Cytochemical and patch-clamp studies of calcium influx through voltage-dependent Ca²⁺ channels in vestibular supporting cells of guinea pigs

Abstract

To clarify whether or not vestibular supporting cells have voltage-dependent Ca²⁺ channels, cytochemical and patch-clamp studies were performed using cells isolated from the ampullae of the semicircular canal of the guinea pig. Image analysis used fura-2 as a Ca²⁺-sensitive fluorescence dye and showed that the intracellular Ca²⁺ concentration ([Ca²⁺]_i) increased with bath application of high (150 mM)K⁺, but was unaffected by 80 mM K⁺. The increase in [Ca²⁺]_i induced by high K⁺ was completely blocked by 1 μM nifedipine as an L-type Ca²⁺ channel antagonist. In the patch-clamp whole-cell recording of the isolated supporting cells, the voltage-dependent inward current was induced by a depolarizing pulse lasting 2 s in a high (50 mM) Ca²⁺ and tetraethylammonium-containing external solution replaced by choline chloride and a Cs⁺-containing internal solution. The inward current was obtained when the membrane was depolarized to –50 mV and maximum current was observed at –10 to +10 mV. This inward current was completely blocked by 1 μM nifedipine. These findings strongly suggest that voltage-dependent Ca²⁺ channels exist in the vestibular supporting cells and regulate Ca²⁺ concentration in the vestibular endolymph.