Cholesterol Influences Voltage-Gated Calcium Channels and BK-Type Potassium Channels in Auditory Hair Cells

The influence of membrane cholesterol content on a variety of ion channel conductances in numerous cell models has been shown, but studies exploring its role in auditory hair cell physiology are scarce. Recent evidence shows that cholesterol depletion affects outer hair cell electromotility and the voltage-gated potassium currents underlying tall hair cell development, but the effects of cholesterol on the major ionic currents governing auditory hair cell excitabilityare unknown. We investigated the effects of a cholesterol-depleting agent (methyl beta cyclodextrin, MβCD) on ion channels necessary for the early stages of sound processing. Large-conductance BK-type potassium channels underlie temporal processing and open in a voltage- and calcium-dependent manner. Voltage-gated calcium channels (VGCCs) are responsible for calcium-dependent exocytosis and synaptic transmission to the auditory nerve. Our results demonstrate that cholesterol depletion reduced peak steady-state calcium-sensitive (BK-type) potassiumcurrent by 50% in chick cochlear hair cells. In contrast, MβCD treatment increased peak inward calcium current (∼30%), ruling out loss of calcium channel expression or function as a cause of reduced calcium-sensitive outward current. Changes in maximal conductance indicated a direct impact of cholesterol on channel number or unitary conductance. Immunoblotting following sucrose-gradient ultracentrifugation revealed BK expression in cholesterol-enriched microdomains. Both direct impacts of cholesterol on channel biophysics, as well as channel localization in the membrane, may contribute to the influence of cholesterol on hair cell physiology. Our results reveal a new role for cholesterol in the regulation of auditory calcium and calcium-activated potassium channels and add to the growing evidence that cholesterol is a key determinant in auditory physiology

Practices employed by audiologists in the management of adult patients with multidrug-resistant tuberculosis in South Africa

Introduction: Aminoglycosides used for treating multidrug-resistant (MDR) tuberculosis are ototoxic, leading to a need for audiological monitoring. While audiologists monitor ototoxicity, currently there are no guidelines on monitoring in the South African context. Therefore, the findings of this study might help to motivate the establishment of a more in-depth ototoxicity monitoring policy, which facilitates uniformity among audiologists managing patients with MDR tuberculosis. Therefore, the study aimed to describe the audiological practices employed by audiologists in the management of adult patients with MDR tuberculosis in South Africa.Method: A descriptive survey design was used. A questionnaire was developed and included elements of the American Speech-Language and Hearing Association (1994) guidelines for monitoring ototoxicity. Ninety-three audiologists contributed data to this study. Descriptive statistics were used in the analysis of the data.Results: Sixty-eight percent (%) of the respondents were aware of the international guidelines, 93% provided pre-treatment counselling and 87% conducted a baseline assessment. Nineteen per cent of the respondents conducted high-frequency audiometry, while 74% carried out a monthly evaluation, 72% performed a full audiological assessment after the cessation of the MDR tuberculosis treatment, and 96% conducted post-treatment counselling. Modifications to the international guidelines include not conducting speech and immittance audiometry, as well as testing certain frequencies. The reasons for these modifications include limited specialised equipment, time constraints, large caseloads and understaffed departments.Conclusion: There are no explicit guidelines on ototoxicity monitoring in South Africa. Consequently, audiologists are having to modify the international guidelines. Thus, there is no consistency in managing patients with MDR tuberculosis. This highlights the need for South Africa to develop context-relevant ototoxicity monitoring guidelines to appropriately manage patients with MDR tuberculosis

Anticipation in a unique family with Charcot-Marie-Tooth syndrome and deafness: delineation of the clinical features and review of the literature.

