Characterization of the calcium influx induced by depolarization of guinea pig cochlear spiral ganglion cells.
We examined dynamic changes in intracellular calcium ion concentrations ([Ca2+]i) in isolated cochlear spiral ganglion cells (SGCs) of the guinea pig using digital imaging microscopy and the Ca(2+)-sensitive fluorescence dye fura-2. [Ca2+]i in SGCs was 83 +/- 22 nM (n = 50, means +/- SD) in cell somata at the resting state. Reversible increases in [Ca2+]i were elicited during membrane depolarization by high K+ (150 mM). This increase in [Ca2+]i was not observed under conditions of depolarization in Ca(2+)-free medium containing 1 mM EGTA. In addition, these increases in [Ca2+]i were sensitive to L-type calcium channel ligands, viz., antagonized by nifedipine (50 microM), verapamil (10 microM) and enhanced by BAY K 8644 (1 microM). These observations suggest that increases in [Ca2+]i of cochlear SGCs induced by high K+ are due to an influx of extracellular Ca2+, probably through voltage-gated L-type calcium channels.
Han
D Y
DY
Department of Otolaryngology, Kansai Medical University, Osaka, Japan.
Harada
N
N
Tomoda
K
K
Yamashita
T
T
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000493:pharmacokinetics; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D006168:Guinea Pigs; D015640:Ion Channel Gating / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D008856:Microscopy, Fluorescence; D016501:Neurites / Q000378:metabolism; D009543:Nifedipine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D013136:Spiral Ganglion / Q000187:drug effects / Q000378:metabolism*; D014700:Verapamil / Q000494:pharmacology
D015220:Calcium Channels; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D014700:Verapamil; D009543:Nifedipine; D011188:Potassium; D002118:Calcium