Structural health monitoring using polymer-based capacitive micromachined ultrasonic transducers (CMUTs)

Transducers based on a capacitive micromachined ultrasonic transducer (CMUT) design have been fabricated using a rapid prototyping technique. This results in a device that is constructed principally from polymers, in a process which is simple and inexpensive. The resultant devices can be attached to the surfaces of solids. Their peak sensitivity is in the 80-100 kHz range, making them ideal for applications such as acoustic emission and structural health monitoring. Good low frequency sensitivity leads to applications in vibration monitoring.

Micro-stereolithography as a transducer design method

This paper investigates the use of micro-stereolithography, a rapid prototyping technique, in the manufacture of transducers. It is illustrated for the production of electromagnetic acoustic transducer (EMATs) coils in both meander-line and spiral configurations. A synthetic aperture focussing technique (SAFT) has been applied to the ultrasonic signals from these devices to reconstruct images in metallic objects.

Inhibition of glucose transport in PC12 cells by the atypical antipsychotic drugs risperidone and clozapine, and structural analogs of clozapine

Treatment of schizophrenics with some antipsychotic drugs has been associated with an increased incidence of hyperglycemia and new-onset type 2 diabetes. Some of these drugs also inhibit glucose transport in rat pheochromocytoma (PC12) cells. The current study was designed to examine the effects of the atypical antipsychotic drugs--risperidone, clozapine and analogs of clozapine on glucose uptake in PC12 cells. Glucose transport was measured in cells incubated with vehicle or drug over a range of concentrations (0.2-100 microM). Uptake of 3H-2-deoxyglucose was measured over 5 min and the data were normalized on the basis of total cell protein. Risperidone and clozapine inhibited glucose transport in a dose-dependent fashion with IC(50)'s estimated to be 35 and 20 microM, respectively. The clozapine metabolite, desmethylclozapine, was considerably more potent than the parent drug, whereas clozapine N-oxide was essentially inactive. The structural analogs of clozapine, loxapine and amoxapine, both inhibited glucose transport with amoxapine being the least potent. The ability of the drugs to inhibit glucose transport was significantly decreased by including 2-deoxyglucose (5 mM) in the uptake medium. Schild analysis of the glucose sensitivity of clozapine, loxapine and risperidone indicated that 2-deoxyglucose non-competitively antagonized the inhibitory effects of these drugs. Moreover, clozapine and fluphenazine inhibited glucose transport in the rat muscle cell line, L6. These studies suggest that the drugs may block glucose accumulation directly at the level of the glucose transporter (GLUT) protein in cells derived from both peripheral and brain tissue. Furthermore, this work may provide clues about how the antipsychotic drugs produce hyperglycemia in vivo.

Glucose metabolism in relation to schizophrenia and antipsychotic drug treatment

It has been reported in the earlier literature that many patients with psychoses had abnormalities in glucose metabolism as revealed by glucose tolerance testing. This observation is reinforced by the fact that the schizophrenic population appears to have about a 2-3-fold increased risk for Type II diabetes mellitus. However, some uncertainty remains about the relative risk value because there have been numerous case reports of patients who developed hyperglycemia and even Type II diabetes apparently as a consequence of treatment with antipsychotic drugs. Schizophrenic patients with abnormal glucose metabolism have a higher prevalence of drug-induced tardive dyskinesia than patients with a normal glucose profile. Treatment with the new atypical antipsychotics has a much lower risk of movement disorders; however, weight gain, hyperglycemia, and diabetes are emerging as significant side effects. Because glucose is essential for energy metabolism in neurons, any change in the effective glucose levels in brain that result from drug therapy may have significant clinical implications. It is not clear whether the glycemic state of schizophrenics contributes to their psychotic symptoms or modulates the incidence of drug side effects. Basic research shows that the drugs which cause hyperglycemia in patients appear to inhibit neuronal glucose transport which may partly explain their effects. This paper reviews the relevant literature in a preliminary attempt to understand the implications of such clinical findings in the light of basic research.

