Biomedical subjects

C Solsona

Publications and source records attributed to C Solsona.

47 records · Page 3Linked to original sources

PubMed1989

Botulinum toxin type A blocks the morphological changes induced by chemical stimulation on the presynaptic membrane of Torpedo synaptosomes.

The action of botulinum neurotoxin on acetylcholine release, and on the structural changes at the presynaptic membrane associated with the transmitter release, was studied by using a subcellular fraction of cholinergic nerve terminals (synaptosomes) isolated from the Torpedo electric organ. Acetylcholine and ATP release were continuously monitored by chemiluminescent methods. To catch the membrane morphological changes, the quick-freezing method was applied. Our results show that botulinum neurotoxin inhibits the release of acetylcholine from these isolated nerve terminals in a dose-dependent manner, whereas ATP release is not affected. The maximal inhibition (70%) is achieved at neurotoxin concentrations as low as 125 pM with an incubation time of 6 min. This effect is not linked to an alteration of the integrity of the synaptosomes since, after poisoning by botulinum neurotoxin type A, they show a nonmodified occluded lactate dehydrogenase activity. Moreover, membrane potential is not altered by the toxin with respect to the control, either in resting condition or after potassium depolarization. In addition to acetylcholine release inhibition, botulinum neurotoxin blocks the rearrangement of the presynaptic intramembrane particles induced by potassium stimulation. The action of botulinum neurotoxin suggests that the intramembrane particle rearrangement is related to the acetylcholine secretion induced by potassium stimulation in synaptosomes isolated from the electric organ of Torpedo marmorata.

Acetylcholine↗

PubMed1989

Pertussis toxin prevents the inhibitory effect of adenosine and unmasks adenosine-induced excitation of mammalian motor nerve endings.

Pertussis toxin (PTX), which blocks certain classes of guanine nucleotide binding proteins (G proteins), consistently blocked the inhibitory effects of adenosine (100 microM-250 microM) on quantal acetylcholine (ACh) secretion in rat phrenic nerve hemidiaphragm preparations. PTX pretreatment also highlighted long-lasting increases in evoked ACh release elicited by adenosine. The results suggest that specific G proteins are involved in mediating the inhibitory effects of adenosine at motor nerve endings.

Acetylcholine↗

PubMed1988

Depolarization-stimulated protein phosphorylation in pure cholinergic nerve endings.

Cholinergic synaptosomes obtained from the electric organ of Torpedo marmorata have been used to study chemical stimulation-stimulated protein phosphorylation. Cholinergic synaptosomes were exposed to elevated K+0 concentrations or other chemical depolarizing agents such as gramicidin or secretagogues as the calcium ionophore A23187. During depolarization several synaptosomal proteins increase their state of phosphorylation. This phenomenon depends on the presence of Ca2+ in the external medium. These results suggest that stimulation of protein phosphorylation may be implicated in the acetylcholine release process and could represent a modulation mechanism in the neurotransmitter release machinery at this cholinergic synapse.

Animals↗

PubMed1988

Ouabain induces acetylcholine release from pure cholinergic synaptosomes independently of extracellular calcium concentration.

We have studied the correlation between [3H]ouabain binding sites, (Na+ + K+)ATPase (EC 3.6.1.3) activity and acetylcholine (ACh) release in different subcellular fractions of Torpedo marmorata electric organ (homogenate, synaptosomes, presynaptic plasma membranes). Presynaptic plasma membranes contained the greater number of [3H]ouabain binding sites, in good agreement with the high (Na+ + K+)ATPase activity found in this fraction. Blockade of this enzymatic activity by ouabain dose-dependently induced ACh release from pure cholinergic synaptosomes, either in the presence or absence of extracellular calcium ions. We suggest that one of the mechanisms involved in the ouabain-induced ACh release in the absence of Ca2+o may be an increase in Na+i that could (a) evoke Ca2+ release from internal stores and (b) inhibit ATP-dependent Ca2+ uptake by synaptic vesicles.

Acetylcholine↗

PubMed1987

Botulinum neurotoxin inhibits depolarization-stimulated protein phosphorylation in pure cholinergic synaptosomes.

Botulinum neurotoxin, a strong blocker of acetylcholine release at peripheral cholinergic synapses, inhibits depolarization-stimulated protein phosphorylation in pure cholinergic synaptosomes isolated from the electric organ of Torpedo marmorata. Moreover, tetrodotoxin has the same effect on protein phosphorylation when cholinergic synaptosomes are depolarized by veratridine. Correlation between presynaptic protein phosphorylation and acetylcholine release is suggested by the fact that botulinum neurotoxin blocks specifically neurotransmitter release without affecting membrane depolarization and calcium fluxes in our synaptosomal preparation.

Animals↗

PubMed1987

ATP release from pure cholinergic synaptosomes is not blocked by tetanus toxin.

Tetanus toxin (TeTx) is a neurotransmission impairing toxin that acts on several neurotransmitter systems. TeTx also inhibits the K+-induced release of acetylcholine (ACh) from synaptosomes isolated from the electric organ of Torpedo. Neither the membrane potential and depolarization, nor the depolarization-induced calcium uptake into cholinergic nerve terminals is modified after TeTx poisoning. On the other hand, it is known that, when cholinergic nerve terminals are stimulated, there is a release of ATP associated with the release of ACh. We have explored the action of TeTx on this co-release, and have found that there is no action of TeTx on the nucleotide release. Thus, TeTx blocks ACh release without modifying ATP release.

Acetylcholine↗

PubMed1987

Structural changes at pure cholinergic synaptosomes during the transmitter release induced by A-23187 in Torpedo marmorata. A freeze-fracture study.

