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Biomedical subjects

S Fuchs

Publications and source records attributed to S Fuchs.

At least 55 records · Page 3Linked to original sources
PubMed1988

Increased levels of acetylcholine receptor alpha-subunit mRNA in experimental autoimmune myasthenia gravis.

To gain insight into the regulatory mechanisms underlying the blockade and loss of acetylcholine receptor (AChR) in myasthenia, we have followed AChR alpha-subunit mRNA levels in leg muscles of myasthenic and normal rabbits and rats. Northern blots of RNA preparations from normal and myasthenic animals were hybridized with a mouse AChR alpha-subunit cDNA probe. Our experiments indicate a specific increase (4-7-fold) in the levels of alpha-subunit mRNA in animals with experimental autoimmune myasthenia gravis (EAMG), in comparison with control animals. Actin mRNA levels were essentially unchanged. Our results thus suggest that EAMG is accompanied by an increased level of AChR gene transcription.

Animals↗
PubMed1988

Cellular aspects of myasthenia gravis.

Several cellular aspects were investigated in a large series of patients with MG. First, non-Ag-specific proliferation was tested by measuring the response to r-IL2. Thymocytes from most MG patients showed hyperactivity to r-IL2. Peripheral blood lymphocytes (PBL) from some patients also showed a high response to r-IL2. These responding patients were generally those tested before thymectomy, presenting a high anti-AChR Ab titer and a severe form of the disease. Second, Ag-specific proliferation of MG PBL was assayed using 8 synthetic peptides corresponding to selected domains of torpedo or human AChR. Only 2 peptides gave a positive response in a significant number of patients, essentially in those presenting high anti-AChR Ab titer. The first is located near the alpha-bungarotoxin binding site and the second is in a cytoplasmic domain, according to models predicting the AChR transmembrane orientation. The positive results were essentially obtained with the human peptides; the corresponding torpedo peptides were positive in very few patients. Both human and torpedo peptides which include a part of the alpha-bungarotoxin binding site were negative. Finally, although morphological abnormalities were clearly visible in thymic hyperplasia, no correlation could be established between the thymus type and the cellular proliferation either to r-IL2, or to the peptides. Overall, our data indicate that cell-dependent mechanisms participate in the pathogenesis of MG, but the level of their involvement deserves further investigation.

Humans↗
PubMed1988

Anti-idiotypes against a monoclonal anti-haloperidol antibody bind to dopamine receptor.

Anti-idiotypic antibodies were raised in rabbits by immunization with a monoclonal anti-haloperidol antibody. Some of these anti-idiotypic antibodies bind in a concentration dependent manner to bovine striatal membranes. Following affinity purification, these antibodies inhibit haloperidol binding to striatal membranes and deplete [3H]-spiperone binding sites from a solubilized preparation of striatal membranes. It is thus concluded that these anti-idiotypic antibodies are an internal image of haloperidol and as such can interact with D2-dopamine receptors.

Animals↗
PubMed1988

Antibodies against haloperidol specific to the butyrophenone moiety.

Polyclonal and monoclonal antibodies to the D2-dopamine receptor antagonist haloperidol were produced by immunization with haloperidol conjugated to bovine serum albumin either through the tertiary hydroxy group of the piperidine ring (halo(OH)-BSA), or through the keto group of the butyrophenone (halo(CO)-BSA). Polyclonal rabbit antisera raised against halo(OH)-BSA exhibited high affinity for [3H]haloperidol. A fraction of these antibodies also bound [3H]spiperone with high affinity. Inhibition of the [3H]spiperone binding by various butyrophenone derivatives displayed a specificity similar to that observed for the inhibition of [3H]spiperone binding to the D2-dopamine receptor. Both monoclonal antibodies raised against halo(CO)-BSA(AG-58) and against halo(OH)-BSA(AC-91) exhibited high binding affinities to haloperidol. Monoclonal antibody AG-58 cross-reacted primarily with butyrophenone derivatives that are closely related to haloperidol in their substitutions on the piperidine ring. On the other hand, monoclonal antibody AC-91 cross-reacted with a wide range of butyrophenones with binding specificities resembling those of the dopamine receptor.

Animals↗
PubMed1988

In vitro proliferative responses and antibody titers specific to human acetylcholine receptor synthetic peptides in patients with myasthenia gravis and relation to HLA class II genes.

To investigate which parts of the acetylcholine receptor are involved in the initiation and development of myasthenia gravis (MG), peptides representing different sequences of the human acetylcholine receptor alpha-subunit were synthesized. These peptides were tested for their ability to stimulate T cells of myasthenic patients and healthy control patients in proliferation assays and to bind to sera antibodies. Three of eight peptides discriminated significantly between the two groups in the proliferation assay, as well as in their ability to bind to serum antibodies. HLA-DR3 and DR5 were associated with proliferative responses to specific AChR peptides in the group of myasthenics. Acetylcholine receptor epitopes that might play a specific role in myasthenia gravis thus were demonstrated.

