[An implantable piezoelectric hearing aid transducer for inner ear deafness. II: Clinical implant]

A miniature, hermetically sealed implant was development and manufactured in several clinical and technical iteration steps based on the prototype of an implantable piezo-electric hearing-aid transducer described in Part 1 of the work presented here. The transducer is made of pure titanium (medical grade 2, ASTM F67) and designed to be implanted into the mastoid cavity. Transfer of mechanical oscillations to an ossicle in the middle ear is effected by a fixed directly coupling rod of pure titanium or via suitable coupling elements. The transducer is highly tuned with a resonance frequency in the range of 7-10 kHz, depending on the dynamic mass load. Below this resonance and down to low frequencies, the frequency response of elongation is smooth with a very small ripple of less than +/- 1 dB. Unlike the prototype, an increase in vibration amplitude of around 10 dB was achieved for a comparable power consumption. Vibration amplitude at low and middle frequencies is about 60 nm with a transducer voltage of 1 V, corresponding to an equivalent sound-pressure level of around 100 dB SPL at up to 1 kHz. At higher frequencies of up to 10 kHz, the output level increases to beyond 130 dB SPL. Nonlinear distortions at maximum volume (1 V) are extremely small (THD < 0.1%) throughout the whole transfer range. Due to an extremely short attack time (50 microseconds) and short release time (approximately 2 ms), the dynamic properties of the transducer allow good transmission of audio signals with fast changes in the time domain, i.e., plosives in speech signals. Electric power consumption at full volume and broadband signals is in the region of 1 microW. Unlike electromagnetic transducers described in the literature, the low power consumption of this piezoelectric transducer allows the realization of fully implantable hearing aids for rehabilitation of moderate to severe sensorineural hearing loss.

Mechanically and ATP-induced currents of mouse outer hair cells are independent and differentially blocked by d-tubocurarine

Mechano-electrical transducer channels (MET) and ATP-gated ion channels (P2X receptors) of hair cells have several properties in common: they share the same location at the apex of the cell, both channels are non-selective for cations and blocked by aminoglycosides and pyrazinecarboxamides (amiloride-related compounds). In this study, we test the relationship and possible identity of these two channel types. Using whole-cell patch-clamp recordings of outer hair cells (OHCs) of the cultured neonatal mouse cochlea and a fluid jet to stimulate their hair bundles mechanically, we show that d-tubocurarine, a blocker of P2X2 receptors, blocks MET channels with a half-blocking concentration of 2.3 microM. In contrast, the KD for the P2X2 receptors was 90 microM and 84 microM measured in hair cells and Xenopus oocytes, respectively. When hair bundles of OHCs were simultaneously stimulated with saturating mechanical stimuli and superfused by 100-300 microM ATP, transducer currents and ATP-activated currents were elicited simultaneously. Their amplitudes were additive, however. We conclude that MET- and ATP-activated currents are mediated by two distinct channel populations in hair cells.

A totally implantable drug delivery system for local therapy of the middle and inner ear

Local therapy of middle and inner ear diseases is being used, but is restricted to cases of ear drum perforation or to repeated invasive intratympanic drug application by the physician. In accordance with the Medical Device Directive (class III), a bone-anchored, totally implantable drug delivery system (TI-DDS) has been developed. It includes a micropump for subcutaneous, patient-controlled activation, a drug reservoir and a septum port. A thin guide-wired catheter leads from the pump outlet to the point of application in the mastoid or middle ear cavities. Local inner ear therapy with suitable drugs is possible by positioning the catheter's end near the round window membrane. The system requires no battery and will offer a wide range of patient-controlled bolus applications (25 microliters per activation). We first analyzed the three-dimensional implantation geometry of the mastoid cavity. Basic micromechanical problems have been solved in order to create several prototypes. The TI-DDS has already undergone extensive in vitro testing. Recent results of pump rate precision and digital pressure force testing are promising. Local drug treatment for conditions such as lidocaine-sensitive tinnitus, secretory otitis media, Meniere's disease, localized pain and intralesional cancer is under discussion. Furthermore, local application of future biotechnological trophic factors for inner ear treatment is anticipated. The basic engineering is completed and initial animal tests are in preparation.

Short-term immunotherapy: a prospective, randomized, double-blind, placebo-controlled multicenter study of molecular standardized grass and rye allergens in patients with grass pollen-induced allergic rhinitis

BACKGROUND

Short-term immunotherapy (STI) can be beneficial for patients who are noncompliant with long-term specific immunotherapy.

OBJECTIVE

The efficacy and tolerance of STI with seven preseasonal injections of molecular standardized allergens from grass and rye pollen has been investigated in a double-blind, placebo-controlled multicenter study with 87 patients at 12 German University hospitals.

METHODS

Symptoms of the eyes, nose, and bronchi and use of symptomatic drugs were documented daily in diaries by patients with allergic rhinitis to grass and/or rye pollen and without bronchial asthma. Patients were monitored by skin prick test titration and measurement of levels of specific IgE and IgG4.

RESULTS

The median nasal score for the 10 weeks with the strongest symptoms during the grass pollen season was significantly lower (p = 0.014) with 35.0 for STI (n = 41) versus 69.0 for placebo (n = 40); the overall symptom score was 54.0 for STI versus 97.5 for placebo (p = 0.020). Only STI-treated patients exposed to less than 40 pollen grains per cubic meter per week showed a significantly lower nasal symptom score of 39.0 versus 75.0 for placebo (p = 0.006); these patients also had fewer nasal symptoms and less use of topical nasal drugs (p < 0.001). The threshold dose in skin prick tests was significantly higher, being 9.06 histamine equivalent for skin prick test (HEP) for STI-treated patients who received the maximum dose (n = 22) versus 4.33 HEP for placebo (p = 0.005). Specific IgE levels were significantly higher, being 55.9 SU/ml for STI versus 39.2 SU/ml for placebo after seven injections (p = 0.006) and level of specific IgG4 was 5.36% for STI versus 1.28% for placebo (p < 0.001). No severe systemic reactions were observed.

CONCLUSION

STI with seven preseasonal injections with molecular standardized allergens is effective and well tolerated.

