EXISTENCE OF VOLTAGE-DEPENDENT CA2- CYTOCHEMICAL AND WHOLE-CELL PATCH-CLAMP STUDIES( CHANNELS IN VESTIBULAR DARK CELLS )

To determine whether functional Ca2+ channels are present in vestibula r dark cells, changes in intracellular Ca2+ concentration ([Ca2+](i)) due to K+ applications were measured using the Ca2+-sensitive dye (fur a-2) and patch-clamp whole-cell recordings were made in dark cells iso lated from the ampullae of the semicircular canal of the guinea pig. E xchange of the external solution with a buffer medium containing a hig h K+ concentration (80 mM K+ or 150 mM K+) caused a concentration-depe ndent increase in [Ca2+](i) in vestibular dark cells. Application of 1 mu M nifedipine as a Ca2+ channel antagonist completely blocked the i ncrease in [Ca2+](i). Further treatment with 10 mu M BAY K 8644 as a C a2+ channel agonist caused an increase in [Ca2+](i). In the patch-clam p whole-cell recordings a 1-s depolarizing pulse given into the dark c ell in the presence of a high barium concentration (50 mM Ba2+) induce d an inward current. In determining the current-voltage relationship, a current was detected at a potential that depolarized at -50 mV and w as maximal at +10 mV. This inward current was completely blocked by 1 mM La3+ as a Ca2+ channel antagonist. These findings suggest the prese nce of voltage-dependent Ca2+ channels in dark cells, which have a pre sumed function in the regulation of [Ca2+](i) in the vestibular endoly mph.