Liquid filament switch for ultra-fast exchanges of solutions at excised patches of synaptic membrane of crayfish muscle

A liquid filament switch is described which can exchange the solution passing an excised outside-out patch of postsynaptic membrane within less than 1 ms. Application and washout of transmitter can be repeated at high rates. Results of such rapid activations by glutamate are shown for the excitatory and the inhibitory channel of crayfish muscle. The excitatory channel is activated within less than 0.5 ms, and after an initial peak of openings desensitizes with a time constant of 5 ms to a low steady-state level. A kinetic scheme of these reactions is proposed. The activation of the inhibitory channel is slower, and this channel desensitizes more slowly than the excitatory one.

Human sodium channel myotonia: slowed channel inactivation due to substitutions for a glycine within the III-IV linker

1. Three families with a form of myotonia (muscle stiffness due to membrane hyperexcitability) clinically distinct from previously classified myotonias were examined. The severity of the disease greatly differed among the families. 2. Three dominant point mutations were discovered at the same nucleotide position of the SCN4A gene encoding the adult skeletal muscle Na+ channel alpha-subunit. They predict the substitution of either glutamic acid, valine or alanine for glycine1306, a highly conserved residue within the supposed inactivation gate. Additional SCN4A mutations were excluded. 3. Electrophysiological studies were performed on biopsied muscle specimens obtained for each mutation. Patch clamp recordings on sarcolemmal blebs revealed an increase in the time constant of fast Na+ channel inactivation, tau h, and in late channel openings as compared to normal controls. tau h was increased from 1.2 to 1.6-2.1 ms and the average late currents from 0.4 to 1-6% of the peak early current. 4. Intracellular recordings on resealed fibre segments revealed an abnormal tetrodotoxin-sensitive steady-state inward current, and repetitive action potentials. Since K+ and Cl- conductances were normal, only the increase in the number of non-inactivating Na+ channels has to be responsible for the membrane hyperexcitability. 5. Length, ramification and charge of the side-chains of the substitutions correlated well with the Na+ channel dysfunction and the severity of myotonia, with alanine as the most benign and glutamic acid as the substitution with a major steric effect. 6. Our electrophysiological and molecular genetic studies strongly suggest that these Na+ channel mutations cause myotonia. The naturally occurring mutants allowed us to gain further insight into the mechanism of Na+ channel inactivation.

The European Stroke Scale

BACKGROUND AND PURPOSE

For detecting therapeutic effect and matching of treatment groups in stroke trials, a scale that meets the clinimetric criteria is of the utmost importance.

METHODS

The European Stroke Scale consists of 14 items selected for their specificity and their prognostic value. It is designed for patients with middle cerebral artery stroke. Interrater reliability, internal consistency, and time for completion were investigated in 74 patients. Intrarater reliability was studied in 38 patients. To establish concurrent validity, two trials were performed in 20 and 44 patients. The scale was correlated with the MCA Neurological Scale, the Canadian Stroke Scale, the Scandinavian Stroke Scale, the Barthel Index, and the Rankin Scale. Correlations were calculated by means of Spearman's correlation coefficient. The trial in 44 patients also investigated the prognostic validity of the scale for 1-month and 8-month neurological, functional, and handicap status. These data were analyzed by linear regression.

RESULTS

Interrater (kappa value range, 0.62 to 0.85) and intrarater (kappa value range, 0.65 to 1.00) reliability for each item was good, and internal consistency was excellent (Cronbach's alpha coefficient, 0.92). Mean time for completion was 8.2 minutes (range, 4 to 14 minutes). Correlations of the European Stroke Scale with other neurological scales ranged from 0.93 to 0.95. The correlation with the Barthel Index and the Rankin Scale was 0.84 and -0.86. The R2 values for prognostic validity ranged from 0.45 to 0.81 (P < or = .0001).

CONCLUSIONS

The European Stroke Scale has been developed according to the clinimetric criteria.