The inhibition of GLUT1 glucose transport and cytochalasin B binding activity by tricyclic antidepressants

Under normal metabolic conditions glucose is an important energy source for the mammalian brain. Positron Emission Tomography studies of the central nervous system have demonstrated that tricyclic antidepressant medications alter cerebral metabolic function. The mode by which these drugs perturb metabolism is unknown. In the present study the interactions of tricyclic antidepressants with the GLUT1 glucose transport protein is examined. Amitriptyline, nortriptyline, desipramine, and imipramine all inhibit the influx of 3-O-methyl glucose into resealed erythrocytes. This inhibition is observed with drug concentrations in the millimolar range. All four antidepressants also noncompetitively displace cytochalasin B binding to GLUT1. The K(I) for this displacement ranges from 0.56 to 1.43 millimolar. This value is in a range greater than that associated with clinical doses and this effect may not be directly applicable to side effects observed with normal use. The observed interaction of these drugs with GLUT1 may reflect an affinity for other glucose-transport or glucose-binding proteins, and may possibly contribute to tricyclic antidepressant toxicity.

Chemical properties of alcohols and their protein binding sites

Alcohols affect a wide array of biological processes including protein folding, neurotransmission and immune responses. It is becoming clear that many of these effects are mediated by direct binding to proteins such as neurotransmitter receptors and signaling molecules. This review summarizes the unique chemical properties of alcohols which contribute to their biological effects. It is concluded that alcohols act mainly as hydrogen bond donors whose binding to the polypeptide chain is stabilized by hydrophobic interactions. The electronegativity of the O atom may also play a role in stabilizing contacts with the protein. Properties of alcohol binding sites have been derived from X-ray crystal structures of alcohol-protein complexes and from mutagenesis studies of ion channels and enzymes that bind alcohols. Common amino acid sequences and structural features are shared among the protein segments that are involved in alcohol binding. The alcohol binding site is thought to consist of a hydrogen bond acceptor in a turn or loop region that is often situated at the N-terminal end of an alpha-helix. The methylene chain of the alcohol molecule appears to be accommodated by a hydrophobic groove formed by two or more structural elements, frequently a turn and an alpha-helix. Binding at these sites may alter the local protein structure or displace bound solvent molecules and perturb the function of key proteins.

Dopamine receptor antagonists modulate glucose uptake in rat pheochromocytoma (PC12) cells

A variety of dopaminergic ligands were evaluated for their ability to alter glucose transport in PC12 cells. Certain antipsychotic drugs which targeted D2 dopamine receptors, such as pimozide, fluphenazine and chlorpromazine, inhibited glucose uptake (with IC50's in the range of 2-40 microM). By contrast, haloperidol and sulpiride (also D2 antagonists) showed marginal activity. The atypical antipsychotic drug, clozapine (a D4 antagonist), also effectively inhibited glucose transport by the cells. Ligands specific for D1 receptors did not interfere with glucose uptake. Time course studies revealed that a short incubation with the drugs (1-5 min) was sufficient to block glucose transport. These findings may have implications for the adverse effects of these drugs and for the interpretation of imaging studies of brain glucose metabolism in patients on antipsychotic medications.

Antipsychotic drugs affect glucose uptake and the expression of glucose transporters in PC12 cells

1. Adherence of the PC12 cell line to poly-l-lysine (PLL) on tissue culture dishes stimulated glucose transport into the cells. Fluphenazine, chlorpromazine, clozapine and haloperidol inhibited glucose uptake in this system after a short (30 min) preincubation with drug. The IC50's for this effect were typically in the range of 5-40 microM. 2. Following longer exposures of the drugs (24 hr), there was a significant increase (approximately 3-fold) in the cellular levels of the glucose transporter (GLUT) isoforms, GLUT1 and GLUT3. 3. Long-term incubation (48 hr), especially with the phenothiazine drugs, was accompanied by a marked reduction in cell growth and proliferation. The rank ordering of the potencies of the drugs was essentially the same for these various effects: fluphenazine > chlorpromazine > clozapine approximately haloperidol. 4. It is suggested that the effects on glucose transport reported here may complicate the interpretation of positron emission tomography (PET) studies that rely on the uptake of radiolabeled glucose analogs to measure the physiological response to these drugs.

