7 mv) had to be applied to induce [Ca 2+] i increase upon subsequent repolarization. [Ca 2+] i response and inward current could not be evoked in calcium-free solution. Both responses were restored when calcium was added to the medium.
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