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Biomedical subjects

A Murgia

Publications and source records attributed to A Murgia.

At least 37 records · Page 2Linked to original sources
PubMed1997

Differential subunit dependence of the actions of the general anesthetics alphaxalone and etomidate at gamma-aminobutyric acid type A receptors expressed in Xenopus laevis oocytes.

The effects of subunit composition of the gamma-aminobutyric acid (GABA) type A receptor on the multiple actions of the general anesthetics alphaxalone and etomidate were investigated. The abilities of the two drugs to activate directly Cl- currents and to modulate GABA-evoked Cl- currents mediated by human recombinant GABA(A) receptors composed of alpha1, gamma2S, and either beta1, beta2, or beta3 subunit expressed in Xenopus laevis oocytes were compared. Both alphaxalone and etomidate evoked Cl currents in alpha1 beta1 gamma2S, alpha1 beta2 gamma2S, and alpha1 beta3 gamma2S receptors, an action that was blocked by both SR 95531 and picrotoxin. However, although maximal current activation by alphaxalone varied only slightly with the specific beta subunit isoform present, the efficacy of etomidate showed a rank order of beta3 > beta2 >>> beta1. In addition, beta1 homomeric receptors were markedly activated by etomidate but not by alphaxalone. Conversely, receptors consisting of alpha1 and gamma2S subunits were markedly activated by alphaxalone but not by etomidate. The modulatory effect of alphaxalone was also not markedly influenced by the beta-specific subunit isoform, whereas the modulatory efficacy of etomidate showed a rank order of beta3 > beta2 >> beta1. These results further demonstrate that the actions of general anesthetics at GABA(A) receptors are influenced by receptor subunit composition, and they suggest that the effects of alphaxalone and etomidate are mediated by different binding sites on the receptor complex.

Anesthetics↗
PubMed1996

Amplification of the Xq28 FRAXE repeats: extreme phenotype variability?

We report on a new case of FRAXE mutation identified through the screening of a population of FRAXA-negative mentally retarded individuals. The index case, a 4-year-old boy with distinct minor anomalies and mental retardation with severe verbal impairment, his older brother, referred to as normal, and the mother have undergone careful clinical and molecular evaluation. The molecular defect, characterized by standard Southern blot analysis, is represented by a hypermethylated "full mutation" in the 2 boys and by a unique, altered, presumably unmethylated, band in the mother, which is interpreted as a "premutation." The cytogenetic analysis failed to detect a folate-sensitive Xq27-28 fragile site in either "fully mutated" individual. The phenotype and intellectual performance of the 15-year-old brother of the propositus appeared completely normal. Our propositus shares some traits with previously described FRAXE-mutated subjects, suggesting an association with the Xq28 molecular defect; nevertheless, we find it difficult to reconcile the molecular identity and phenotypic difference in these mutated members of the same family. This could be a case of extreme phenotypic variability or a result of a more complicated molecular mechanism.

Blotting, Southern↗
PubMed1996

Direct activation of GABAA receptors by loreclezole, an anticonvulsant drug with selectivity for the beta-subunit.

Loreclezole, an anticonvulsant and antiepileptic compound, potentiates gamma-aminobutyric acid (GABA) type A receptor function, by interacting with a specific allosteric modulatory site on receptor beta-subunits. A similar selectivity for GABAA receptor beta-subunits is apparent for the direct activation of receptor-operated Cl- channels, by the general anesthetics propofol and pentobarbital. The ability of loreclezole to activate GABAA receptors directly has now been compared, biochemically and electrophysiologically, with that of propofol. In well-washed rat cortical membranes (devoid of endogenous GABA), loreclezole and propofol increased t-[35S]butylbicyclophosphorothionate ([35S]TBPS) binding by up to 28% (at 5 microM) and 80% (at 10 microM), respectively. Higher concentrations (50-100 microM) of both compounds inhibited [35S]TBPS binding with great efficacy, an effect mimicked by GABA. In contrast, the benzodiazepine diazepam increased [35S]TBPS binding, but failed to inhibit this parameter, even at high concentrations. At concentrations of 50-100 microM, loreclezole induced inward Cl- currents in the absence of GABA, in Xenopus oocytes expressing human recombinant GABAA receptors, comprised of alpha 1-, beta 2- and gamma 2S-subunits. At 100 microM, the current evoked by loreclezole was 26% of that induced by 5 microM GABA. The current evoked by 100 microM propofol was 98% of that induced by 5 microM GABA. Currents induced by loreclezole, like those evoked by propofol, were potentiated by diazepam in a flumazenil-sensitive manner and blocked by either bicuculline or picrotoxin. These data suggest that loreclezole shares, with propofol, an agonistic action at GABAA receptors containing the beta 2-subunit and that the different efficacies of the two compounds in this regard, may underlie the difference in their pharmacological profiles. The failure of loreclezole to activate GABAA receptors containing the beta 1-subunit may be responsible for its lack of hypnotic effect.