[First comparisons with laser vibrometry measurements and computer simulation of ear ossicle movements]

The dynamic behavior of the ossicular chain is very complex and is frequency-dependent. To date, this has still not been fully investigated or understood. There remains a lack of measurement procedures to pick up the motion of the ossicles and ear drum simultaneously with sufficient resolution. The presented paper reports simultaneous measurements with laser-Doppler vibrometry at two points of the ossicular chain of cadaver specimens. Motions not observed were derived using mechanical simulation models on a computer and then evaluating appropriate mathematical equations. Using a sound stimulus, the displacement velocities of the umbo and stapes footplate were measured, and the corresponding transfer functions were derived by Fourier transform. Results were used for verification of the computer models. In the current investigations these models were refined and allow for the detailed investigation of the dynamic behavior of the ossicular chain, facilitating the optimal design of passive and active middle-ear implants.

Preoperative assessment of the implantable middle ear pump system using CT scans and conventional X-rays of the temporal bone

A completely implantable micropump system for drug delivery has recently been developed. After implantation in the temporal bone, this microdosage system enables application of drugs into the middle ear and round window area. Successful application of this new technology depends upon a suitable fit of the micropump within the patient's temporal bone. To obtain information about the fit before surgery, we analyzed 50 cadaver temporal bone specimens before total mastoidectomy, using conventional X-ray and spiral CT scans for water volume determination. Spiral CT is a feasible method for preoperative planning of the surgical implantation of the implantable middle ear micropump system (TI-DDS). The best parameter for a preoperative judgment is the volume of the mastoid cavity, as determined by CT. Implantation may be recommended when the mastoid volume, as measured by CT, is greater than 6.6 ml. To be certain that the implantable drug delivery system will be implantable, a cut-off value of 9.3 ml seems to be advisable. Spiral CT imaging is of great value as a tool for testing implantation preoperatively. The imaging is accomplished in approximately 30 seconds. Our preliminary results with cadaveric temporal bones are encouraging. Further studies are needed in order to transfer the results to a clinical implantation situation.

Desensitization of the P2X(2) receptor controlled by alternative splicing

P2X receptors are ion channels gated by extracellular ATP. We report here cloning of a P2X(2) receptor splice variant (P2X(2-2)) carrying a 207 bp deletion in the intracellular C-terminus and the analysis of the corresponding genomic structure of the P2X(2) gene. P2X(2-2) is as highly expressed as the original P2X(2) sequence in various tissues. ATP-activated currents mediated by heterologous expressed P2X(2) or P2X(2-2) receptors showed significant differences in desensitization time constants and steady-state currents in the continuous presence of ATP. These results imply functional differences between cells differentially expressing these P2X(2) isoforms.

[New methods of type II tympanoplasty in erosion of the long incus process]

Reliable methods of reconstruction of the ossicular chain in the situation of an isolated errosion of the long process of the incus using a tympanoplasty type II have not been available until recently. Instead, the tympanoplasty type III has been generally performed with the interposition of an autologous incus. In this presentation, we are describing two methods for reconstruction of the ossicular chain between the in-situ residing incus and the stapes on the other side so that the direct connection eventually will result in a tympanoplasty type II. In the first case, we used ionomeric cement in a way that features two characteristics: the direct connection between the stapes and the long process of the incus could be achieved as well as an articulation that was created on the head of the stapes. Hence, a too stiff connection between the head of the stapes and the long process of the incus could be avoided. In addition, a new method for precise microapplication of cooled bone cement (IONOCAP LV) with a syringe will be presented. In the second method titanium-gold-angle prostheses have been crimped to the long process of the incus and positioned onto the head of the stapes in the way of an articulation. So far, comparison of the audiological results of those two methods of a tympanoplasty type II reveal in average better results than postoperative conductive hearing thresholds of the conventional tympanoplasty type III. If the achieved results can be reproduced on a larger number of patients, the expected audiological results are likely to resemble those of stapes surgery.

Evaluation of performance with the COMBI40 cochlear implant in adults: a multicentric clinical study

The present multicentric clinical study involves 19 centres, 16 of them in German-speaking countries, 1 British, 1 Polish and 1 Hungarian. 60 postlingually deafened adults with a mean age of 47.5 years (20-70) and mean duration of deafness of 5.3 years (0.5-20) have been evaluated with the MED-EL COMBI 40 cochlear implant which implements a high-rate continuous-interleaved-sampling strategy with 8 channels. Safety and effectiveness data have been collected. Speech perception tests include a 16-consonant, an 8-vowel, a sentence and a monosyllabic-word test in all languages and a 2-digit figure test in all languages but English. Test intervals are 1, 3, 6 months and 1 year after first fitting. 41 of the 60 postlingually deafened adult study patients have completed their 6-month evaluation. While their pre-operative monosyllabic-word score was 0%, their mean monosyllabic-word score 6 months after first fitting was 48% (8-90) with a median of 50%. The mean sentence understanding was 84% (24-100) with a median of 90%. The respective values for the 1-year evaluations with 25 patients are a mean of 50% (5-85), with a median of 60% for the monosyllables and a mean of 89% (30-100), with a median of 97%, for the sentences.

Identification of a titratable lysine residue that determines sensitivity of kidney potassium channels (ROMK) to intracellular pH

Potassium (K+) homeostasis is controlled by the secretion of K+ ions across the apical membrane of renal collecting duct cells through a low-conductance inwardly rectifying K+ channel. The sensitivity of this channel to intracellular pH is particularly high and assumed to play a key role in K+ homeostasis. Recently, the apical K+ channel has been cloned (ROMK1,2,3 = Kir1.1a, Kir1.1b and Kir1.1c) and the pH dependence of ROMK1 was shown to resemble closely that of the native apical K+ channel. It is reported here that the steep pH dependence of ROMK channels is determined by a single amino acid residue located in the N-terminus close to the first hydrophobic segment M1. Changing lysine (K) at position 80 to methionine (M) removed the sensitivity of ROMK1 channels to intracellular pH. In pH-insensitive IRK1 channels, the reverse mutation (M84K) introduced dependence on intracellular pH similar to that of ROMK1 wild-type. A detailed mutation analysis suggests that a shift in the apparent pKalpha of K80 underlies the pH regulation of ROMK1 channels in the physiological pH range.

