Lack of association between neuroleptic malignant syndrome and polymorphisms in the 5-HT1A and 5-HT2A receptor genes

OBJECTIVE

The molecular basis of neuroleptic malignant syndrome is unclear, but studies suggest that genetic factors are involved in its pathogenesis. Considering possible involvement of the serotonergic system in neuroleptic malignant syndrome, the authors examined the association between neuroleptic malignant syndrome and polymorphisms of the 5-HT1A and 5-HT2A receptor genes.

METHOD

The authors examined the frequencies of gene polymorphisms in the 5-HT1A (Arg219Leu) and 5-HT2A (Thr25Asn and His452Tyr) receptor genes in 29 patients previously diagnosed with neuroleptic malignant syndrome, 94 neuroleptic-treated patients with schizophrenia who had no history of neuroleptic malignant syndrome, and 94 healthy comparison subjects. Polymerase chain reaction and restriction fragment length polymorphism analyses were used to screen gene mutations.

RESULTS

No polymorphic allele was detected in the patients who had experienced the neuroleptic malignant syndrome.

CONCLUSIONS

The authors cannot conclude that polymorphisms in the 5-HT1A and 5HT2A receptor genes are factors determining susceptibility to the neuroleptic malignant syndrome.

Simple delineation of misery perfusion areas by superimposition of PET on PET images

Oxygen extraction fraction images were superimposed on cerebral blood flow images of positron emission tomography (PET) to depict the so-called misery perfusion area in two patients with moyamoya disease. The superimposed image following extra-intracranial bypass surgery was obtained in one case, which convincingly disclosed attenuation as compared with the preoperative image. This simple PET on PET approach should find an application in the evaluation of misery perfusion and in assessing operative indications for cerebral ischaemic diseases.

Establishment and characterization of tracheal epithelial cell lines, TM01 and TM02-3, from transgenic mice bearing temperature-sensitive simian virus 40 large T-antigen gene

Murine tracheal epithelial cell lines, TM01 and TM02-3, were established from a primary culture of tracheal cells of adult transgenic mice bearing a temperature-sensitive simian virus (SV40) large T-antigen gene. Both TM01 and TM02-3 cells, which grew until confluent monolayers were formed, maintained tight contact with neighboring cells, and retained the characteristics of epithelial cells with microvilli on the surface. These cells grew at a permissive temperature (33 degrees C), but did not at a nonpermissive temperature (39 degrees C), indicating that TM01 and TM02-3 cells undergo temperature-sensitive growth. Large T-antigen was expressed only in the nuclei at 33 degrees C. Sepharose CL-4B column chromatography using a 14C-glucosamine hydrochloride, indicating that both cells produced high molecular weight glycoconjugates, and suggesting that these cells may originate from mucus-producing cells. TM01 cells expressed intercellular adhesion molecular-1 (ICAM-1) in both unstimulated and stimulated (1,000 U/ml tumor necrosis factor-alpha and 500 U/ml interferon-gamma) conditions, whereas TM02-3 cells expressed ICAM-1 only under stimulated conditions. We conclude that these cell lines may serve as a useful model to study the tracheal cell functions under defined in vitro conditions.

Distinctions in agonist and antagonist specificity conferred by anionic residues of the nicotinic acetylcholine receptor

