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Notes: Synthesis of acetylcholine depends on the plasma membrane uptake of choline by a high affinity choline transporter (CHT1). Choline uptake is regulated by nerve impulses and trafficking of an intracellular pool of CHT1 to the plasma membrane may be important for this regulation. We have generated a hemagglutinin (HA) epitope tagged CHT1 to investigate the organelles involved with intracellular trafficking of this protein. Expression of CHT1-HA in HEK 293 cells establishes Na+-dependent, hemicholinium-3 sensitive high-affinity choline transport activity. Confocal microscopy reveals that CHT1-HA is found predominantly in intracellular organelles in three different cell lines. Importantly, CHT1-HA seems to be continuously cycling between the plasma membrane and endocytic organelles via a constitutive clathrin-mediated endocytic pathway. In a neuronal cell line, CHT1-HA colocalizes with the early endocytic marker green fluorescent protein (GFP)-Rab 5 and with two markers of synaptic-like vesicles, VAMP-myc and GFP-VAChT, suggesting that in cultured cells CHT1 is present mainly in organelles of endocytic origin. Subcellular fractionation and immunoisolation of organelles from rat brain indicate that CHT1 is present in synaptic vesicles. We propose that intracellular CHT1 can be recruited during stimulation to increase choline uptake in nerve terminals.

Notes: Abstract: The present experiments tested whether preganglionic stimulation and direct depolarization of nerve terminals by tityustoxin could mobilize similar or different pools of acetylcholine (ACh) from the cat superior cervical ganglia in the presence of 2-(4-phenylpiperidino)cyclohexanol (vesamicol, AH5 183), an inhibitor of ACh uptake into synaptic vesicles. In the absence of vesamicol, both nerve stimulation and tityustoxin increased ACh release. In the presence of vesamicol, the release of ACh induced by tityustoxin was inhibited, and just 16% of the initial tissue content could be released, a result similar to that obtained with electrical stimulation under the same condition. When the impulse-releasable pool of ACh had been depleted, tityustoxin still could release transmitter, amounting to some 10% of the ganglion's initial content. This pool of transmitter seemed to be preformed in the synaptic vesicles, rather than synthesized in response to stimuli, as tityustoxin could not release newly synthesized [3H]ACh formed in the presence of vesamicol, and hemicholinium-3 did not prevent the toxin-induced release. In contrast to the results with tityustoxin, preganglionic stimulation could not release transmitter when impulse-releasable or toxin-releasable compartments had been depleted. Our results confirm that vesamicol inhibits the mobilization of transmitter from a reserve to a more readily releasable pool, and they also suggest that, under these experimental conditions, there might be some futile transmitter mobilization, apparently to sites other than nerve terminal active zones.

Notes: Abstract: GH3 cells present spontaneous Ca2+ action potentials and oscillations of intracellular Ca2+, which can be modified by altering the activity of K+ or Ca2+ channels. We took advantage of this spontaneous activity to screen for effects of a purified toxin (Tx3-1) from the venom of Phoneutria nigriventer on ion channels. We report that Tx3-1 increases the frequency of Ca2+ oscillations, as do two blockers of potassium channels, 4-aminopyridine and charybdotoxin. Whole-cell patch clamp experiments show that Tx3-1 reversibly inhibits the A-type K+ current (IA) but does not block other K+ currents (delayed-rectifying, inward-rectifying, and large-conductance Ca2+-sensitive) or Ca2+ channels (T and L type) in these cells. In addition, we describe the sequence of a full cDNA clone of Tx3-1, which shows that Tx3-1 has no homology to other known blockers of K+ channels and gives insights into the processing of this neurotoxin. We conclude that Tx3-1 is a selective inhibitor of IA, which can be used to probe the role of this channel in the control of cellular function. Based on the effect of Tx3-1, we suggest that IA is an important determinant of the frequency of Ca2+ oscillations in unstimulated GH3 cells.

Notes: Abstract: The present work tested whether pharmacological activation of protein kinase C (PKC) influences the release of [3H]-acetylcholine ([3H]ACh) synthesized in the presence of vesamicol, an inhibitor of the vesicular acetylcholine transporter (VAChT). Newly synthesized [3H]ACh was released from hippocampal slices by field stimulation (15 Hz) in the absence of vesamicol, but as expected [3H]ACh synthesized during exposure to vesamicol was not released significantly by stimulation. Treatment of slices with the PKC activator phorbol myristate acetate (PMA) decreased the inhibitory effect of vesamicol on [3H]ACh release. The effect of PMA was dose-dependent, was sensitive to calphostin C, a PKC-selective inhibitor, and could not be mimicked by α-PMA, an inactive phorbol ester. PMA did not alter the release of [3H]ACh in the absence of vesamicol, suggesting that the site of PKC action could be related to the VAChT. In agreement with this observation, immunoprecipitation of VAChT from 32P-labeled synaptosomes showed that phosphorylation occurs and that incorporation of 32P in the VAChT protein increases in the presence of PMA. We suggest that PKC alters the output of [3H]ACh formed in the presence of vesamicol and also provide circumstantial evidence for a role of phosphorylation of VAChT in this process.

