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S Hoth

Publications and source records attributed to S Hoth.

At least 19 recordsLinked to original sources
PubMed2007

[On the relation between binaural difference potentials and directional hearing].

BACKGROUND: Central auditory processing disorders (CAPD) are associated with reduced discriminatory abilities of the auditory system. One of these abilities is directional hearing, which is based on the evaluation of interaural signal differences. Since these differences affect also the binaural difference potentials (BDP), these derived evoked potentials could be suitable for the objective detection of disabilities in acoustic localization. METHOD: Auditory brainstem responses (ABR) evoked by monaural and binaural stimulation were recorded in 32 adult normal-hearing volunteers at stimulus levels between 10 and 80 dB nHL and the BDP were derived. Additionally, a test of directional hearing was performed and evaluated. RESULTS: BDP are detectable at all stimulus levels without difficulties, with acceptable examination times and with satisfactory reliability in a routine clinical environment. The electrodes can be positioned at the mastoid (A1 and A2) and vertex (Cz) as for conventional ABR recording. Normal ranges are given for latency and amplitude as well as for their lateral differences. CONCLUSION: The spectrum in directional hearing ability as covered by normal-hearing subjects is not mirrored in the parameters of their BDP. Nevertheless, it cannot be ruled out that a real impairment of directional hearing goes along with significantly altered BDP.

Adult↗
PubMed2003

Regulation of the ABA-sensitive Arabidopsis potassium channel gene GORK in response to water stress.

The phytohormone abscisic acid (ABA) regulates many stress-related processes in plants. In this context ABA mediates the responsiveness of plants to environmental stresses such as drought, cold or salt. In response to water stress, ABA induces stomatal closure by activating Ca2+, K+ and anion channels in guard cells. To understand the signalling pathways that regulate these turgor control elements, we studied the transcriptional control of the K+ release channel gene GORK that is expressed in guard cells, roots and vascular tissue. GORK transcription was up-regulated upon onset of drought, salt stress and cold. The wilting hormone ABA that integrates responses to these stimuli induced GORK expression in seedlings in a time- and concentration-dependent manner and this induction was dependent on extracellular Ca2+. ABA-responsive expression of GORK was impaired in the ABA-insensitive mutants abi1-1 and abi2-1, indicating that these protein phosphatases are regulators of GORK expression. Application of ABA to suspension-cultured cells for 2 min followed by a 4 h chase was sufficient to manifest transcriptional activation of the K+ channel gene. As predicted for a process involved in drought adaptation, only 12-24 h after the release of the stress hormone, GORK mRNA slowly decreased. In contrast to other tissues, GORK expression as well as K+(out) channel activity in guard cells is ABA insensitive, allowing the plant to adjust stomatal movement and water status control separately.

Abscisic Acid↗
PubMed2003

[Auditory brainstem responses evoked by direct mechanical stimulation of the ossicular chain. Objective preoperative testing of candidates for implantable hearing aids].

BACKGROUND AND OBJECTIVE: The function of several implantable hearing systems is based on the vibratory excitation of the ossicular chain. For preoperative testing, malleus vibration audiometry has been described [7]. In special cases, it could be desirable to perform objective testing before implantation. We therefore studied the auditory brainstem responses (ABR) evoked by vibratory stimulation of the ear drum. METHOD: The ABR evoked by vibratory and acoustical click stimulation were recorded in 20 subjects with normal hearing at four different stimulus intensities. For the vibratory stimulation (v-ABR), the transducer rod was brought into mechanical contact with the eardrum under microscopic control. This setup was further used for the determination of the individual subjective threshold. The v-ABR were compared to conventional ABR recordings. RESULTS: In all subjects, the v-ABR could clearly be identified. At high stimulus levels, the complete wave pattern was observed in 15 of 20 cases. There is no essential difference between v-ABR and conventional ABR with respect to the incidence and parameters of the potentials. At high stimulus levels, a pronounced stimulus artefact impedes the identification of wave I in some cases. Moreover, the quality of v-ABR is limited by the uncomfortable situation and incomplete relaxation of the subject. CONCLUSIONS: The measurement of vibratory evoked ABR is practicable without hazards for the patient and it yields reliable results. The hearing threshold for click stimuli can be determined from the incidence and amplitude of the responses. The loudness associated with the click stimuli can be estimated from the response latency. Therefore, the investigation of v-ABR not only gives evidence of the individual suitability for implantable hearing aids but its outcome may also be useful as an orientation for the postoperative fitting.

Acoustic Stimulation↗
PubMed2001

A novel K+ channel expressed in carrot roots with a low susceptibility toward metal ions.

