Calcium-Sensitive Nonselective Cation Channel Identified in the Epithelial Cells Isolated from the Endolymphatic Sac of Guinea Pigs |
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Authors: | T Miyashita H Tatsumi H Furuta N Mori M Sokabe |
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Institution: | (1) Department of Otolaryngology, Kagawa Medical University, Kagawa 761-0793, Japan, JP;(2) Department of Physiology, Nagoya University School of Medicine, Nagoya 466-8550, Japan, JP;(3) ICORP ``Cell Mechanosensing Project', Japan Science and Technology Corporation, JP |
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Abstract: | 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 μm), carbonyl cyanide 3-chlorophenylhydrazone (CCCP, 20 μm), or ATP (1 mm), which increased intracellular Ca2+ concentration (Ca2+]i), activated the channel at an estimated Ca2+]i from 0.6 μm to 10 μm. 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.
Received: 24 October 2000/Revised: 10 April 2001 |
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Keywords: | : Nonselective cation channel — Calcium-sensitive channel — Endolymphatic sac — Patch-clamp — Inner ear — Fura-2 |
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