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C Franke

Publications and source records attributed to C Franke.

At least 55 records · Page 3Linked to original sources
PubMed1999

Block of quantal end-plate currents of mouse muscle by physostigmine and procaine.

of quantal end-plate currents of mouse muscle by physostigmine and procaine. Quantal endplate currents (qEPCs) were recorded from hemidiaphragms of mice by means of a macro-patch-clamp electrode. Excitation was blocked with tetrodotoxin, and quantal release was elicited by depolarizing pulses through the electrode. Physostigmine (Phys) or procaine (Proc) was applied to the recording site by perfusion of the electrode tip. Low concentrations of Phys increased the amplitude and prolonged the decay time constants of qEPCs from approximately 3 to approximately 10 ms, due to block of acetylcholine-esterase. With 20 microM to 2 mM Phys or Proc, the decay of qEPCs became biphasic, an initial short time constant taus decreasing to <1 ms with 1 mM Phys and to approximately 0.3 ms with 1 mM Proc. The long second time constant of the decay, taul, reached values of </=100 ms with these blocker concentrations. The blocking effects of Phys and Proc on the qEPC are due to binding to the open channel conformation. A method is described to extract the rate constants of binding (bp) from the sums 1/taus + 1/taul, and the rates of unbinding (b-p) from tau0. taus-1. taul-1 (tau0 is the decay time constant of the control EPC). For Phys and Proc bp of 1.3 and 5. 10(6) M-1 s-1 and b-p of 176 and 350 s-1, respectively, were found. Using these rate constants and a reaction scheme for the nicotinic receptor together with the respective rate constants determined before, we could model the experimental results satisfactorily.

Acetylcholine↗
PubMed1998

The NO synthase inhibitors L-Name and L-NMMA, but not L-arginine, block the mammalian nicotinic acetylcholine receptor channel.

(1) Nitric oxide (NO) synthase inhibitors (NOS-I) such as L-Name (N(G)-nitro L-arginine methyl ester) and L-NMMA (N(G)-monomethyl L-arginine) may enhance anesthesia indirectly by inhibiting the NO pathway. Moreover, NOS-I interact directly with receptor proteins. In an animal study, L-NMMA potentiated muscle relaxants. (2) The present experiments investigate the effects of L-NMMA, L-Name, and L-arginine on the nicotinic acetylcholine receptor channel (nAChR) using patch clamp techniques and a piezo-driven application system. Both NOS-I appear to directly interact with the nAChR in the open as well as in the closed conformation. L-Arginine has no effect.

Animals↗
PubMed1998

Molecular modulation of recombinant rat alpha1beta2gamma2 GABA(A) receptor channels by diazepam.

Recombinant gamma-aminobutyric acid (GABA(A)) receptor channels containing alpha1beta2gamma2-subunits were transiently expressed in HEK293 cells. Modulation by diazepam (DZ) was investigated using the patch-clamp technique with a device for ultra-fast solution exchange. GABA activated Cl(-)-currents were potentiated when DZ > 0.1 microM was added to non-saturating concentrations of GABA (< 0.1 mM GABA). Maximal potentiation of the peak current amplitude by a factor of 2.5 was observed when 1 microM DZ was added to the test-solution. Deactivation of GABA-activated currents after the end of GABA pulses was best fitted with two time constants. After application of DZ + GABA, increase of time constants of deactivation was measured. It was independent on GABA concentration. We conclude that prolongation of deactivation after application of GABA + DZ may be an important mechanism of the modulatory action of DZ at GABA(A) receptor channels.

Animals↗
PubMed1998

High resolution MRI and MRS: a feasibility study for the investigation of focal cerebral ischemia in mice.

