Biomedical subjects

A H Gitter

Publications and source records attributed to A H Gitter.

At least 37 records · Page 2Linked to original sources

PubMed1998

The mammalian auditory hair cell: a simple electric circuit model.

A model based on the potassium current pathway through the hair cell is used to analyze the electrical behavior of mammalian inner and outer hair cells. Without taking into account the effects of calcium it is possible to simulate experimental results concerning the shape and strength of the receptor potential and the frequency dependent ac (alternating current) and dc (direct current) components of the receptor current. This model and a simplified form of it are utilized to explain: (1) Transduction latencies: that the receptor potential follows a stimulating signal with a very short delay, under the assumption of a constant number of open K+ channels in the lateral part of the cell membrane. (2) Transduction gains: why higher potential changes are measured in inner hair cells than in outer hair cells, although the outer hair cells are expected to be exposed to higher stereociliary motions: in inner hair cells a decrease in the conductance of the basolateral membrane causes higher gain (receptor potential increases) and together with an increase of membrane capacitance slower reaction (a larger time constant). (3) Transduction channel kinetics: that the shortest (0.1 ms) as well as the longest (20 ms) possible open times of the transduction channels in the stereocilia have different frequency related effects on the shape of the receptor potentials.

Animals↗

PubMed1997

Ussing chamber for high-frequency transmural impedance analysis of epithelial tissues.

An Ussing chamber was designed for impedance analysis of epithelial tissue and optimized for the use of high-frequency alternating current stimuli. Shielded voltage electrodes, located axially within the electric field of the Ussing chamber, minimized the reactive properties of the set-up. By vectorial subtraction, the small reactive contribution of the optimized Ussing chamber was completely compensated for. This method allowed for transmural impedance measurements in a frequency range of 1-65 kHz. For the first time, Nyquist plots of cultured intestinal cell monolayers (HT-29/B6) are presented. The epithelial monolayers in different stages of confluence showed the impedance locus as a semicircle, with the high frequency end close to the origin. These epithelial monolayers could be modeled by a simple RC-parallel circuit without a series resistance.

Electric Impedance↗

PubMed1997

Measurement of paracellular epithelial conductivity by conductance scanning.

A new method, conductance scanning, allows determination of local para- and transcellular conductivities in flat epithelia. Experiments were performed on kidney distal tubule cells, MDCK clone C11, which form monolayers on permeable supports. Above the apical surface, local voltage drops generated by a sinusoidal current clamp were recorded by means of a scanning microelectrode. Data were collected above cell centres and tight junctions. The scanning signal was always significantly higher above the tight junctions, but was uniformly distributed along the junctions. For determination of conductivities two procedures were applied. Method 1: the supraepithelial potential distribution was computed for given trans- and paracellular currents at all positions of the electrode. In a fit algorithm, the currents were varied until the calculated potential difference equalled the voltage measured. Method 2: after collecting scanning data in control Ringer's, intercellular space width was reduced by mucosal addition of 40 mM sucrose and a second set of data was obtained at decreased paracellular, but presumably unchanged transcellular, conductivity. From these data, trans- and paracellular conductivities were calculated. Results of both methods were in excellent agreement. Confluent MDCK-C11 monolayers exhibited a transepithelial conductivity of 13 mS/cm2. The transcellular pathway contributed 2.6 mS/cm2 (20%) and the paracellular pathway 10. 5 mS/cm2 (80%) to the total conductivity. Collapse of the lateral intercellular spaces decreased the paracellular conductivity to 4 mS/cm2 (60%). Confluent MDCK-C11 monolayers constitute true "leaky" epithelia with homogeneously distributed trans- and paracellular conductivities. In conclusion, conductance scanning fills a methodical gap, which hitherto impeded the functional characterization of tight junctions.

Animals↗

PubMed1995

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.

Animals↗

PubMed1995

Imaging of electrically induced fast motion by video microscopy and triggered flash illumination.

A simple and inexpensive method is described for imaging with video microscopy fast transient events that can be triggered electrically. An electronic system was developed that triggered stroboscopic illumination and generated an electrical step function. The essential feature was precise control of a sub-millisecond time delay between electrical stimulus and the following short pulse of light. With this technique (15 microseconds time resolution, 50 frames/s) different phases of the exocytosis and discharge of nematocysts from Hydra vulgaris can be visualized. It was shown that not only stenoteles, but also desmonemes, can discharge in less than 0.5 ms.

Animals↗

PubMed1995

Chronic hypokalaemia of adults: Gitelman's syndrome is frequent but classical Bartter's syndrome is rare.