Two anionic residues in the nicotinic acetylcholine receptor, Asp-152 in the alpha-subunit and Asp-174 in the gamma-subunit or the corresponding Asp-180 in the delta-subunit, are presumed to reside near the two agonist binding sites at the alphagamma and alphadelta subunit interfaces of the receptor and have been implicated in electrostatic attraction of cationic ligands. Through site-directed mutagenesis and analysis of state changes in the receptor elicited by agonists, we have distinguished the roles of anionic residues in conferring ligand specificity and ligand-induced state changes. alphaAsp-152 affects agonist and antagonist affinity similarly, whereas gammaAsp-174 and deltaAsp-180 primarily affect agonist affinity. Combining charge neutralization on the alpha subunit with that on the gamma and delta subunits shows an additivity in free energy changes for carbamylcholine and d-tubocurarine, suggesting independent contributions of these residues to stabilizing the bound ligands. Since both aromatic and anionic residues stabilize cationic ligands, we substituted tyrosines (Y) for the aspartyl residues. While the substitution, alphaD152Y, reduced the affinities for agonists and antagonists, the gammaD174Y/deltaD180Y mutations reduced the affinity for agonist binding, but surprisingly enhanced the affinity for d-tubocurarine. To ascertain whether selective changes in agonist binding stem from the capacity of agonists to form the desensitized state of the receptor, carbamylcholine binding was measured in the presence of an allosteric inhibitor, proadifen. Mutant nAChRs carrying alphaD152Q or gammaD174N/deltaD180N show similar reductions in dissociation constants for the desensitized compared with activable receptor state and a similar proadifen concentration dependence. Hence, these mutations influence ligand recognition rather than the capacity of the receptor to desensitize. By contrast, the alphaD200Q mutation diminishes the ratio of dissociation constants for two states and requires higher proadifen concentrations to induce desensitization. Thus, the contributions of alphaAsp-152, gamma/deltaAsp-174/180, and alphaAsp-200 in stabilizing ligand binding can be distinguished by the interactions between agonists and allosteric inhibitors.

Fabrication of High Performance Laminated Polarization Splitters Consisting of Thick a-Si:H /SiO(x):H Multilayers

We report fabrication techniques ofa-Si:H/SiO(x):H multilayers having ample thickness and flat layer boundaries for high performance laminated polarization splitters (LPS's). In the new fabrication process we used the following techniques to achieve low stress and high surface flatness: SiO(x):H film deposition by rf sputtering with a mixture of Ar/H(2), two-step deposition using rf bias sputtering, and elimination of surface roughness and defects by mechanical polishing. This process enabled deposition of a multilayer as thick as 265 mum while preserving layer boundaries as flat as 1 nm (rms). As a result, LPS's having low loss, a large aperture, and a long splitting distance were successfully obtained. The high optical performance is applicable to functional devices integrated into fibers or planar waveguides.

Liquid chromatography of guanidino compounds using a porous graphite carbon column and application to their analysis in serum

The retention mechanism of guanidino compounds on a porous graphitic carbon seemed to be mainly hydrophobic interaction, according to the retention factors in buffer solutions and the results of an analysis by computational chemical calculation using molecular mechanics (MM2). The baseline separation of ten guanidino compounds was achieved by the addition of a hydrophobic counterion. The retention mechanism may be dynamic ion-exchange. The stable system was applied to the analysis of guanidino compounds in serum from nephritic patients. The effluent was monitored by a post-column labeling detection method using ninhydrin. The detection limit of guanidino compounds was a few picomoles; however, that of creatinine was one hundredth of those of the other compounds. The reproducibilities of the peak height and area of the ten guanidino compounds using gradient elution were quite high, and the standard deviations were within a few percent (n=5), except for creatinine. The recovery of the compounds from serum was more than 90% (n=5). The reproducibility of retention times was within 1% (n=5).

Residues at the subunit interfaces of the nicotinic acetylcholine receptor that contribute to alpha-conotoxin M1 binding

The two binding sites in the pentameric nicotinic acetylcholine receptor of subunit composition alpha2 beta gamma delta are formed by nonequivalent alpha-gamma and alpha-delta subunit interfaces, which produce site selectivity in the binding of agonists and antagonists. We show by sedimentation analysis that 125I-alpha-conotoxin M1 binds with high affinity to the alpha-delta subunit dimers, but not to alpha-gamma dimers, nor to alpha, gamma, and delta monomers, a finding consistent with alpha-conotoxin M1 selectivity for the alpha delta interface in the intact receptor measured by competition against alpha-bungarotoxin binding. We also extend previous identification of alpha-conotoxin M1 determinants in the gamma and delta subunits to the alpha subunit interface by mutagenesis of conserved residues in the alpha subunit. Most mutations of the alpha subunit affect affinity similarly at the two sites, but Tyr93Phe, Val188Lys, Tyr190Thr, Tyr198Thr, and Asp152Asn affect affinity in a site-selective manner. Mutant cycle analysis reveals only weak or no interactions between mutant alpha and non-alpha subunits, indicating that side chains of the alpha subunit do not interact with those of the gamma or delta subunits in stabilizing alpha-conotoxin M1. The overall findings suggest different binding configurations of alpha-conotoxin M1 at the alpha-delta and alpha-gamma binding interfaces.

