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R Rüdel

Publications and source records attributed to R Rüdel.

At least 73 records · Page 4Linked to original sources
PubMed1992

Interleukin-2 inhibits sodium currents in human muscle cells.

The effect of the T cell growth factor interleukin-2 (IL-2) on muscular Na+ channels was studied in myoballs produced from primary human muscle cultures. The transient Na+ inward currents of the myoballs, elicited by repetitive stimulation at 1 Hz and recorded in the whole-cell mode, were inhibited by IL-2 applied to the external solution, the half maximum effect occurring at 300 U/ml. The effect was complete within 5 s and was totally reversible, the on and off effects having identical time courses. The h infinity curve was shifted in negative direction indicating that the mechanism of IL-2 action is a conversion of the Na+ channels into a state of inactivation. The reaction of the IL-2 solution with an anti IL-2 antibody neutralized the inhibitory effect on the Na+ currents, indicating a specific effect of the peptide growth factor interleukin-2 on muscular Na+ channels. The connection of IL-2 and Na+ channels may be important in inflammatory processes of muscle and nerve.

Humans↗
PubMed1992

Whole-cell recordings of chloride currents in cultured human skeletal muscle.

Chloride currents in human myoballs were investigated with the tight-seal whole-cell recording method in a wide range of membrane voltages (-125 to +145 mV). Two current components having different kinetics could be distinguished. In more than 90% of the myoballs the following results were obtained. At negative potentials, the amplitude of the Cl- current was small and independent of time. The amplitude of the current increased as the membrane potential was made more positive. At potentials positive to +75 mV, the current increased monoexponentially with time. Inactivation occurred only during very long (greater than 3 s) pulses. When such a test pulse was preceded by a conditioning pulse to +60 mV, the current at potentials more than +90 mV was markedly smaller than in the absence of a prepulse, and no activation was provoked by strongly pulses. Recovery from inactivation could only be measured at potentials negative to -40 mV. The Cl- conductance at -85 mV was 5.9 +/- 3.64 microS/cm2 (SD; n = 10). In about 5% of the myoballs a kinetically different current was visible, characterized by fast inactivation at highly positive potentials. The current amplitudes were substantially larger in such cases, the Cl- conductance at -85 mV being 12.2 +/- 9.02 microS/cm2 (n = 4).

Calcium↗
PubMed1992

Single-channel recordings of chloride currents in cultured human skeletal muscle.

The Cl- channels in human myoballs were investigated with several recording techniques. Three types of channels were found and dubbed "small", "intermediate", and "large", according to their different conductance. The intermediate Cl- channel was observed most frequently. It was active at the resting potential immediately after seal formation in cell-attached as well as in excised patches. Its Cl- selectivity was rather high (PCl/PNa = 9.46; PCl/PMeSO4 = 7.85 where P denotes permeability) and the slope conductance at the reversal potential with [Cl-]o/[Cl-]i equal to 160 mM/42 mM was 31 pS. The channel showed an open-channel substructure with two subconductance levels having equal amplitudes. It can conduct two kinetically different currents that correspond to the activating and the inactivating Cl- current components described by Zachar et al. (1992). The small Cl- channel had a conductance of 10 pS at the reversal potential, a PCl/PNa of 2.7, and a PCl/PMeSO4 of 22.6. Its open probability was biggest negative to -85 mV, resulting in an inactivating whole-cell Cl- current component. Because of the small channel density and conductance the contribution of this channel type to the whole-cell current seems to be small. Patches with only one small channel were never observed which suggests that this channel type occurs in clusters. A third type of channel with very large conductance (250 pS) was seen only four times.

Chlorides↗
PubMed1992

The acute paralysis in Guillain-Barré syndrome is related to a Na+ channel blocking factor in the cerebrospinal fluid.