Resonant tectorial membrane motion in the inner ear: its crucial role in frequency tuning

The tectorial membrane has long been postulated as playing a role in the exquisite sensitivity of the cochlea. In particular, it has been proposed that the tectorial membrane provides a second resonant system, in addition to that of the basilar membrane, which contributes to the amplification of the motion of the cochlear partition. Until now, technical difficulties had prevented vibration measurements of the tectorial membrane and, therefore, precluded direct evidence of a mechanical resonance. In the study reported here, the vibration of the tectorial membrane was measured in two orthogonal directions by using a novel method of combining laser interferometry with a photodiode technique. It is shown experimentally that the motion of the tectorial membrane is resonant at a frequency of 0.5 octave (oct) below the resonant frequency of the basilar membrane and polarized parallel to the reticular lamina. It is concluded that the resonant motion of the tectorial membrane is due to a parallel resonance between the mass of the tectorial membrane and the compliance of the stereocilia of the outer hair cells. Moreover, in combination with the contractile force of outer hair cells, it is proposed that inertial motion of the tectorial membrane provides the necessary conditions to allow positive feedback of mechanical energy into the cochlear partition, thereby amplifying and tuning the cochlear response.

Extracellular K+ and intracellular pH allosterically regulate renal Kir1.1 channels

The channels that control K+ homeostasis by mediating K+ secretion across the apical membrane of renal tubular cells have recently been cloned and designated ROMK1, -2, and -3. Native apical K+ channels are indirectly regulated by the K+ concentration at the basolateral membrane through a cascade of intracellular second messengers. It is shown here that ROMK1 (Kir1.1) channels are also directly regulated by the extracellular (apical) K+ concentration, and that this K+ regulation is coupled to intracellular pH. The K+ regulation and its coupling to pH were assigned to different structural parts of the channel protein. K+ regulation is determined by the core region, which comprises the two hydrophobic segments M1 and M2 and the P region. Decoupling from pH was achieved by exchanging the N terminus of ROMK1 by that of the pH-insensitive channel IRK1 (Kir2.1). These results suggest an allosteric regulation of ROMK1 channels by extracellular K+ and intracellular pH, which may represent a novel link between K+ homeostasis and pH control.

[Minimally invasive ENT surgery. Progress due to modern technology]

Three fundamentals have to be fulfilled to optimize minimally, invasive surgery: three-dimensional imaging, free maneuverability of the instruments, sensorial feedback. Projection of two pictures from a stereoendoscope and subsequent separation with a LCD shutter allows three-dimensional videoendoscopy to be performed. A high-frequency shutter technique (100/120 Hz) presents pictures from the two video cameras to the right and left eye, respectively, so that the surgeon has spatial vision of the operative field. Steerable instruments have four component: a control unit, rigid shaft, steerable multi-joints, distal effector. The steerable multi-joints give two additional degrees of freedom compared to conventional rigid instruments in endoscopic surgery. For intuitive movements, however, an electronic control system is necessary that is comparable to the "master-slave" principle in remote technology. A remote manipulator system with six degrees of freedom is now available. Additionally, a multifunctional distal tip permits different surgical steps to be performed without changing the instrument. For better control of the instrument and the operative procedure tactile feedback can be achieved with appropriate microsensor systems. Recent projects suggest that an artificial sensor system can be established within the foreseeable future.

[Transfacial approach, craniofacial resection and midfacial degloving in surgery of malignant tumors of the anterior cranial base and adjacent paranasal sinuses]

Malignancies of the nose, paranasal sinuses and anterior skull base are characterized by their hidden locations and late clinical manifestation. This explains why most of the patients at the University of Tübingen were diagnosed in an advanced tumor stage (15 T1/T2; 33 T3/T4). Surgical treatment was possible in 35 cases and depended on tumor location and extent. A lateral rhinotomy for a transfacial approach was performed in 8 tumors of the middle level and 6 tumors of the upper level as described by Sebileau. An advantage of this procedure was the exposure provided with a working direction parallel to skull base and orbit allowing a secure en bloc resection. In 9 cases the malignant growth was localized in the upper level infiltrated the anterior skull base and required a craniofacial resection. An alternative to transfacial resection of nasal and sinus tumors was the midfacial degloving technique. Without creating visible facial scars we were able to resect reliably 5 malignancies of the middle level that extended in part to the sphenoid sinus and the nasopharynx. Complications occurred in 2 cases. When also considering non-malignant tumors (n = 42), the following complications occurred with this technique: stenosis of the lacrimal duct, stenosis of the nasal vestibule and a perceptive disorder of the infraorbital nerve. Endonasal surgery was restricted to small malignancies of the nasal cavity. In contrast, surgical treatment of advanced tumors required a wide and clear three-dimensional exposure for an oncologically secure resection.

Expression of neurotrophin receptor trkB in rat cochlear hair cells at time of rearrangement of innervation

The spatio-temporal distribution of the high-affinity neurotrophin receptor trkB was monitored during postnatal development of the rat cochlea. In addition to expression in presumptive afferent type I collaterals, afferent type II fibers, and efferent fibers, trkB immunoreactivity also transiently appeared in the sensory hair cells themselves, from postnatal days 5-9 in the basal turn, and from postnatal days 9-13 in the apical turn. A comparison of trkB with p75(NGFR), which is expressed in afferent and efferent fibers, and GAP-43 and synaptophysin, which are expressed in efferent fibers, revealed a time/space correlation of trkB receptor expression in hair cells with the rearrangement of their innervation. Co-expression of the neurotrophin receptor and its ligand has been proposed to be functionally involved in regulating the survival of neurons independent of target-derived neurotrophin factor. Thus, the presence of trkB in target hair cells, suggests that auto/paracrine mechanisms play a role during this critical period of rearrangement of neural connections.