Toxins selective for subunit interfaces as probes of nicotinic acetylcholine receptor structure

The pentameric structure of the nicotinic acetylcholine receptor with two of the five subunit interfaces serving as ligand binding sites offers an opportunity to distinguish features on the surfaces of the subunits and their ligand specificity characteristics. This problem has been approached through the study of assembly of subunits and binding characteristics of selective peptide toxins. The receptor, with its circular order of homologous subunits (alpha gamma alpha delta beta), assembles in only one arrangement, and through mutagenesis, the residues governing assembly can be ascertained. Selectivity of certain toxins is sufficient to readily distinguish between sites at the alpha gamma and alpha delta interfaces. By interchanging residues on the gamma and delta subunits, and ascertaining how they interact with the alpha-subunit, determinants forming the binding sites can be delineated. The alpha-conotoxins, which contain two disulfide loops and 12-14 amino acids, show a 10,000-fold preference for the alpha delta over the alpha gamma subunit interface with alpha epsilon falling between the two. The waglerins, as 22-24 amino acid peptides with a single core disulfide loop, show a 2000-fold preference for alpha epsilon over the alpha gamma and alpha delta interfaces. Finally, the 6700 Da short alpha-neurotoxin from N. mossambica mossambica shows a 10,000-fold preference for the alpha gamma and alpha delta interfaces over alpha epsilon. Selective mutagenesis enables one to also distinguish alpha-neurotoxin binding at the alpha gamma and alpha delta subunits. This information, when coupled with homology modeling of domains and site-directed residue modification, reveals important elements of receptor structure and conformation.

Pancreatic exocrine dysfunction associated with mitochondrial tRNA(Leu)(UUR) mutation

We report on pancreatic exocrine dysfunction in families that have the mitochondrial tRNA(Leu)(UUR) gene mutation. These families exhibited maternally inherited diabetes mellitus (DM) and an A to G substitution at nt 3243 of the mitochondrial tRNA(Leu)(UUR) gene (A3243G mutation). Pancreatic necropsy samples from one proband showed accumulation of degenerated mitochondria in pancreatic acinar cells. Pancreatic exocrine dysfunction was recognised by a functional pancreatic study. This study indicates that exocrine pancreatic dysfunction may be associated with the A3243G mutation.

[Analysis of postoperative shivering following the deliberate mild hypothermia during neurosurgery]

We induced deliberate mild hypothermia in 96 patients who underwent intracranial operations using a water blanket and a convective device blanket. The lowest temperature measured at the tympanic membrane during mild hypothermia was adjusted to 34.5 degrees C. The patients were divided into two groups in respect to the occurrence of postoperative shivering, and the relationship between the perioperative parameters and the occurrence of postoperative shivering was evaluated. Shivering was observed postoperatively in 29 to 96 patients (30.2%). In the group with shivering (SV), age was significantly lower and body weight and body surface area were significantly larger than the group without shivering (NSV). Urinary output was significantly larger in SV than in NSV. Tympanic membrane, nasopharyngeal, and rectal temperatures at the end of surgery and nasopharyngeal, rectal, and peripheral temperatures just after the extubation were significantly lower in SV than in NSV. These results suggest that sufficient rewarming of both the core and peripheral temperatures is important to prevent the postoperative shivering following the mild hypothermic therapy in neurosurgical patients, especially in young patients.

