Aminoglycoside antibiotics impair calcium entry but not viability and motility in isolated cochlear outer hair cells.
J. Neurosci. Res.. 1989-10-01; 24(2): 338-346
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1. J Neurosci Res. 1989 Oct;24(2):338-46.
Aminoglycoside antibiotics impair calcium entry but not viability and motility in
isolated cochlear outer hair cells.
Dulon D(1), Zajic G, Aran JM, Schacht J.
(1)Kresge Hearing Research Institute, University of Michigan, Ann Arbor
Cochlear outer hair cells have been well established as primary targets of the
ototoxic actions of aminoglycoside antibiotics. These cells, isolated from the
guinea pig cochlea and maintained in short-term culture, were used as a model for
evaluating the acute effects of gentamicin on cell viability,
depolarization-induced transmembrane calcium flux, and depolarization-induced
motile responses. On the basis of morphology and fluorochromasia, the presence of
extracellular gentamicin as high as 5 mM did not affect the viability of the
cells for up to 6 hr, the longest time tested. Viable cells showed binding of
fluorescently tagged gentamicin to their base but excluded the drug from their
cytoplasm. In response to [K+]-depolarization, intracellular calcium levels
(monitored with the fluorescent calcium-sensitive dye fluo-3) increased from a
resting value of 218 +/- 102 nM to 2,018 +/- 1,077 nM concomitant with a cell
shortening of 0.7% +/- 1.3%. The depolarization-induced calcium increase was
apparently caused by calcium entry into the cell as it was inhibited by the
calcium-channel blocker methoxyverapamil and prevented in the absence of
extracellular calcium. Both gentamicin and neomycin blocked the [K+]-induced
calcium increase at an IC50 of 50 microM. Despite the inhibition of calcium entry
the ability of the outer hair cells to shorten under [K+]-depolarization was not
impaired; in fact, cell shortening was even more pronounced in the absence of
calcium influx (2.6% +/- 1.4%). This argues effectively against the existence of
a calcium-dependent actomyosin-mediated component in [K+]-induced shape
changes.(ABSTRACT TRUNCATED AT 250 WORDS)
PMID: 2585554 [Indexed for MEDLINE]