The effect of cerebrospinal fluid (CSF) from patients with severe polyradiculoneuritis (Guillain-Barré syndrome, GBS) on voltage-dependent Na+ channels of myoballs was studied. The transient Na+ currents, elicited by repetitive stimulation at 1 Hz, were inhibited by the CSF from most of the GBS patients to 10%-40% the control value. The inhibition was complete in about 5 s and was fully reversible. Such inhibition was never seen with control CSF. The blocking property of the CSF from GBS patients was lost after the number of cells and the protein content had been lowered by means of a clinical filtration technique for cerebrospinal fluid. The results demonstrate that in Guillain-Barré syndrome blocking factors of Na+ channels are present in the CSF, impairing neuron impulse conduction, and thereby causing muscular weakness and sensory disturbances in the affected patient.

Cerebrospinal Fluid↗
PubMed1992

Chloride channels in cultured human skeletal muscle are regulated by G proteins.

The regulation of Cl- channels in human myoballs by G proteins was studied using whole-cell and inside-out patch recordings. After perfusion of the cell with 0.1 mM GTP[gamma S], the specific Cl- conductance, GCl, at standard resting potential (-85 mV) was increased from 5.9 microS/cm2 to 103 microS/cm2, and the kinetics upon stepping the potential to positive values was changed from an activating current with very slow inactivation to a fast inactivating current with no potential-dependent activation. These effects were not affected by the simultaneous blockade of several signal cascades involving G proteins. Addition of the protein kinase blockers PKI (25 microM), H8 (10 microM), or of the phospholipase-A2-blocking agent quinacrine (10 microM), had not much influence on these GTP[gamma S] effects. Buffering of the intracellular Ca2+ concentration (0.1 microM) or addition of the Ca2+/calmodulin antagonist trifluoperazine (50 microM) was also without effect. Pre-incubation of the cells with pertussis toxin or with cholera toxin did not change GCl. In excised inside-out patches voltage-clamped at -85 mV, application of GTP[gamma S] influenced the "intermediate" Cl- channel, the Cl- channel type having the highest density in these cells, by increasing the number of transitions in a half-conductance state. The probability of the channel being in one of the two conducting states rose from 0.015 to 0.67, and the kinetics of the single-channel currents was changed so that, on average, it was similar to the whole-cell current kinetics seen after application of GTP[gamma S]. It is concluded that a G protein is directly interacting with these channels.

Chlorides↗
PubMed1991

The different use dependences of tocainide and benzocaine are correlated with different effects on sodium channel inactivation.

To study the mechanism of use dependence, we investigated the influence of 0.5 mM tocainide on the amplitude of sodium currents elicited by membrane depolarizations with standard test pulses in voltage-clamped human myoballs. For comparison, the experiments were also conducted with 1 mM benzocaine, a drug with almost no use dependence. These concentrations were so chosen that without stimulation and at a holding potential of -135 mV, either drug blocked about 50% of the channels (tonic block). With repetitive stimulation at 1 Hz, tocainide blocked about 75% of the channels that had remained open in the rested state (phasic block), while benzocaine had little such effect. The potential dependence of steady-state inactivation (h infinity curves) of the sodium channels in these myoballs depended on the duration of the prepotential indicating that they possess at least two states of inactivation: fast and intermediate. The two drugs differed in their effects on these two states. Benzocaine always produced a left-shift of the h infinity curve, no matter whether the duration of the conditioning pulse was short (8 ms) or long (512 ms) indicating that it can bind when the channel is in the state of fast inactivation. Tocainide shifted the h infinity curve only with long prepulses, i.e. when the sodium channels were in the state of intermediate inactivation. The recovery from inactivation, a process governed by two time constants in the absence of drugs, was also differently influenced by the two drugs. In the presence of tocainide, the channels mainly recovered with the slow time constant and this time constant was significantly increased, whereas benzocaine did not substantially modify this biphasic process.(ABSTRACT TRUNCATED AT 250 WORDS)

Benzocaine↗
PubMed1991

Linkage data suggesting allelic heterogeneity for paramyotonia congenita and hyperkalemic periodic paralysis on chromosome 17.