Preservation of the non-rectangular cuticular plate/cell axis angle of outer hair cells

Motile properties of outer hair cells (OHCs) may contribute to sharp tuning and amplification in the mammalian cochlea. Shape changes of isolated OHCs in response to various physical and chemical influences have been investigated intensively. However, determinations of shape may have been influenced by unanticipated effects of preparation and preservation of the OHCs investigated. Thus, in a first step, lengths of freshly isolated OHCs from the guinea pig cochlea were determined using a video-enhancing magnification system. The cuticular plate/cell axis angle (CP/CA angle) was then measured in native cells and under the influence of potassium chloride and potassium gluconate incubation. To show the influence of glutaraldehyde (GA) fixation on the isolated OHCs, fixative-dependent changes on cell length and CP/CA angle were recorded in native and preincubated OHCs. In these experiments, the cell length of vital isolated OHCs was between 41.5 micrometers, in the basal turn, and 103.7 micrometers, in the apical turn. The average CP/CA angle was 106 degrees +/- 4.2 degrees (n = 324 cells, turns 1-4) with no statistically significant differences for the four turns. Under the influence of potassium chloride, cell length was reduced by 8.1%. Potassium gluconate incubation led to a shortening of cell length, followed by a 5.3% increase after 5 min. The CP/CA angle under potassium chloride was decreased (97.0 degrees) and was then increased under the influence of potassium gluconate (110.7 degrees) as a result of cuticular plate tilting. Cell shrinkage after fixation depended on the fixative's osmolarity and on the GA concentration. Increased GA levels amplified cell shrinkage from 34% for hypo-osmolar solutions to 15% in iso-osmolar and 29% in hyperosmolar solutions. The CP/CA angle of native and incubated OHCs was not different from those fixed with GA. The present data provide a rational basis for isolated OHC shape parameters. Moreover, functionally induced changes can be better interpreted when OHCs are influenced by fixatives, as shown in the GA experiments.

Cell-specific expression of the alpha 9 n-ACh receptor subunit in auditory hair cells revealed by single-cell RT-PCR

Single-cell reverse transcription polymerase chain reaction was carried out in three different cell types from the organ of Corti of the four-day old rat. For this purpose, pieces of the organ of Corti were mounted under a differential-interference contrast video microscope. Two different mounting configurations were used to allow imaging of cells from two almost orthogonal angles. This method afforded unequivocal recognition of various cell types in the vital tissue, and extraction of nucleus and cytoplasm of specified individual cells with a patch pipette. Messenger RNA encoding the alpha 9 acetylcholine (ACh) receptor subunit was detected and sequenced from individual outer hair cells and inner hair cells, but was not found in Deiters' cells. The identical Deiters' cells were positive for a P2x receptor subunit. This indicates cell-specific expression of the alpha 9 subunit in inner hair cells and outer hair cells and supports the hypothesis that this subunit contributes to calcium (Ca2+) permeable ionotropic ACh receptors (ACh-R). ACh-dependent Ca2+ concentration increase has been observed in both outer hair cells and inner hair cells.

Subunit-specific inhibition of inward-rectifier K+ channels by quinidine

Distinct inward-rectifier K+ channel subunits were expressed in Xenopus oocytes and tested for their sensitivity to the channel blocker quinidine. The 'strong' inward-rectifier K+ channel IRK1 was inhibited by quinidine with an EC50 of 0.7 mM, while the 'weak' rectifier channel ROMK1 was only moderately inhibited. ROMK1(N171D)-IRK1C-term chimeric channels, which carry both sites for strong rectification of IRK1 channels (the negatively charged D171 in the second transmembrane domain and the IRK1-C-terminus including E224), displayed strong rectification like IRK1, but showed weak sensitivity to quinidine-like ROMK1, suggesting independence of quinidine binding and rectification mechanisms. Moreover, BIR10 and BIR11, two strong rectifier subunits originally cloned from rat brain, exerted subunit-specific sensitivity to quinidine, being much higher for BIR11. Quinidine blockade of IRK1 was not voltage-dependent, but strongly dependent on the pH in the superfusate. These results strongly suggest a subunit-specific interaction of inward-rectifier K+ channels with neutral quinidine within membrane lipid bilayers.

Synaptophysin and GAP-43 proteins in efferent fibers of the inner ear during postnatal development

A rearrangement of afferent and efferent fibers occurs in the postnatal development of the inner ear. Growth and synaptogenesis was explored during this critical period by immunohistochemically monitoring the expression of GAP-43 and synaptophysin. Both proteins were colocalized in efferent fibers beyond postnatal day 3 (pn3). Two distinct synaptophysin- and GAP-43-positive fibers innervated different parts of inner hair cells in the first and second postnatal weeks, respectively. GAP-43-positive efferents projecting to outer hair cells upregulated synaptophysin with base to apex gradient between postnatal day 5 and postnatal day 14. In efferents projecting to outer hair cells GAP-43 was downregulated about 6 days beyond synaptogenesis. In efferents projecting to inner hair cells, however, GAP-43 remained upregulated even beyond pn18, indicating continuous synapse replacement of this fiber type. Both proteins thus improved as excellent markers for growth and synaptogenesis of distinct postnatal efferent fibers.

Abolition of the receptor potential response of isolated mammalian outer hair cells by hair-bundle treatment with elastase: a test of the tip-link hypothesis

To test the hypothesis that the tip-links of hair-cell stereocilia are essential for mechanoelectrical transduction, tip-links of isolated outer hair cells (OHCs) of the guinea-pig cochlea were eliminated with a proteolytic enzyme, elastase, and the influence on the receptor potential measured with the whole-cell patch-clamp technique. Within 45 s of immersion of the hair bundle in 20 IU/ml elastase, the receptor potential in response to direct deflection of the hair bundle was irreversibly abolished. The electrical input impedance of the cell remained unchanged, implying that the channels of the basolateral membrane were not affected by elastase. The effect of elastase on the receptor potential was comparable to changes seen after mechanically induced hair-bundle damage. As a further control, a putative transduction-channel blocker, dihydrostreptomycin (68 microM), which does not affect tip-links, was applied to the hair bundle. Although the receptor potential was also blocked by dihydrostreptomycin, the effect was reversible. The results suggest that tip-links are required for mechanoelectrical transduction of mammalian OHCs.

Benign supraclavicular tumorous lymphangiectasia--a new disease?