An ethanol-sensitive variant of the PC12 neuronal cell line: sensitivity to alcohol is associated with increased cell adhesion and decreased glucose accumulation

A stable variant of the PC12 cell line (PC12.4) has been isolated on the basis of its cell adhesive properties and morphological characteristics. Cells from the PC12.4 subline differ from the parental cell line in that they readily adhere to untreated plastic surfaces and grow individually rather than aggregated in large clusters. When compared to the PC12.1 cell line (original phenotype), PC12.4 cells were found to have a more rapid growth rate (24 h vs. 40 h doubling time) and higher production of lactate but lower glucose metabolism as judged by the accumulation of 3H-2-deoxyglucose. Western blot analyses also revealed differences between PC12.1 and PC12.4 cells with respect to the expression of glucose transporters (GLUTs) and the subcellular distribution of the heat shock protein (Hsp) Hsp60. We have reported here that PC12.4 cells were far more sensitive to growth inhibition by ethanol when compared with PC12.1 cells and appeared to be more dependent upon glutamine and serum for cell growth. The cytostatic effects of ethanol were most pronounced when the cells were cultured in medium with low concentrations of serum and glutamine. Thus, there appears to be an interplay between energy metabolism in the cell and the response to ethanol.

Symptoms of patients with myasthenia gravis receiving treatment

The symptoms of myasthenia gravis (MG) are often simply classified as excessive fatigue rather than evaluated as different signs of disease progression. The purpose of this study was to evaluate the medical symptoms of patients with MG who had been under treatment for many years. Patients diagnosed with MG were compared to healthy controls. A survey questionnaire was used and differences were evaluated using non-parametric statistics. Health care givers should be aware of these differences in order to facilitate early appropriate treatment, to decrease disability, and to increase the quality of life.

Attachment of PC12 cells to adhesion substratum induces the accumulation of glucose transporters (GLUTs) and stimulates glucose metabolism

The levels of glucose transporters (GLUTs), specifically GLUT3 and GLUT1, increased dramatically in PC12 cells that were cultured on suitable adhesion substrata (poly-1-lysine [PLL]) and induced to differentiate with nerve growth factor (NGF). Closer examination of this response revealed that: (1) cellular attachment to PLL was sufficient to stimulate the increase in GLUT immunoreactivity, and (2) NGF alone was not effective unless the cells were cultured on PLL-treated surfaces. The response to PLL was detected as early as 4 hr after plating the cells and peaked within 24-48 hr. Other adhesion substrata, such as collagen and poly-1-ornithine, evoked a similar response, although the latter polymer was far less effective. The increase in GLUTs appeared to result from an accumulation of existing transporters because this response was not blocked by inhibiting protein synthesis. Cellular adhesion to PLL was also accompanied by a rapid activation of glucose metabolism. Thus, specific recognition of the adhesion substratum not only provides a context for cell attachment, but also elicits important functional changes in GLUT activity.

Neuronal differentiation in PC12 cells is accompanied by diminished inducibility of Hsp70 and Hsp60 in response to heat and ethanol

The stress response of PC12 cells was characterized by evaluating the production of heat shock proteins of the 70 kDa (Hsp70), 60 kDa (Hsp60) and 90 kDa (Hsp90) families by western blot analysis. Induction of Hsp synthesis was elicited by brief exposure to elevated temperatures or by addition of ethanol to the cultures. Normal PC12 cells responded to stress with rapid up-regulation of Hsp70 and Hsp60 production. However, fully differentiated PC12 cells (induced by nerve growth factor, NGF) failed to produce Hsp70 or Hsp60 in response to heat or ethanol treatment. The disappearance of the heat shock response of the cells was directly related to the extent of neuronal differentiation. The cellular levels of the constitutive proteins, Hsc70 and Hsp90, were not altered by differentiation of the cells. Production of Hsps was restored in the differentiated cells by removal of NGF which coincided with the loss of neurite expression and retraction of processes.

A comparison of the effects of hard rock and easy listening on the frequency of observed inappropriate behaviors: control of environmental antecedents in a large public area

Observation of clients at a state mental health hospital by direct care staff indicated that they appeared to act in more inappropriate ways when "hard rock" or "rap" music was played in an open courtyard than when "easy listening" or "country" music was played. A study was conducted to compare the inappropriate behavior of clients when hard rock and rap music were played (21 days), followed by easy listening and country and western music (21 days). This comparison was followed by a reversal phase in which hard rock and rap music were again played (18 days). The behaviors of the clients were observed and recorded via a controlled methodology. The results demonstrated that more inappropriate behavior was observed under conditions in which hard rock and rap music were played than when easy listening and country western music were played. The implications of these findings are discussed.