Animals↗
PubMed1996

Expression of native GABAA receptors in Xenopus oocytes injected with rat brain synaptosomes.

Oocytes from the frog Xenopus laevis were shown recently to express native nicotinic acetylcholine receptors after injection with purified Torpedo electroplaque membrane vesicles. Injection of Xenopus oocytes with rat cortical or nigral synaptosomes has now been shown to result in the expression of gamma-aminobutyric acid type A (GABAA) receptor-mediated Cl- currents. Electrophysiological characterization of the responses of these receptors to GABA and other agents revealed that they were incorporated into the oocyte membrane and that they retained their original pharmacological properties, such as sensitivity to Cl- channel blockers, benzodiazepines, and general anesthetics. These results suggest that this approach to the expression of heterologous proteins in Xenopus oocytes may facilitate the study of native synaptic proteins derived from brain tissue.

Anesthetics↗
PubMed1995

Primary biliary cirrhosis: lung involvement.

Sub-clinical lung impairment, mostly represented by a reduced diffusion of alveolar gases, is a recognised complication of advanced primary biliary cirrhosis. The aim of the study was to evaluate the prevalence and type of pulmonary involvement in primary biliary cirrhosis and the relationship between lung function abnormalities and selected epidemiological and clinical variables. Sixty-one patients with different stages of primary biliary cirrhosis consecutively seen in our outpatient clinic were evaluated. The advancement of primary biliary cirrhosis was characterised by the histological stage, the presence of signs of portal hypertension and the Mayo Risk Score: a Cox regression model using serum bilirubin and albumin levels, prothrombin time, age and degree of oedema as selected variables. We measured static and dynamic lung volumes, by means of a spirometer, and diffusing capacity for carbon monoxide. Rheumatological disorders were evaluated by an independent rheumatologist. No patient complained of respiratory symptoms. Airway obstruction was present in one patient. In 24 patients (39%) the alveolar diffusion capacity was reduced. We did not find any significant relationship between diffusing capacity and smoking habits, advancement of liver disease and concomitant Sjogren syndrome. Reduced diffusion capacity showed a significant correlation with the presence of complete or incomplete CREST syndrome (p < 0.01) and with the presence of circulating anti-centromere antibodies (p < 0.05). Alveolar diffusion capacity is frequently impaired in patients with primary biliary cirrhosis, usually in the absence of clinical manifestations. These alterations mostly affect patients with concomitant CREST syndrome.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Construction and characterization of a yeast artificial chromosome library for Xpter-Xq27.3: a systematic determination of cocloning rate and X-chromosome representation.

We describe the construction and characterization of a human X-chromosome-specific yeast artificial chromosome (YAC) library. Starting with 60 micrograms of hybrid cell line genomic DNA, we generated over 150,000 recombinants, over 90% of which range from 150 to 500 kb. From these recombinants, 3300 human-positive YACs (representing coverage of 4.5 X chromosomes) were identified by genomic human DNA hybridization. Mapping of random clones revealed that they are derived from the X chromosome in a regionally unbiased fashion, and screening with single-copy X-chromosome probes has repeatedly produced YACs from the library. By determining the frequency of YAC clones containing both hamster and human repetitive sequences, we estimated that approximately 11% of clones contain discontiguous sequences. Taken together, the low cocloning rate, the unbiased coverage, and a consistent recovery of YACs using specific X-chromosome markers indicate that YAC technology can be used for extensive cloning and mapping purposes. Because a certain amount of genomic rearrangement is present in YAC libraries, chromosome walking must be undertaken with a degree of caution.

Animals↗
PubMed1991

Linkage analysis of neurofibromatosis type 1. Study of a homogeneous North Italian population with five DNA markers of chromosome 17.

The authors report the results of a genetic analysis performed in 34 neurofibromatosis type 1 (NF1) Italian families using five loci tightly linked to NF1: D17S33, D17S82, D17S83, D17S37, and D17S36. A two-point linkage analysis was performed with the LINKAGE and the CRI-MAP programs. The map of the region was constructed using the MAP90 program. Data from the present study lend further support to evidence that all NF1 mutations are allelic and that the NF1 locus resides in the proximal region of chromosome 17q. Close linkage of NF1 to all the markers was found. Two of them, namely D17S82 and D17S83, showed the highest linkage with a value of 0 recombination frequency and lod scores of 3.77 and 4.02, respectively. The best map found is D17S33-D17S82-NF1-D17S83-D17S37-D17S36+ ++. The authors stress that knowledge of precise order is essential; if D17S82 and D17S83 are proved to flank the NF1 gene, they allow an acceptable presymptomatic diagnosis in informative families.

