Cytochemical and patch-clamp studies of calcium influx through voltage-dependent Ca2+ channels in vestibular supporting cells of guinea pigs.
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 Ca(2+)-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 microM 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 microM nifedipine. These findings strongly suggest that voltage-dependent Ca2+ channels exist in the vestibular supporting cells and regulate Ca2+ concentration in the vestibular endolymph.
Mori
Y
Y
Department of Otolaryngology, Hiroshima University School of Medicine, Japan.
Amano
T
T
Sasa
M
M
Yajin
K
K
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002586:Cesium / Q000494:pharmacology; D002794:Choline / Q000494:pharmacology; D004563:Electrochemistry; D004710:Endolymph / Q000187:drug effects / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism; D005456:Fluorescent Dyes; D016257:Fura-2; D006168:Guinea Pigs; D006651:Histocytochemistry; D007091:Image Processing, Computer-Assisted; D008564:Membrane Potentials / Q000187:drug effects; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology; D026902:Potassium Channel Blockers; D012665:Semicircular Canals / Q000166:cytology / Q000378:metabolism; D019789:Tetraethylammonium / Q000494:pharmacology; D014722:Vestibule, Labyrinth / Q000166:cytology / Q000378:metabolism*
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D005456:Fluorescent Dyes; D026902:Potassium Channel Blockers; D002586:Cesium; D019789:Tetraethylammonium; D009543:Nifedipine; D002794:Choline; D011188:Potassium; D002118:Calcium; D016257:Fura-2