Kdc1 is a novel K+-channel gene cloned from carrot roots, and which is also present in cultured carrot cells. We investigated the characteristics of the ionic current elicited in Xenopus oocytes coinjected with KDC1 (K+-Daucus carota 1) and KAT1 (from Arabidopsis thaliana) RNA. Expressed heteromeric channels displayed inward-rectifying potassium currents whose kinetics, voltage characteristics, and inhibition by metal ions depended on KDC1:KAT1 ratios. At low KDC1:KAT1 ratios, Zn2+ inhibition of heteromeric K+ current was less pronounced compared to homomeric KAT1 channels, while at higher KDC1:KAT1 ratios, the addition of Zn2+ even produced an increase in current. Under the same conditions, the Ni2+ inhibition of the current was also reduced, but no current increase was observed. These effects might be explained by the unusual amino acid composition of the KDC1 protein in terms of histidine residues that are absent in the pore region, but abundant (four per subunit) in the proximity of the pore entrance. Channels like KDC1 could be at least partially responsible for the higher resistance of carrot cells in the presence of metals.

Animals↗
PubMed2001

The latency of evoked otoacoustic emissions: its relation to hearing loss and auditory evoked potentials.

The latencies of transient evoked otoacoustic emissions (TEOAE), distortion product otoacoustic emissions (DPOAE) and auditory brainstem responses (ABR) have been studied in 173 patients with cochlear hearing impairment. No systematic or significant correlation between the OAE latency and the hearing loss at the corresponding frequency could be found, whereas the ABR latencies increase by a small but significant amount with increasing hearing loss. This can be explained by a broadening of the excited area and its shifting towards a more apical position if the hair cell population in the basal turn is depleted. Because of the considerable intersubject variability of OAE latencies the data do not allow to decide whether they are not influenced by cochlear hearing loss or whether an effect is merely not observable. The large variability is attributed to the interindividual differences of OAE generation time and return delay whereas the travel time of the primary wave is less variable as can be seen from the low variability of ABR latencies.

Acoustic Stimulation↗
PubMed2001

The pore of plant K(+) channels is involved in voltage and pH sensing: domain-swapping between different K(+) channel alpha-subunits.

Plant K(+) uptake channel types differ with respect to their voltage, Ca(2)+, and pH dependence. Here, we constructed recombinant chimeric channels between KST1, a member of the inward-rectifying, acid-activated KAT1 family, and AKT3, a member of the weakly voltage-dependent, proton-blocked AKT2/3 family. The homologous pore regions of AKT3 (amino acids 216 to 287) and KST1 (amino acids 217 to 289) have been exchanged to generate the two chimeric channels AKT3/(p)KST1 and KST1/(p)AKT3. In contrast to AKT3 wild-type channels, AKT3/(p)KST1 revealed a strong inward rectification reminiscent of that of KST1. Correspondingly, the substitution of the KST1 by the AKT3 pore led to less pronounced rectification properties of KST1/(p)AKT3 compared with wild-type KST1. Besides the voltage dependence, the interaction between the chimera and extracellular H(+) and Ca(2)+ resembled the properties of the inserted rather than the respective wild-type pore. Whereas AKT3/(p)KST1 was acid activated and Ca(2)+ insensitive, extracellular protons and Ca(2)+ inhibited KST1/(p)AKT3. The regulation of the chimeric channels by cytoplasmic protons followed the respective wild-type backbone of the chimeric channels, indicating that the intracellular pH sensor is located outside the P domain. We thus conclude that essential elements for external pH and Ca(2)+ regulation and for the rectification of voltage-dependent K(+) uptake channels are located within the channel pore.

Amino Acid Sequence↗
PubMed2000

Differential expression and regulation of K(+) channels in the maize coleoptile: molecular and biophysical analysis of cells isolated from cortex and vasculature.

UNLABELLED: Recently, two K(+) channel genes, ZMK1 and ZMK2, were isolated from maize coleoptiles. They are expressed in the cortex and vasculature, respectively. Expression in Xenopus oocytes characterized ZMK1 as an inwardly rectifying K(+) channel activated by external acidification, while ZMK2 mediates voltage-independent and proton-inhibited K(+) currents. In search of the related gene products in planta, we applied the patch-clamp technique to protoplasts isolated from the cortex and vasculature of Zea mays coleoptiles and mesocotyls. In the cortex, a 6-8 pS K(+) channel gave rise to inwardly rectifying K(+) currents. Like ZMK1, this channel was activated by apoplastic acidification. In contrast, protoplasts from vascular tissue expressing the sucrose transporter ZmSUT1 were dominated by largely voltage-independent K(+) currents with a single-channel conductance of 22 pS. The pronounced sensitivity to the extracellular protons Ca(2+), Cs(+) and Ba(2+) is reminiscent of ZMK2 properties in oocytes. Thus, the dominant K(+) channels in cortex and vasculature most likely represent the gene products of ZMK1 and ZMK2. Our studies on the ZMK2-like channels represent the first in planta analysis of a K+ channel that shares properties with the AKT3 K(+) channel family. KEYWORDS: K(+) channel, voltage-independent, proton block, maize coleoptile.