Probucol treatment attenuates the aortic atherosclerosis in Watanabe heritable hyperlipidemic rabbits

We examined the effect of probucol on the aortic atherosclerosis already developed in Watanabe heritable hyperlipidemic (WHHL) rabbits at the initiation of treatment. In WHHL rabbits treated with probucol for 5 months from 8 months old, the lesion area in the aorta was significantly (P < 0.05) reduced when compared with that in untreated animals as well as animals at age 8 months. In contrast, plasma cholesterol levels in the probucol-treated group and untreated group during the experiment were not significantly different. LDL prepared from rabbits receiving probucol for 5 months showed resistance to oxidation by copper ions. Plasma CETP activity was significantly (P < 0.05) increased by probucol treatment. An immunohistochemical study showed that macrophages were abundant in the atherosclerotic lesions of untreated rabbits whereas smooth muscle cells were predominant in lesions of probucol-treated rabbits. These results suggest that the atherosclerotic lesion in WHHL rabbits can regress when treated by probucol and that the attenuation of atherosclerosis in this animal involves effects of probucol other than a decrease in plasma cholesterol, for example anti-oxidant activity.

Dried green leaf powders of Jew's mellow (Corchorus), persimmon (Diosphyros kaki) and sweet potato (Ipomoea batatas poir) lower hepatic cholesterol concentration and increase fecal bile acid excretion in rats fed a cholesterol-free diet

A cholesterol-free diet containing dried powder of Jew's mellow leaves, persimmon leaves or sweet potato leaves respectively at 5% level as dietary fiber was fed to male Sprague-Dawley rats for about one month. The experiment was conducted twice except for sweet potato leaves. In the groups fed the diet mixed with powders of any of the three different dried green leaves, the hepatic cholesterol concentration significantly decreased. Such lowering was not observed in serum cholesterol concentration compared with the control (cellulose) group. A significant increase in fecal weight was observed in all the groups fed the green leaf samples. All the dried green leaves increased fecal excretion of bile acids per gram or per day compared with the control group in both experiments, but only the dried Jew's mellow leaves showed an increased excretion of neutral sterols. These results suggest that lowering of hepatic cholesterol by powdered green leaves is not necessarily due to the same factor, but to the increased fecal excretion of bile acids due to inhibited enterohepatic circulation in animals given these samples.

[Low-dose levodopa therapy of autistic disorder: evaluation of clinical effectiveness]

Based upon the hypothesis that brain monoamine metabolism is disorganized in some children with an autistic disorder, we tried low dose levodopa therapy (0.5 mg/kg/day) proposed by Segawa, et al. We treated 20 patients with an autistic disorder diagnosed according to DSM-IV, and evaluated the effectiveness. A double blind cross over method was applied in this study because of the small number of patients. Drug effects were observed carefully by the psychologists and pediatric neurologists using an evaluation sheet consisting of twenty items. No significant effectiveness was observed in this study, although four cases (20%) showed some improvement. In conclusion, administration of low dose levodopa to autistic children resulted in no clear clinical improvements of autistic symptoms.

Neuroleptic malignant syndrome and hydroxylase gene mutations: no association with CYP2D6A or CYP2D6B

To examine a possible association between debrisoquine 4-hydroxylase gene mutations and neuroleptic malignant syndrome, we assessed frequencies of wild type and A and B mutant alleles of the CYP2D6 gene in 24 patients with a history of neuroleptic malignant syndrome, 50 patients with neuroleptic-treated schizophrenia but no history of neuroleptic malignant syndrome, and 50 healthy controls. Allele frequencies did not differ significantly between these groups. Homozygotes for CYP2D6A and for CYP2D6B, which indicate a poor-metabolizer phenotype for the CYP2D6 substrate, were not detected among the neuroleptic malignant syndrome cases. This result indicates no excess of poor CYP2D6 metabolizers in neuroleptic malignant syndrome. The aetiology of neuroleptic malignant syndrome is not explainable in terms of CYP2D6 gene mutations.

