Biomedical subjects

A H Gitter

Publications and source records attributed to A H Gitter.

At least 55 records · Page 3Linked to original sources

PubMed1992

Ultrastructure of cultured marginal cells of the guinea pig cochlea.

Explants of stria vascularis and spiral ligament of guinea pig cochlea were kept in primary culture. On the explant, proliferating marginal cells advanced by 15 microns/day, suggesting that in vivo defects of the strial epithelium can be covered by new marginal cells. The marginal cells growing in the cell culture dish had a diameter of 12.8 +/- 0.7 microns and formed an epithelial monolayer. Adjacent cells were connected by desmosomes and tight junctions. The cells were uniformly polarized. The apical membrane had small invaginations and numerous microvillus-like extensions, and the convoluted lateral membrane interdigitated with adjacent cells. The basal infoldings were smaller in cultured cells than in vivo; mitochondria were dispersed in the entire cytoplasm rather than concentrated in basolateral infoldings. The basal membrane infoldings of cultured marginal cells did not interdigitate with underlying fibroblast-like cells. Marginal cells were separated from underlying fibroblast-like cells by a fluid-filled space which was sometimes enlarged, leading to the formation of "domes" in the otherwise planar epithelium.

Animals↗

PubMed1992

Electrically evoked motile responses of mammalian type I vestibular hair cells.

Vestibular hair cells, type I and II, with membrane potentials around -64 mV were prepared from guinea pig ampullar cristae and maculae. In type I cells, current injection, application of voltage steps during membrane patch-clamping, or extracellular alternating current (ac) fields evoked fast length changes of 50 nm to 500 nm of the cell "neck." Mechanical responses were determined by computerized video techniques with contrast-enhanced digital image subtraction (DIS) and interpeak pixel counts (IPPC) or by double photodiode measurements. These techniques allowed spatial resolutions of 300 nm, 120 nm, and 50 nm, respectively. In contrast to measurements of high-frequency movements of auditory outer hair cells (OHCs), the mechanical responses of type I VHCs were restricted to low frequencies below 85 Hz. In addition to recently reported slow motility of VHCs, the present results suggest that fast mechanical VHC responses could significantly influence macular and cupular mechanics. Isometric and isotonic variants are discussed. The observed frequency maxima gap between VHCs and OHCs is suggested to contribute to a clear separation of the auditory and the vestibular sensory modality.

Animals↗

PubMed1992

[Marginal cells of the stria vascularis in vitro].

Explants of stria vascularis and spiral ligament of the guinea pig cochlea were cultivated and after 2 days fibroblast-like cells were found growing around the explant. Marginal cells advanced at 15 microns/day to the border of the explant, and after 2 weeks they proliferated on top of a thin layer of fibroblast-like cells outside the explant, replacing several layers of fibroblast-like cells. Tight junctions and interdigitations of the lateral membranes were found between all neighbouring marginal cells. Their apical surface was covered by microvillus-like membrane extensions. The basal membrane of the new marginal cells did not interdigitate with the underlying membranes of fibroblast-like cells; there was always a gap between the two cell types. The results demonstrate that marginal cells of the stria vascularis are capable of repairing damage to the epithelium, such as may be caused by endolymphatic hydrops, even if the luminal side contains perilymph-like fluid. Furthermore, the cell culture allows living, clearly identified marginal cells to be studied in vivo.

Animals↗

PubMed1991

Primary culture of vital marginal cells from cochlear explants of the stria vascularis.

Explants of the stria vascularis and spiral ligament were dissected from guinea pig cochleae and were successfully cultivated for several weeks. After 2 days, fibroblast-like cells of the spiral ligament covered the bottom of the cell culture dish around the explant. Marginal cells of the stria vascularis proliferated and grew on the luminal surface towards the border of the explant at a rate of 15 microns/day. At day 6 in culture the proliferating marginal cells reached the border of the explant and then advanced to the bottom of the cell-culture dish. There the marginal cells replaced fibroblast-like cells and built an epithelial hexagonal-shaped monolayer. Light microscopic and transmission electron microscopic investigations revealed that the cultured cells were viable and that typical morphological characteristics of marginal cells were preserved. Cultivation of these cells provides a unique model for studies of physiological properties of marginal cells of the stria vascularis.