Application of magnetic resonance to animal models of cerebral ischemia

The present review has been compiled to highlight the role of magnetic resonance imaging (MRI) and MR spectroscopy (MRS) for the investigation of cerebral ischemia in the animal experimental field of basic research. We have focused on stroke investigations analyzing the pathomechanisms of the disease evolution and on new advances in both nuclear MR (NMR) methodology or genetic engineering of transgenic animals for the study of complex molecular relationships and causes of the disease. Furthermore, we have tried to include metabolic and genetic aspects, as well as the application of functional imaging, for the investigation of the disturbance or restitution of functional brain activation under pathological conditions as relates to controlled animal experiments.

Rapid activation, desensitization, and resensitization of synaptic channels of crayfish muscle after glutamate pulses

Completely desensitizing excitatory channels were activated in outside-out patches of crayfish muscle membrane by applying glutamate pulses with switching times of approximately 0.2 ms for concentration changes. Channels were almost completely activated with 10 mM glutamate. Maximum activation was reached within 0.4 ms with greater than or equal to 1 mM glutamate. Channel open probability decayed with a time constant of desensitization of 2 ms with 10 mM glutamate and more rapidly at lower glutamate concentrations. The rate of beginnings of bursts (average number of beginnings of bursts per time bin) decayed even faster but approximately in proportion to the glutamate concentration. The dose-response curve for the channel open probability and for the rate of bursts had a maximum double-logarithmic slope of 5.1 and 4.2, respectively. Channels desensitized completely without opening at very low or slowly rising glutamate concentrations. Desensitization thus originates from a closed channel state. Resensitization was tested by pairs of completely desensitizing glutamate pulses. Sensitivity to the second pulse returned rapidly at pulse intervals between 1 and 2 ms and was almost complete with an interval of 3 ms. Schemes of channel activation by up to five glutamate binding steps, with desensitization by glutamate binding from closed states, are discussed. At high agonist concentrations bursts are predominantly terminated by desensitization. Quantal currents are generated by pulses of greater than 1 mM glutamate, and their decay is determined by the duration of presence of glutamate and possibly by desensitization.

A molecular scheme for the reaction between acetylcholine and nicotinic channels

In outside-out patches of mouse-muscle membrane, embryonic-like channels were activated by pulses of acetylcholine (ACh). On increasing the ACh concentration, the rate of desensitization, 1/tau d, increased linearly with the peak open probability, indicating desensitization from the open state. Desensitization had only one time constant tau d at each ACh concentration. Recovery from desensitization was only approximately 10 times slower than desensitization, whereas the probability of steady-state channel opening, declined to < 0.01 with > 10(-6) M ACh. The peak probability of opening in > 10(-4) M ACh pulse was close to 1. A linear reaction scheme was not compatible with these results. The scheme had to be expanded resulting in a circular scheme with two additional ACh binding steps to desensitized channel states. The approximate rate constants of all reaction steps in the circular scheme could be determined using computer simulations. The model predicted that clusters of channel opening had the average duration tau d at the respective ACh concentration. In cell-attached patches on intact muscle fibers, similar average cluster durations were observed at the respective ACh concentration. This indicates that tau d in the intact muscle fibers has similar values as in outside-out patches.

Error Awareness in a Saccade Countermanding Task

Abstract: Stop-signal tasks can be used to analyze mechanisms of action control and error monitoring. Previous event-related potential (ERP) studies indicated enhanced stop-signal N2 amplitudes for unsuccessful compared with successful inhibition. The aim of this study was to further investigate whether stop-signal related and response-related ERP components would reflect different aspects of error processing. ERPs were recorded during a saccade countermanding task, i.e. a stop-signal task with oculomotor response. Error awareness was obtained from subjective accuracy ratings. The response-related error positivity (Pe) was more pronounced for perceived than for unperceived errors whereas awareness of an error did not modulate the magnitude of the error negativity (Ne). This result is in accordance with previous findings. Stop-signal related ERPs revealed enhanced N2 amplitudes for incorrect (unsuccessfully stopped) trials compared with correct trials. However, this enhancement was restricted to perceived errors. The results support the idea that the stop-signal itself provides a performance feedback and the N2 reflects aspects of conscious response monitoring of unsuccessful inhibition.

