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Biomedical subjects

A Cupello

Publications and source records attributed to A Cupello.

At least 73 records · Page 4Linked to original sources
PubMed1990

Stimulation of 36Cl- influx into rabbit cerebral cortex microsacs by the endogenous antigen S-100.

The rate of accumulation of 36Cl- ions into rabbit cerebral cortex microsacs has been studied under various conditions. Such a parameter is increased by 164% by 10(-4) M GABA, the effect being reversed in the presence of 10(-4) M bicuculline and 10(-4) M picrotoxin. Incorporation of the endogenous antigen S-100, by a preincubation of the fraction with the protein in the presence of 2.5 mM Ca++, brings about a 56% stimulation of 36Cl- influx rate. This effect does not seem to be additive with that of GABA. The S-100 effect is reversed by picrotoxin but not by bicuculline. The overall pattern of data suggests an action of the antigen directly at the GABAA receptor complex and in particular at the GABA activated Cl- channel.

Animals↗
PubMed1989

The mechanism by which intracellular GABA increases Cl- outward permeability across Deiters' neurone plasma membranes.

The present experiments aimed to clarify how the interaction of gamma-amino-butyric acid (GABA) with its receptors on the cytoplasmic side of the Deiters' neurone plasma membrane causes Cl- permeability to be higher in the in----out than in the opposite direction. To this end, the rate of 36Cl- in----out passage was studied in basal conditions, with GABA on the cytoplasmic side and in the presence of both GABA and an increased ionic strength buffer on that side. The results show that an increase in ionic strength reverses the GABA effect of 36Cl- permeability. The reversion being caused by changes in the buffer on the intracellular but not on the extracellular side. Our interpretation of this result is that the interaction of GABA with its cytoplasmic side receptors induces an exposure of positive charges only at the intracellular mouth of the intraneuronal GABA gated Cl- channels. This asymmetry would be the basis of the reported higher Cl- permeability in the in----out direction.

Chlorides↗
PubMed1989

Further studies on the effect of ASF factor on Cl- permeability across the Deiters' neurone plasma membrane.

Experiments have been performed in order to assess whether the antisecretory factor (ASF) can influence the permeation of Cl- ions across the Deiters' neurone plasma membrane in the outward direction. ASF is a naturally occurring, acidic protein with a molecular weight of about 60,000, which specifically inhibits enterotoxin-induced intestinal secretion. Both basal and "intracellular" GABA activated Cl- permeability was studied, and the result confirmed the existence of GABAA receptors on the Deiters' membrane cytoplasmic side. ASF completely abolished the effect of "intracellular" GABA on Cl- permeability in the outward direction. However, ASF did not influence the basal Cl- permeability in the outward direction.

Animals↗
PubMed1988

Direct evidence for the presence of GABAA receptors on the cytoplasmic side of the Deiters' neurone membrane.

A newly developed micromethod has been used for studying the rate of passage of 36Cl- ions across single nerve membranes from rabbit Deiters' neurones. The application of gamma-aminobutyric acid (GABA) on the cytoplasmic side of those membranes increases the rate of passage of 36Cl- ions from that side to the other one across the membrane. The maximal effect is exerted by 10(-6) M GABA and it fades at higher neurotransmitter concentrations (10(-5) M to 3.3 x 10(-3) M). The cause of this fading of the effect appears to be a receptor desensitization phenomenon. The 10(-6) M GABA effect is reversed by both 10(-4) M picrotoxin and 10(-5) M bicuculline. The overall pattern of the data indicates the presence of GABAA receptors on the cytoplasmic side of these nerve membranes.

Animals↗
PubMed1988

A microelectrophoretic method for the evaluation of GABA transaminase activity.

The reduction to the micro-scale of a recently described electrophoretic method for the evaluation of GABA catabolism by GABA-T is presented. The micromethod involves the electrophoresis, in 1 mm diam. capillaries, of small samples of mixtures of [14C]GABA and its metabolites. By coupling this procedure to previously devised micromethods, it was possible to evaluate GABA-T attack to 14C labeled GABA diffusing across a single microdissected neuronal membrane.

4-Aminobutyrate Transaminase↗
PubMed1988

Axoplasmic RNA species synthesized in the isolated squid giant axon.