A novel acetylcholine receptor-related peptide blocks canine cardiac ganglia and inhibits the nicotinic receptor of PC-12 cells

A 13 amino acid peptide from the calf muscle acetylcholine receptor has been previously shown to bind both snake neurotoxins and acetylcholine. In the experiments reported here a modified complementary peptide (cAChR) derived from that acetylcholine receptor peptide was tested for biological activity in a canine heart preparation. It was expected that the modified complementary peptide would exhibit either acetylcholine-like effects or acetylcholine inhibiting effects, since, as a complementary peptide to the receptor, it should resemble acetylcholine. In these studies cAChR was administered via the sinus node artery of dog hearts in intact animals which were anesthetized with pentobarbital, intubated, and prepared with local cardiac electrograms and force gauges. cAChR was also injected directly into thoracic sympathetic ganglia. Both approaches demonstrated cAChR inhibition of neural transmission, cAChR was added to the medium of carbachol stimulated PC-12 cells. In these cells, derived from a rat pheochromocytoma, sodium flux is controlled by neural nicotinic receptors. With or without preincubation cAChR inhibited carbachol stimulation of sodium flux, exhibiting a Ki of approximately 9 x 10(-5) (similar to that of hexamethonium). Thus cAChR appears to be a novel synthetic peptide which interrupts nicotinic cholinergic neural transmission by acting as an antagonist of the neural nicotinic receptor.

Diagnostic sensitivity of the laboratory tests in myasthenia gravis

The diagnostic sensitivity of three laboratory tests [serum antiacetylcholine receptor antibody (AChR-ab) assay, the repetitive nerve stimulation (RNS) test, and, the single fiber EMG (SFEMG)] for myasthenia gravis (MG) was compared in 120 patients. In all cases, at least one of the tests was abnormal. SFEMG was the most sensitive test, being abnormal in 92% of cases, followed by the RNS test (77%) and the AChR-ab assay (73%). SFEMG was abnormal in all cases with negative AChR-ab and RNS tests, in 97% of cases with negative AChR-ab assay, in 89% of cases with negative RNS test, and in 89% of cases with mild MG. We conclude that one of these three tests is abnormal in all cases of MG, and that the SFEMG is most sensitive in the diagnosis of MG.

Fetal acidosis and hyperlacticaemia diagnosed by cordocentesis in pregnancies complicated by maternal diabetes mellitus

Fetal blood samples were obtained by cordocentesis (ultrasound guided needle aspiration) from 28 pregnant Type 1 diabetic women between 20 and 40 weeks' gestation. Analysis of the deviations from normal values of blood pH and plasma lactate showed significant acidosis (p less than 0.001) and hyperlacticaemia (p less than 0.01) in the third trimester, but not in the second trimester. Blood PO2 and PCO2 levels did not differ significantly from normal values. The pH showed significant correlations with PO2 (r = 0.54; p less than 0.01) PCO2 (r = -0.70; p less than 0.001), lactate (r = -0.46; p less than 0.05), fetal glycosylated haemoglobin (r = -0.53; p less than 0.01), and maternal glycosylated haemoglobin (r = -0.57; p less than 0.01). Plasma lactate showed significant correlations with PO2 (r = -0.54; p less than 0.01), PCO2 (r = 0.50; p less than 0.05), and pH (r = -0.46; p less than 0.05). Neither pH nor lactate showed significant correlations with birthweight. These observations suggest that some fetuses of diabetic women are significantly acidotic and hyperlacticaemic in the third trimester. This may provide a possible explanation for the phenomenon of late intrauterine fetal death in pregnancies complicated by maternal diabetes mellitus.

The alpha-neurotoxin erabutoxin b causes fade at the rat end-plate

d-Tubocurarine and the alpha-neurotoxins from snake venom are antagonists at the nicotinic acetylcholine receptor. It is well established that d-tubocurarine causes fade in neuromuscular transmission during repetitive nerve stimulation but paradoxically there are many reports which indicate that the alpha-neurotoxins do not cause such fade. We found that high concentrations of erabutoxin b (100-150 nM) from the venom of Laticauda semifasciata did not cause much fade in the rat diaphragm preparation. However, low concentrations of toxin (5 nM) caused severe fade which was similar to the effects of d-tubocurarine. The data suggest that fade may be caused by toxin binding to a high-affinity site on the postsynaptic acetylcholine receptor.