Kinetics of homomeric GluR6 glutamate receptor channels

We studied the kinetics of the unedited version of rat GluR6 glutamate (glu) receptor channels, GluR6Q, in outside-out patches using a system for submillisecond solution exchange. Half-maximum activation of the channels was reached with approximately 0.5 microM glu. The maximum slope of the double-logarithmic plot of the peak current versus glu was approximately 1.3, indicating that at least two binding steps are necessary to open the channels. Currents in response to a pulse of 10 microM glu had a short rise time (10-90% of peak current) of approximately 220 microseconds at approximately 20 degrees C. The rise time increased with falling glu concentration, reaching approximately 6.0 ms with 10 microM glu. In the continued presence of glu, the channels desensitized, and this desensitization can be described with a single time constant of approximately 7.0 ms for a pulse of 10 microM glu. The steady-state current in response to a long pulse of 10 microM glu was below 1/280th of the peak current. The time constant of desensitization was found to be independent of concentration between 30.0 and 0.3 microM glu, but to be increased for lower concentrations. After a short pulse of 1 ms duration and 10 or 0.3 microM glu, currents decayed with a time constant of approximately 2.5 ms. Recovery from desensitization after a pulse took approximately 5 s, and the half-time of recovery was approximately 2.2 s. Continuous application of low concentrations of glutamate reduced the peak currents in response to a pulse of 10 microM glu markedly. Fifty percent response reduction was observed in the continuous presence of approximately 0.3 microM glu. Our results for homomeric GluR6 agree with a cyclical reaction scheme developed for completely desensitizing, glu-activated channels on crayfish muscles.

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.

Characteristics of Na+ channels and Cl- conductance in resealed muscle fibre segments from patients with myotonic dystrophy

1. Electrical and contractile properties of resealed fibre segments were investigated by a variety of in vitro techniques. The preparations were removed from skeletal muscles of normal subjects and of eight patients with myotonic dystrophy. 2. Several hours after removal, fibre segments from normal subjects and those patients in whom myotonia was the primary symptom had resting membrane potentials of approximately -80 mV. In contrast, fibre segments obtained from patients in whom muscle dystrophy was more expressed were depolarized (-60 to -70 mV). 3. Contractions induced in fibre segments of myotonic muscle which had normal potentials were characterized by slowed relaxation which was due to electrical after-activity. 4. After single stimuli, long-lasting (3-100) runs of action potentials were recorded intracellularly from the myotonic muscle. In some of these fibre segments complex repetitive discharges were observed: multiple sites of locally gated currents were identified. 5. The three-electrode voltage clamp was used to determine the total membrane conductance, gm, and the ion component conductances. All fibres of a particular patient had similar conductances. However, the Cl- conductance varied from patient to patient from normal (74% of gm) to low values (30% of gm). The K+ conductance was normal in all fibres of all patients. 6. The patch-clamp technique was used to record currents through single Na+ channels of the sarcolemma. After treatment of the fibre segments with collagenase gigaohm seals were routinely obtained. The rate of success was greater when using the cell-attached mode than the inside-out mode. 7. Sodium channel currents were elicited by depolarizing voltage steps which produced an initial burst of Na+ channel openings. Up to ten channels were activated simultaneously when the patch was depolarized to potentials more positive than -30 mV. The Na+ channels re-opened very rarely in controls. The macroscopic sodium current, INa, was reconstructed by averaging depolarizing pulses. The time constant of rapid decay of INa reflecting macroscopic inactivation, the onset of INa and the amplitude of INa were voltage dependent. The mean amplitude of the current produced by re-openings was on average only 0.11 +/- 0.04% of the amplitude of the peak current. 8. Late openings of the Na+ channels were frequent in patches on the myotonic fibre segments. The amplitude of the current produced by re-openings was as high as about 0.75 +/- 0.11% of the amplitude of the peak current.(ABSTRACT TRUNCATED AT 400 WORDS)

