[Otolithic membrane evolution. Otolithic membrane structure in amphibia and reptiles. ].
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Animals↗
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Tectorial membrane and otolithic membrane of pigeon inner ear. A scanning electron microscope study.
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Animals↗
Identification of a structural constituent and one possible site of postembryonic formation of a teleost otolithic membrane.
A gelatinous otolithic membrane (OM) couples a single calcified otolith to the sensory epithelium in the bluegill sunfish (Lepomis macrochirus) saccule, one of the otolithic organs in the inner ear. Though the OM is an integral part of the anatomic network of endorgan structures that result in vestibular function in the inner ear, the identity of the proteins that make up this sensory accessory membrane in teleosts, or in any vertebrate, is not fully known. Previously, we identified a cDNA from the sunfish saccular otolithic organ that encoded a new member of the collagen family of structural proteins. In this study, we examined biochemical features and the localization of the saccular collagen (SC) protein in vivo using polyclonal antisera that recognize the noncollagenous domains of the SC protein. The SC protein, in vivo, was identified as a 95-kDa glycoprotein in sunfish whole-saccule lysate and in homogenates of microdissected saccular OMs. Immunohistochemical analyses demonstrated that the SC protein was localized within one of the two distinct layers of the sunfish saccular OM. The SC protein was also detected within the cytoplasm of supporting cells at the edges of the saccular sensory epithelium, indicating that these cells are a primary site for the synthesis of this structural protein. Further studies of the organization of this matrix molecule in the OM may help clarify the role of this sensory accessory membrane in vestibular sensory function.
Animals↗
Proteins of the gelatinous layer of the trout saccular otolithic membrane.
Although the otolithic membrane is thought to play an important role in the stimulation of vestibular hair cells, little is known about its chemical composition. We analyzed proteins of the gelatinous layer of this structure from the trout saccule, a probable organ of hearing in fish, by SDS-polyacrylamide gel electrophoresis. A relatively small number of major proteins were detected in homogenates of the 'membrane' layer, with apparent molecular weights ranging from 35 to greater than 300 kDa. Six bands, with molecular weights of 35, 43, 65, 94, 100, and 160 kDa, were particularly prominent. Periodic acid-Schiff (PAS) staining indicated that the 43, 94, 100, and 160 kDa bands were glycoproteins. Lectin binding on nitrocellulose blots confirmed the PAS results, and further suggested that the 35 and 65 kDa bands may be glycoproteins. Incubation of blots with human anti-collagen type II antibodies suggested that the 94 kDa band was a component of collagen type II or a related protein.
Animals↗
[Modeling of the structure and mechanics of the otolith membrane].
Behavior of otoliths of mammals against static (gravitation and changed pressure in the surrounding endolymph) and dynamic loads was surveyed using analytic and computerized (the finite difference method) models of the otolith membrane (OM). It was presumed that OM consists of gel-like and otoconial layers differing in mechanic and thickness. Comparison with available experimental data allowed to assess magnitudes of mechanic parameters of the gel-like layer responsible for OM interaction with the receptor hair cells (Yung's module for the layer is 1-10 N/m2 with the viscosity in the order of 1 poise), the characteristic times of otolith dynamics (T2 approximately 0.03 s, T1 approximately 10(-6)-10(-5) s), and the impact of changed endolymph pressure on the OM behavior. As was shown, inertial drift of mammalian OM is not so dependent on OM mass as on the relation of OM pressure on the molecular surface to Yung' module of the gel-like layer overlieing the macula.
Basilar Membrane↗
Structural basis for mechanical transduction in the frog vestibular sensory apparatus: I. The otolithic membrane.