Isolated squid stellate nerves and giant fiber lobes were incubated for 8 hr in Millipore filtered sea water containing [3H]uridine. The electrophoretic patterns of radioactive RNA purified from the axoplasm of the giant axon and from the giant fiber lobe (cell bodies of the giant axon) demonstrated the presence of RNA species with mobilities corresponding to tRNA and rRNA. The presence of labeled rRNAs was confirmed by the behavior of the large rRNA component (31S) which, in the squid, readily dissociates into its two constituent moyeties (17S and 20S). Comparable results were obtained with the axonal sheath and the stellate nerve. In all the electrophoretic patterns, additional species of radioactive RNA migrated between the 4S and the 20S markers, i.e. with mobilities corresponding to presumptive mRNAs. Chromatographic analysis of the purified RNAs on oligo(dT)cellulose indicated the presence of labeled poly(A)+ RNA in all tissue samples. Radioactive poly(A)+ RNA represented approximately 1% of the total labeled RNA in the axoplasm, axonal sheath and stellate nerve, but more than 2% in the giant fiber lobe. The labeled poly(A)+ RNAs of the giant fibre lobe showed a prevalence of larger species in comparison to the axonal sheath and stellate nerve. In conclusion, the axoplasmic RNAs synthesized by the isolated squid giant axon appear to include all the major classes of axoplasmic RNAs, that is rRNA, tRNA and mRNA.

Animals↗
PubMed1988

"Intracellular" GABA affects the equilibrium distribution of Cl- across the plasma membrane of a GABA acceptive neuron.

The permeability of Cl- ions through single microdissected plasma membrane from Deiters' neurons was studied by a microtechnique. In particular, the time course of the passage of 36Cl- ions from a microchamber, M1, to another one, M2, across the membrane was followed. This study was performed with or without gamma-amino-butyric acid (GABA) in the two microchambers. The results suggest that in basal conditions the high intracellular concentration normally present in these neurons, 3.3 mM (1), causes a higher permeability of Cl- in the direction inside----outside in the respect of the plasma membrane. "Extracellular" GABA, 0.1 mM, is able to abolish this imbalance in Cl- permeability in the two opposite directions. This event appears to be the basis for GABA induced hyperpolarization of these neurons.

Animals↗
PubMed1988

Phosphatidylserine increases in vivo the synaptosomal uptake of exogenous GABA in rats.

A sonicated liposome suspension of gamma-aminobutyric acid (GABA) and phosphatidylserine (liposome-entrapped GABA), intraperitoneally administered in rats, inhibited EEG epileptic activity induced by penicillin, whereas GABA did not. A significant increase (20.4%) in brain radioactivity accumulation occurred at 5 min after i.p. administration of [14C]GABA associated with phosphatidylserine in comparison with the administration of [14C]GABA; such an increase persisted after 20 min. However, the accumulation of radioactivity into brain synaptosomes demonstrated a 24.1% increase at 5 min and subsequently showed a 43.3% increase at 20 min after injection of liposome-entrapped GABA. The above findings suggest that phosphatidylserine stimulates exogenous GABA uptake into brain GABAergic nerve terminals.

Animals↗
PubMed1988

GABA A receptors on the cytoplasmic side of the Deiters' neurone plasma membrane: mechanism and functional implications.

A micromethod has been used for studying the passage of 36Cl- ions between two microchambers across the GABA acceptive plasma membrane of the rabbit Deiters' neurone, under various different conditions. The presence of 3.3 mM GABA, steady state intracellular concentration in situ (Okada & Shimada, 1976), on the cytoplasmic side of those membranes prolongs remarkably the time for the achievement of 36Cl- equilibrium across the membranes (from 4 minutes to 30 minutes). The effect appears to be mediated by "intracellularly oriented" GABAA receptor complexes as studied with GABAA antagonists such as bicuculline and picrotoxin. Intracellular GABA is still active in this effect at 10(-6) M. This phenomenon is discussed as, when coupled with the intracellular ATP producing machinery, being of importance for synaptically released GABA hyperpolarizing action on these neurones. The action of intracellular GABA on "internally oriented" receptors appears to involve the exposure of positively charged loci at the cytoplasmic side of the membrane. The consequent accumulation of intracellular Cl- at the membrane inner side would account for the higher overall permeability of those ions in the in----out direction. This circumstance was assessed by blocking the intracellular GABA effect either working at a relatively basic pH (8.4) inside or increasing the ionic strength in the intracellular compartment.

Animals↗
PubMed1987

Increase in chloride ion permeability across the nerve cell membrane after the endogenous antigen S-100 incorporation.