Acridine Orange↗

PubMed1991

The resting potential of marginal cells in stria vascularis explants.

In order to examine the intracellular potential of stria vascularis marginal cells (MCs) under direct visual control, a short-term organ culture of guinea pig stria vascularis (SV) was developed. The experimental conditions allowed exposure of the luminal surface of the SV to artificial endolymph or perilymph. Using conventional microelectrodes and inverted bright-field microscopy, impalement of MCs from the endolymphatic side through the luminal cell membrane was achieved. With artificial perilymph at the luminal side a small positivity at the cell surface and low negative intracellular potentials were recorded at room temperature (23 degrees C). The initial recording was -6.5 +/- 5.0 mV while the stable recording was -4.0 +/- 3.6 mV. Similar results were obtained at a bath temperature of 37 degrees C. Furthermore, subtotal exposure of the luminal cell surface to artificial endolymph did not result in a significant potential change.

Animals↗

PubMed1991

[A brief history of hearing research. III. Microscopic anatomy].

The present review provides merely a glimpse of the vast field of modern anatomy of the ear, which began with the introduction of the light microscope and histological techniques. Owing to the poor accessibility and small size of the inner ear, the investigation of its structure was highly dependent on the development of modern histological techniques, i.e. fixation, embedding, sectioning and staining of tissue, which took place in the 19th century. In 1824 Huschke discovered the papilla spiralis acoustica and in 1851 Corti described the structure of the sensory epithelium of the inner ear, and also detected the outer hair cells. A little later Deiters also found the inner hair cells, while Leydig discovered the stereocilia on the hair cells. In 1863 Hensen showed that the hair cells were provided with nerve endings, but it was Retzius who proved that the nerve fibres terminate at the basal end of the hair cells. He concluded from his studies that the hair cells are the actual receptors of the organ of hearing. Hensen, Retzius and Held provided morphometric data of the cochlea which are still largely valid today. In 1926 Held managed to isolate single hair cells. He also described two different types of nerve fibre in the cochlea. In 1926, Kolmer was the first to propose that apart from afferent nerve fibres there might also be an efferent innervation of the cochlea. In 1942 this was confirmed by Rasmussen. In animal experiments, he and others demonstrated the efferent nature of the olivo-cochlear bundle by dividing the nerve, which subsequently showed secondary descending degeneration.(ABSTRACT TRUNCATED AT 250 WORDS)

Anatomy↗

PubMed1990

Visualization and functional testing of acetylcholine receptor-like molecules in cochlear outer hair cells.

The efferent nerve endings at outer hair cells (OHCs) have been suggested to regulate active mechanical processes in the cochlea. The discovery of acetylcholine (ACh)-producing and -degrading enzymes in these synapses gave rise to the speculation that ACh might be one of the efferent transmitters. However, there has as yet been no identification and characterization of any corresponding receptor in OHCs which is required for further clarification of this question. In the present paper existence, location and first characterization of acetylcholine receptors (AChRs) in OHCs are reported. Using two anti-AChR monoclonal antibodies, AChR epitopes were found forming a cup at the basal end of the OHCs opposite to the efferent nerve endings. Furthermore, the studied molecules could be shown to extend through the cell membrane. In addition, the denervated OHC AChR-epitopes seem to move by lateral diffusion. Application of Carbachol and ACh to the basal pole of OHCs induced a weak, reversible cell contraction. Pharmacological controls revealed, that hte motile responses were mediated by the AChRs.

Acetylcholine↗

PubMed1990

Cell potential and motility of isolated mammalian vestibular sensory cells.

Vestibular hair cells (VHCs) were isolated from the guinea pig inner ear. Using the whole cell variant of the patch clamp recording technique a zero current cell potential of -63.1 +/- 9.9 mV was measured in macular hair cells. Depolarization and repolarization were accompanied by mechanical responses of the solitary VHCs. In addition to the evoked motile events spontaneous shape changes of VHCs were observed. Implications for vestibular micromechanics of the observed evoked force generation in VHCs are discussed.

Animals↗

PubMed1990

The cell potential of isolated inner hair cells in vitro.