Molecular forms of acetylcholinesterase from the skeletal muscle of the ammocoete of the lamprey Petromyzon marinus

1. We have studied the cholinesterase activity from the skeletal muscle of the ammocoete of the lamprey Petromyzon marinus. 2. On the basis of pharmacologic and kinetic criteria, we conclude that the enzyme is true acetylcholinesterase, not pseudocholinesterase. 3. The acetylcholinesterase was found to be present in both globular and asymmetric forms. 4. In contrast to muscle of adult spawning lamprey, where globular esterase is almost exclusively G4, we found that muscle from ammocoete also contains significant amounts of G1 and G2. 5. This difference may be related to the physiological states of the lamprey during the various stages of its life cycle.

Multiple effects of alpha-toxins on the nicotinic acetylcholine receptor

Very low concentrations (5 nM) of alpha-toxin from the venom of Naja naja atra produced a characteristic fade in muscle compound action potential and tetanus induced by repetitive nerve stimulation which was identical to the effects of curare. High concentrations of alpha-toxin and all concentrations of alpha-bungarotoxin reduced the response but produced very little fade in comparison to curare. These results suggest that alpha-toxins have more than one effect at the neuromuscular junction.

Forskolin counteracts the effects of the organophosphate soman at the neuromuscular junction

When neuromuscular transmission had been blocked using an organophosphate, function could be restored by treatment of the muscle with forskolin which increases the rate of desensitization of the nicotinic acetylcholine receptor. This suggests that excess post-synaptic depolarization due to acetylcholinesterase inhibition might be reversed by procedures which promote receptor desensitization.

Overlap myasthenic syndrome: combined myasthenia gravis and Eaton-Lambert syndrome

A patient with a known history of pernicious anemia had the combined features of autoimmune myasthenia gravis (MG) and the Eaton-Lambert syndrome (ELS). Initially, this patient had all the features typical of MG, and after thymectomy developed all the typical features of ELS. In view of the coexistence of two autoimmune neuromuscular transmission disorders in one patient, we termed this disorder "overlap myasthenic syndrome."

Maternal oxygen therapy for intrauterine growth retardation

Humidified oxygen (55%) was administered continuously through a face mask to 5 patients whose pregnancies (4 singleton and 1 twin) were all complicated by severe intrauterine growth retardation, oligohydramnios, high blood-flow impedance in the fetal aorta and umbilical artery, and low mean blood-velocity in the fetal thoracic aorta. All the fetuses were hypoxic and 2 were acidotic. After maternal hyperoxygenation, the fetal pO2 increased to within or near the normal range, and resulted in a sustained increase in the mean blood-velocity in the fetal thoracic aorta. 5 fetuses survived with minimum neonatal morbidity. The effect of maternal hyperoxygenation on the fetal pO2 in such cases may prove to be a useful method of assessing placental function and guiding management.

Agonist and blocking effects of choline at the neuromuscular junction

The effects of choline chloride were studied at the voltage-clamped frog neuromuscular junction by measuring miniature endplate currents and equilibrium dose response curves for acetylcholine applied by microionophoresis. Choline reduced the amplitude and shortened the time constant of miniature endplate currents in a dose dependent manner. Dose response curves carried out in the presence of low doses of choline (200 microM) were shifted to the right and the apparent dissociation constant for ACh was increased without affecting the Hill coefficient or the maximum conductance at the endplate. Higher doses of choline shifted the curve even further to the right but reduced the Hill coefficient and maximum conductance. Choline ionophoretic dose response curves were carried out but the conductance response was only about 1% of the response to comparable concentrations of ACh. In the presence of ethanol, which reduces the agonist dissociation constant, choline responses were increased and the dose response curve analysis revealed that the efficacy of choline was about 17% in comparison to ACh. Similar effects were measured at rat endplates. Rat nerve-muscle preparations were used to investigate the effects of choline upon neuromuscular transmission.

Reversal of organophosphate-induced muscle block by neomycin

The organophosphate, diisopropyl fluorophosphate, and the aminoglycoside antibiotic, neomycin, both independently block neuromuscular transmission. At the neuromuscular junction, neomycin reduces the presynaptic release of acetylcholine, whereas diisopropyl fluorophosphate irreversibly inhibits acetylcholinesterase, thereby increasing the acetylcholine concentration. In the rat diaphragm preparation, the block in neuromuscular transmission caused by diisopropyl fluorophosphate could be reversed by adding neomycin.