Acute appendicitis in late adulthood: incidence, presentation, and outcome. Results of a prospective multicenter acute abdominal pain study and a review of the literature

BACKGROUND

Acute appendicitis is the second most common cause of surgical abdominal disease in late adulthood. It is a serious condition: major errors in management are made frequently and the condition is associated with significant morbidity and mortality. Data collected within a multicenter prospective trial and a literature review were used to analyze diagnostic and therapeutic difficulties in detail.

METHODS

In a multicenter intervention study (MEDWIS A 70) data from 2,280 patients with acute abdominal pain were collected prospectively. Patients with histologically proven acute appendicitis, aged 50 years and older (n=102), were compared with younger patients (n=417) to determine differences in presentation, clinical course, and outcome. The basis for the literature review was a Medline search for appendicitis in late adulthood and in the elderly, covering the years 1980-1998. In addition, studies on clinical presentation of acute appendicitis in all age groups were also reviewed and appropriate data were extracted.

RESULTS

Patients aged 50 years and older with acute abdominal pain had a significantly higher incidence of surgery. Fourteen percent had acute appendicitis (27% in younger patients), with an increased complication rate (20% vs. 8%) and mortality (3% vs. 0.2%). Significantly more signs and symptoms suggestive of acute abdominal disease and peritonitis were recorded among older patients, reflecting the higher perforation rate (35% vs. 13%). Clinical presentation of appendicitis in younger patients was far more ambiguous. There were no significant differences in outcome between older and younger patients as regards perforations. Perforations are directly associated with treatment delay. Overall delay is a result of late presentation of older patients to hospital and postadmission delay.

CONCLUSIONS

Appendicitis in late adulthood is characterized by a delay in treatment, high perforation rates, and unfavorable outcome parameters, all mutually correlating. Older patients with acute abdominal pain are high-risk patients, unlike their younger counterparts. They have to be clinically evaluated by experienced surgeons within a narrow time margin. The problem of late presentation and/or referral should be addressed, perhaps by education of primary care physicians and the public.

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.

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.

Ultrasonography for diagnosis of acute appendicitis: results of a prospective multicenter trial. Acute Abdominal Pain Study Group

A prospective multicenter observational trial was performed to assess the performance and clinical benefit of ultrasonography of the appendix in the routine clinical examination. Included in the study were 2280 patients with acute abdominal pain from 11 surgical departments in Germany and Austria. Ultrasonography of the appendix was performed in 870 (38%) of the patients (range 16-85%). The overall sensitivity of ultrasonography of the appendix was 55% (13-90%), the specificity 95% (range 82-100%), positive predictive value 81% (50-100%), and negative predictive value 85% (68-96%). With respect to single ultrasound scan findings, adequate sensitivity (44%) was achieved only with the target phenomen, not with the other criteria. There were no correlations between the ultrasound findings of the appendix and the diagnostic accuracy of the clinician, the negative appendectomy rate, or the perforated appendix rate. From the study it can be concluded that there is no proven clinical benefit of ultrasound scanning of the appendix in the routine clinical diagnosis.

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.

Clinical benefit of a diagnostic score for appendicitis: results of a prospective interventional study. German Study Group of Acute Abdominal Pain

HYPOTHESIS

Clinical use of a diagnostic score improves decision making in acute appendicitis.

DESIGN

A before-and-after trial comparing a group of patients undergoing standard diagnostic workup with no additional diagnostic support (phase 1) with a group of patients undergoing additional diagnostic support with a score (phase 2).

SETTING

Eight departments of surgery in Germany and Austria.

PATIENTS

Eight hundred seventy patients with acute abdominal pain in phase 1 (October 1, 1994, to April 30, 1995) and 614 patients in phase 2 (February 1, 1995, to August 15, 1995).