Paramyotonia congenita (PC), an autosomal dominant non-progressive muscle disorder, is characterised by cold-induced stiffness followed by muscle weakness. The weakness is caused by a dysfunction of the sodium channel in muscle fibre. Parts of the gene coding for the alpha-subunit of the sodium channel of the adult human skeletal muscle (SCN4A) have been localised on chromosome 17. To investigate the role of this gene in the etiology of PC, a linkage analysis in 17 well-defined families was carried out. The results (zeta = 20.61, theta = 0.001) show that the mutant gene responsible for the disorder is indeed tightly linked to the SCN4A gene. The mutation causing hyperkalemic periodic paralysis (HyperPP) with myotonia has previously been mapped to this gene locus by the same candidate gene approach. Thus, our data suggest that PC and HyperPP are caused by allelic mutations at a single locus on chromosome 17.

Alleles↗
PubMed1991

Stereoselective interaction of tocainide and its chiral analogs with the sodium channels in human myoballs.

The effects of both enantiomers of tocainide and of some of its chiral analogs on the inactivation of the sodium current in human myoballs were investigated with the whole-cell recording technique. Structure and electron densities of the applied compounds were calculated and compared to the results. Both the R(-) and the S(+) enantiomers had little effect on fast inactivation determined with short prepulses according to Hodgkin and Huxley (1952; h infinity curve). When the inactivating prepulses used in this pulse protocol were prolonged to 1024 ms, both tocainide enantiomers increased inactivation severely, suggesting that the drug binds to the channel when it is in the state of intermediate inactivation (Fakler et al. 1990). Tetrodotoxin-resistant "juvenile" sodium channels were more affected than tetrodotoxin-sensitive "adult" channels. The R form was four times as effective as the S form. The compound obtained by substitution of the methyl group on the chiral centre of tocainide with a benzyl group, although in the less potent S form, affected inactivation of the juvenile sodium channels much more than the potent (R)-tocainide. Two additional substitutions, performed on the aromatic ring of tocainide, gave a compound that was most potent in shifting the inactivation curves, but without any selectivity for juvenile or adult channels.

Humans↗
PubMed1991

Voltage-dependent K+ channels in the sarcolemma of mouse skeletal muscle.

The voltage-dependent K+ channels of the mammalian sarcolemma were studied with the patch-clamp technique in intact, enzymatically dissociated fibres from the toe muscle of the mouse. With a physiological solution (containing 2.5 mM K+) in the pipette, depolarizing pulses imposed on a cell-attached membrane patch activated K+ channels with a conductance of about 17 pS. No channel activity was observed when the pipette solution contained 2 mM tetraethylammonium (TEA), or 2 mM 4-aminopyridine (4-AP). Whole cell recordings from these very small muscle fibres showed the well-known delayed rectifier K+ outward current with a threshold of about -40 mV. The whole-cell current was completely blocked by 2 mM TEA in the bath, suggesting that the TEA-sensitive channels in the patch were also delayed rectifier channels. The inactivation properties of the channels were studied in the cell-attached mode. Averaged single-channel traces showed at least two types of channels discernible by their inactivation time course at a test potential of 60 mV. The fast type inactivated with a time constant of about 150 ms, the slow type with a time constant of about 400 ms. A little channel activity always remained during pulses lasting several minutes, indicating either the presence of a very slowly inactivating third type of K+ channel, or the tendency of the fast inactivating channels to re-open at constant voltage. No difference was seen in the single-channel amplitudes of the different types of K+ channels. The well characterized adenosine-5'-triphosphate-(ATP)-sensitive and Ca(2+)-dependent K+ channels, although present, were not active under the conditions used.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Sodium and potassium channels in epithelial cells from thymus glands and thymomas of myasthenia gravis patients.

In both normal and neoplastic epithelial cells from human thymus glands and thymomas, respectively, we found voltage-gated sodium and potassium channels that resemble the adult-type Na channel and the delayed outward rectifier K channel, respectively, of human skeletal muscle and mammalian nervous system. These voltage-gated ion channels might be part of a communication system between epithelial cells and other components of the microenvironment of the thymus.

Electric Conductivity↗
PubMed1991

Altered sodium channel behaviour causes myotonia in dominantly inherited myotonia congenita.

