Nitroprusside suppresses cochlear potentials and outer hair cell responses.
Biochemical and pharmacological evidence supports a role for nitric oxide (NO) in the cochlea. In the present experiments, we tested sodium nitroprusside (SNP), an NO donor, applied by intracochlear perfusions on sound-evoked responses of the cochlea (CM, cochlear microphonic; SP, summating potential; EP, endocochlear potential; CAP, compound action potential) and in vitro on outer hair cell (OHC) voltage-induced length changes and current responses. In vivo application of SNP in increasing concentrations (10, 33, 100, 330 and 1000 microM) reduced all sound-evoked responses starting at about 300 microM. The responses continued to decline after a postdrug wash. At 1 mM SNP decreased EP slowly (approximately 80 min) whereas at 10 mM it reduced EP more rapidly (approximately 20 min). Ferricyanide (1 mM) and S-nitroso-N-acetylpenicillamine (SNAP; 1 mM) had no effect on sound-evoked cochlear potentials. Ferricyanide (1 mM and 10 mM) and ferrocyanide (10 mM) had no effect on EP. In vitro, SNP (10 mM) significantly reduced both OHC voltage-induced length changes and whole-cell outward currents. Results suggest that SNP, possibly acting by released NO, influences cochlear function through effects at the stria vascularis and at the OHCs.
Chen
C
C
Kresge Hearing Research Laboratory of the South, Department of Otorhinolaryngology and Biocommunication, Louisiana State University Medical Center, New Orleans 70112-2234, USA.
Nenov
A
A
Skellett
R
R
Fallon
M
M
Bright
L
L
Norris
C H
CH
Bobbin
R P
RP
D000161:Acoustic Stimulation; D000200:Action Potentials / Q000187:drug effects*; D000818:Animals; D003051:Cochlea / Q000166:cytology / Q000187:drug effects*; D003055:Cochlear Microphonic Potentials / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005260:Female; D005292:Ferricyanides / Q000494:pharmacology; D006168:Guinea Pigs; D018072:Hair Cells, Auditory, Outer / Q000166:cytology / Q000187:drug effects*; D007202:Indicators and Reagents / Q000008:administration & dosage / Q000494:pharmacology; D008297:Male; D009569:Nitric Oxide / Q000502:physiology; D009599:Nitroprusside / Q000008:administration & dosage / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D010396:Penicillamine / Q000031:analogs & derivatives / Q000494:pharmacology; D010477:Perfusion; D026423:S-Nitroso-N-Acetylpenicillamine; D014665:Vasodilator Agents / Q000008:administration & dosage / Q000494:pharmacology*
D005292:Ferricyanides; D007202:Indicators and Reagents; D014665:Vasodilator Agents; C007931:hexacyanoferrate III; D009599:Nitroprusside; D009569:Nitric Oxide; D026423:S-Nitroso-N-Acetylpenicillamine; D010396:Penicillamine