Inner hair cells (IHCs) were isolated from the 3rd and 4th turn of the guinea-pig cochlea using a new microsurgical technique. Microelectrode impalements in vitro with conventional microelectrodes yielded intracellular potentials of -14 +/- 7 mV (mean +/- SD, N = 43) at 24 degrees C. This suggested depletion of intracellular K+ in the isolated IHCs. Whole-cell recordings with patch-clamp suction electrodes of 11 +/- 3 M omega when filled with KCl Ringer demonstrated reloading of the cytoplasmic compartment with K+ (time constant t = 26.3 +/- 3.5 s), resulting in stable intracellular potentials after equilibration of -58.7 +/- 7.3 mV (mean +/- SD, N = 6) which is close to the K+ Nernst potential. The results suggest that IHC membranes are predominantly potassium-permeable. Assuming that in vivo the apical membranes of IHCs are exposed to endolymph-like fluid, the lower resting potentials of IHCs can be explained with the potassium permeability ratio of their apical and basolateral membranes. In whole-cell recordings, injection of hyperpolarizing current induced larger changes of the intracellular potential than depolarizing current. Oscillatory potential fluctuations were not observed, neither spontaneous nor in response to rectangular current pulses.

Animals↗

PubMed1990

[A short history of hearing research. I. Antiquity].

This review describes important steps in the history of basic research on the function of the hearing organ. The present, first part revisits the period between Empedocles and Galen, focussing on the ideas of Empedocles and Aristotle. It is unlikely that they knew the cochlea. Based upon a more general theory of interaction, however, Empedocles in the fifth century B.C. compared the hearing organ with a bell and claimed that it is capable of not only receiving, but also generating sound. Using Empedocles's theories of sound and the four elements, Aristotle proposed that sound is sensed by an air-filled resonant cavity in the head located behind the eardrum. The postulated cavity may have been identified with, or at least included, the middle ear. Aristotle's ideas dominated the theory of hearing for two millenniums.

Ear↗

PubMed1990

[A short history of hearing research. II. Renaissance].

The history of basic research on the function of the hearing organ is revisited. The present, second part of the review covers the period between the renaissance of anatomical research in the 16th century and the beginning of modern hearing research at the end of the 19th century. Andreas Vesalius gave the two ossicles malleus and incus their names. His scholar Philippus Ingrassia found 1546 the third ossicle, the stapes. The cochlea was discovered 1552 by Bartholomeus Eustachius and denoted as cochlea 1561 by Gabriel Falloppio. Thomas Willis speculated 1672 that different "tones" (species audibilis) may excite different fibres of the nervus acusticus. In collaboration with the physicist Edme Mariotte, Joseph Guichard DuVerney developed in 1683 a theory of the tonotopical organisation of the cochlea, the encoding of acoustic information by mechanical spectral analysis. The scholastic dogma of Aristotle's aer implantatus was contradicted by Domenico Cotugno as late as 1760. DuVerney's theory was, together with Georg Simon Ohm's law on the applicability of the Fourier analysis to sound waves, the basis of Hermann Helmholtz' famous theory of hearing of 1863. Due to the lack of detailed knowledge about the function of nerves, however, no clear ideas were developed about the acoustical information carried to the brain by the acoustic nerve. Also in the 19th century, Alphonso Corti discovered the organ that was named after him by Albert von Kölliker, and Flouren's experiments demonstrated the function of the vestibular organs. Furthermore, the foundations of auditory psychophysics were laid by Alfred M. Mayer and others.

Audiology↗

PubMed1989

[Transduction and motor disorders of cochlear hair cells in Menière and aminoglycoside hearing loss].

The auditory reception by cochlear hair cells is a mechano-electrical process of transducing based on ionic channels in the outer cell membrane. In addition, outer hair cells seem to control actively the non-linear micromechanics of the inner ear on the basis of fast and slow motor properties. These active motor properties of outer hair cells are obviously disturbed in acute attacks of Ménière's disease or in aminoglycoside intoxication. Their dysfunction may thus partly explain the resulting deafness.

Aminoglycosides↗

PubMed1988

Active movements of the cuticular plate induce sensory hair motion in mammalian outer hair cells.