Calcium or magnesium concentration affects the severity of organophosphate-induced neuromuscular block

When the rat diaphragm muscle was treated with düsopropyl fluorophosphate, an organophosphate inhibitor of acetylcholinesterase, a decrement in the compound action potential and in the force of contraction was observed. It was found that the decrement produced by 30 Hz nerve stimulation for 1 s could be reversed by lowering the calcium concentration or increasing the magnesium concentration.

Curare can reverse the failure in muscle contraction caused by an AChE inhibitor

Diisopropyl fluorophosphate, which is an organophosphate inhibitor of acetylcholinesterase, caused an irreversible block of neuromuscular transmission in the rat diaphragm preparation. This block could be reversed by the addition of a competitive antagonist of acetylcholine such as D-tubocurarine.

Agonist and inhibitory effects of pyridostigmine at the neuromuscular junction

When all of the AChE at the endplate is irreversibly inhibited by phospholine iodide the ionophoretically induced ACh endplate currents are increased more than 10-fold in amplitude. The reversible AChE inhibitor pyridostigmine only increases the current to about half this value because its effects are obscured by receptor blocking. It was found that pyridostigmine can activate the receptor ion channels when released by ionophoresis at the endplate, thus suggesting that agonist-like desensitization could contribute to the blocking effects.

Batrachotoxinin-A N-methylanthranilate, a new fluorescent ligand for voltage-sensitive sodium channels

Batrachotoxin and its derivatives have become important tools for the study of membrane excitability by virtue of their effects on voltage-sensitive sodium channels. Recent studies have shown that the 2,4-dimethylpyrrole carboxylate ester normally occurring in the 20-alpha position of batrachotoxin may be replaced by a benzoate moiety without loss of activity. We have now extended this series of active batrachotoxin derivatives and report here the synthesis of batrachotoxinin-A 20-alpha-N-methylanthranilate. The new fluorescent compound is highly toxic (LD50 approx. 15 micrograms/kg, i.p. mouse) and binds to the same receptor site of voltage-sensitive sodium channels as batrachotoxin with an equilibrium dissociation constant Kd = 180 nM (in the presence of scorpion toxin). These fluorescence and binding properties have been exploited to achieve successful visualization of sodium channels at mammalian nodes of Ranvier. Batrachotoxinin-A 20-alpha-N-methylanthranilate should prove to be a useful compound for studies of sodium channel distribution and for investigations of the microenvironment of the batrachotoxin binding site.

Temperature dependence of single channel currents and the peptide libration mechanism for ion transport through the gramicidin A transmembrane channel

A study of the temperature dependence of gramicidin A conductance of K+ in diphytanoyllecithin/n-decane membranes shows the plot of In (single channel conductance) as a function of reciprocal temperature to be nonlinear for the most probable set of conductance states. These results are considered in terms of a series of barriers, of the dynamics of channel conformation, vis-a-vis the peptide libration mechanism, and of the effect of lipid viscosity on side chain motions again as affecting the energetics of peptide libration.

The effects of alcohols and diols at the nicotinic acetylcholine receptor of the neuromuscular junction

A series of straight chain aliphatic alcohols from ethanol to octanol were tested at voltage-clamped frog endplates. In the presence of high concentrations of ethanol (greater than 1 M) the individual current responses to ionophoretic pulses of ethanol were reduced in amplitude and the dose-response curve for acetylcholine was shifted to the right. All the alcohols tested had this effect and their potency increased with the length of the carbon chain. The results were interpreted to indicate that as the molecular weight of the alcohol increased, its potency as a channel blocker also increased. The diol derivative of ethanol, which is ethylene glycol (ethanediol), was totally inactive up to 400 mM. However, 1,3-propanediol was a more potent blocker than propanol. After dose-response curves were carried out in high doses of ethanol and propanediol, the number of receptors was found to be permanently reduced. This effect could be due to irreversible denaturation of the receptor and therefore reversible denaturation could account for some of the reversible blocking effects caused by such drugs. An additional effect on the receptor was observed in that low concentrations of ethanol and propanol reduced the apparent dissociation constant for acetylcholine, thus increasing the amplitude of individual responses and shifting the dose-response curve to the left.