We describe an isolated recurrent non-inflammatory tumorous swelling of the supraclavicular fossa in four premenopausal women. Ultrasonography, magnetic resonance imaging and computer tomography of the neck each suggested an inhomogeneous mass consistent with "lymphangioma." In each patient the clinical course and histopathologic findings suggested that the swellings were due to chronic localized lymph stasis with subsequent lymphangiectasia, possibly initiated by intermittent obstruction of the juncture of the thoracic or right lymph duct with the internal jugular vein. Enlargement may have been hormonally triggered by estrogens as each woman was taking oral contraceptive pills at the onset of the disease. To characterize this unique entity, we have termed the disorder benign supraclavicular tumorous lymphangiectasia.

Subunit-dependent assembly of inward-rectifier K+ channels

Inward-rectifier, G-protein-regulated and ATP-dependent K+ channels form a novel gene family of related proteins which share two transmembrane segments as a common structural feature. These K+ channels are only distantly related to the voltage-gated Shaker-type K+ channels comprising six transmembrane segments. Although the quaternary structure of voltage-gated K+ channels has been extensively studied in the past, little is known about subunit assembly of inward-rectifier K+ channels. Differential sensitivity of inward-rectifier K+ channels to voltage-dependent pore block by spermine was used to analyse subunit assembly. It is shown that inward-rectifier K+ channel proteins are composed of four subunits whose assembly obeys the rules of a binomial distribution. 'Strong' and 'mild' inward-rectifier K+ channel subunits (BIR10 and ROMK1) which are co-expressed in individual auditory hair cells form hetero-tetramers. Distribution of these hetero-tetramers, however, is not binomial. Hetero- and homo-oligomeric channels form with similar probabilities resulting in independent channel populations with distinct functional properties.

Caloric evoked motile responses of mammalian vestibular sensory cells

Evokation of caloric nystagmus in microgravity argues against thermal convection as a sufficient explanation for a caloric nystagmic response. By contrast, caloric nystagmus observed in weightlessness suggests a gravity independent mechanism. Here we demonstrate that direct caloric stimulation of isolated living vestibular hair cells from the guinea pig evoked mechanical responses of the sensory cells. Heating of the mechanoreceptor cells from 37 degrees C to 42 degrees C resulted in elongation cooling of the cells from 37 degrees C to 30 degrees C induced shortening of vestibular hair cells. The observed mechanism might contribute to the caloric evokation of a nystagmus both on earth and in orbit.

Immunological identification of candidate proteins involved in regulating active shape changes of outer hair cells

By employing immunological methods, it has been demonstrated that myosin, myosin light chain (MLC) and myosin light chain kinase (MLCK) proteins in outer hair cells (OHC) are immunologically different from isoforms in platelets, smooth muscle and heart muscle, and are probably more related to isoforms found in red blood cells (RBC). Moreover, proteins related to band 3 protein (b3p) and protein 4.1 (p 4.1), ankyrin as well as fodrin and spectrin, but not glycophorin, have been identified in isolated OHCs. Both OHCs and RBC differ from other motile non-muscle cells in their lack of smooth muscle isoforms of actin, their common high levels of spectrin-, ankyrin- and band 3-like proteins, as well as the expression of the 80 kDa protein 4.1 isoform. The data support the notion that motility of OHC may be based upon regulation of the b3p/p 4.1/ankyrin complex, and thus may be reminiscent to the active shape changes in RBC.

A threshold decrease for electrically stimulated motor responses of isolated aging outer hair cells from the pigmented guinea pig

When outer hair cells are isolated from guinea pig cochleas and are placed in normal Hank's medium, they exhibit aging as a slow tonic reduction in length and increase in diameter. During this time the lateral subsurface cisternae become progressively vesiculated and the optical density of the border seen under phase-contrast microscopy decreases. A study of 65 outer hair cells was carried out using video imaging of this process. The base of each cell bonded to the Petri dish and the motility of the cuticular plate was recorded in two ways. To quantify the slow contraction of each preparation, the dimensions of the cell were measured from video replay. Displacements of the cuticular plate in response to an alternating electric field in line with the cell axis were also monitored using a video tracking technique. The amplitude of a 1 Hz stimulus required to cause a visually detectable motor response above baseline noise decreased as the cell degraded. Typically, fresh cylindrical cells exhibiting high optical contrast showed relatively small movements for field strengths up to 2 kVm-1. However, as the cell depolarized, the rigidity initially decreased and the cell could respond to field strengths down to 0.1 kVm-1 before cell death ultimately occurred. Such a threshold phenomenon in the isolated OHC has not been demonstrated directly until now. This result explains the variability of electromotility in aging in vitro preparations from the cochlea.

Acute hyperpolarization and elongation of cochlear outer hair cells on superfusion with cis-platinum

The acute effects of cis-platinum on isolated cochlear outer hair cells (OHC) were investigated with whole-cell patch-clamps and measurements of cell length changes. Our findings demonstrated that cis-platinum reversibly induced a hyperpolarization and cellular elongation. These results suggest that the effects produced are the result of an interaction between cis-platinum and transduction channels in OHC. These acute effects are distinctly different from the chronic, irreversible ones that are followed by death of the OHC. The exact mechanism of these chronic effects remains unknown as yet.

Sound-induced displacement responses in the plane of the organ of Corti in the isolated guinea-pig cochlea

Sound-induced displacement responses in the plane of the organ of Corti were studied in the apical turn in the isolated temporal-bone preparation of the guinea-pig cochlea. Swept sinusoidal sound stimuli (100-500 Hz) were delivered closed-field to the external auditory meatus. The surface of the organ of Corti was continuously monitored using a CCD video camera. Displacement responses in the plane of the organ of Corti were determined by analyzing the change of the location of the cells (pixel-by-pixel) within the visual field of the microscope. Displacement responses followed the stimulus amplitude and were observable at Hensen's cells, three rows of outer hair cells and inner hair cells. The most prominent displacement responses were over the outer hair cells; the maximum amplitude was 0.6-1.7 microns at 100 dB SPL. Tuned displacement responses were found; the Q10 dB was 1.3 +/- 0.6. The best frequency was tonotopically organized, decreasing toward the apex with a space constant of 0.4-0.9 mm/oct. The motion was directed either strial-apically or strial-basally in a frequency dependent manner. With the aid of laser interferometric measurements of the transverse displacement, it was concluded that sound stimulation does not induce slow DC motion in the organ of Corti for the isolated temporal-bone preparation.