Eye-tracking device comparisons of three methods of magnetic resonance image series displays

This study evaluated the effectiveness of three kinds of display methods for magnetic resonance (MR) image interpretation using an eye-tracking device. Seven radiologists interpreted head MR studies by using a single monitor (17-inch, 1,024 X 1,280 bit) in the 4 images/screen display format. Three paging modes were compared: (A) rapid paging only, (B) multiple image series display at the same slice position with consecutive rapid paging, and (C) simultaneous display of multiple series with each image series being browsed independently. Using an eye-mark camera, the radiologist's point of fixation and the duration of fixation were recorded during actual image interpretation. In mode A, the duration of fixation was short, and the points of fixation were distributed randomly over the visual field. In mode B, the points of fixation were clustered chiefly on a specific image series. In mode C, the points of fixation were not clustered on a specified series, but the duration of viewing the T2 series was relatively long. The total tracing area in mode B and C was smaller than that in mode A. Multiple series display, in which selected key series of slices could be viewed effectively, was found to be suitable for MR image interpretation.

Immortalized gastric epithelial cell line GSM06 synthesizes hyaluronan under the influence of simian virus 40 large T-antigen expression

GSM06 is a cell line established from the stomach of transgenic mouse harboring a temperature-sensitive simian virus 40 (SV40) large T-antigen gene. 3H-labeled macromolecules produced by the cells incubated with [3H] glucosamine were characterized to examine whether or not GSM06 cells synthesize mucin (mucus glycoprotein). The GSM06 cells grew until a confluent monolayer formed at 33 degrees C (the permissive temperature for SV40 large T-antigen expression), and the 3H-labeled macromolecules appeared in both cell extract and medium during culture for at least 1 week. Unexpectedly, almost all 3H-labeled macromolecules, which were excluded from a column of Sepharose CL-4B, were identified as hyaluronan by analyses using Sepharose CL-2B chromatography, cesium trifluoroacetate equilibrium centrifugation, treatment with dithiothreitol, and trypsin, hyaluronidase, and chondroitinase ABC digestion. At a nonpermissive temperature (39 degrees C), GSM06 cells grew only slightly, but produced much more hyaluronan than at 33 degrees C. The results indicate that GSM06 cells produce not mucin, but hyaluronan, and that the expression of large T-antigen may influence hyaluronan synthesis in GSM06 cells.

A model of the nicotinic receptor extracellular domain based on sequence identity and residue location

We have modeled the extracellular domains of individual subunits (amino acids 31-200) in the nicotinic acetylcholine receptor using sequence homology with copper binding proteins of known crystal structure, plastocyanin and pseudoazurin, and data from recent site-specific mutagenesis, antibody mapping, and site-directed labelling studies. These data formed an initial model that was refined using molecular dynamics and mechanics as well as electrostatic and solvation energy calculations. The sequences between residues 31 and 164 in the alpha 1-subunit and corresponding residues in homologous receptor subunits show similarity with the core sequence of the cation binding site in plastocyanin and pseudoazurin, a region in the template proteins characterized by multiple hairpin loops. In addition to defining the subunit interfaces that comprise the site for agonist and competitive antagonist binding in more detail, the findings show that negatively charged residues cluster in domains arranged to diminish electrostatic free energy of the complex. Electrostatic factors also appear to distinguish the ligand binding interfaces, alpha gamma and alpha delta, from the other three interfaces on the pentameric receptor.

6-Pyruvoyl-tetrahydropterin synthase deficiency with generalized dystonia and diurnal fluctuation of symptoms: a clinical and molecular study

We report the case of a 44-year-old woman with a partial 6-pyruvoyl tetrahydropterin synthase (6-PTS) deficiency, whose predominant clinical symptom was generalized dystonia with marked diurnal fluctuation. Dystonia was present in the eyelids, oromandibular region, trunk, and extremities (Meige syndrome plus double hemiplegia-like dystonia). A marked and sustained positive response to levodopa was observed. A molecular genetic study revealed a homozygous mutation (I114V) in the 6-PTS gene. This study indicates that genetic abnormality in the 6-PTS gene may be a hereditary dystonia disorder. We speculate that our patient has residual 6-PTS activity in the central nervous system, such as in the liver, and we suggest that residual, but insufficient production of tetrahydrobiopterin may play an important role in causing diurnal fluctuation of symptoms.