The mechanical coupling of the otoliths to the hair cell sensory stereocilia at the surface of the vestibular sensory epithelium is mediated by two layers of extracellular matrix, each one with a specific role in the mechanical transduction process. The first is a rigid layer in direct contact with the otolithic mass and is known as the otolithic membrane or gelatin membrane. This structure consists of a dense, randomly cross linked filament network that uniformly distributes the force of inertia of the non-uniform otolithic mass to all stereocilia bundles. The second layer formed by a columnar organization of filaments secures the otolithic membrane above the surface of the epithelium. The long columnar filaments are organized in parallel to the stereocilia bundles and are anchored to the apical surface of the supporting cells. The zonula adherens at the apical region of each supporting cell displays a thick polygonal bundle of actin filaments forming at the surface of the epithelium a transcellular honeycomb organization that provides mechanical ground support for the columnar filament layer. The dominant aspect of this columnar filament layer indicates that it may also have an important role in attenuating the force of inertia of the large otolithic mass during acceleration, screening stresses that would be directed to an effective bending of the stereocilia bundles.
Animals↗
[Experimental study of streptomycin on 45Ca intake of otolithic membranes].
45CaCO3 was injected into guinea pigs, and the radioactivity in otolithic membranes of utriculi and sacculi, auditory ossicles and femora was determined by liquid scintillation spectrometry, to study the dynamic effect of streptomycin on calcium content of otolithic membranes, as a means to explore the mechanism of streptomycin ototoxicity. The results showed that otoconium was a dynamic structure which took up 45Ca in a time course generally comparable to that of bone. Saccular otolithic membranes showed greater intake than utricular membranes. The calcium ion concentration of saccular endolymph was greater than that of the utriculus and the two maculas were not identical. Streptomycin may influence 45Ca uptake in the two macular otolithic membranes, causes calcium metabolic disorder and a fall of otolithic calcium content. It is possible that the fluid environments of the endolymph have changed, therefore dysfunction of otolithic organ may occur. This hypothesis may be one of the explanation of the mechanism of streptomycin ototoxicity.
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Hair-bundle stiffness dominates the elastic reactance to otolithic-membrane shear.
Efficient transduction by acousticolateralis organs requires that a stimulus force principally deflect hair bundles, rather than flex other structural elements. Hair bundles might therefore be expected to provide a large fraction of the impedence to shear motions of otolithic membranes and other accessory structures. We measured the stiffness for shear motions of the bullfrog's saccular otolithic membrane, and determined the stiffness due to a single hair bundle and its associated extracellular filaments; this component is termed the elemental stiffness. Stiffness measurements were made by displacing the base of a flexible probe whose tip was coupled to the otolithic membrane, and simultaneously measuring the flexion of the probe and the displacement of the membrane. The average elemental stiffness, about 1350 microN.m-1, only modestly exceeded the stiffness of individual hair bundles. The hair bundles therefore provide the dominant component of stiffness in the bullfrog's sacculus, and thus account for a significant component of impedance to otolithic-membrane shear. As a corollary, stiffness changes or active movements in hair bundles should influence the mechanical responses of this and other receptor organs.
Animals↗
[A study of the otolithic membranes of the saccule and utricle of the guinea pig].
By scanning electron microscopy the otolith membranes of the sacculus and utriculus of adult guinea-pigs were examined. The spatial arrangement of otoconia was found to differ from the standard scheme. New forms of imperfect otoconia were detected. Differences in morphological parameters of otoconia in the labyrinthine structures were revealed. Factors responsible for the development of imperfect otoconia on the otolith membrane are described and their relation to the potential changes in the sensitivity of otolith receptors is discussed.
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Toadfish saccular hair cell bundle has a preferred orientation in the otolithic membrane.
The macula of the saccule of the toadfish, Opsanus tau, is covered by an otolithic membrane containing sockets into which the stereocilia and kinocilia of the hair cells project. We have found that the hair cell bundle has a distinct eccentric orientation within this space of the otolithic socket. Although the sockets of the otolithic membrane are irregular in shape, all kinocilia are located closet to the same border of the sockets. Since the socket is a fluid or gel filled space through which the hair cell bundle moves, this orientation may have some significance for transduction since it leaves a larger space in the on direction for stereociliary movement.