Amino Acid Sequence↗
PubMed1988

Criteria for an increased specificity of MRI interpretation in elderly subjects with suspected multiple sclerosis.

We reviewed the MRIs of 49 asymptomatic volunteers (age range, 31 to 77 years) and of 50 MS patients (age range, 14 to 63) for areas of increased signal (AIS) and features discriminating MS lesions from lesions seen with normal aging. We obtained optimal specificity of MRI interpretation (100%) if we required at least two of the following three AIS features--size greater than or equal to 6 mm, abutting ventricular bodies, infratentorial location--for a positive MRI diagnosis of MS. Applying these criteria to the MRIs of elderly patients with suspected MS should significantly improve specificity (p less than 0.001) over current quantitative criteria (at least three AIS greater than or equal to 3 mm) without significantly decreasing sensitivity.

Adolescent↗
PubMed1988

Factors influencing posttraumatic seizures in children.

The ideal treatment of children with head trauma would include prevention of posttraumatic seizures. Ninety-two of 937 children with head injuries (9.8%) experienced posttraumatic seizures. In 94.5% of these patients (87 of 92), seizures developed within the first 24 hours after injury. Three children convulsed between 24 hours and 7 days, but only 2 children developed seizures after the 1st week. Factors found to influence the likelihood of seizures included severe head injury (GCS, 3 to 8), diffuse cerebral edema, and acute subdural hematoma (P less than 0.001). Seizures occurred in 35% of severely head-injured children compared to 5.1% with minor head injury (P less than 0.001). A less significant correlation (P less than 0.1) was noted between seizures and open, depressed skull fractures. We found no significant correlation between seizure occurrence and numerous other factors including age, sex, fracture location and type (other than open, depressed fractures), parenchymal injuries, fixed neurological deficits, and cranial operation. Based on our observations, we recommend the prophylactic use of anticonvulsants in children at higher risk for posttraumatic seizures: those with diffuse cerebral edema, acute subdural hematoma, open, depressed skull fracture with parenchymal damage, or severe head injury (GCS less than or equal to 8).

Adolescent↗
PubMed1987

Phosphorylation of the acetylcholine receptor by protein kinase C and identification of the phosphorylation site within the receptor delta subunit.

Purified acetylcholine receptor is rapidly and specifically phosphorylated by partially purified protein kinase C, the Ca2+/phospholipid-dependent enzyme. The receptor delta subunit is the major target for phosphorylation and is phosphorylated on serine residues to a final stoichiometry of 0.4 mol of phosphate/mol of subunit. Phosphorylation is dose-dependent with a Km value of 0.2 microM. Proteolytic digestion of the delta subunit phosphorylated by either protein kinase C or the cAMP-dependent protein kinase yielded a similar pattern of phosphorylated fragments. The amino acids phosphorylated by either kinase co-localized within a 15-kDa proteolytic fragment of the delta subunit. This fragment was visualized by immunoblotting with antibodies against a synthetic peptide corresponding to residues 354-367 of the receptor delta subunit. This sequence, which contains 3 consecutive serine residues, was recently shown to include the cAMP-dependent protein kinase phosphorylation site (Souroujon, M. C., Neumann, D., Pizzighella, S., Fridkin, M., and Fuchs, S. (1986) EMBO J. 5, 543-546). Concomitantly, the synthetic peptide 354-367 was specifically phosphorylated in a Ca2+- and phospholipid-dependent manner by protein kinase C. Furthermore, antibodies directed against this peptide inhibited phosphorylation of the intact receptor by protein kinase C. We thus conclude that both the cAMP-dependent protein kinase and protein kinase C phosphorylation sites reside in very close proximity within the 3 adjacent serine residues at positions 360, 361, and 362 of the delta subunit of the acetylcholine receptor.

Animals↗
PubMed1987

Species specificity of anti-acetylcholine receptor antibodies elicited by synthetic peptides.

Two peptides corresponding to amino acid residues 351-368 of the alpha-subunits of Torpedo and human acetylcholine receptor (AChR) were synthesized. These peptides contain a segment (residues 355-364) which displays the greatest variability in amino acid sequence between the two species. Antibodies elicited against the two peptides cross-reacted with the respective native AChRs and were shown to be species specific by radioimmunoassay, immunoblotting, and immunofluorescence microscopy. Thus, antibodies against the Torpedo peptide cross-reacted with Torpedo AChR but did not bind to mammalian or chicken AChR. Antibodies against the human peptide proved to be specific probes for mammalian muscle AChR. They cross-reacted with mammalian AChR (human, calf, mouse, and rat) but not with Torpedo or chicken AChR. These antibodies were also shown to react preferentially with the extrajunctional form of muscle AChR, as compared to their reactivity with junctional muscle AChR. In immunofluorescence experiments, the anti-human peptide antibody stained AChR aggregates in sectioned or ethanol-permeabilized rat and mouse myotubes grown in culture but did not stain living myotubes. This indicates that the sequence 351-368 of the alpha-subunit of mammalian AChR is on the cytoplasmic face of muscle cell membranes, as predicted theoretically.