Evidence that certain peripheral anti-acetylcholine receptor antibodies do not interact with brain BuTX binding sites

The cross-reactivity of rat brain alpha-bungarotoxin (BuTX) binding sites with peripheral anti-acetylcholine receptor (nAChR) polyclonal and monoclonal antibodies was investigated in Triton extracts of several brain areas and purified whole brain putative receptors using radioimmunoassays and IgG/CNBr-Sepharose 4B immunoaffinity chromatography. The effects of the chronic intracerebral administration of antibodies on [125I]BuTX binding and food and water intake were also investigated. It was concluded that brain BuTX sites do not share antigenic determinants with peripheral nAChRs. Additionally, no evidence was found to support the suggestions that anti-nAChR antibodies affect food and water intake, or that chronic administration of antibodies alters [125I]BuTX binding in the hypothalamus of rats.

An enzyme-linked immunoabsorbent assay for measuring antibodies against muscle acetylcholine receptor

An enzyme-linked immunoabsorbent assay has been developed for measuring anti-acetylcholine receptor antibodies from sera of patients with myasthenia gravis or tissue culture supernatants from hybridomas. Acetylcholine receptor from a detergent extract of muscle tissue was bound indirectly to microtiter plates via a monoclonal anti-receptor antibody already coupled to the polyvinyl plates. Myasthenic sera or antibodies in tissue culture media were then tested for binding to the acetylcholine receptor attached to the monoclonal antibody. Anti-receptor antibodies were detected in the serum of 80% of myasthenic patients when assayed by this method and the levels of antibody corresponded fairly well with antibody titers determined by an immunoprecipitation assay. Occasional myasthenic patients had serum antibodies which reacted specifically with the monoclonal antibody attached to the microtiter plate. The assay described here was far less time-consuming than immunoprecipitation assays, required only small quantities of receptor, and did not require the use of radioisotopes such as 125I-alpha-bungarotoxin.

Naturally occurring anti-idiotypic antibodies in myasthenia gravis patients

Aberrant regulation of the immune system can lead to the development of autoimmune diseases such as myasthenia gravis. Autoantibodies against the nicotinic acetylcholine receptor (AChR) are found in the serum of myasthenia gravis patients and trigger a reduction of AChR at the muscle endplate resulting in increased muscle fatiguability. It is possible that the autoimmune response results from altered idiotype anti-idiotype network interactions. Here we have used a monoclonal anti-AChR antibody (ACR-24, gamma 1, kappa) in an enzyme-linked immunoabsorbent assay (ELISA) to measure anti-AChR immunoglobulin in human sera. In this assay, ACR-24 is attached to microtitre plates followed by the addition of solubilized human AChR which is bound by the immobilized ACR-24. However, during the development of this assay, it was observed that certain myasthenic patients appeared to have antibodies which bound to ACR-24 alone. This unexpected finding suggested that we had discovered naturally occurring anti-idiotype antibodies in myasthenic sera.

Use of synthetic gramicidins in the determination of channel structure and mechanism

The syntheses of (1-13C) Trp9 gramicidin A (GA), (1-13C) Trp11 GA, (1-13C) Trp13 GA, (1-13C) Trp15 GA, and D . Leu2 GA are verified by means of high performance liquid chromatography, carbon-13 nuclear magnetic resonance, circular dichroism and characterization of transport properties. The use of these and other synthetic gramicidins is discussed in terms of determining ion binding sites within the channel, helix sense of the channel, the basis of monovalent vs divalent cation selectivity, and means of modulating channel conductance.

Effects of ethidium bromide on the nicotinic acetylcholine receptor

Ethidium bromide was tested for electrophysiological effects at the postsynaptic membrane of the frog muscle endplate. At low concentrations ethidium bromide blocked the open ion channel of the nicotinic acetylcholine receptor and reduced its open time. The rates for channel blocking and unblocking were calculated giving a dissociation constant of 139 nM at -80 mV membrane potential.

Single channel properties of D-Leu2-gramicidin A. Side chain modulation of channel lifetime

The channel forming properties of synthetic gramicidin A and DLeu2-gramicidin A were compared in black lipid membranes. The most probable single channel conductance was identical for both derivatives but in each case a distribution of smaller channel sizes was observed. However, the lifetime of the channel formed by DLeu2-gramicidin A was considerably shorter than for gramicidin A. The DLeu2 substitution is considered to interfere with the head to head hydrogen bonding which forms the conducting dimer, thus destabilizing the dimeric structure of the channel and reducing the lifetime. This represents the first demonstration of side-chain modulation of channel lifetime.