Combined NMR imaging and spectroscopy have been applied to mouse brain during focal cerebral ischemia. The present study evaluated the feasibility of NMR measurements on mice in order to fine-tune the sequences and experimental setup for systematic investigations on stroke including future studies on transgenic animals. The acquisition of high quality diffusion-weighted, perfusion-weighted, and T2-weighted images (DWI, PWI, T2-WI, respectively) is demonstrated and complemented by measurements of 1H volume-selective spectroscopy and spectroscopic imaging (SI). Despite the small volume of the mouse brain, a satisfactory signal-to-noise ratio can be achieved with reasonably short measurement times. C57black/6J mice with an average body weight of 25 g were studied using state-of-the-art NMR sequences at 4.7 T. After induction of focal cerebral ischemia, the lesion was found clearly distinguishable in all imaging techniques. The apparent diffusion coefficient (ADC) was reduced in the ischemic region, and an expansion of the affected volume was observed with ongoing ischemia time. In the H spectra of ischemic animals a distinct change in the concentrations of NAA and lactate was visible. This is the first report on both SI data and perfusion-weighted imaging on mouse brain. It is demonstrated that the perfusion deficit during ischemia can be well demarcated. The spatial resolution of changes in metabolite concentrations allows the clear differentiation of elevated lactate levels in ischemic brain tissue.

Animals↗
PubMed1998

Purified IgG from seropositive and seronegative patients with mysasthenia gravis reversibly blocks currents through nicotinic acetylcholine receptor channels.

The mechanism of block of nicotinic acetylcholine receptor (nAChR) channels by purified antibodies from patients with myasthenia gravis (MG) was investigated by using an ultrafast system for solution exchange at outside-out patches. IgG of MG patients and controls was purified by using protein A-Sepharose columns. Probes from 9 seropositive MG patients and 3 seronegative MG patients were tested. As a preparation, cultured mouse myotubes expressing the embryonic-type nAChR channels were used. Twenty-millisecond pulses of 1.0 mM ACh were applied repetitively to outside-out patches. Outside-out patches were preexposed with IgG in concentrations between 0.1 and 200 mg/L during application of ACh pulses. The peak current amplitude was reduced to values between 6% and 71% of control for the 9 seropositive and 3 seronegative MG patients. The block was concentration dependent and fully reversible after washout of antibodies. Incubation with IgG from different control patients did not reduce the peak current amplitude. In addition, our findings with purified IgG from seronegative MG patients support the idea of the immunopathogenesis of this disorder and may allow the development of a diagnostic test for seronegative MG patients.

Acetylcholine↗
PubMed1998

Multiple mechanisms of block by the anesthetic isoflurane of a gamma-aminobutyric acid activated chloride channel in crayfish.

Outside-out patches were excised from the membrane of the deep extensor abdominal muscle (DEAM), containing gamma-aminobutyric acid (GABA)-activated chloride channels, in the crayfish Astacus astacus. GABA and isoflurane (iso) were applied in pulses by a liquid filament switch, and their effects on the GABA-elicited chloride currents were investigated. Application of iso alone elicited no current responses and pre-application of iso prior to GABA had no effects on the GABA-elicited current. Co-application of GABA and iso resulted in a reduction of the initial chloride current and subsequent decline of the current to a steady state, indicating that iso binds to the receptor after GABA has bound. Recovery currents at the end of the co-application pulse, their amplitudes decreasing with pulse duration, confirmed this suggestion. Open-time distributions of the blocked channel showed a shift of the long open-time towards a new time constant, indicating a second block mechanism via the long open state A5Os of the channel. Removal of GABA and iso after reaching the equilibrium state of the block resulted in recovery currents containing exclusively openings from the long open state A5Os, confirming the suggestion of an open channel block only at one of the open states.

Anesthetics↗
PubMed1998

Kinetics of AMPA-type glutamate receptor channels in rat caudate-putamen neurones show a wide range of desensitization but distinct recovery characteristics.

alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptor channels of rat caudate-putamen neurones were studied by ultrafast application of agonists to outside-out vesicles taken from medium-sized spiny neurones in thin slices. Upon application of 10 mM glutamate for 50 ms, fast rising and desensitizing currents were activated. Ten to 90% rise time values were approximately 0.5 ms. Dose-response studies revealed an EC50 of 0.63 mM glutamate. In double logarithmic coordinates, the curve had a maximal slope between 1.33 and 1.85 at low concentrations, indicating at least two binding sites for glutamate. Rise time increased with low agonist concentrations, whereas desensitization kinetics showed only a weak dependence on concentration. The time constant of desensitization was fitted with one exponential and ranged between 2 and 11 ms, with a mean of 6.19+/-2.31 ms (n = 239). Following brief glutamate pulses (1 ms) currents decayed with time constants of 2.7+/-0.23 ms (n = 12). Recovery from desensitization was investigated by double-pulse experiments. Recovery time constants fell in two subgroups with respective mean values of 110.6+/-14.2 ms (n = 8) and 288.6+/-33.2 ms (n = 8). By adding low glutamate concentrations to the bath solution, predesensitization of AMPA-type receptors without channel opening could be shown. A 50% reduction in control amplitude was achieved with 5.2+/-2.1 microM (n = 22) glutamate in the background. We hypothesize a circular reaction scheme with at least two binding sites for glutamate to describe activation, desensitization and recovery from desensitization in rat caudate-putamen neurones.