Cotyledon↗
PubMed2000

[Expert system for aiding diagnosis in hearing tests].

For expert systems intended to aid diagnosis, a structure with five levels is proposed. These levels are the original area, the parameter and a reduced parameter layer, the classification and the final-decision layer. On the basis of this structures, an expert system was developed specifically for neonatal hearing screening with transitory evoked otoacoustic emissions (TEOAE). In a second step, this system was investigated for its suitability to classify emissions, regardless of patient age. For the comparison measurements in 252 mainly adult patients, some with an acquired hearing impairment, were used. To adapt the pass/fail decision to the extended evaluation criteria, the false classifications from a first run with the new data were used for training. Thereafter, the expert system, working with a wider data basis, classified the new data with a sensitivity that was increased by 4.8% to 97.2%, and a 2.0% improvement in specificity to 95.5% when classifying new data, These results, together with those of 97.3% and 94.3% achieved with exclusively neonatal TEOAE classification, clearly show the advantage of the expert system structures chosen, and document evidence of the practical applicability of the method.

Adult↗
PubMed1999

Auxin-induced K+ channel expression represents an essential step in coleoptile growth and gravitropism.

Auxin-induced growth of coleoptiles depends on the presence of potassium and is suppressed by K+ channel blockers. To evaluate the role of K+ channels in auxin-mediated growth, we isolated and functionally expressed ZMK1 and ZMK2 (Zea mays K+ channel 1 and 2), two potassium channels from maize coleoptiles. In growth experiments, the time course of auxin-induced expression of ZMK1 coincided with the kinetics of coleoptile elongation. Upon gravistimulation of maize seedlings, ZMK1 expression followed the gravitropic-induced auxin redistribution. K+ channel expression increased even before a bending of the coleoptile was observed. The transcript level of ZMK2, expressed in vascular tissue, was not affected by auxin. In patch-clamp studies on coleoptile protoplasts, auxin increased K+ channel density while leaving channel properties unaffected. Thus, we conclude that coleoptile growth depends on the transcriptional up-regulation of ZMK1, an inwardly rectifying K+ channel expressed in the nonvascular tissue of this organ.

Animals↗
PubMed1999

AKT3, a phloem-localized K+ channel, is blocked by protons.

The potassium-channel gene, AKT3, has recently been isolated from an Arabidopsis thaliana cDNA library. By using the whole-mount and in situ hybridization techniques, we found AKT3 predominantly expressed in the phloem. To study the physiological role of this channel type, AKT3 was heterologously expressed in Xenopus oocytes, and the electrical properties were examined with voltage-clamp techniques. Unlike the plant inward-rectifying guard cell K+ channels KAT1 and KST1, the AKT3 channels were only weakly regulated by the membrane potential. Furthermore, AKT3 was blocked by physiological concentrations of external Ca2+ and showed an inverted pH regulation. Extracellular acidification decreased the macroscopic AKT3 currents by reducing the single-channel conductance. Because assimilate transport in the vascular tissue coincides with both H+ and K+ fluxes, AKT3 K+ channels may be involved in K+ transport accompanying phloem loading and unloading processes.

Arabidopsis↗
PubMed1999

Distinct molecular bases for pH sensitivity of the guard cell K+ channels KST1 and KAT1.

Acid-induced potassium uptake through K+ channels is a prerequisite for stomatal opening. Our previous studies identified a pore histidine as a major component of the acid activation mechanism of the potato guard cell K+ channel KST1 (1). Although this histidine is highly conserved among all plant K+ uptake channels cloned so far, the pH-dependent gating of the Arabidopsis thaliana guard cell K+ channel KAT1 was not affected by mutations of this histidine. In both channels, KST1 and KAT1, aspartate mutants in the K+ channel consensus sequence GYGD adjacent to the histidine (KST1-D269N and KAT1-D265N) were inhibited by a rise in the extracellular proton concentration. pH changes affected the half-maximal activation voltage V(1)/(2) of the KST1 mutant, whereas in the mutant channel KAT1-D265N an acid-induced decrease in the maximum conductance gmax indicated the presence of a proton block. In contrast to the wild type KST1, the S4-mutant channel KST1-R181Q exhibited an activation upon alcalization of the extracellular solution. From our electrophysiological studies on channel mutants with respect to the pore histidine as well as the aspartate, we conclude that the common proton-supported shift in the voltage dependence of KST1 and KAT1 is based on distinct molecular elements.