Chromosomes, Human, Pair 17↗
PubMed1990

Cell surface vitamin D-binding protein (GC-globulin) is acquired from plasma.

Vitamin D-binding protein (DBP) is an abundant plasma protein. The observation of immunodetectable, cell-associated DBP on peripheral blood mononuclear cells and placental cytotrophoblasts had presented the question of the origin, function, and precise subcellular localization of cell-associated DBP. Using anti-human DBP F(ab')2 with fluorescence-activated cytometric analysis and immunogold electron microscopy, we detected DBP on the plasmalemma of U937 cells, a monoblastic, histiocytic cell line grown in media supplemented with fetal calf serum (FCS). DBP was then removed from FCS by actin affinity chromatography followed by anti-DBP immunoaffinity chromatography. U937 cells in this DBP-free medium exhibited nearly identical growth rates to cells grown in medium containing native FCS. However, in contrast to cells grown with native FCS, those grown for seven to eight generations with DBP-free FCS exhibited less cell-surface DBP as quantified by fluorescence-activated cytometric analysis (73% decrease) and immunoelectron microscopy (88% decrease). DBP mRNA could not be detected in U937 cells, placental tissues, freshly prepared resting and stimulated B and T lymphocytes, or lymphocyte-derived cell lines by Northern analysis. In addition, using the sensitive reverse transcriptase/polymerase chain reaction assay no DBP fragments were detectable in U937 cells. We conclude that U937 cell-associated DBP is exogenously derived from plasma and is located on the plasmalemma. Based upon this conclusion, we postulate that specific binding sites for DBP may exist on the plasma membranes of certain cell types.

Blotting, Northern↗
PubMed1989

Oncologic causes of precocious puberty.

Tumors are rare, but well-documented causes of precocious puberty in both sexes. The therapeutic and prognostic implications of a diagnosis of cancer require that the presence of a neoplastic process be ruled out in any case of precocious puberty. Granulosa-cell tumor of the ovary and Leydig-cell tumor of the testis are the most frequent gonadal tumors inducing precocious pseudopuberty in the two sexes. Adrenal tumors sustain a variety of endocrine syndromes, the most frequent one being virilization with or without hypercortisolism. Pure feminizing adrenal neoplasms have been described. For reasons not yet well understood, hypothalamochiasmatic glioma (beta-HCG) secreting tumors have almost never been described in association with female precocious puberty. Among these neoplasia, pineal germ-cell tumor inducing sexual maturation must be included. Hypothalamochiasmatic glioma and craniopharyngioma are the two cerebral tumors capable of inducing true precocious puberty. Even if equally distributed between both sexes, these tumors interfere with sexual maturation less frequently in girls than in boys. Hypothalamic hamartoma is considered a benign tumor, since it does represent a space-occupying mass. It more correctly could be called a malformation if its histologic characteristics are recalled. This cerebral lesion is now frequently described in children with true precocious puberty, probably because of improved diagnostic imaging methods.

Child↗
PubMed1987

Effect of verapamil on aldosterone secretion in primary aldosteronism.

Intracytoplasmic calcium seems to act as second messenger for aldosterone secretion. Both in vitro and in vivo studies demonstrate that drugs which block calcium entry cause a decreased responsiveness of glomerulosa cells to Angiotensin II and potassium. In order to evaluate the effect of a calcium channel blocking agent (Verapamil) in conditions of abnormal aldosterone secretion, we have studied 11 patients with primary aldosteronism, 5 with idiopathic hyperaldosteronism (IHA) and 6 with aldosterone producing adenoma (APA). In our study plasma aldosterone levels decreased after Verapamil infusion in IHA whereas no significant variations were observed in APA patients. These results suggest that calcium blockade can interfere with a possible regulatory system which plays a greater role in idiopathic aldosteronism.

Aldosterone↗
PubMed1986

Effect of verapamil on the aldosterone-stimulating properties of metoclopramide: in vitro and in vivo studies.

The role of calcium in the regulation of aldosterone secretion has been recently clarified. Angiotensin II and potassium stimulate aldosterone secretion through a calcium-entry dependent mechanism, while ACTH action is both calcium and cyclic AMP dependent. To establish whether also the so-called aldosterone dopaminergic regulatory system is calcium-dependent we have studied, in vitro and in vivo, the effect of verapamil, a calcium entry blocker agent, on the aldosterone-stimulating properties of the antidopaminergic drug, metoclopramide. In the rat adrenal cells perfusion system, verapamil blocked both angiotensin II and metoclopramide-stimulated aldosterone. This effect on metoclopramide action seems to be present also in vivo in normal subjects: in fact aldosterone response was slightly but significantly reduced after pretreatment with verapamil. In conclusion the results suggest that also the dopaminergic system could regulate aldosterone secretion through calcium-mediated mechanisms.

Adrenal Glands↗