We evaluated 27 adult patients with chronic hypokalaemia (K+ = 2.9 +/- 0.2 mmol/l), documented over at least 5 years, in whom the cause of the hypokalaemia had not been clarified in spite of previous testing. In 15 patients it was possible to establish a diagnosis by a thorough outpatient workup (diuretic abuse (n = 5), surreptitious vomiting (n = 8), laxative abuse (n = 1), renal tubular acidosis (n = 1)). Commonly utilized tests such as measurements of plasma renin activity, plasma aldosterone, and urinary potassium concentration proved not to be useful in the differential diagnosis of these patients. In contrast the following were diagnostically important: in surreptitious vomiting the hypochloraemia, the mild renal insufficiency, and the extremely low urinary chloride concentration; in diuretic abuse the high urinary concentration of chloride together with repeatedly positive toxicology screens for diuretics; in laxative abuse the high stool weight and extremely low urinary sodium concentration. In the remaining 12 patients none of these diagnoses applied and further tests for suspected Bartter's syndrome were done in the hospital.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

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.

Action Potentials↗

PubMed1994

[Are tip links the basis for mechanosensitivity of hair cells?].

The singular sensitivity of cochlear outer hair cells suggests an extremely efficient exploitation of the energy supplied by the mechanical stimulus. If, however, the transduction channels were located at one end of the hair bundle's tip links, not more than 1/250 of the stimulus energy could be used to change the open probability of the channels. Furthermore, the mechanosensitive nematocytes of Hydra vulgaris possess a sensory hair bundle with horizontal links and have a transduction mechanism with functional properties similar to those of hair cells, even though tip links are absent between stereocilia. Therefore, I propose that the transduction channels of hair cells are connected to the short row-to-row horizontal links at the distal ends of neighboring stereocilia. These links, as well as the tip links, are oriented in accordance with the directionality of hair cell mechanosensitivity. The elastic elements connected with the horizontal links receive a larger part of the stimulus energy than the tip links. Since the short horizontal links resemble rigid rods rather than "spare springs", the points of insertion of these links in the stereocilia (i.e., the transduction channels) must move a distance upsilon parallel to the longitudinal axis of the stereocilium when the hair bundle is deflected by an angle phi. Computation shows that upsilon is proportional to phi. In the stereocilium, elastic elements ("gating springs") connect the cytoskeleton and transduction channel. The force in the gating springs that is counteracting the movement of the transduction channels may be varied in the process of adaptation by an active motor, as has been proposed in other investigations.

Animals↗

PubMed1993

Structure, pharmacology and function of GABA-A receptors in cochlear outer hair cells.

There is evidence that the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) is released from some efferent olivocochlear nerve endings terminating at outer hair cells (OHCs). Using monoclonal antibodies against postsynaptic GABAA receptor from bovine cerebral cortex we confirm the presence of GABA and benzodiazepine bindings sites of alpha- and beta-subunits of GABAA receptors at the basal pole of isolated OHCs. Whole-cell recording with viable OHCs revealed that the application of 10(-3)-10(-8) M GABA to the cell surface was followed by a concentration-dependent hyperpolarization of the outer cell membrane. Hyperpolarization was increased in the presence of 2.5 x 10(-5) M chlorazepate, a benzodiazepine derivative. Electrophysiological effects caused by GABA alone or in combination with chlorazepate were specifically inhibited by 10(-6) M of the GABA-receptor antagonist picrotoxin. Moreover, 10(-5)-10(-7) M GABA caused reversible slow elongation of the cylindrical hair cell body in OHCs examined. These neurotransmitter-induced motile responses were specifically blocked by 10(-4) M picrotoxin. The results suggest that a subpopulation of OHCs express alpha- and beta-subunits of GABAA receptors which both form a GABA/benzodiazepine-receptor complex at the basal pole of isolated OHCs. These receptors are thought to allow GABA which is released from efferent auditory nerve terminals to bind to the cell surface of OHCs, resulting in GABAA-receptor activation. This probably gates a GABAA-receptor-associated chloride channel in the postsynaptic OHC membrane, allowing hyperpolarization and elongation of the cell.

Animals↗

PubMed1993

Forces involved in length changes of cochlear outer hair cells.