Animals↗
PubMed1999

[Improvement in the objective diagnosis of hearing disorders by a new technique of simultaneous recording of acoustic and electrical responses of the auditory system].

The measurements of transitory evoked otoacoustic emissions (TEOAE) and auditory brainstem responses (ABR) are widely used in objective audiometry for the diagnosis of conductive or sensorineural hearing losses. In some cases only one of these signals is required for a complete diagnosis, while other cases may require both methods to define findings. With conventional equipment the measurement of TEOAE and ABR is performed with different devices at different times. Devices for simultaneous recording of both signals are currently not available or described, although the physiological circumstances and apparatus requirements would favor such an approach. In the present work a prototype for the simultaneous measurement of TEOAE and ABR is presented and its application tested in 33 normal-hearing adults. The equipment used was based on a general purpose laboratory computer connected to an acoustic stimulator and a dual-channel data acquisition system. Stimuli were composed of click sequences for the cancellation of linear signal components and were presented by an ear canal probe (Otodynamics) which also picked up the microphone signal within the outer ear canal. The EEG activity containing the ABR was recorded through surface electrodes fixed at the patient's vertex and mastoid. Acoustic and electric signals were processed simultaneously, resulting in three independent records representing a non-linear TEOAE and the low and high level ABR. The main advantages of the new approach are an improvement in information output and enhancement in the accuracy of determining the site and extent of a hearing impairment.

Adult↗
PubMed1999

Susceptibility of the guard-cell K(+)-uptake channel KST1 to Zn(2+) requires histidine residues in the S3-S4 linker and in the channel pore

Potassium channels are inhibited by several mono- and divalent cations. To identify sites involved in the interaction between K(+) channels and cationic effectors, we expressed the potato (Solanum tuberosum L.) guard-cell K(+)-uptake channel KST1 in Xenopus oocytes. This channel was reversibly blocked by extracellular Zn(2+) in the micromolar range. In the presence of this heavy metal, steady-state currents were reduced in a pH-dependent but voltage-independent manner. Since Zn(2+)-inhibition was less effective at elevated external proton concentrations, we generated alanine mutants with respect to both extracellular histidines in KST1. Whereas substitution of the pore histidine H271 resulted in a reduced blockade by Zn(2+), the channel mutant KST1-H160A in the S3-S4 linker lost most of its Zn(2+ )sensitivity. Since both histidines alter the susceptibility of KST1 to Zn(2+), the block may predominantly result from these two sites. We thus conclude that the S3-S4 linker is involved in the formation of the outer pore.

Journal Article↗
PubMed1999

The Nicotiana tabacum plasma membrane aquaporin NtAQP1 is mercury-insensitive and permeable for glycerol.

A new aquaporin from Nicotiana tabacum (cv. Samsun) was characterized. It shares sequence homology to the Arabidopsis thaliana PIP1 protein family. By two-phase partitioning and immunoblot analysis, plasma membrane localization could be demonstrated. The corresponding mRNA is highly abundant in roots and flowers, while it is rarely expressed in leaves and stems. Functional expression in Xenopus oocytes revealed that NtAQP1 can mediate glycerol transport in addition to water flow. However, NtAQP1 is impermeable for Na+, K+ and Cl- ions. The water permeability and selectivity could not be modulated by addition of mercurials or the activity of cAMP-dependent protein kinases.

Animals↗
PubMed1998

Nuclear import and nucleolar accumulation of the human ribosomal protein S7 depends on both a minimal nuclear localization sequence and an adjacent basic region.

In the course of the eukaryotic ribosomal biogenesis, both the nuclear import and export are involved. We have studied the nuclear and nucleolar localization of the human ribosomal protein S7. We examined the subcellular distribution of the S7:beta-galactosidase fusion protein in SAOS-2 cells. We have identified two evolutionarily conserved domains, both of which are necessary for S7 nuclear and nucleolar targeting: amino acids 98 to 109 and 115 to 118. Out of the S7 protein context, a fragment 98...118, containing these domains, is sufficient for nuclear transport and nucleolar accumulation. Interestingly, a tetrapeptide 115KRPR118, which can act as an independent nuclear localization signal (NLS), is not sufficient for exclusively nuclear accumulation of the S7 protein if the adjacent region 98...109 is deleted. In addition, site-directed mutagenesis revealed that critical residues for nuclear targeting in this tetrapeptide and in the full-length S7 protein are different. While mutation of a Pro117 significantly impaired nuclear import of S7, similar substitution within the tetrapeptide-NLS had no effect on nuclear targeting. This suggests that to function perfectly, proper secondary structure of the S7 nuclear targeting domain is required.

Amino Acid Sequence↗