[Comparison of methods for early detection of noise vulnerability of the inner ear. Amplitude reduction of otoacoustic emissions are most sensitive at submaximal noise impulse exposure]

Noise-induced temporary impairment of cochlear function was measured with several audiometric tests in order to evaluate which method best predicts a vulnerable cochlea. We tested 10 normally-hearing and 13 subjects who were positive for temporary threshold shifts (TTS). The latter were selected from 194 soldiers who demonstrated a TTS higher than 15 dB after regular training with firearms. Acoustic distortion products (DPOAE), click-evoked otoacoustic emissions (TEOAE), upper limit of hearing (ULH) and pure-tone and high-frequency audiometry were used to evaluate possible increased vulnerability of the cochlea. Tests were conducted at lower sound intensities (white noise, 90 dB SPL, 5 min; impact noise, 100 or 106 dB SPLs, 10 impulses/s, 5 min). Seventy per cent of the TTS-positive soldiers studied exhibited significant reductions of TEOAE amplitudes, whereas a stable emission was observed in all control subjects. DPOAE alterations were seen in 38% of the soldiers tested. These results indicate that TEOAE is the most sensitive, objective method for detecting a positive disturbance in cochlear function. Although the upper limit of hearing was also a very sensitive method, variability of this psychoacoustic method depended on the help and experience of the subjects being tested.

Strong voltage-dependent inward rectification of inward rectifier K+ channels is caused by intracellular spermine

Inward rectifier K+ channels mediate the K+ conductance at resting potential in many types of cell. Since these K+ channels do not pass outward currents (inward rectification) when the cell membrane is depolarized beyond a trigger threshold, they play an important role in controlling excitability. Both a highly voltage-dependent block by intracellular Mg2+ and an endogenous gating process are presently assumed to underly inward rectification. It is shown that strong voltage dependence of rectification found under physiological conditions is predominantly due to the effect of intracellular spermine. Physiological concentrations of free spermine mediate strong rectification of IRK1 inward rectifier K+ channels even in the absence of free Mg2+ and in IRK1 mutant channels that have no endogenous rectification.

[Detection of GABA(A) receptor mRNA in cochlear tissue. An in situ hybridization study]

Gamma-aminobutyric acid (GABA) and the GABAergic system play an important role in the efferent modulation of cochlear function. We examined surface preparations of guinea pig and mouse cochleae by in situ hybridization using radioactive labelled oligonucleotides for several subunits of the GABAA receptor. Frozen sections of rat and guinea pig brain (cortex, hippocampus, cerebellum) served as controls. In the mouse cochlea the mRNA of the alpha-1 and alpha-5, beta-1 and gamma-1 subunit were detected, while in guinea pig cochlea mRNA of the alpha-1, alpha-4, alpha-5, and gamma-1 subunit of the GABAA receptor were found. Positive signals were located in the regions of the outer hair cells and had a weaker intensity in the inner hair cells. In the brain sections the several subunits were detected in a variable distribution in the cerebellum, hippocampus and cortical regions. Rat specimens exhibited stronger signals than guinea pig brain sections. These investigations have extended previous results of immunocytochemical experiments from our laboratory demonstrating mRNA sequences of GABAA receptor subunits in the mammalian inner ear. Detection of these nucleotide sequences using surface preparations of the cochlea on a molecular level by in situ hybridization supports the importance of GABA as a cochlear neurotransmitter. Furthermore, it can be concluded that the mammalian cochlea is able to express a GABA-dependent neurotransmission system.

Electromotile responses and frequency tuning of isolated outer hair cells of the guinea pig cochlea

Isolated outer hair cells (OHC) of the guinea pig cochlea were exposed to external alternating electric fields parallel to the longitudinal axis of the cells. This resulted in oscillations of the cells' length that were measured photoelectrically using a ratiometric light amplifier. At 5 Hz and elongations up to 300 nm, amplitude of the cell length during oscillation was a linear function of the amplitude of the sinusoidal electric field. When increasing the stimulus frequency up to 32 kHz, OHC length changes followed the stimulus cycle-by-cycle. Oscillations at frequencies above 32 kHz escaped the experimental approach by their small amplitudes and could not be excluded. The frequency dependence of the motile response measured at 5-12,000 Hz had low-pass filter characteristics in cells of the second, third and fourth turns of the cochlea. However, frequency tuning of the motile response was absent in each OHC and systematic differences between different turns were not observed.

A structural determinant of differential sensitivity of cloned inward rectifier K+ channels to intracellular spermine

Large subtype-specific differences in the sensitivity of cloned inward-rectifier K+ channels of the IRK1, BIR10 and ROMK1 subtype to being blocked by intracellular spermine (SPM) are described. It is shown, by site-directed mutagenesis, that the four orders of magnitude larger SPM sensitivity of BIR10 channels compared to ROMK1 channels may be explained by a difference in a single amino acid in the putative transmembrane segment TMII. This residue, a negatively charged glutamate in BIR10, is homologous to the residue in IRK1 and ROMK1 which has previously been shown to change gating properties and Mg2+ sensitivity. Differential block by physiological SPM concentrations is suggested as a major functional difference between subtypes of inward-rectifier K+ channels.

Kir2.1 inward rectifier K+ channels are regulated independently by protein kinases and ATP hydrolysis

Second messenger regulation of IRK1 (Kir2.1) inward rectifier K+ channels was investigated in giant inside-out patches from Xenopus oocytes. Kir2.1-mediated currents that run down completely within minutes upon excision of the patches could be partly restored by application of Mg-ATP together with > 10 microM free Mg2+ to the cytoplasmic side of the patch. As restoration could not be induced by the ATP analogs AMP-PNP or ATP gamma S, this suggests an ATPase-like mechanism. In addition to ATP, the catalytic subunit of cAMP-dependent protein kinase (PKA) induced an increase in current amplitude, which could, however, only be observed if channels were previously or subsequently stimulated by Mg-ATP and free Mg2+. This indicates that functional activity of Kir2.1 channels requires both phosphorylation by PKA and ATP hydrolysis. Moreover, currents could be down-regulated by N-heptyl-5-chloro-1-naphthalenesulfonamide, a specific stimulator of protein kinase C (PKC), suggesting that PKA and PKC mediate inverse effects on Kir2.1 channels. Regulation of Kir2.1 channels described here may be an important mechanism for regulation of excitability.

