Outer hair cells in vitro contract in response to various stimuli: electrical stimulation, K+-depolarization, elevation of intracellular calcium or osmotic changes of the extracellular medium. The characteristics of motile responses induced by K+-depolarization, osmotic changes, and calcium injection were compared in this study in order to delineate the underlying mechanisms. Slow shape changes in outer hair cells were induced by changes of the osmolality or the K+/Na+-ratio of the bathing medium, or by intracellular injections of calcium. K+- and osmotically induced contractions of isolated outer hair cells had identical morphological features and the same rate (50-200 nm/s) and amplitude (up to greater than 10% of original length) of shortening. The shortening of the cells was linearly related to an increase in volume in both cases. In contrast, the active contraction induced by Ca2+/ATP exhibited a somewhat faster rate and no increase in volume. Furthermore, the K+-induced contractions in outer hair cells, unlike those reported in smooth muscle cells, were unaffected by the removal of external Ca2+ (i.e. medium without Ca2+/Mg2+ and supplemented with 1 mM EGTA) or the presence of D600, an inhibitor of the Ca2+ inward current. The results strongly suggest that K+ induces shape changes of outer hair cells via osmotic forces and that intracellular calcium mediates contractions by a different mechanism.

Adenosine Triphosphate↗

PubMedDate not supplied

Some functional and morphologic correlates in inner ear pathologies: first observations using electrically evoked/pure tone derived potentials.

After reviewing a typical example of functional and morphologic correlations in a cochlear and vestibular comparative study of three aminoglycosidic antibiotics and discussing clinical and experimental observations in Menière's disease and experimental endolymphatic hydrops, some difficulties in studying morphofunctional correlations are discussed. A particular electrophysiologic method, based on electrical stimulation of the ear and acoustic masking, notably with continuous pure tones, is illustrated in normal and pathologic experimental conditions in the guinea pig. This method, which allows the observation of frequency-specific compound responses, whatever the frequency, should find useful experimental and clinical applications, particularly because it allows accurate measurements at low frequencies.

Amikacin↗

PubMedDate not supplied

Comparative tests of gentamicin ototoxicity.

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Animals↗

PubMedDate not supplied

X-ray microanalysis and ion microscopy of guinea pig cochlea and kidney after cisplatin treatment.

The detection of platinum in cochlear outer hair cells (OHCs) and renal proximal tubule cells was attempted by X-ray microanalysis and ion microscopy. Platinum was not detected by X-ray microanalysis in the lysosomes of OHCs or proximal tubule cells after 10 days treatment with 1.5 mg/kg of cisplatin. In the guinea pigs treated with 1.5 mg/kg of cisplatin for 14 days, platinum was detected by a wave-length-dispersive microanalyzer in only the lysosomes of kidney fixed by freezing. Ion microscopy failed to detect platinum. Improvement of fixation methods, longer administration of cisplatin and the use of more sensitive tools will be needed to detect the platinum inside the OHCs.

Animals↗

PubMedDate not supplied

Comparative ototoxicity of cisplatin during acute and chronic treatment.

Functional and morphological alterations were compared in guinea pig cochleae treated acutely (7.5 mg/kg x 2) and chronically (1.5 mg/kg x 10) with cisplatin. Drastic and rapid hearing impairments using compound action potential were observed only after the second injection during acute treatment. During chronic treatment, threshold changes were observed abruptly after 8 or 9 days of treatment. Morphological changes of outer hair cells were stronger in the acute treatment than the chronic one, and they appeared to concur with the functional data. Partial damage in the stria vascularis was observed only after acute treatment. From these results, it was suspected that acute and chronic ototoxic mechanisms differed according to the pharmacokinetics of cisplatin in the inner ear fluid and tissues.

Animals↗

PubMedDate not supplied

Testing for "recruitment" by electrocochleography. Preliminary results.

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Acoustic Stimulation↗

PubMedDate not supplied

Electrical stimulation of the ear: experimental studies.

The possibility of stimulating the ear by way of an electrode on the round window in order to relieve tinnitus or to produce auditory sensations has been investigated experimentally in guinea pigs. The deleterious effects of DC currents applied to a normal cochlea clearly demonstrate that this means is unsuitable for use in relieving tinnitus in hearing patients. Although AC currents do not cause further damage in ears with the organ of Corti already destroyed by aminoglycosides, the effects of DC currents in such cases have still to be investigated before they can be recommended for the relief of tinnitus in totally deaf patients. Electrical stimulation of the round window combined with masking has made it possible to record responses of auditory neural elements from the eighth nerve to the auditory cortex. This technique could be promising for the basic study of the central auditory nervous system, both experimentally and clinically, and could lead to a more accurate evaluation of candidates for cochlear prostheses.

Animals↗

PubMedDate not supplied

Electrical stimulation of the ear: clinical applications.

Electrical stimulation of the ear in humans was performed with an extracochlear electrode on the round window. With positive currents, suppression of tinnitus could be induced. With negative currents, auditory sensations were evoked. Since electrical stimulation with DC currents may be hazardous in the long term, it cannot yet be proposed for the suppression of tinnitus. However, electrically evoked hearing sensations with AC currents seem to be of definite interest for some totally deaf patients.

Deafness↗