Animals↗
PubMed1998

Simple data from history and physical examination help to exclude bowel obstruction and to avoid radiographic studies in patients with acute abdominal pain.

OBJECTIVE: To assess the value of plain abdominal radiographs and of data from the medical history and physical examination in the diagnosis of acute abdominal pain in general and of bowel obstruction in particular. DESIGN: Prospective study. SETTING: 4 university and 2 community hospitals, Germany. SUBJECTS: 1254 patients with acute abdominal pain lasting less than 7 days, and with no history of abdominal injury including surgery. INTERVENTIONS: Standardised and structured medical history and physical examination, study of results of plain abdominal radiographs. MAIN OUTCOME MEASURES: Positive predictive value and sensitivity of clinical variables and abdominal film with respect to the diagnosis at discharge. RESULTS: 48 patients (3.8%) had bowel obstruction. 704 patients (56.1%) had plain abdominal films taken at the time of initial presentation. 111 studies (15.8%) showed important findings leading to diagnosis or immediate treatment, 455 (64.7%) showed unimportant or no findings. In 138 (19.6%) results of films were not reported. 16 of 45 single variables were of help in diagnosing bowel obstruction. The six with the highest sensitivity were distended abdomen, increased bowel sounds, history of constipation, previous abdominal surgery, age over 50, and vomiting. If only patients presenting with any two of these symptoms had had radiographs taken, 300 (42.6%) could have been avoided without loss in diagnostic accuracy. CONCLUSION: A considerable number of plain abdominal films taken for patients with acute abdominal pain could be avoided by focusing on clinical variables relevant to the diagnosis of bowel obstruction.

Abdominal Pain↗
PubMed1998

Voltage-gated Ca2+ currents in rat gastric enterochromaffin-like cells.

Enterochromaffin-like (ECL) cells are histamine-containing endocrine cells in the gastric mucosa that maintain a negative membrane potential of about -50 mV, largely due to voltage-gated K+ currents [D. F. Loo, G. Sachs, and C. Prinz. Am. J. Physiol. 270 (Gastrointest Liver Physiol. 33): G739-G745, 1996]. The current study investigated the presence of voltage-gated Ca2+ channels in single ECL cells. ECL cells were isolated from rat fundic mucosa by elutriation, density gradient centrifugation, and primary culture to a purity > 90%. Voltage-gated Ca2+ currents were measured in single ECL cells using the whole cell configuration of the patch-clamp technique. Depolarization-activated currents were recorded in the presence of Na+ or K+ blocking solutions and addition of 20 mM extracellular Ca2+. ECL cells showed inward currents in response to voltage steps that were activated at a test potential of around -20 mV with maximal inward currents observed at +20 mV and 20 mM extracellular Ca2+. The inactivation rate of the current decreased with increasingly negative holding potentials and was totally abolished at a holding potential of -30 mV. Addition of extracellular 20 mM Ba2+ instead of 20 mM Ca2+ increased the depolarization-induced current and decreased the inactivation rate. The inward current was fully inhibited by the specific L-type Ca2+ channel inhibitor verapamil (0.2 mM) and was augmented by the L-type Ca2+ channel activator BAY K 8644 (0.07 mM). We conclude that depolarization activates high-voltage-activated Ca2+ channels in ECL cells. Activation characteristics, Ba2+ effects, and pharmacological results imply the presence of L-type Ca2+ channels, whereas inactivation kinetics suggest the presence of additional N-type channels in rat gastric ECL cells.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1998

[Clinical value of diagnostic score for appendicitis: results of a prospective intervention study].