INTERVENTIONS

Structured and standardized history and clinical investigation in all patients with computer-based documentation; introduction of the diagnostic score after phase 1 and computer-supported use of the score in phase 2.

RESULTS

The 2 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, 86% vs 78%; positive predictive value, 67% vs 50%; and accuracy, 88% vs 81%). There were no differences in the rates of perforated appendix, appendectomy with normal findings, and complications; however, the delayed appendectomy rate (2% vs 8%) and the delayed discharge rate (11% vs 22%) were significantly lower with diagnostic support by the score (P = .02).

CONCLUSIONS

Integration of a score into the diagnostic process may have unforeseen clinical effects. The tested score cannot be recommended as a standard tool for diagnostic decision making in acute appendicitis.

Dynamic changes of magnetic resonance imaging abnormalities in relation to inflammation and glial responses after photothrombotic cerebral infarction in the rat brain

This investigation analyzed the potential of high-resolution magnetic resonance imaging (MRI) at a field strength of 7T to depict leukocyte infiltration and glial responses after focal cerebral ischemia induced by photothrombotic occlusion of cerebral microvessels. For this purpose we superimposed multiparametric MRI (apparent diffusion coefficient, T2, perfusion-weighted, and gadolinium-DTPA-enhanced T1-weighted imaging) on tissue sections stained for phagocytes and astrocytes and, moreover, assessed the regional distribution of tissue pH and ATP content by invasive biochemical methods. Comparing the histological data with the various MRI parameters, high-resolution MRI did not allow a spatial discrimination between distinct areas of phagocyte accumulation or astroglial scar formation, based on image contrast or even quantitative parameter value differences. However, MRI parameters underwent characteristic changes and differentiated distinct stages of tissue remodeling between days 3 and 14 after photothrombosis. Low apparent diffusion coefficient (ADC) and high T2 values indicated an early stage (3 days) with necrosis and beginning glial activation. Normal ADC and reduced T2 elevation characterized an infarct with advanced glial activation and infiltration of hematogenous cells at 7 days after photothrombosis. Heterogeneous ADC together with T2 elevation reflected a late infarct stage (14 days) when pseudocystic degeneration and scar formation had occurred.

Altered gating and conductance of Na+ channels in hyperkalemic periodic paralysis

Electrophysiological studies on muscle fibres from patients with hyperkalemic periodic paralysis with myotonia have shown that the episodes of weakness are caused by a sustained depolarization of the sarcolemma to potentials between -40 and -60 mV. In muscle fibre segments from three such patients this sustained depolarization was caused by noninactivating Na+ channels with reduced single-channel conductance blocked by TTX and procainamide. As the chloride conductance was normal, myotonia may be best explained with the abnormal reopenings of the Na+ channels. The recently described genetic linkage between hyperkalemic periodic paralysis with myotonia and the gene coding for the TTX-sensitive Na+ channel suggests an altered primary structure of this channel causing its abnormal function.

Open channel block by physostigmine and procaine in embryonic-like nicotinic receptors of mouse muscle

Embryonic-like nicotinic channels were studied in mouse myotubes. Channel currents were measured by patch-clamping outside-out excised patches to which pulses of agonists and drugs could be applied by a liquid filament switch. The holding potential of the patches was generally around 40 mV. Pulses of 10(-4) M acetylcholine elicited average channel currents which reached a peak open probability, P(o,peak,) of 0.93 within 0.5 ms and decayed with a time constant of desensitization of 20-80 ms. When physostigmine (10(-5) to 10(-3) M) or procaine (3 x 10(-5) to 10(-3) M) was added to the acetylcholine pulses, a fast decay component of the current appeared which shortened to a time constant of 0.5 ms for the maximal drug concentrations. The fast decay was followed by a slow one which declined in amplitude with increasing concentrations of the drugs. After the end of pulses of 10 M acetylcholine plus 3 x 10(-4) M physostigmine the average current rose again, reaching a peak with approximately 5 ms delay, and then decayed slowly. The amplitude of this recovery current was approximately 0.4 P(o,peak) after 5 ms pulses and decreased with increasing pulse duration due to desensitization. The results can be quantitatively modelled based on a circular reaction scheme involving desensitization. Physostigmine and procaine bind to the open state to cause channel block. Also, the blocked channel was subject to desensitization. The rate constants of block were 6 x 10(6) M(-1) s(-1) for physostigmine and 2 x 10(6) M(-1) s(-1) for procaine, and the rate of unblocking was 200 s(-1) for both blockers (at -40 mV and 20 degrees C).