[Highly reproducible technique for the estimation of trabecular bone density: three slice method on peripheral quantitative CT]

The reproducibility of bone mineral density (BMD) measurements with peripheral quantitative CT has been limited by the repositioning error. In this study, 1 mm-step 3-slice scan data were used to compensate for this error in trabecular BMD of the distal radius. The assessment was based on the liner relations between the cross-sectional area and trabecular bone mineral content and trabecular area ratio, on the condition that the trabecular bone is defined by a BMD value. The estimated reproducible errors of less than 2% under clinical conditions indicate that the method is reliable for follow-up examination.

Proprotein-processing endoprotease furin controls the growth and differentiation of gastric surface mucous cells

Gastric surface mucous cells originate from progenitor cells at the isthmus of the gastric gland, from where the cells migrate to the luminal surface. With migration they form secretory granules and express TGF alpha. We found that proprotein-processing endoprotease furin-positive cells were layered around the upper one fourth of the gastric glands of adult rats, whereas they were distributed along an outer epithelial layer in fetal rats. Because the furin-positive cell layer was localized from the upper cell proliferating zone to the less proliferating pit-cell region in the gastric gland unit, we examined the role of furin in the growth and differentiation of surface mucous cells by using the cell line, GSM06. This cell line is derived from the gastric surface mucous cells of transgenic mice harboring the temperature-sensitive simian virus 40 T antigen. At T antigen-active temperature (33 degrees C), the cells grew to confluency, whereas at T antigen-inactive temperature (39 degrees C), the cells ceased growing. At 33 degrees C, the cells exhibited a high level of furin expression with a negligible level of periodic acid Schiff (PAS)-positive materials and a low level of TGF alpha. In contrast, at 39 degrees C the cells produced a high level of PAS-positive materials, TGF alpha, and secretory granules, with a negligible level of furin expression. To further examine the role of furin, we established a GSM06 cell line introduced with either a sense or an antisense furin cDNA. The cells with sense furin expression produced fewer PAS-positive materials and a low level of TGF alpha even at 39 degrees C, whereas the cells with antisense furin expression exhibited more PAS-positive materials and TGF alpha even at 33 degrees C. When furin expression was suppressed by its antisense oligonucleotide, the cell growth was retarded with enhanced expression of the differentiated characteristics. Thus, we conclude that furin is instrumental in controlling the growth of the surface mucous cells.

Evaluation of the role of lactate dehydrogenase in oxalate synthesis

The kinetic properties of lactate dehydrogenase (LDH) (EC 1.1.1.27) from spinach leaves were studied in order to evaluate the possible roles of LDH in the production of oxalate. LDH was purified by affinity chromatography on affigel blue and oxamate agarose columns. The pH optimum for the reduction of pyruvate was 7.25, while that for the reduction of glyoxylate was 7. The rate of reduction of pyruvate and glyoxylate at the optimum pH indicated substrate inhibition at concentrations above 8 and 40 mM, respectively. The maximum activity of LDH with pyruvate was about three times greater than with glyoxylate. The pH optimum for the oxidation of lactate was 9, with very low activity below pH 8. Substrate inhibition was apparent at lactate concentrations above 10 mM. LDH was inactive with glyoxylate in the oxidative reaction, which would lead to the biosynthesis of oxalate.

