The Journal of Neuroscience, December 15, 2000, 20(24):8996-9003
Water Permeability of Cochlear Outer Hair Cells: Characterization
and Relationship to Electromotility
Inna A.
Belyantseva1,
Gregory I.
Frolenkov1,
James B.
Wade2,
Fabio
Mammano3, and
Bechara
Kachar1
1 Section on Structural Cell Biology, National
Institute on Deafness and other Communication Disorders, National
Institutes of Health, Bethesda, Maryland 20892, 2 Department of Physiology, University of Maryland School
of Medicine, Baltimore, Maryland 21201, and 3 Laboratory of
Biophysics and Istituto Nazionale di Fisica della Materia,
International School for Advanced Studies, Trieste, Italy, 34014
The distinguishing feature of the mammalian outer hair cells (OHCs)
is to elongate and shorten at acoustic frequencies, when their
intracellular potential is changed. This "electromotility" or
"electromechanics" depends critically on positive intracellular pressure (turgor), maintained by the inflow of water through yet uncharacterized water pathways. We measured the water volume flow, Jv, across the plasma membrane of
isolated guinea pig and rat OHCs after osmotic challenges and estimated
the osmotic water permeability coefficient,
Pf, to be
~10
2 cm/sec. This value is
within the range reported for osmotic flow mediated by the water
channel proteins, aquaporins. Jv was
inhibited by HgCl2, which is known to block
aquaporin-mediated water transport. Pf
values that were estimated for OHCs from neonatal rats were of the
order of ~2×103 cm/sec,
equivalent to that of membranes lacking water channel proteins. In an
immunofluorescence assay we showed that an anti-peptide antibody
specific for aquaporins labels the lateral plasma membrane of the OHC
in the region in which electromotility is generated. Using patch-clamp
recording, we found that water influx into the OHC is regulated by
intracellular voltage. We also found that the most pronounced increases
of the electromotility-associated charge movement and of the expression
of OHC water channels occur between postnatal days 8 and 12, preceding
the onset of hearing function in the rat. Our data indicate that
electromotility and water transport in OHCs may influence each other
structurally and functionally.
Key words:
mechanosensory transduction; electromotility; water
permeability; aquaporins; voltage-dependent capacitance; postnatal
development; organ of Corti; patch clamp
Copyright © 2000 Society for Neuroscience 0270-6474/00/20248996-08$05.00/0
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