Rapid activation and desensitization by glutamate of excitatory, cation-selective channels in locust muscle

Outside-out patches of membrane were excised from extensor tibiae muscles of locusts. L-Glutamate or its agonists were applied to such patches in short pulses by means of a lipid filament switch. Cationselective, excitatory channels were activated by quisqualate, L-glutamate and aspartate (in decreasing order of effectivity), but not by ibotenate, kainate, N-methyl-D-aspartate and glycine. At high agonist concentrations, channel activation reached a peak within 1 ms. Two kinetic types of channels have been identified: L-channels with on average relatively long and S-channels with short openings. Both types of channel openings showed surprisingly high rates of desensitization, channel activity declining after the initial surge to zero with time constants of about 25 and 3 ms, respectively. The L-channels exhibit open times close to those of channels recorded in M omega-seal studies. The S-channel has not been reported previously.

Kinetic constants of the acetylcholine (ACh) receptor reaction deduced from the rise in open probability after steps in ACh concentration

Outside-out patches of enzymatically dissociated adult and denervated mouse muscle fibers were superfused repetitively by pulses of acetylcholine (ACh) containing solution. Up to 300 channels opened simultaneously 300 microseconds after the beginning of a 1,000 microM ACh pulse corresponding to a peak current i of almost -1 nA. Single responses to ACh were averaged and the concentration dependence of i and of the rise time tr from 0.1 i to 0.9 i was measured. In adult receptors, i increased proportional to the second to third power of ACh concentration, whereas in embryonic-type receptors it was proportional to the first to the second power. tr increased from approximately 0.3 ms at 1,000 microM ACh to a plateau value of approximately 5 ms for adult and of approximately 10 ms for embryoniclike receptors at concentrations less than 10 microM ACh. The concentration dependence of i and tr was simulated using the standard model of ACh binding with different combinations of rate constants and two and three binding sites for ACh. The calculated curves were compared to the measurements and a set of well fitting rate constants was determined for adult and embryoniclike receptors. Three binding sites for ACh were necessary to fit the dose response for i for adult receptors. A method for deriving rate constants in a model of ACh-receptor interaction is described that avoids analysis of open-closed kinetics of single channels, which in rapid systems, as the ones studied here, are at the limit of the frequency response of the current measurement.

[Status report on epidemiology of acute appendicitis]

The current incidence of appendicitis is about 100 per 100,000 person-years in Europe/America. Whereas the appendectomy rate is still decreasing, the incidence of appendicitis is now nearly stable. During the last 30 years the incidence of perforated appendicitis has not changed (approximately 20 per 100,000 person-years). Established risk factors for acute appendicitis are age (peak: 10-19 years), sex, and ethnic group/race. Classical theories (diet, hygiene) present illuminating models to explain the rise and fall of incidence in the last century; however, from a contemporary perspective the evidence is insufficient. The study of the epidemiology of appendicitis is complicated by the influence of referral, infrastructure, and surgical treatment strategy on the incidence of acute appendicitis. Therefore, there is a strong need for good prospective studies with high-quality data (e.g., studies directed by a central pathology department).