[Maturation of postsynaptic acetylcholine receptors in cochlear outer hair cells]

Sound transduction in the inner ear is controlled by olivocochlear efferents terminating predominantly at outer hair cells (OHC). Development of efferent fibers and thereby of postsynaptic OHC receptors was studied immunohistochemically in 13 cochleae from fetal guinea pigs. The gestational ages of the animals ranged from gestational day (GD) 35 to GD 56. To visualize nicotinic acetylcholine receptors (nAChR), sera were used from myasthenia gravis patients with confirmed nAChR antibodies. At GD 53 no staining was observed, whereas at GD 58 a striking nAChR-immunoreactivity was found. In cochleae from adult animals postsynaptic receptors were visualized at the bases of all three rows of OHCs. The region of the inner hair cells (IHC) was not stained. The present results indicate that nAChRs in guinea pig cochleae develop between GD 53 and GD 58. Maturation of the postsynaptic nAChRs coincides with development of OHC motile properties.

[Drug therapy of acute inner ear hearing loss in childhood and adolescence]

Sensorineural hearing loss in early childhood may severely interfere with normal speech and language development. This by itself requires pursuit of an effective therapeutic procedure. Here we report the results of therapy with a rheological agent and procaine-HCl with or without the addition of steroids. Immunological testing was also studied for possible circulating antibodies in sera of affected children. Retrospective analysis of therapeutic results showed that the therapeutic procedure employed may be beneficial, since hearing improved considerably in some cases. Since an autoimmune-related sensorineural hearing loss has been postulated for some years, results presented here could be used as an argument for the presence of antibody-related inner ear disorders in early childhood. These findings suggest that circulating antibodies in children suffering from sensorineural hearing losses produce an inflammatory process involving inner ear structures. Circulating antibodies may also indicate a secondary immune reaction. However, sensory hearing loss occurring in early childhood may be steroid sensitive.

Electromotility of outer hair cells from the cochlea of the echolocating bat, Carollia perspicillata

Isolated outer hair cells (OHCs) and explants ot the organ of Corti were obtained from the cochlea of the echolocating bat, Carollia perspicillata, whose hearing range extends up to about 100 kHz. The OHCs were about 10-30 microns long and produced resting potentials between -30 to -69 mV. During stimulation with a sinusoidal extracellular voltage field (voltage gradient of 2 mV/microns) cyclic length changes were observed in isolated OHCs. The displacements were most prominent at the level of the cell nucleus and the cuticular plate. In the organ of Corti explants, the extracellular electric field induced a radial movement of the cuticular plate which was observed using video subtraction and photodiode techniques. Maximum displacements of about 0.3-0.8 microns were elicited by stimulus frequencies below 100 Hz. The displacement amplitude decreased towards the noise level of about 10-30 nm for stimulus frequencies between 100-500 Hz, both in apical and basal explants. This compares well with data from the guinea pig, where OHC motility induced by extracellular electrical stimulation exhibits a low pass characteristic with a corner frequency below 1 kHz. The data indicate that fast OHC movements presumably are quite small at ultrasonic frequencies and it remains to be solved how they participate in amplifying and sharpening cochlear responses in vivo.

Intracellular calcium changes by hyposmotic activation of cochlear outer hair cells in the guinea pig

During continued exposure to a hypotonic solution, isolated outer hair cells (OHCs) from the guinea pig cochlea showed a regulatory volume decrease (RVD) after initial cell swelling. In the absence of extracellular Ca2+, RVD was significantly inhibited. Using Ca(2+)-sensitive dye fura-2, accompanying changes of the intracellular Ca2+ concentrations ([Ca2+]i) of OHC were investigated. Hyposmotic activation resulted in a [Ca2+]i increase associated with cell shortening and swelling. In a Ca(2+)-free solution, [Ca2+]i was not significantly increased during hyposmotic activation although shortening and swelling of the OHC was observed. These results suggest that the increase in [Ca2+]i during hyposmotic activation is mainly based on an influx or extracellular Ca2+ which precedes the RVD.

Gamma-aminobutyric acidA-receptor messenger ribonucleic acid (alpha-1 subunit) detection by in situ hybridization

The inhibitory neurotransmitter gamma-aminobutyric acid (GABA) is most likely involved in the efferent cochlear neurotransmission. In situ hybridization (ISH) results in specific annealing of a labelled nucleic acid probe to complementary sequences in fixed tissue and allows subsequent visualization of the location of the probe. We used the ISH technique to localize messenger ribonucleic acid (mRNA) sequences of the alpha-1 subunit of the GABAA receptor with an S-35 labeled oligonucleotide probe. Experiments were performed in rat and guinea pig brain sections and surface tissue preparations of the guinea pig cochlea. Positive signals were obtained for the alpha-1 probe in cortical and hippocampal regions of the rat brain and had weaker expression in the guinea pig brain. Alpha-1 subunit mRNA was localized in Purkinje cells and in stellate and basket cells of the stratum moleculare in the rat and guinea pig cerebellum. In surface tissue preparations of the guinea pig cochlea mRNA sequences of the alpha-1 subunit were detectable with high signal expression. Positive signals were seen on both sides of the tunnel of Corti, predominantly in the region of the outer hair cells. The results indicate expression of GABAA-receptor mRNA in cochlear tissue, supporting the importance of GABAA receptors in cochlear neurotransmission.