Pure cholinergic synaptosomes isolated from the electric organ of Torpedo marmorata were stimulated by calcium ionophore A-23187. The effect of time course of stimulation on the changes in intramembrane particles (IMPs) on presynaptic membranes was studied by quick-freezing and aldehyde-fixation freeze-fracture. We showed that the decrease of small-particle density at the P-face and the increase of large-particle density at the E-face was maximum after 30 sec of A-23187 stimulation. Later, the density of synaptic vesicles decreased. We suggest that the redistribution of IMPs on the presynaptic membrane and acetylcholine (ACh) release from pure cholinergic synaptosomes have a similar time course when triggered by A-23187.

Acetylcholine↗

PubMed1985

Modulation of the endogenous acetylcholine release from rat striatal slices.

The dopaminergic modulation of the acetylcholine release from rat striatal slices has been investigated using a chemiluminescent method. Dopamine, more efficiently than apomorphine, decreased the potassium-evoked release of acetylcholine. The effect of dopamine antagonists, haloperidol and sulpiride, has been studied, and haloperidol was a better antagonist than sulpiride to the dopamine effect. Haloperidol elicited an acetylcholine release from striatal slices at 0.1 nM, probably by removing endogenous dopamine from dopaminergic receptors.

Acetylcholine↗

PubMed1982

Binding of beta-bungarotoxin to Torpedo electric organ synaptosomes. A high resolution autoradiographic study.

Isolated pure cholinergic synaptosomes from Torpedo electric organ were incubated in vitro with beta-bungarotoxin for 15, 30 and 60 min and processed for electron microscopy. It was found that no morphological damage was seen after 15 min but by contrast, severe disruption of synaptosomes was present at 30 or 60 min after incubation with toxin. Synaptosomes were incubated also for 15 min in the presence of 125I-labelled beta-bungarotoxin and the binding was evaluated by electron microscopic autoradiography. The toxin was found to bind to the presynaptic membrane. The surface density of toxin binding sites was calculated to be around 3000/micron2. In a minor population of synaptosomes, the toxin was translocated into large vesicles suggesting that the toxin-receptor complexes underwent endocytosis in such vesicles. These results give further support to the view that inhibition of transmitter release by the toxin is produced by its action on plasma membrane.

Animals↗

PubMed1981

Effects of ouabain and electrical stimulation on the fine structure of nerve endings in the electric organ of Torpedo marmorata.

The cycle of synaptic vesicles was studied in isolated nerve terminals and in the electric tissue of Torpedo marmorata. The synaptosomes, as used in this investigation, were a pure cholinergic subcellar fraction that captured dextran particles as an extracellular marker. This endocytotic phenomenon was enhanced by potassium depolarization. Field electrical stimulation (1 Hz and 10 Hz) of the electric organ induced the appearance of membrane foldings into presynaptic terminals. Morphometric studies showed that the number of synaptic vesicles did not decline until after at least 30 min. On the other hand, at 10 Hz these changes were accompanied by an increase in length of the membrane of the terminal. At 15 min of recovery after prolonged stimulation, there was a great increase in density of synaptic vesicles with a large number of vesicles of small diameter. This increase was accompanied by a decrease of membrane length, suggesting that reformation of vesicles is related to retrieval of membrane. Pharmacological stimulation with ouabain produced changes similar to those of long-term electrical stimulation. These changes in membrane were accompanied by a decrease of the population of synaptic vesicles and a wide variation in their diameters. It is concluded that structural changes reported here could not be correlated with kinetics of the transmitter release.

Animals↗

PubMed1980

Calcium fluxes in isolated pure cholinergic nerve endings from the electric organ of Torpedo marmorata.

1. Ca fluxes were studied in a pure cholinergic preparation of nerve endings from Torpedo electric organ. In standard physiological saline solution (280 mM Na+, 3 mM K+) the calcium uptake was at the rate of 8 nmole per mg of protein per minute, equivalent to a calcium influx of 0.6 pmole/cm2 x sec. 2. The rate of calcium uptake was enhanced when synaptosomes were depolarized, increasing potassium concentration in the external medium. Maximum stimulation was reached when the potassium concentration was over 50 mM and averaged 20 nmole Ca2+ per mg protein per minute, equivalent to calcium influx of about 1.5 pmole/cm2 x sec. 3. Protoveratrine and tytiustoxin also stimulated calcium uptake into the nerve terminals and their effect was blocked by tetrodotoxin. Tetrodotoxin didn't block calcium uptake in K+-stimulated synaptosomes. Some inhibitors of transmitter release such as Dantrolene, Verapamil, BetaBungarotoxin and adenine nucleotides prevented the stimulatory effect on calcium uptake by depolarizing agents. 4. The calcium entry increased roughly linearly with a slope proportional to external calcium concentrations up to 20 mM. This effect was greatly increased when either 100 mM K+ or protoveratrine were added to the external medium. 5. Most of the loss of isotope from 45Ca-loaded synaptosomes occurred by a sodium-dependent calcium efflux mechanism with half-activation at 13 mM Na+. This may be equivalent to 1.65 pmole/cm2 x sec. 6. In sodium-free and calcium-free solutions, a residual efflux (5 nmole per mg protein per min) is observed. Metabolic inhibitors such as CN- enhanced this residual efflux. 7. Morphological studies using sodium-free fixation solutions and radioautographic detection of 45Ca are consistent with calcium sequestration by intracellular organelles by a similar mechanism to the calcium buffering system described in disrupted synaptosomes. Synaptic vesicles may play an important role in this calcium sequestration.

Adenine Nucleotides↗