The clinical benefit of a diagnostic score for acute appendicitis was tested in a prospective interventional multicenter study on patients with abdominal pain. The study was performed in two consecutive phases: standard diagnostic work-up with no additional diagnostic support (870 patients) and additional diagnostic support with a score (614 patients). The two groups were comparable with respect to signs, symptoms and investigations related to acute appendicitis. Diagnostic performance of the final examiner decreased with the score: specificity from 86% to 78%, positive predictive value from 67% to 50% and accuracy from 88% to 81%. There were no differences in the perforated appendix, negative appendectomy and complication rate, however, the delayed appendectomy rate (2% versus 8%) and the delayed discharge rate (11% versus 22%) were significantly lower with diagnostic support by the score. In summary, the score cannot be recommended as a standard diagnostic tool for diagnostic decision making in acute appendicitis.

Abdomen, Acute↗
PubMed1998

[Is ultrasound examination in acute appendicitis dispensable? Acute Abdominal Pain Study Group].

In a prospective multicenter observational trial, the performance and clinical benefit of ultrasound of the appendix was evaluated in the clinical routine. Ultrasound of the appendix was performed in 870 of 2280 patients (38%); the overall sensitivity was 55% (range: 13 to 90%), specificity 95%, positive and negative predictive value 81 and 85%. There was no correlation between the frequency or accuracy of ultrasound and the accuracy of the clinician, the negative appendectomy or perforation rate.

Abdomen, Acute↗
PubMed1997

Activation kinetics and single channel properties of recombinant alpha1beta2gamma2L GABA(A) receptor channels.

Recombinant alpha1beta2gamma2L GABA(A) receptor channels, transiently expressed in HEK 293 cells, were investigated using the patch-clamp technique in combination with a device for ultra-fast solution exchange. The dose-response relationship revealed an EC50 of 11.6 +/- 0.9 microM and saturated with 3 mM GABA. The slope between 0.001 and 0.01 mM GABA was 2.2 +/- 0.4, indicating at least three binding sites for GABA. The rise time decreased from about 120 ms at 0.001 mM GABA to about 0.8 ms at 10 mM GABA. Single channel openings were grouped in bursts with an average duration of 10.3 +/- 3.0 ms. More than 95% of the current was represented by a single channel slope conductance of about 29 pS.

Cell Line↗
PubMed1997

Distribution of desensitization time constants of mouse embryonic-like nicotinic and homomeric GLUR6 glutamate receptor channels.

The distribution of the desensitization time constant, tauD, of two different, molecular well defined ligand gated receptor channels was analyzed: the embryonic-like nicotinic receptor (nAChR) channel of cultured mouse myotubes and recombinant, homomeric GluR6 receptor channels transiently expressed in HEK293 cells. Experiments were performed using outside-out patches in combination with a system for fast application of agonists which allows solution exchange within 0.1 ms. In response to application of saturating concentrations of acetylcholine (ACh) or glutamate (Glu). the peak current was reached in a submillisecond range and decayed monexponentially in the presence of the agonist, due to desensitization. tauD varied from 10 ms to 100 ms with a mean value of 55.0 +/- 22.6 ms (n = 133) in response to pulses of 10(-4) M ACh for embryonic-like nAChR channels and from 2.6 ms to 8.9 ms with a mean value of 5.0 +/- 1.9 ms (n = 35) in response to pulses of 10(-2) M Glu for homomeric GluR6 receptor channels. The reason for the high variability of the time course of desensitization is at present unclear.

Animals↗
PubMed1997

Influence of olfactory bulbectomy and subsequent imipramine treatment on 5-hydroxytryptaminergic presynapses in the rat frontal cortex: behavioural correlates.