The cause of increased excitability in autosomal dominant myotonia congenita (MyC) was studied in resealed greater than 3-cm long segments of muscle fibres from eight patients. Three hours after biopsy only about 50% of the fibre segments had regained a normal resting potential. This differs from our experiences with normal muscle or other disorders of myotonia (e.g. recessive generalized myotonia) where nearly all cut fibres reseal and repolarize during this time. When the depolarized MyC fibre segments were placed in a solution containing 1 microM tetrodotoxin (TTX) they repolarized to -80 to -90 mV. In fibre segments with normal resting potential, in the absence of TTX, spontaneous myotonic runs were recorded intracellularly, occasionally with double spikes. For only one of the eight patients, the Cl- conductance was reduced (50% of the total membrane conductance vs the usual 75%), for the rest of the patients the steady-state current-voltage relationship was normal. Sodium currents through single membrane channels were recorded with a patch clamp. For every patient re-openings of the Na+ channels were observed throughout 10-ms depolarizing pulses. These are very uncommon in normal muscle. At potentials positive to the resting potential, the duration of the re-openings increased, but the current amplitude was the same. It is concluded that in myotonia congenita re-openings of Na+ channels are the major cause of hyperexcitability and that Cl- conductance is normal. If it is reduced in rare cases, it may potentiate the myotonia.

Action Potentials↗
PubMed1991

Confirmation of linkage of hyperkalaemic periodic paralysis to chromosome 17.

Linkage studies were performed in six European families with hyperkalaemic periodic paralysis (PPII) with myotonia, an autosomal dominantly inherited disorder characterised by episodic weakness. The weakness is caused by non-inactivating sodium channels of reduced single channel conductance of the muscle fibre membrane. Recently, portions of the gene coding for the alpha subunit of the sodium channel of the adult human skeletal muscle (h-Na2) have been cloned and localised on chromosome 17q with no recombinants to the human growth hormone locus (GH1). Linkage between these two chromosome 17 markers and the disease was shown in our families (Z = 7.14, 0 = 0.00). These results, combined with the linkage data of a single large American family, suggest that the disease is caused by dominant mutations of the adult sodium channel, and that it is probably a genetically homogeneous disorder. Hyperkalaemic periodic paralysis is the first non-progressive myotonic disorder to be localised on the human genome.

Chromosomes, Human, Pair 17↗
PubMed1991

Absence of acetylcholine-induced current in epithelial cells from thymus glands and thymomas of myasthenia gravis patients.

We investigated the activity of ion channels in epithelial cells from human thymus glands and thymomas kept in short-term cell culture by clamping the membrane potential of the cells at -85 mV and determining the membrane current flowing on application of acetylcholine, glycine, or gamma-aminobutyric acid. In concentrations of up to 10(-3) M, none of the neurotransmitters induced any detectable current. This suggests (1) that there are no acetylcholine receptors (AChRs) or other products of the AChR gene family having ion-channel properties in the membranes of these epithelial cells, and (2) that the alpha-bungarotoxin-binding protein of thymus and thymoma has no AChR-like ion-channel property. These results support the hypothesis that the cross-reacting structures that elicit the anti-AChR autoimmune response in thymoma-associated myasthenia gravis are antigens having only limited homology with the AChR. Myasthenia gravis not associated with thymoma might have a different pathogenesis.

Acetylcholine↗
PubMed1990

Inactivation of human sodium channels and the effect of tocainide.

The inactivation of the sodium channels in human medulloblastoma cells was investigated with the whole-cell recording technique. The potential dependence of inactivation ("inactivation curve") was determined by imposing a series of prepulses of varying amplitude on the membrane potential and measuring the maximum sodium current flowing after each prepulse at the test potential of -20 mV. The time dependence of inactivation was investigated by determining inactivation curves with prepulses of variable duration. A prolongation of the prepulse increased the degree of inactivation, even when the prepulse duration was much greater than the time constant for fast inactivation. This is explained by the existence of two additional states of "intermediate" inactivation of the sodium channel, the transition to which is slower than that to the state of fast inactivation and faster than that to the state of slow inactivation. The antiarrhythmic drug tocainide had no effect on fast inactivation, but a strong effect on intermediate inactivation. This explains the use dependence of this drug. The reaction model given by Chiu (1977) for the transitions from the open into the closed state of inactivation and vice versa is extended.