Charcot-Marie-Tooth disease (CMT) is a clinically and genetically heterogeneous group of polyneuropathies characterized by degeneration of peripheral nerves, resulting in distal muscle atrophy, sensory loss, and deformities of hands and feet. We have studied 34 individuals in a large 84-member four-generation central Illinois family with autosomal dominant Charcot-Marie-Tooth and deafness. Nerve conduction velocities are consistent with type 1 CMT. Audiological evaluation revealed both auditory neuropathy and cochlear involvement in affected individuals. There is increasing clinical severity and younger age of onset of CMT and deafness with each progressive generation, suggestive of anticipation (P < 0.05). The proband, a female diagnosed at birth with hypotonia, bilateral vocal cord palsy, swallowing incoordination, and hearing impairment, died at age 18 months. Another individual died at the age of 3 months from hypotonia later attributed to CMT. Genetic analysis indicated that affected individuals in this family do not have the common 1.4 Mb duplication associated with type 1A CMT; however, all affected individuals have a unique G to C transversion at position 248 in coding exon 3 of the peripheral myelin PMP22 gene located on chromosome 17p11.2-p12. This mutation is predicted to cause an Ala67Pro substitution in the second transmembrane domain of PMP22, consistent with the molecular cause of the CMT phenotype. However, it does not explain the cochlear component of the deafness, the clinical observation of anticipation, and other features in this family

Amplitude and area ratios of summating potential/action potential (SP/AP) in Meniere\u27s disease.

CONCLUSIONS: Our results suggest that summating potential/action potential (SP/AP) area ratio may not necessarily have higher sensitivity in the diagnosis of endolymphatic hydrops of Meniere\u27s disease (MD) than SP/AP amplitude ratio in transtympanic electrocochleography (ECochG). OBJECTIVE: Recent studies suggested that SP/AP area curve ratio was more sensitive to endolymphatic hydrops in comparison with SP/AP amplitude ratio in extratympanic ECochG. The purpose of the present study was to evaluate the utility of the SP/AP area curve ratio in transtympanic ECochG for the diagnosis of MD. PATIENTS AND METHODS: A retrospective chart review of 198 patients (209 ears) was conducted in cases of MD. RESULTS: With regard to SP/AP amplitude ratio, 57.1% in definite cases of MD (group 1), 39.6% in probable cases of MD (group 2), and 50.0% in the cases who had transformed from probable MD to definite MD (group 3) showed abnormally high values, respectively. Abnormally high values were observed in 43.9%, 27.7%, and 30.0% in SP/AP area ratio in groups 1, 2, and 3, respectively, indicating that abnormal values were observed more frequently in the amplitude ratio than in the area ratio in all three groups

Recovery of Hearing in Cisplatin-Induced Ototoxicity in the Guinea Pig with Intratympanic Dexamethasone

The purpose of this study was to investigate the effectiveness of intratympanic dexamethasone injection as a therapeutic agent against cisplatin-induced ototoxicity. Animals were randomly divided into three groups. Group one received intraperitoneal cisplatin alone, group two, received intratympanic dexamethasone after cisplatin ototoxicity had been demonstrated. Group three, which is control group, received intratympanic dexamethasone.Then we made three measurements. First we measured the baseline distortion product otoacustic emission (DPOAEs) of all the guine pigs. Second we injected cisplatin intraperitoneal group one and two the same day. Third we measured DPOAEs after 72 h of group one and two. Moreover DPOAEs were measured at the end of the first and second week only in group two. Cochleae were harvested and processed for electron microscopy after then. Values of The DPOAEs amplitudes and signal-to-noise ratio (SNR) at 1–6 kHz frequencies for group 1 after the injections significantly decreased over those before injections (P < 0.05). In group 3, there were no significant differences in DPOAE amplitude and SNR values When they are compare before and after their intratympanic dexamethasone injections (P > 0.05). In group 2, the DPOAEs measurements were close to significance at the end of the second week (P = 0.056). Intratympanic dexamethasone injection did not cause any ototoxic effect. Although intratympanic dexamethasone did not reach the statistically significant results, the measurements were close to significance. Intratympanic dexamethasone might have a significant therapeutic effect after cisplatin ototoxicity with different dose and application regimens