It has been suggested that active motor capacities may explain the high sensitivity and sharp tuning of auditory transduction in the mammalian cochlea. Recently, slow and fast motile responses of isolated outer hair cells (OHCs) have been demonstrated. These consist of reversible length changes in the cylindrical cell body. Here we show that isolated OHCs are also capable of slow and fast movements of the cuticular plate (CP) which cause passive displacements of the stereocilia. The molecular mechanisms that underlie the slow movements appear to reside in the highly organized actomyosin cytoskeleton in the CP. Additional, fast movements of the CP were observed in OHCs which were exposed to alternating electrical fields. These rapid mechanical events followed the electrical stimulus cycle-by-cycle, and unlike the slow movements, did not depend on the actomyosin skeleton in the CP. The fast motility of the CP and the attached stereocilia suggest an additional active mechanism which may contribute to the sensitivity and the sharp tuning of the cochlea near threshold. By controlling the operating point of the reticular lamina and of the hair bundles, the slow CP and stereociliary movements may influence basilar membrane homeostasis and temporary threshold shift at high sound pressure levels.

Adenosine Triphosphate↗

PubMed1988

[Microsurgically collected living inner hair cells allow measurements of ion channels and cell potential].

Living inner hair cells of the mammalian inner ear were dissected microsurgically from guinea-pig cochleae in the absence of proteolytic enzymes. They were kept in short-time culture for 2 hours. Viability of the preparation was monitored by registration of the cell potential with impaled microelectrodes. The patch-clamp technique allowed the identification of 3 types of ionic channels in the basolateral cell membrane. Isolated living inner hair cells are a new model allowing to investigate the cellular basis of physiological function and pathophysiological disorders of sound perception.

Animals↗

PubMed1987

Fast motility of isolated mammalian auditory sensory cells.

Auditory sensory cells (hair cells) are responsible for sound transduction in the cochlea of the inner ear. In the presence of a longitudinal a.c. field isolated living outer hair cells showed reversible motile responses. They followed the stimulus up to at least 1 kHz. Control experiments in the presence of cytochalasin B, phalloidin and dinitrophenol excluded actomyosin as a molecular basis of the high frequency motility. The results suggest, that outer hair cells might amplify sound-induced oscillations in the inner ear and thus increase sensitivity and frequency selectivity of hearing.

Actomyosin↗

PubMed1987

A low-cost voltage stepper device for use in patch-clamp experiments.

A simple and inexpensive device is described which generates voltage steps or cycles of steps of defined amplitude and duration either automatically (triggered by internal or computer clock pulses) or on manual command. The device facilitates the investigation of the voltage dependence of ion channel currents in patch-clamp experiments.

Animals↗

PubMed1987

High-conductance K+ channel in apical membranes of principal cells cultured from rabbit renal cortical collecting duct anlagen.

Using the patch clamp technique, one type of K+ channel was identified in the apical cell membrane of cultured principal cells of rabbit renal collecting ducts in the cell-attached or excised-patch configuration. The channel was highly selective for K+ over Na+ (typically 30-70-fold) and had a conductance of 180, SD +/- 39 pS (n = 6), referred to a situation of 140 mmolar K+-Ringer solution present on either surface of the patch membrane. Channel activity was completely blocked by Ba2+ (5 mmol/l) and partially inhibited by Na+. The latter was evidenced by a deviation from Goldman rectification at high cytoplasm-positive membrane potentials, which was observed when Na+ competed with K+ for channel entrance from the cytoplasmic surface. Channel open probability depended strongly on membrane voltage and cytoplasmic Ca2+ concentration. Open-close kinetics exhibited double exponential behaviour, with a strong voltage dependence of the slow open time constant. Infrequently also a substate conductance level was identified. The voltage and calcium dependence suggest that the channel plays a role in adjusting K+ secretion to Na+ absorption in the fine regulation of cation excretion in renal collecting ducts.

Animals↗

PubMed1986

Membrane potential and ion channels in isolated outer hair cells of guinea pig cochlea.

Single outer hair cells from guinea pig cochlea were prepared by microdissection and cultured for several hours in a modified Hanks' medium. Cells, which were viable, judged by morphological criteria, were investigated with the patch-clamp technique. Membrane potentials up to -70 mV could be measured in the cultured cells. Ion channels were found in the basolateral membrane and in the cuticular region of the hair cells. These ion channels could play an important role in transducing sound-induced sterociliary motion into membrane depolarizations, thereby regulating the contractile state of the outer hair cells and in turn the resonance properties of the cochlear amplifier.

Animals↗