Diffusion- and perfusion-weighted MR imaging of transient focal cerebral ischaemia in mice

Temporary focal ischaemia was induced in wild-type C57Black/6 mice by thread occlusion of the middle cerebral artery (MCA). Recirculation was started after 60 min and maintained for 24 h, after which the mouse brain was frozen in situ. Development of the cerebral infarct was monitored by diffusion-, perfusion- and T(2)-weighted magnetic resonance imaging (MRI) during ischaemia, during the early reperfusion period of 90 min, and at 24 h after reperfusion. Ischaemia caused a marked reduction of the perfusion signal intensity and of the apparent diffusion coefficient (ADC) of tissue water in the ipsilateral MCA territory. In sham-operated control animals ADC remained unchanged. Hemispheric lesion volume after 1 h MCA occlusion was 53 +/- 6% (n = 6), as defined by an ADC decrease of more than 20%. Recirculation reduced hemispheric lesion volume to only 27 +/- 13%, while there was a trend towards secondary lesion growth at 24 h. Post-ischaemic recovery of perfusion was slow, heterogeneous and incomplete. A region-of-interest analysis showed only partial and transient recovery of the ADC, particularly in the dorsolateral cortex and lateral caudate putamen, which may be explained by inadequate reperfusion in these regions. Detailed MRI studies of cerebral ischaemia and reperfusion may now also be performed in the transgenic mice.

Schwartz-Jampel syndrome: II. Na+ channel defect causes myotonia

Skeletal muscle fibers from a patient with Schwartz-Jampel syndrome were studied in vitro. The fibers had normal resting membrane potentials, but their resting [Ca2+]i was elevated. The resting potentials were unstable and spontaneous depolarizations caused twitching in all fibers. Stimulated contractions were characterized by markedly slowed relaxation which was due to electrical after-activity. Neither curare (0.7 microM), tocainide (50 microM), nor phenytoin (80 microM) had an effect on the myotonic activity. In contrast, procainamide (200 microM) suppressed the hyperexcitability without affecting the twitch amplitude. The steady-state current-voltage relation was normal in 5 fibers, but altered in 3 others. These latter fibers had an increased specific membrane resistance owing to a decreased Cl- conductance. The Na+ channels were investigated in the cell-attached patch clamp mode. In all patches on either type of fiber, depolarizing pulses elicited delayed, synchronized openings of Na+ channels. These abnormal openings occurred even after the surface membrane repolarized. We hypothesize that these altered membrane conductances are responsible for the hyperexcitability and the associated slowed relaxation.

Activation and desensitization of embryonic-like receptor channels in mouse muscle by acetylcholine concentration steps

1. Pulses of acetylcholine (ACh) in concentrations between 0.1 and 1000 microM were applied repetitively to outside-out patches of enzymatically denervated (14 days) mouse muscle with the liquid filament switch. Solutions superfusing the patch could be changed rapidly (within 0.2 ms). 2. Single-channel activity was studied under steady-state conditions in the outside-out and in the cell-attached mode. The single-channel conductance was 26 pS in outside-out patches, characteristic for embryonic-like channels. Apparent mean open time was about 2.5 ms, a shorter component of closed times was 800 microseconds and burst length was about 5 ms. 3. Channel currents elicited by pulses of ACh were averaged. The time-to-peak current was concentration dependent and decreased from a level of about 10 ms below 10 microM to about 400 microseconds at 100 microM-ACh. 4. For a typical experiment, the average peak current, imax, increased from -0.4 pA with 0.1 microM to -82 pA with 1000 microM-ACh, close to the value at saturation. The half-maximal response was at 60 microM-ACh. The dose-response curves for imax had double-logarithmic slopes of 1.1-1.3, consistent with two binding sites at the embryonic nicotinic acetylcholine receptor (nAChR). 5. The current elicited by ACh pulses decreased rapidly after the peak. The time constant of desensitization increased from 20-50 ms with 1000 microM-ACh to up to more than a second with 1 microM-ACh. 6. The current in steady state (fully desensitized) increased up to 10 microM-ACh, but decreased slightly to values of imax/100 to imax/500 when higher concentrations were applied. 7. In addition to the well-known differences between adult and embryonic nAChR concerning the apparent mean open time and burst length, we found differences in the slope of the dose-response curve for imax, in the ratio of peak to steady-state response, and in the rise time of the response.