Motion or force generation of outer hair cells may contribute to active modulation of cochlear mechanics. In order to determine the force involved in length changes of outer hair cells, a new in vitro method was used. In the first series of experiments, apical and basolateral extracellular spaces of outer hair cells of the guinea-pig cochlea were separated. Changes of the voltage between the two extracellular spaces induced reversible, proportional changes of the cell length of 4.4 nm/mV if the cell had a length of 80 microns. In the second series of experiments, cell elongations in response to negative pressure applied to the basal end of the cells were measured and corrected for frictional effects. From these data, the compliance of the longitudinal axis of the hair cells was calculated. It was 220 +/- 130 m/N (n = 25) and 240 +/- 170 m/N (n = 24) for cells of the third and fourth cochlear turns, respectively, if the water permeability of the cell membrane was neglected. If the water permeability was taken into account, the compliance was probably around 500 m/N [corrected]. Thus, a mechanism that changes the cell length by 1 microm must generate a static force of at least around 2 nN in an outer hair cell of the organ of Corti [corrected]. Electromotility of outer hair cells, induced by changes of the electrical potential difference across the outer hair cell, is a mechanism that generates this force.

Animals↗

PubMed1993

Cell potential of isolated outer hair cells as a function of extracellular K+ concentration.

Outer hair cells were isolated from apical turns of the guinea pig cochlea. The membrane potential differences of cells in extracellular medium with 5.8, 14.0, 28.9 or 67.5 mmol/l of potassium were -72.0 +/- 0.6 (mean +/- SEM, n = 93), -50.1 +/- 2.1 (n = 4), -37.7 +/- 0.5 (n = 73) or -20.0 +/- 1.5 mV (n = 16), respectively. Membrane depolarization can explain two thirds of the K(+)-induced shortening of isolated outer hair cells.

Animals↗

PubMed1992

gamma-Aminobutyric acid receptor activation of outer hair cells in the guinea pig cochlea.

Gamma-aminobutyric acid (GABA), the main inhibitory neurotransmitter of the central nervous system, may also be released from olivocochlear efferent nerves reaching the outer hair cells of the cochlea. In the present study the cell potential of isolated outer hair cells of the third and fourth turns of the guinea pig cochlea was measured with patch-clamp electrodes. GABA-receptor agonists and antagonists were applied extracellularly. The cell membrane hyperpolarized in a reversible manner with increasing concentrations of extracellular GABA. Half-maximal hyperpolarization (2 mV) was achieved with approximately 10(-7) M GABA. Desensitization was not observed. The hyperpolarizing effect of GABA was potentiated by the benzodiazepine clorazepate and was blocked by picrotoxin.

Animals↗

PubMed1992

High frequency radial movements of the reticular lamina induced by outer hair cell motility.

Recently, it was shown in cochlear explants from the guinea pig cochlea that electrokinetic motile responses of outer hair cells can induce radial and transverse motion of the reticular lamina. Here we demonstrate, that the radial component of these motions can be measured up to high frequencies (15 kHz). Cochlear explants were taken from guinea pig inner ears and exposed to a sinusoidal electric field. A double photodiode was used as a linear position detector with high spatial and temporal resolution to detect radial movements in the plane of the reticular lamina. The organ of Corti of the second, third and fourth cochlear turns was stimulated with frequencies of the electrical field between 0.5 Hz and 20 kHz. Sinusoidal movements of up to 15 kHz were recorded. At higher frequencies the signal-to-noise ratio became too small. The largest responses were measured at the three rows of outer hair cells. If the strength of the electrical field was 2 kV/m, into which the cochlear explants were placed, the amplitudes of outer hair cell movements were around 1 micron at 1 Hz and 10 nm at 10 kHz. Uncoupling of the outer hair cells from the tunnel of Corti and from the inner hair cells decreased the oscillations of inner hair cells but did not affect outer hair cells. The movements showed frequency dependent amplitudes like a complex low-pass filter but no best frequency was observed.

Animals↗

PubMed1992

C-type potassium channels in the lateral cell membrane of guinea-pig outer hair cells.

The basolateral cell membrane of outer hair cells (OHC) from the mammalian cochlea is known to contain K(+)-channels. The prevailing type, a high-conductance K(+)-channel was further characterized in the present study in order to support its classification as C channel. OHC were isolated from the 3rd and 4th turn of the guinea-pig cochlea. Cell-attached and excised inside-out patches of the lateral cell membrane were investigated. The C-type channel had a selectivity for K+ over Na+ of 12:1 to 20:1 and displayed Goldman-type rectification and voltage-dependence of the open probability. The kinetics of both opening and closing could be described by time constants in the range of ms. The channel provides a calcium- and voltage-activated pathway through OHC lateral membranes for passive K+ transport.

Animals↗

PubMed1992

Characterization of marginal and Claudius' cells growing from cochlear explants in vitro.

