Existence of voltage-dependent Ca2+ channels in vestibular dark cells: cytochemical and whole-cell patch-clamp studies.
To determine whether functional Ca2+ channels are present in vestibular dark cells, changes in intracellular Ca2+ concentration ([Ca2+]i) due to K+ applications were measured using the Ca(2+)-sensitive dye (fura-2) and patchclamp whole-cell recordings were made in dark cells isolated from the ampullae of the semicircular canal of the guinea pig. Exchange of the external solution with a buffer medium containing a high K+ concentration (80 mM K+ or 150 mM K+) caused a concentration-dependent increase in [Ca2+]i in vestibular dark cells. Application of 1 microM nifedipine as a Ca2+ channel antagonist completely blocked the increase in [Ca2+]i. Further treatment with 10 microM BAY K 8644 as a Ca2+ channel agonist caused an increase in [Ca2+]i. In the patch-clamp whole-cell recordings a 1-s depolarizing pulse given into the dark cell in the presence of a high barium concentration (50 mM Ba2+) induced an inward current. In determining the current-voltage relationship, a current was detected at a potential that depolarized at-50 mV and was maximal at +10 mV. This inward current was completely blocked by 1 mM La3+ as a Ca2+ channel antagonist. These findings suggest the presence of voltage-dependent Ca2+ channels in dark cells, which have a presumed function in the regulation of [Ca2+]i in the vestibular endolymph.
Imon
K
K
Department of Otolaryngology, Hiroshima University School of Medicine, Japan.
Amano
T
T
Ishihara
K
K
Sasa
M
M
Yajin
K
K
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000032:analysis* / Q000187:drug effects; D005454:Fluorescence Polarization; D006168:Guinea Pigs; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D014722:Vestibule, Labyrinth / Q000737:chemistry* / Q000187:drug effects
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D009543:Nifedipine