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Models of the dynamics of otolithic membrane and hair cell bundle mechanics.
Dynamic behavior of an otolithic membrane (OM) was studied analytically using simplified homogeneous viscoelastic (Kelvin-Voight body) model of the OM. The OM was represented by a thin plate attached to a macular plane. Viscoelastic properties of the OM determine the specific times (T(1) and T(2)) and frequency-dependent behavior of the local displacements of the membrane caused by the inertial time-dependent forces. Two kinds of an otolith stimulation were analyzed: step-function and harmonic accelerations of the membrane. Results of the modeling were compared with the known experimental data to estimate the Young's modulus E and viscosity mu of a gel layer: E is of order of 10 N/m(2), mu is of order of 1 poise in the range of frequency 0.2-2 Hz. It has allowed us to estimate the values of T(1) (10(-5)-10(-6) sec) and T(2) ( approximately 3 x 10(-2) sec). A relationship of the motion equation of the OM with well-known overdamped pendulum model of the otolith was discussed. The model of stereocilia tip-links deformation in the case, when the HCBs passively follow gel deformation, was proposed and analyzed. It was shown that for slender and long HCBs with the lengths comparable to a thickness of effective gel layer, a relative deformation of the tip-links of stereocilia caused by OM acceleration depends on time and the distance from the macular plane. The results of the modeling suggest that this type of the HCB may be responsible for analysis of fine temporal (frequency) structure of the OM acceleration.
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Incorporation of radioactive calcium into otolithic membranes of the guinea pig after aminoglycoside treatment.
The influence of neomycin and streptomycin on the calcium metabolism of the otolithic membranes was investigated in the guinea pig. After chronic treatment with either drug, animals were injected intraperitoneally with radioactive calcium. Retention of calcium in the serum was unaffected by drug treatment, as was the incorporation of radioactivity into bone (femur and otic capsule). Both drugs inhibited the calcium uptake into saccular and utricular otolithic membranes by 30 to 40%.
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Visualisation of domains in the avian tectorial and otolithic membranes with monoclonal antibodies.
The staining patterns observed with six monoclonal antibodies (mAbs) raised in vitro against a fraction derived from the utricular macula were examined with cryosections of the auditory and vestibular organs of the avian inner ear. These antibodies revealed several distinct domains within the gelatinous membranes. Three different labelling patterns were observed in the tectorial membrane. Staining was seen either throughout the entire tectorial membrane, restricted to its core, or in a narrow zone lying close to the surface of the basilar papilla. In the maculae, the mAbs stained either the striolar region of the otolithic membrane or the entire structure. One monoclonal which labelled otoconia, stained small otoconia in their entirely, whilst larger otoconia were only labelled around their periphery. Only one of the mAbs stained the cupulae of the semi-circular canal ampullae and this antibody stained neither the tectorial nor the otolithic membranes. These results suggest that there are biochemically distinct regions in the gelatinous membranes of the inner ear and indicate that these matrices are not simply homogeneous extracellular structures.
Animals↗
Ultrastructural changes of statoconia after segmentation of the otolithic membrane.
The chick vestibule transformed from a homogeneous epithelial layer at day 2 (stage 15) into a pseudo-stratified epithelial layer at day 4 (stage 24). The apical columnal appearance of sensory cells was evident by day 6 (stage 29). In the supporting cells of the saccule and utricle large rough endoplasmic reticulum cisterns filled with material similar to the primitive organic matrix. Fibrillar material of the otolithic membrane remained attached to the supporting cells and accumulated over the saccule and utricle. The primitive otolithic membrane acquired stress-like lines and statoconial units emerged from the upper surface without a central core. Statoconia thickened at the periphery and a central core formed. Calcium was deposited between the fibrils of older statoconia which were located on top of the segmenting membrane. DIAMOX inhibited statoconia formation and/or prevented calcium and the matrix from associating. Large statoconia (100-200 microns diameter) were formed in embryos injected with this carbonic anhydrase inhibitor. Gel electrophoresis of immature statoconial complexes yielded at least 5 major protein bands between 25 and 210 kDa. Ouabain-sensitive potassium-dependent p-nitrophenylphosphatase activity was demonstrated in the endolymphatic sac of newly hatched chicks.
