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A Pastuszko

Publications and source records attributed to A Pastuszko.

70 records · Page 4Linked to original sources
PubMed1982

Energetics of gamma-aminobutyrate transport in rat brain synaptosomes.

The energetics of active transport of gamma-aminobutyric acid (GABA) by neuronal synapses has been studied using preparations of synaptosomes from rat brain. The maximal (steady state) accumulation of GABA by synaptosomes was measured as a function of the transmembrane potassium concentration gradient (which is equal to the transmembrane electrical potential in this system), the sodium concentration gradient, and the external chloride concentration. The steady state [GABA]i/[GABA]o increased as the second power of [K+]i/[K+]o which indicates that GABA is transported with a net charge of +2. The GABA gradient was dependent on [Na+]o/[Na+]i to a power of between 1.2 and 2.1 but was almost independent of [Cl-]. It is concluded that a neutral GABA molecule is cotransported with 2 Na+ to give a net charge of +2. The coupling of GABA transport to the transmembrane electrical potential and the Na+ concentration gradient is sufficient to provide the energy for the measured GABA concentration gradient in rat brain synaptosomes.

Animals↗
PubMed1982

Neurotransmitter metabolism in rat brain synaptosomes: effect of anoxia and pH.

Synaptosomes isolated from the rat cerebral cortex by means of a discontinuous Ficoll gradient carry out net, sodium-dependent, veratridine-sensitive accumulation of gamma-aminobutyric acid (GABA), serotonin, norepinephrine, and dopamine. The intrasynaptosomal contents of the four neurotransmitters are: 30.4 nmol/mg protein, 17.4 pmol/mg protein, 13.5 pmol/mg protein, and 21.2 pmol/mg protein, respectively. Anaerobic preincubation of synaptosomes causes an irreversible decrease in the rates of neurotransmitter accumulation but does not affect the rates of their release. The inhibitory effect of anaerobiosis is enhanced by increased concentration of [H+] (decreased pH) in the medium. The most sensitive is the uptake of dopamine, the least that of serotonin. The rates of neurotransmitter efflux are unaffected by anaerobiosis. Synaptosomes leak catecholamines, GABA, and serotonin into the medium when subjected to anaerobiosis, and reintroduction of oxygen is accompanied by a rapid reaccumulation of all four neurotransmitters. It is concluded that: (1) Responses of synaptosomes to anaerobiosis are remarkably similar to the behavior of intact brain in hypoxia and ischemia. (2) Neurotransmitter uptake systems are more sensitive to short periods of anaerobiosis than either the energy metabolism or ion transport. (3) Some neurotransmitter uptake systems are more easily damaged by anaerobiosis than others.

Aerobiosis↗
PubMed1981

Net uptake of gamma-aminobutyric acid by a high-affinity system of rat brain synaptosomes.

Rat brain synaptosomes isolated on discontinuous Ficoll gradient carry out rapid net uptake of gamma-aminobutyric acid through a high-affinity system (Km = 6.25 microM; Vmax = 1.2 nmol/min per mg of protein). The uptake of the labeled neurotransmitter is dependent on sodium concentration and is abolished by addition of 40 microM veratridine or 0.5 mM 2,4-diaminobutyric acid. Homoexchange in this preparation accounts for less than 10% of the measured uptake of gamma-amino[14C]butyric acid. It is concluded that the high-affinity transport exhibits properties characteristic of a system that is responsible for the rapid removal of gamma-aminobutyric acid from the synaptic cleft after neuronal transmission.

Aminobutyrates↗
PubMed1981

Effects of in vitro hypoxia and lowered pH on potassium fluxes and energy metabolism in rat brain synaptosomes.

Synaptosomes isolated on isosmotic Ficoll density gradients are an effective model for some aspects of neuronal function. They maintain metabolic energy levels ([ATP]/[ADP] [Pi]) and transplasma membrane electrical potentials very similar to those of neurons in the intact brain. The concentration of K+ in the external medium (K+-sensitive electrode), O2 uptake, and cytochrome c reduction (550 nm minus 540 nm) were simultaneously monitored in synaptosomal suspensions. Oxidative metabolism is the primary source of intrasynaptosomal ATP and at pH 7.4 anaerobiosis results in K+ leakage at 4.5 +/- 0.8 nmol/min/mg protein with glucose as substrate and 10.7 +/- 1.9 nmol/min/mg protein with lactate plus pyruvate (10:1) as substrate. Reintroduction of oxygen initiates complete (ouabain-sensitive) reuptake of K+ at initial rates of 35.4 +/- 3.2 nmol/min/mg protein and 18 +/- 1.7 nmol K+/min/mg protein, respectively. The rates of K+ leakage and reuptake fall when the pH is lowered from 7.4 to 6.0 but recover fully if the pH is raised to the original value. The rates of K+ release and uptake decrease when the Na+ concentration in the medium is decreased and increase when the Ca2+ concentration is decreased. The intrasynaptosomal [K+] under aerobic conditions was 77.3 +/- 3 mM and the calculated K+ diffusion potential was -72 mV. Anaerobic incubation of the synaptosomes from up to 20 min and at pH values from 7.4 to 6.0 did not produce irreversible impairment of any of the measured variables. These results suggest that permanent loss of brain function following prolonged hypoxia and ischemia is not due to irreversible damage to the synapses with respect to these parameters but rather to impairment of some other neuronal functions.

Adenosine Diphosphate↗
PubMed1980

Effect of anesthesia on membrane fluidity and acetylcholinesterase activity in rat brain synaptosomes.

Anesthesia by means of ketamine induces an increase of fluidity in the hydrophobic area of rat brain synaptic membranes, as proved by the spin label 16-doxyl stearate, in contrast with no change induced in the order parameter of 5-doxylstearate that probes the membrane surface. These effects are qualitatively similar to those observed by ketamine addition in vitro. On the contrary, acetylcholinesterase from synaptic membranes, although inhibited in vitro by ketamine, is activated in ketamine-anesthetised rats suggested that metabolic changes are at the basis of the effects observed in vivo.

Acetylcholinesterase↗
PubMed1980

Action of barbiturates on activity of acetylcholinesterase from synaptosomal membranes.

The acetylcholinesterase from synaptosomal membranes is inhibited by anesthetics: Nembutal, brietal, and thiopental. Nembutal and brietal decrease the Km for acetylthiocholine, without changes in Vmas. A noncompetitive type of inhibition is produced by thiopental. This anesthetic decreases Arrhenius plot discontinuity by about 4 degrees C and increases activation energies. Nembutal and brietal do not change Arrhenius plot discontinuities, but they increase activation energies. These results suggest that barbiturates change lipid-protein interactions in synaptosomal membranes.

Acetylcholinesterase↗