Frequency response of mature guinea-pig outer hair cells to stereociliary displacement

Outer hair cells (OHC) were isolated from the apical two turns of the guinea-pig cochlea and their hair-bundle stimulated mechanically by a glass probe. In accordance with in vivo data (Dallos, 1985), the resting membrane potential was typically -64 mV (N = 200). The maximum amplitudes of the receptor potentials were between 0.4 and 5.2 mV peak-to-peak, with mean of 1.5 mV +/- 0.9 mV (N = 81). The sensitivity was 0.015 mV/nm or 2 mV/deg. The frequency response of the receptor potential followed a first order low-pass filter characteristic with a corner frequency of about 63 Hz. For frequencies up to at least 1.6 kHz, the frequency response of mechanoelectrical transduction was dominated by the electrical input impedance of the cell. The presence of a single time constant in the voltage response to stereociliary deflection implies that the frequency response of mechanoelectrical transduction far exceeds that of the electrical input impedance of the cell; its time constant must be faster than 100 microseconds. Under in vivo conditions, OHC should be capable of providing a sufficiently large receptor potential to supply enough energy for electromechanical feedback.

Short antisense oligonucleotide-mediated inhibition is strongly dependent on oligo length and concentration but almost independent of location of the target sequence

The inhibitory effect of short antisense oligodeoxynucleotides (aODNs) on cRNA expression in Xenopus oocytes was measured using an electrophysiological assay based on subunit-specific block of cloned alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate receptors. The effect of both phosphorothioate-modified (PS) and phosphodiester (PO) aODNs was strongly length dependent with a half-maximal inhibition calculated for an oligo length of 7.6 nucleotides (nt) and 9.9 nt, respectively. More than 95% inhibition was mediated by a PS aODN of 12 nt and by PO aODNs > or = 15 nt. At a given length PS and PO aODNs showed differential dependence of their inhibitory effect on the injected aODN concentration (half-maximal inhibition at 18 ng/microliter for a PO 12-mer and at 0.19 ng/microliter for a PS 12-mer) and differential saturation behavior. The inhibitory effect of aODNs, even as short as 8 nt for PS oligomers, was highly sequence specific, but almost independent of the position of the respective target site on the cRNA (for PS 8-mers, > or = 70% expression inhibition throughout the tested target sites from the translation initiation to the 3'-untranslated region). Thus, short PS aODNs can be reliably used in order to specifically inhibit protein expression in experiments addressing physiological, molecular biological, and perhaps even therapeutical issues.

Transitory endolymph leakage induced hearing loss and tinnitus: depolarization, biphasic shortening and loss of electromotility of outer hair cells

There are types of deafness and tinnitus in which ruptures or massive changes in the ionic permeability of the membranes lining the endolymphatic space [e.g., of the reticular lamina (RL)] are believed to allow potassium-rich endolymph to deluge the low [K+] perilymphatic fluid (e.g., in the small spaces of Nuel). This would result in a K+ intoxication of sensory and neural structures. Acute attacks of Ménière's disease have been suggested to be an important example for this event. The present study investigated the effects of transiently elevated [K+] due to the addition of artificial endolymph to the basolateral cell surface of outer hair cells (OHC) in replicating endolymph-induced K+ intoxication of the perilymph in the small spaces of Nuel. The influence of K+ intoxication of the basolateral OHC cell surface on the transduction was then examined. Intoxication resulted in an inhibition of the physiological repolarizing K+ efflux from hair cells. This induced unwanted depolarizations of the hair cells, interfering with mechanoelectrical transduction. A pathological longitudinal OHC shortening was also found, with subsequent compression of the organ of Corti possibly influencing the micromechanics of the mechanically active OHC. Both micromechanical and electrophysiological alterations are proposed to contribute to endolymph leakage induced attacks of deafness and possibly also to tinnitus. Moreover, repeated or long-lasting K+ intoxications of OHC resulted in a chronic and complete loss of OHC motility. This is suggested to be a pathophysiological basis in some patients with chronic hearing loss resulting from Ménière's syndrome.

[Functional screening evaluation of hearing aids]

A complaint about a malfunctioning hearing aid (HA) usually will require thorough testing of all aspects of hearing aid functions by the hearing aid dispenser. However, ENT physicians can also detect defects easily by following the simple screening procedure described here. Before testing the HA function, the following questions should be answered: Are the body of the hearing aid and ear mold intact? Is the ear canal free of irritation and is the acoustic isolation of the ear canal by the HA sufficient? A rough estimate of HA function can be accomplished by covering the HA with the hand. If the HA is switched on, a feedback, high-pitched sound should be produced. HA amplification can be assessed by using a stethoclip. After the examination is completed, all switches should be put back into their previous positions. Although these basic procedures are not equivalent to diligent and comprehensive acoustical testing, they are still useful for the otologist to detect major faults in the HA before referring the patient to the hearing aid dispenser.

Specific glutathione-SH inhibition of toxic effects of metabolized gentamicin on isolated guinea pig hair cells

The present investigation has shown that only metabolized gentamicin (mG) but not native gentamicin (G) is cytotoxic for isolated guinea pig outer hair cells (OHC). Using FURA-2 fluorescence, both G and mG were found to reduce intracellular free Ca2+ concentrations in unstimulated OHC and inhibit increases in intracellular Ca2+ concentrations during K(+)-induced depolarization. Glutathione-SH (GSH), a detoxificating agent, did not interfere with G and mG effects on intracellular Ca2+ concentration. In non-stimulated OHC, mG but not G induced pathological OHC depolarization, indicating the opening of transduction channels to allow influx of K+ ions. GSH completely inhibited the lytic effect of mG. Electrophysiological investigations also revealed that GSH probably inhibits mG-induced pathological opening of transduction channels. These results suggest that GSH selectively inhibits mG-specific toxic effects on the guinea pig OHC, possibly by enzymatic detoxification.

Acute gentamicin ototoxicity in cochlear outer hair cells of the guinea pig

The acute effects of the aminoglycoside antibiotics gentamicin on isolated cochlear outer hair cells (OHC) was investigated by whole-cell patch-clamp and measurements of the intracellular potassium level by means of the potassium-sensitive dye PBFI. In addition, the accompanying length changes of OHC are described. It could be shown that gentamicin at different concentrations reversibly induces a hyperpolarization by about 5-10 mV, potassium outflow from the cytoplasm (by about 22 mM) and a cellular elongation (by about 10%). It is suggested that these effects are the result of an interaction between gentamicin and the cochlear transduction channels in OHC as suggested earlier. These acute effects are distinctly different from the chronic gentamicin effects which are based on the metabolization of the antibiotics to cause the death of the OHC by interaction with the phosphoinositide signalling cascade.