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Tonotopic variations of calcium signalling in turtle auditory hair cells
Author(s) -
Ricci A. J.,
GrayKeller M.,
Fettiplace R.
Publication year - 2000
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2000.00423.x
Subject(s) - bapta , biophysics , hair cell , membrane potential , cochlea , chemistry , depolarization , patch clamp , calcium , conductance , intracellular , voltage dependent calcium channel , electrophysiology , anatomy , biology , neuroscience , biochemistry , physics , organic chemistry , condensed matter physics
1 Turtle cochlear hair cells are electrically tuned by a voltage‐dependent Ca 2+ current and a Ca 2+ ‐dependent K + current ( I BK(Ca) ). The effects of intracellular calcium buffering on electrical tuning were studied in hair cells at apical and basal cochlear locations tuned to 100 and 300 Hz, respectively. 2 Increasing the intracellular BAPTA concentration changed the hair cell's resonant frequency little, but optimized tuning at more depolarized membrane potentials due to a positive shift in the half‐activation voltage (V ½ ) of the I BK(Ca) . 3 The shift in V ½ depended similarly on BAPTA concentration in basal and apical hair cells despite a 2·4‐fold difference in the size of the Ca 2+ current at the two positions. The Ca 2+ current amplitude increased exponentially with distance along the cochlea. 4 Comparison of V ½ values and tuning properties using different BAPTA concentrations with values measured in perforated‐patch recordings gave the endogenous calcium buffer as equivalent to 0·21 mM BAPTA in low‐frequency cells, and 0·46 mM BAPTA in high‐frequency cells. 5 High conductance Ca 2+ ‐activated K + (BK Ca ) channels recorded in inside‐out membrane patches were 2‐fold less Ca 2+ sensitive in high‐frequency than in low‐frequency cells. 6 Confocal Ca 2+ imaging using the fluorescent indicator Calcium Green‐1 revealed about twice as many hotspots of Ca 2+ entry during depolarization in high‐frequency compared to low‐frequency hair cells. 7 We suggest that each BK Ca channel is gated by Ca 2+ entry through a few nearby Ca 2+ channels, and that Ca 2+ and BK Ca channels occupy, at constant channel density, a greater fraction of the membrane area in high‐frequency cells than in low‐frequency cells.