1. Alterations of 5-hydroxytryptaminergic mechanisms are thought to play a special role in the pathogenesis of depression and antidepressant treatments are assumed to restore these changes. 2. We have used one of the most reliable models of depression, the olfactory bulbectomized rat to study the long term consequences of this manipulation and of subchronic imipramine treatment on two parameters of 5-hydroxytryptaminergic presynapses, 5-hydroxytryptamine (5-HT) transporter density and tryptophan hydroxylase apoenzyme concentration, in the frontal cortex as well as on active avoidance learning several weeks after bulbectomy. 3. The Bmax value of [3H]-paroxetine binding and the concentration of the 5-HT synthesizing enzyme were both significantly elevated in the frontal cortex of bulbectomized rats compared to sham-operated controls. 4. Imipramine treatment, either by daily injections or by subcutaneous implantation of slow release imipramine-containing polymers reduced the elevated tryptophan hydroxylase apoenzyme levels in the frontal cortex of bulbectomized, but not of sham-operated control rats and restored the deficient learning performance of bulbectomized rats. 5. Both effects were more pronounced after continuous drug administration by imipramine-releasing polymers compared to daily i.p. injections. 6. These findings indicate that bulbectomy leads to a compensatory 5-hydroxytryptaminergic hyperinnervation of the frontal cortex. Chronic antidepressant treatment seems to attenuate the increased output of the 5-hydroxytryptaminergic projections in the frontal cortex through the destabilization of the rate limiting enzyme of 5-HT synthesis of the 5-hydroxytryptaminergic nerve endings in this brain region.

Adrenergic Uptake Inhibitors↗
PubMed1997

Interaction of midazolam with the nicotinic acetylcholine receptor of mouse myotubes.

The effects of midazolam on the peripheral embryonic nicotinergic acetylcholine receptor (nAChR) of mouse myotubes were studied to elucidate the mechanism of its effect on neuromuscular transmission. Standard patch clamp techniques on outside-out patches were used. Pulses of 10(-4) M acetylcholine (ACh) applied by a liquid filament switch technique elicited macroscopic channel currents with a peak current amplitude of approximately 40 pA within <1 ms. The current decayed with a time constant of 30-100 ms due to desensitization. When midazolam was added in stepwise increased concentrations (10(-7) M to 7 x 10(-4) M) to the pulses, the current decay became bi-exponential, and a concentration-dependent decrease of the fast component of decay was observed. The current amplitude, however, was reduced slightly, and only at high concentrations of midazolam. This may indicate that midazolam binds to the open channel to cause the block. The rate constant of block (b(+1)) was found to be 1.8 x 10(6) M/s. Recovery experiments revealed a rate of unblocking (b(-1)) of approximately 2 x 10(-1) s(-1). After preincubation of the patches with midazolam, a substantial reduction of the current amplitude was seen at very low midazolam concentrations (<10(-7) M), which suggests an additional closed channel block with a Kd of approximately 10(-6) M. This closed channel block may be responsible for the muscle-relaxing effects of midazolam.

Acetylcholine↗
PubMed1997

Isoflurane and sevoflurane interact with the nicotinic acetylcholine receptor channels in micromolar concentrations.

BACKGROUND: This study was performed to elucidate and compare the effects of sevoflurane and of isoflurane on the nicotinic acetylcholine receptor of mouse myotubes. The experiments were done with special reference to anesthetic concentrations considerably less than those used for clinical anesthesia. METHODS: The patch-clamp technique was used to record acetylcholine-activated currents from the embryonic type of the nicotinic acetylcholine receptor in the outside-out mode. A piezo-driven liquid filament switch was used for the ultrafast application of acetylcholine alone or in combination with isoflurane or sevoflurane. In addition, the patches were preexposed to either anesthetic, preceding the activation with acetylcholine. RESULTS: The current elicited by acetylcholine was reduced reversibly and in a concentration-dependent manner by both anesthetics, which were equally effective. Preexposure of the patches to isoflurane or sevoflurane showed an additional inhibition that was present at micromolar concentrations. The time courses of current decay could be fitted by single exponentials for isoflurane. At higher concentrations of sevoflurane, the current decay became biexponential. In contrast to isoflurane, sevoflurane increased the time constants of desensitization when applied in low concentrations. CONCLUSIONS: At the nicotinic acetylcholine receptor, isoflurane and sevoflurane act primarily through the same mechanisms: Both affect the open and the closed state of the channels in concentrations equal to and less than those encountered clinically. The kinetics of desensitization, however, are altered in a different manner. Thus there may be several different sites of interaction.

Anesthetics, Inhalation↗