Animals↗
PubMed1987

Hypernatremia and metabolic alkalosis as a consequence of the therapeutic misuse of baking soda.

When used appropriately, baking soda (sodium bicarbonate, USP) is a nontoxic, readily available, multipurpose product found in many households. We report an infant who presented with hypernatremia and metabolic alkalosis due to the addition of baking soda to her water. This case represents the possible dangerous use of a common household product in infants owing to the lack of proper warning labels.

Alkalosis↗
PubMed1986

Analysis of acetylcholine receptor phosphorylation sites using antibodies to synthetic peptides and monoclonal antibodies.

Three peptides corresponding to residues 354-367, 364-374, 373-387 of the acetylcholine receptor (AChR) delta subunit were synthesized. These peptides represent the proposed phosphorylation sites of the cAMP-dependent protein kinase, the tyrosine-specific protein kinase and the calcium/phospholipid-dependent protein kinase respectively. Using these peptides as substrates for phosphorylation by the catalytic subunit of cAMP-dependent protein kinase it was shown that only peptides 354-367 was phosphorylated whereas the other two were not. These results verify the location of the cAMP-dependent protein kinase phosphorylation site within the AChR delta subunit. Antibodies elicited against these peptides reacted with the delta subunit. The antipeptide antibodies and two monoclonal antibodies (7F2, 5.46) specific for the delta subunit were tested for their binding to non-phosphorylated receptor and to receptor phosphorylated by the catalytic subunit of cAMP-dependent protein kinase. Antibodies to peptide 354-367 were found to react preferentially with non-phosphorylated receptor whereas the two other anti-peptide antibodies bound equally to phosphorylated and non-phosphorylated receptors. Monoclonal antibody 7F2 reacted preferentially with the phosphorylated form of the receptor whereas monoclonal antibody 5.46 did not distinguish between the two forms.

Amino Acid Sequence↗
PubMed1986

Localization of a highly immunogenic region on the acetylcholine receptor alpha-subunit.

Antibodies to synthetic peptides were employed in order to map domains on the alpha-subunit of the acetylcholine receptor to which several monoclonal antibodies are directed. Five peptides corresponding to residues 1-20, 126-143, 169-181, 330-340 and 351-368 of the receptor alpha-subunit were synthesized and antibodies against them were elicited. The anti-peptide antibodies were employed along with the monoclonal antibodies to identify fragments of S. aureus V8 protease digested- alpha-subunit in immunoblotting experiments. Our results demonstrate that a highly immunogenic region of the alpha-subunit is located on a carboxy-terminal 14 kDa portion of the alpha-subunit. This region also seems to undergo antigenic changes during muscle development. A monoclonal antibody directed against the cholinergic binding site of the acetylcholine receptor reacted with an 18 kDa segment of the alpha-subunit which bound alpha-bungarotoxin as well as antibodies directed against peptide 169-181.

Animals↗
PubMed1986

Mapping of the cAMP-dependent phosphorylation sites on the acetylcholine receptor.

We have synthesized a tetradecapeptide corresponding to residues 354-367 of the delta-subunit of Torpedo acetylcholine receptor. This peptide contains the sequence Arg-Arg-Ser-Ser which has been proposed as the site for phosphorylation of the acetylcholine receptor (AChR) by an endogenous cAMP-dependent protein kinase. We have shown that the synthetic peptide can be phosphorylated by the catalytic subunit of bovine heart cAMP-dependent protein kinase. Antibodies elicited against peptide 354-367 were shown to cross-react with native AChR and to bind specifically to the delta- and gamma-subunit as detected by immunoblotting. Furthermore, antipeptide antibodies were shown to inhibit specifically the cAMP-dependent phosphorylation of both the delta- and gamma-subunits. This suggests that the phosphorylation sites in the delta- and gamma-subunits are highly cross-reactive, and is in agreement with the demonstration that an endogenous cAMP-dependent kinase phosphorylates these two subunits, probably on homologous sequences. Tryptic digestion of the delta-subunit isolated from phosphorylated AChR yields a single 25-kd phosphorylated fragment. Immunoblotting experiments allowed us to map peptide 354-367 within this phosphorylated fragment.

Amino Acid Sequence↗