Notes: We regret that we must retract the article Visualization of the Vesicular Acetylcholine Transporter in Living Cholinergic Cells by M. S. Santos, J. Barbosa Jr., C. Kushmerick, M. V. Gomez, V. F. Prado, and M. A. M. Prado (J. Neurochem. 74, , 2000). We have made an unintentional mistake in the construction of the enhanced green fluorescent protein (EGFP) vectors, and consequently the vesicular acetylcholine transporter (VAChT) and its truncated forms are incorrectly expressed. We have repeated the key experiments with proper constructs and have found that the expression pattern is clearly different from that reported in the article. The truncated form of VAChT, without the C-terminal tail, presents a distinct pattern of expression when compared to VAChT, and we have found no evidence that the C-terminal tail of VAChT is able to drive EGFP to varicosity sites. As a consequence of this problem, our earlier conclusions were incorrect. We apologize for this mistake and for any problems that we may have caused.

Notes: Synaptic vesicle proteins are suggested to travel from the trans-Golgi network to active zones via tubulovesicular organelles, but the participation of different populations of endosomes in trafficking remains a matter of debate. Therefore, we generated a green fluorescent protein (GFP)-tagged version of the vesicular acetylcholine transporter (VAChT) and studied the localization of VAChT in organelles in the cell body and varicosities of living cholinergic cells. GFP–VAChT is distributed to both early and recycling endosomes in the cell body and is also observed to accumulate in endocytic organelles within varicosities of SN56 cells. GFP–VAChT positive organelles in varicosities are localized close to plasma membrane and are labeled with FM4-64 and GFP–Rab5, markers of endocytic vesicles and early endosomes, respectively. A GFP–VAChT mutant lacking a dileucine endocytosis motif (leucine residues 485 and 486 changed to alanine residues) accumulated at the plasma membrane in SN56 cells. This endocytosis-defective GFP–VAChT mutant is localized primarily at the somal plasma membrane and exhibits reduced neuritic targeting. Furthermore, the VAChT mutant did not accumulate in varicosities, as did VAChT. Our data suggest that clathrin-mediated internalization of VAChT to endosomes at the cell body might be involved in proper sorting and trafficking of VAChT to varicosities. We conclude that genesis of competent cholinergic secretory vesicles depends on multiple interactions of VAChT with endocytic proteins.

Notes: Background Sedation limits the clinical utility of classical H, antihistamines. while newer antihistamincs such as loratadine and terfenadine arc non-sedating. However, clinical use of terfenadine has been associated with rare but severe cardiac arrhythmias, in particular lorsades de pointes.Objective To establish a quantitative experimental model for assessing the sedating and cardiotoxicity potential of non-sedating and sedating antihistamines.Methods Drugs were administered intravenously and the integrated amplitude of the conical electroencephalogram (EEC) signal was recorded. The threshold dose that depressed EEG activity was compared with the dose required lo inhibit by 50% the peripheral bronchospasm elicited by 10 μg/ kg i.v., of histamine. In separate studies, the electrocardiogram (ECG) and cardiovascular effects of loratadine (30 and 100mg/kg, i.v.). terfeuadine (10mg/kg. i.v.). promethazine (5mg/kg. i.v.) and diphenhydramine (20 mg kg, i.v.) were evaluated.Results The sedating antihistamines. diphenhydramine and promethazine. depressed the integrated EEG at doses between 0.6 and 2.0 limes their peripheral antihisiamine doses. Loratadine had no EEG depressant activity at 100 mg kg. i.v., a dose more than I 70 times its LD50 (0.58 mg kg, i.v.) against histamine bronchospasm. We were unable lo evaluate the EEG effects of terfenadine. because it produced cardiovascular collapse at 10 mg/kg. i.v. Loratadine and promethazinc did not produce adverse cardiovascular effects. nor did they alter normal ECG activity. Diphenhydramine produced brady-cardia followed by a transient hypertensive phase without affecting the QTc interval. In contrast, terfenadine elicited hypotension, bradycardia and significant arrhythmogenic activiy, causing a prolongation of the QTc interval and a torsades de pointes like ventricular arrhythmia. Pharmacokinetic studies after i.v. administration of loraladine (30 and 100 mg/kg) demonstrated plasma levels of loratadine and its major metabolite descarboethoxyloratadine to be several orders of magnitude greater than levels found in humans at the clinical dose of 10mg.Conclusion The CNS depressant effects of H1 antihislamines arc promcthazine≅ diphenhdramine ≫ loratadine = placebo. Of the non-sedating antihistamines. loratadine was devoid of adverse cardiovascular effects whereas terfenadine caused a pronounced disruption of the normal ECG. characterized by a torsades de pointes-like effect.

Notes: We extend the Clusters model to account for the presence of rigid inclusions and use it to analyze the experimental sintering kinetics of composites of 60SiO2·24B2O3·16Na2O glass particles and zirconia fibers. We followed the densification kinetics of such composites as a function of the particle size, volume fraction of fibers, fiber to pore size ratio, temperature, and time of thermal treatment. The parameters of the extended Clusters model are the glass particle size distribution and shape factor, the fiber volume fraction and radii, the glass viscosity and surface tension, the number of nucleating sites per unit surface, and the crystal growth rate in the parent glass. Hydrostatic tensions caused by the fibers were also included in the calculations. The modified Clusters model with only one adjustable parameter, which is largely dominated by viscosity but also includes particle shape, allowed us to account for the effect of surface crystallization and fiber content as inhibitors of densification and successfully describe the sintering kinetics of the studied composites.