Acetazolamide↗
Otolithic membranes of the saccule and utricle in man.
The otolithic membranes of the human saccule and utricle can be prepared as whole mounts or surface specimens for microscopic examination. They are not simple, homogeneous, gelatinous structures as heretofore described. Instead, each shows a definite and characteristic fibrillar design, which appears to be correlated with the known cytoarchitectural pattern of the underlying neuroepithelium.
Ear, Inner↗
Observation of the otolithic membrane by low-vacuum scanning electron microscopy.
Untreated specimens (i.e. not fixed, dehydrated or embedded) of the otolithic membrane from the sacculus of guinea pigs were observed at the ultrastructural level by low-vacuum scanning electron microscopy (LVSEM). This technique revealed the presence of a 15- to 20-mu m-thick layer of an amorphous substance (the supraotolithic cupula zone) on the surface of the otoliths, which was not detectable by conventional methods. Elemental analysis of this substance revealed relatively high concentrations of oxygen, sodium, phosphorus, chlorine, potassium and calcium. This amorphous substance was thought to have a role in fixing the otoliths onto the sensory epithelium. In addition, the tips of the triangular portions of the otoliths were not sharp as shown by conventional SEM and were seen to be more rounded by LVSEM.
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[The utricular otolith membrane in the guinea pig].
Several types of otoconia are present in the otolithic membrane of the utricle of fetal, young and adult guinea pigs. These include smooth, transitional and rough otoconia, and a few rhombohedrons. The smooth otoconia are nearly the same numeric fraction in all the specimens. The mean size of otoconia increases only during the course of gestation. Our measurements indicate that the diameter (d) and the length (l) of otoconia are related linearly as: d = 0.4l + 0.4. The smooth otoconia seem to be independent morphological form which is not derived from more "primitive", rough or transitional ones. The otoconia consist mainly of CaCO3 and contain Na, Mg and trace amount of K. The chemical composition of otoconia is similar in fetal, young and adult guinea pigs.
Aging↗
Standards for quantification of elements in the otolithic membrane by electron probe X-ray microanalysis: calibration curves and electron beam sensitivity.
An absolute quantitative standardization technique has been developed to measure Ca and K weight fractions (WF) in the otolithic membrane of the saccule and utricle by scanning electron microscopy and electron probe X-ray analysis using the peak-to-background (P/B) ratio method. Microcrystalline salt standards were used to calibrate Ca and K K alpha P/B or Y = (P/B).Z2/A (Z = atomic number; A = atomic weight) against WF at 10, 15, 20 and 25 kV accelerating voltage. The effect of voltage on the calibration, plotting the coefficient of correlation (r) as a function of voltage, was not dependent on the voltage in the range 10-25 kV for Ca standards. K standards were also independent when P/B was corrected for Z2/A. Background counts in the otoconia (Bo) were obtained at 5, 25, 50, 100, 200 and 500 s and used to test the electron beam sensitivity of saccular and utricular otoconia. Bo was not dependent on the spectra acquisition time, with the exception of Bo under K alpha K peak in the saccule at 10 kV. Ca and K WF were determined at 10, 15, 20 and 25 kV in the saccule and utricle, showing similar values regardless of the voltage used. This method of calibration offers several advantages, such as stability, homogeneity, known composition of the standards, high reproducibility at different voltages even without Z2/A correction and the similarity between the otoconia and crystal standards. We recommend the application of this method for other elements and biomineral systems.
Animals↗