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Action of 2,3‐butanedione monoxime on capacitance and electromotility of guinea‐pig cochlear outer hair cells
Author(s) -
Frolenkov Gregory I.,
Mammano Fabio,
Kachar Bechara
Publication year - 2001
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.1469-7793.2001.0667h.x
Subject(s) - chemistry , biophysics , membrane potential , capacitance , okadaic acid , hair cell , conductance , voltage clamp , analytical chemistry (journal) , biochemistry , cochlea , phosphatase , anatomy , chromatography , biology , electrode , phosphorylation , mathematics , combinatorics
1 Whole‐cell patch‐clamp recordings were obtained from isolated cochlear outer hair cells (OHCs) while applying 2,3‐butanedione monoxime (BDM) by pressure. BDM (5 m m ) shifted the range of voltage sensitivity of membrane capacitance and cell length in the hyperpolarised direction by ‐49.6 ± 4.0 mV (n = 12; mean ± s.e.m. ), without appreciable effects on membrane conductance. The shift was completely reversible and dose dependent, with a Hill coefficient of 1.8 ± 0.4 and a half‐maximal dose of 3.0 ± 0.8 m m (values ± s.d. ). 2 The shift of the capacitance curve was also reproducible in cells whose natural turgor had been removed. BDM had no detectable effect on the capacitance of Deiters’ cells, a non‐sensory cell type of the organ of Corti. 3 The effect of BDM on membrane capacitance was faster than that of salicylate. At similar saturating concentrations (20 m m ), the time constant of the capacitance changes was 1.8 ± 0.3 s (n = 3) for salicylate and 0.75 ± 0.06 s (n = 3) for BDM. The recovery periods were 13 ± 1 s and 1.7 ± 0.4 s, respectively (means ± s.e.m. ). 4 The effect of BDM, a known inorganic phosphatase, was compared to the effects of okadaic acid, trifluoperazine and W‐7, which are commonly used in studies of protein phosphorylation. Incubation of OHCs with okadaic acid (1 μ m , 30‐60 min) shifted the voltage sensitivity of the membrane capacitance in the hyperpolarised direction. Incubation with trifluoperazine (30 μ m ) and W‐7 (150 μ m ) shifted it in the opposite, depolarised direction. BDM induced hyperpolarising shifts even in the presence of W‐7. 5 Simultaneous measurement of membrane capacitance and intracellular free Ca 2+ concentration ([Ca 2+ ] i ) showed that BDM action on OHC voltage‐dependent capacitance and electromotility is not mediated by changes of [Ca 2+ ] i . 6 Our results suggest that: (a) the effects of BDM are unrelated to its inorganic phosphatase properties, cell turgor conditions or Ca 2+ release from intracellular stores; and (b) BDM may target directly the voltage sensor of the OHC membrane motor protein.