36Cl fluxes through microdissected Deiters' neuronal membranes have been studied in a microchamber device simulating the extra- and intracellular compartments. GABA stimulates Cl- permeability through the membranes by 24%. Also, S-100/Ca2+ incorporation into the Deiters' membrane increases 36Cl- permeation to a similar extent. The two effects do not appear to be additive. This circumstance is interpreted as indicating that S-100/Ca2+ exerts its effects via postsynaptic GABAA receptor complexes.

Animals↗
PubMed1987

Effect of anti-S-100 serum on 36Cl- ion permeability across the Deiters' neuron plasma membrane.

1. A microtechnique allowing the study of single plasma membranes from the gamma-aminobutyric acid (GABA)-acceptive Deiters' neuron has been utilized in order to assess the effect of both S-100 protein and its antiserum on 36Cl- permeability through such membranes. 2. The results show that both S-100 (in the Ca2+ form) incorporation onto the external side of the membranes and their preincubation with anti-S-100 serum stimulate 36Cl- permeability. 3. These effects are not additive with that of GABA, indicating that both S-100 and anti-S-100 act via the GABAA receptor complexes on Deiters' membranes. 4. When the membranes were incubated first with S-100/Ca2+ and then with anti-S-100, the second treatment resulted in the disappearance of the S-100 effect. However, the anti-S-100 effect was fully displayed.

Animals↗
PubMed1987

An electrophoretic method for the determination of the proportion of gamma-aminobutyric acid in a mixture of labeled neurotransmitter and its catabolites.

An electrophoretic method for the separation of gamma-aminobutyric acid (GABA) from its metabolites after GABA-transaminase attack is presented. The method is based on the fact that at neutral pH GABA has no net electrical charge, whereas its major metabolites, succinic acid and Krebs cycle intermediates, are negatively charged. The method appears to be especially suitable for evaluation of true-labeled neurotransmitter within the radioactivity which is found in synaptosomes after labeled GABA-uptake studies.

4-Aminobutyrate Transaminase↗
PubMed1987

Specific binding of 36Cl- ions to rat cerebellar membranes: effect of GABA and S-100 protein.

36Cl- ions display specific binding to rat cerebellum membranes. Although this binding at a 136Cl-1 of 2 X 10(-7) M is only 18% of total binding, it shows several interesting characteristics. It is higher in a GABA receptor rich region such as the cerebellum than in the cerebral cortex. It is higher in synaptic than in total membranes of the cerebral cortex. 36Cl- binding to cerebellar membranes in inhibited by 10(-4) M picrotoxin and by 10(-4) M GABA, the GABA effect being antagonized by bicuculline. All these characteristics appear to point out that 36Cl- specifically binds to GABAA receptor associated Cl- channels in their closed state. The brain specific antigen S-100 also is able to inhibit 36Cl- binding to rat cerebellar membranes.

Animals↗
PubMed1987

Micromethods for the study of GABA biochemistry and function at single GABA acceptive membranes.

Three different micromethods for studying GABA biochemistry and function at single microdissected GABA-acceptive neuronal membranes are discussed. The basis for such studies is the possibility of obtaining by microdissection single Deiters' neurons from the lateral vestibular nucleus of the rat and the rabbit. From these isolated cells the plasma membrane may be prepared and studied. The first micromethod allows the study of the Na+ independent diffusion of GABA through such a plasma membrane which is postsynaptic to GABA-ergic boutons. A modification of such method allows also the study of the effects of GABA-ergic drugs on Cl- permeability. The second method allows the study by microelectrophoresis in capillaries of GABA catabolism by GABA-T associated with microdissected single Deiters' membranes. The third one was developed in order to study the characteristics of Na+ dependent GABA carrier activity present on such membranes.

Animals↗
PubMed1987

GABAA receptor complexes are present on both sides of a GABA-acceptive neuronal membrane.

A micromethod allowing the study of the characteristics of single GABA-acceptive membranes microdissected from Deiters' neurones was used in order to assess the effects of both "extra"- and "intra"-cellular GABA on Cl- permeability. The results indicate that GABA can activate Cl- permeability in the in----out direction when it is present on the cytoplasmic side of the membrane. Moreover, as already described, it can activate Cl- permeability in the opposite direction when present on the "extracellular" side of the membrane. Both these phenomena are blocked by GABAA receptor inhibitors, bicuculline and picrotoxin. The presence of GABAA receptors on both sides of the membrane is discussed as the possible basis for synaptically released GABA hyperpolarising action on these neurones.

Animals↗