Calcium-sensitive nonselective cation channel identified in the epithelial cells isolated from the endolymphatic sac of guinea pigs.
We identified a Ca2+-sensitive cation channel in acutely dissociated epithelial cells from the endolymphatic sac (ES) of guinea pigs using the patch-clamp technique. Single-channel recordings showed that the cation channel had a conductance of 24.0 +/- 1.3 pS (n = 8) in our standard solution. The relative ionic permeability of the channel was in the order K+ = Na+ > Ca2+ >> Cl-. This channel was weakly voltage-dependent but was strongly activated by Ca2+ on the cytosolic side at a concentration of around 1 mm in inside-out excised patches. With cell-attached patches, however, the channel was activated by much lower Ca2+ concentrations. Treatment of the cells, under cell-attached configuration, with ionomycin (10 microm), carbonyl cyanide 3-chlorophenylhydrazone (CCCP, 20 microm), or ATP (1 mm), which increased intracellular Ca2+ concentration ([Ca2+]i), activated the channel at an estimated [Ca2+]i from 0.6 microm to 10 microm. It is suggested that some activators of the channel were deteriorated or washed out during the formation of excised patches. Based on this Ca2+ sensitivity, we speculated that the channel contributes to the regulation of ionic balance and volume of the ES by absorbing Na+ under certain pathological conditions that will increase [Ca2+]i. This is the first report of single-channel recordings in endolymphatic sac epithelial cells.
Miyashita
T
T
Department of Otolaryngology, Kagawa Medical University, Kagawa 761-0793, Japan.
Tatsumi
H
H
Furuta
H
H
Mori
N
N
Sokabe
M
M
D000255:Adenosine Triphosphate; D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D002614:Chelating Agents / Q000493:pharmacokinetics; D004594:Electrophysiology; D004712:Endolymphatic Sac / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism; D005439:Flufenamic Acid / Q000494:pharmacology; D016257:Fura-2 / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism*; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques
D000894:Anti-Inflammatory Agents, Non-Steroidal; D002614:Chelating Agents; D007473:Ion Channels; D007476:Ionophores; D015759:Ionomycin; D005439:Flufenamic Acid; D000255:Adenosine Triphosphate; D002118:Calcium; D016257:Fura-2