Insulin stimulates production of glycoconjugate layers on the cell surface of gastric surface mucous cell line GSM06

The mechanism of regulation of mucus production in the gastric mucosa remains unclear. Recently, we established a gastric surface mucous cell line GSM06, which produces periodic acid-Shiff (PAS)-positive glycoconjugate (mucus) layers on the cell surface, from transgenic mice harboring a temperature-sensitive simian virus 40 large T-antigen gene. In this study, GSM06 cells were examined for its production of PAS-positive glycoconjugate layers to acid secretagogues and growth factors. The cells were cultured at nonpermissive temperature (39 degrees C) for 3-18 days and stained with PAS. Insulin (1-30 microg/ml; 0.29-8.6 microM) time- and dose-dependently increased production of glycoconjugates on the cell surface. When glycoconjugate layers produced by stimulation of insulin (3-30 microg/ml; 0.86-8.6 microM) were removed from the cell surface of GSM06 cells by a mild trypsin treatment, PAS-positive materials were remarkably decreased (day 18). In addition, morphological findings indicate that a high concentration of insulin (30 microg/ml; 8.6 microM) produced thick PAS-positive glycoconjugate layers just like normal gastric surface mucosa on the cell surface on day 18. In contrast, histamine (0.1-100 microM), carbachol (0.1-100 microM), gastrin-17 (0.1-100 nM), epidermal growth factor (0.01-10 ng/ ml; 1.7-1,700 pM), transforming growth factor-alpha (0.01-10 ng/ml; 1.8-1,800 pM), and fetal bovine serum (1-10%) did not increase glycoconjugate production. These findings suggest that insulin is a stimulator of glycoconjugate production, and stimulates production of glycoconjugate layers on the cell surface in the gastric surface mucous cell line GSM06.

Mutations in the proteolipid protein gene in Japanese families with Pelizaeus-Merzbacher disease

Pelizaeus-Merzbacher disease (PMD) is a rare X-linked dysmyelinating disorder of the CNS resulting from abnormalities in the proteolipid protein (PLP) gene. Exonic mutations in the PLP gene are present in 10 to 25% of all cases. In investigating genotype-phenotype correlations, we screened five Japanese families with PMD for PLP gene mutations and compared their clinical manifestations. We identified two novel nucleotide substitutions in exon 5, at V208N and at P210L, in two families. In the remaining three families, there were no mutations detected. Although all patients satisfied the criteria for the classical form of PMD, two families not carrying the mutations showed milder clinical manifestations than those with the mutations. Since linkage analysis has shown homogeneity at the PLP locus in patients with PMD, our findings suggest that there may be genetic abnormalities other than exonic mutations that cause milder forms of PMD.

Anionic residue in the alpha-subunit of the nicotinic acetylcholine receptor contributing to subunit assembly and ligand binding

To ascertain the anionic sites on the nicotinic receptor to which acetylcholine and other quaternary ammonium ligands bind, we have examined the role of an aspartyl residue (Asp-152) in the alpha-subunit. Prior photolytic labeling with agonist analogues of the neighboring residues Trp-149 and Tyr-151 suggests that their side chains reside on the binding face (also termed the (+)- or counterclockwise face) of the alpha-subunit. Asp-152 presents an anionic charge in the vicinity of these aromatic residues. Modification of the aspartate to asparagine (D152N) creates a glycosylation signal (Asn-152-Gly-Ser), and we find, on the basis of altered electrophoretic migration, that glycosylation occurs at this position upon cotransfection of the mutant alpha-subunit with beta-, gamma-, and delta-subunits. Glycosylation results in a reduction in the capacity of the receptor to assemble; this reduction is manifest in the initial step of dimer formation between the alphagamma- and alphadelta-subunits. The alpha-subunit mutant receptor reaching the assembled pentamer exhibits an altered selectivity for certain ligands. Little reduction in alpha-bungarotoxin binding is observed, whereas affinities for agonists and competitive alkaloid antagonists are reduced substantially. Separation of the contributions of charge removal and glycosylation addition shows that both factors affect agonist affinity, with the charge influence being far more predominant. These findings raise the possibility that a component of the coulombic attraction stabilizing the binding of agonists comes from the aspartyl residue at position 152 in the alpha-subunit.