Tissue specimens of stria vascularis together with spiral ligament were transferred from the guinea pig cochlea to tissue culture dishes. To characterize and identify cells growing out from the explants, indirect immunofluorescence microscopy was used. The expression of the intermediate-sized filaments vimentin and cytokeratin 18 in cells on the surface of tissue specimens and in cells growing out from the explants after different cultivation periods were compared. Basically, three types of cells grew from the explants during several days: marginal cells, Claudius' cells and fibroblast-like cells. In primary cultures of explants, growth of marginal cells was observed in 25% of the dishes. Their proliferative activity, estimated by the use of the BrdUrd-DNA antibody, started in the stria vascularis and continued across the attachment of Reissner's membrane down to the bottom of the cell culture dish. The newly-formed marginal cells expressed cytokeratin 18 in the same way that original marginal cells on the tissue specimen do. If the newly-formed marginal cells were in contact with fibroblast-like cells or were forming groups (domes) on the bottom, they expressed vimentin. In 3% of the dishes growth of Claudius' cells was observed. Proliferative activity of these cells was found at the point where the basilar membrane was attached to the spiral ligament. New Claudius' cells spread at the opposite side of an explant when compared with the location of new marginal cells. Original as well as newly-formed Claudius' cells contained cytokeratin 18. Fibroblast-like cells were commonly present in cultures and contained only vimentin.

Animals↗

PubMed1992

[A short history of hearing research. IV: Physiology].

In 1863, Hensen concluded from measurements of the width of the basilar membrane that tones of high and low pitch were represented at the base and apex of the cochlea, respectively. According to his calculations on the tonotopic representation of sound stimuli in the cochlea Helmholtz proposed additional resonators that would transmit the amplified signal to the afferent nerve endings. He speculated that the pillar cells of the tunnel of Corti or strands of the basilar membrane might be these proposed resonators. The resonance theory was contradicted by Wien in 1905. However, further experiments by Held and Kleinknecht in 1927 and by Békésy in 1928 demonstrated that Helmholtz's ideas on the tonotopic dispersion of the vibration of the basilar membrane were correct. Békésy measured the vibration of the cochlear partition in human and animal cadavers and discovered the travelling-wave of the basilar membrane. At the turn of the century Ter Kuile noted that the vibration of the cochlear partition caused a deflection of the sensory hairs of the hair cells, the auditory receptor cells. Wever and Bray described in 1930 stimulus-evoked electrical currents near the cochlea with a wave form similar to that of the original sound stimulus. It was Adrian who later coined the term "cochlear microphonics" for this phenomenon. According to calculations of Gold (1948) and others active mechanical amplification would be required for such a sharp tuning in the cochlea. The first to measure action potentials of the afferent auditory nerve was Tasaki (1954).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Stiffness, compliance, elasticity and force generation of outer hair cells.

Isolated outer hair cells (OHCs) were partially sucked into especially designed cell capillaries allowing an experimental reconstitution of the cells' electroanatomy. The experimental approach separated the apical from the basolateral parts of the cells thus forming an artificial scala media and scala tympani. Resistance between both was 121 +/- 42 M omega. A sequence of negative and positive pressures was applied to the basal cell pole allowing "pulling" or "pushing" of the sensory cell investigated. The resulting length changes together with the known pressures allowed the estimation of an actual longitudinal compliance of 354 +/- 35 m/N. Following "pulling" OHCs tended to resume their initial shape after the force had ceased to be effective indicating elastic distortions. The calculated elasticity modulus of OHCs amounted to 6.1 +/- 3.4 kN/m2. From this data an actual longitudinal whole cell stiffness of OHCs of 3 x 10(-3) N/m was calculated. Ultrasound scanning of immobilized OHCs identified the cuticular plate (CP) and a central core between CP and basal cell pole as structures contributing to the cells' acoustic stiffness. Changes of the potential differences between the artificial scala media and scala tympani resulted in active length changes following the command voltage with a slope of delta 1/(1 x U) = 0.055 V-1. Assuming the validity of Hooke's law, the force generation associated with the active length changes can be calculated since the compliance is known.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

The length of isolated outer hair cells is temperature dependent.

In the mammalian cochlea, motile properties of outer hair cells may contribute to sharp tuning and amplification. Length changes of isolated outer hair cells in response to various physical and chemical stimuli have therefore been investigated by many laboratories. The present study shows that alteration of temperature changes the length of outer hair cells of the guinea pig cochlea as much as 0.22 micron/degrees C. Thus, length changes in response to alterations of temperature are similar to length changes in response to other physical and chemical stimuli.

Animals↗