Cerebellar Neoplasms↗
PubMed1990

Human nicotinic acetylcholine receptor: the influence of second messengers on activation and desensitization.

The amplitude and time course of acetylcholine(ACh)-induced membrane current were determined in cells of the human medulloblastoma cell line TE 671. ACh was applied and washed out very rapidly (about 50 ms) by a shift of a cell between two streams of solution, one of which contained the transmitter. ACh-induced current was recorded in the whole-cell mode of patch clamping. The time course of activation of the ACh-induced current could not be resolved because the method of ACh application was still too slow. Desensitization started immediately with ACh application; it could be described by two time constants. With an ACh concentration of 3 microM, the fast time constant was about 0.5 s and the slow time constant was about 3.9 s. When the ACh concentration was raised in steps to 100 mM, the peak amplitude of the current increased, reached a maximum at 1 mM and decreased again. The rate of desensitization was directly correlated with increasing ACh concentration. Current amplitude and desensitization time constants were not affected by intracellular application of cAMP or of a catalytic subunit of a cAMP-dependent protein kinase. When the intracellular calcium concentration was raised at a constant magnesium concentration, desensitization time constants remained unaffected, but the current amplitude decreased. This decrease is not caused by a decrease in single-channel conductance, therefore it may represent a decrease in the number of activatable channels.

Acetylcholine↗
PubMed1990

[Dystrophia myotonica (Steinert disease)--a frequently misdiagnosed disease].

Dystrophia myotonica (Steinert's disease) is the most common hereditary disease of the neuromuscular system in adults. Its mode of inheritance is autosomal dominant. The gene responsible for its is located on chromosome 19 in the linkage domain of the loci for the apolipoproteins C2, C1 und E and of the creatine kinase of skeletal muscle (CKMM). Myotonic dystrophy is categorized in an adult and in a congenital form. In the adult form, the characteristic findings are muscular atrophy in certain regions of the body (face, neck and distally in the extremities) and myotonia. Cataract, intraocular hypotension, gonadal atrophy, conduction abnormalities in the heart and hearing deficiencies appear quite often in the course of the disease. In the congenital form, general muscle weekness (particularly pronounced in the face) is the leading finding, combined with retarded loco motor and mental development. A decisive criterion for the diagnosis of this form is the occurrence of myotonic dystrophy in the patient's mother. Electromyographic investigation is indicated when a suspicion of myotonic dystrophy cannot be ascertained on the basis of clinical and genetic findings. Myotonic runs in the EMG will then corroborate the suspicion. Recent electrophysiological investigations have indicated that at least three different types of channels for the passage of ions through the membrane of the skeletal muscle cells show abnormal behaviour, i.e. the channel for Cl-, Na+ and K+. These findings corroborate the hypothesis that the abnormality responsible for myotonic dystrophy is situated in the membrane systems. A pharmacological treatment of the muscular dystrophy has not yet been developed.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromosomes, Human, Pair 19↗
PubMed1989

Human acetylcholine receptors desensitize much faster than rat acetylcholine receptors.

The process of acetylcholine receptor (AChR) desensitization in the presence of transmitter was evaluated for human myoballs and medullo-blastoma cells. The cell under investigation was placed in one of two parallel streams of solution ejected from a double-barrelled pipette. Ultrafast (less than 50 ms) application of acetylcholine (ACh) in a specific concentration was accomplished by a shift of the cell into the other stream. ACh-induced current was measured in the whole-cell mode of patch clamping. Parameters for AChR desensitization were almost identical for the two types of human cells. Desensitization could be described by two time constants. With an ACh concentration of 3 microM, the fast time constant, tau f, was about 0.4 s and the slow time constant, tau s, was about 3.6 s. When the ACh concentration was raised to 10 microM, desensitization became faster. We also measured desensitization of the AChRs in rat myoballs and compared the values to our results from human cells. With 3 microM ACh, tau f in rat myoballs was 2.3 s and tau s was 12.7 s. Thus, rat AChRs desensitize more slowly than human AChRs. However, desensitization times for rat AChRs obtained in our experiments are much faster than published values. Therefore, ultrafast solution change would seem to be requisite for correct assessment of the desensitization process.

Acetylcholine↗