Effects of 4-(2-hydroxyethyl)-1-piperazine-ethanesulfonic acid (AH5183) on rat cortical synaptosome choline uptake, acetylcholine storage and release

Atomic Force Microscopy-Based Force Spectroscopy and Multiparametric Imaging of Biomolecular and Cellular Systems

During the last three decades, a series of key technological improvements turned atomic force microscopy (AFM) into a nanoscopic laboratory to directly observe and chemically characterize molecular and cell biological systems under physiological conditions. Here, we review key technological improvements that have established AFM as an analytical tool to observe and quantify native biological systems from the micro- to the nanoscale. Native biological systems include living tissues, cells, and cellular components such as single or complexed proteins, nucleic acids, lipids, or sugars. We showcase the procedures to customize nanoscopic chemical laboratories by functionalizing AFM tips and outline the advantages and limitations in applying different AFM modes to chemically image, sense, and manipulate biosystems at (sub)nanometer spatial and millisecond temporal resolution. We further discuss theoretical approaches to extract the kinetic and thermodynamic parameters of specific biomolecular interactions detected by AFM for single bonds and extend the discussion to multiple bonds. Finally, we highlight the potential of combining AFM with optical microscopy and spectroscopy to address the full complexity of biological systems and to tackle fundamental challenges in life sciences.

Inertial picobalance reveals fast mass fluctuations in mammalian cells

The regulation of size, volume and mass in living cells is physiologically important, and dysregulation of these parameters gives rise to many diseases. Cell mass is largely determined by the amount of water, proteins, lipids, carbohydrates and nucleic acids present in a cell, and is tightly linked to metabolism, proliferation and gene expression. Technologies have emerged in recent years that make it possible to track the masses of single suspended cells and adherent cells. However, it has not been possible to track individual adherent cells in physiological conditions at the mass and time resolutions required to observe fast cellular dynamics. Here we introduce a cell balance (a 'picobalance'), based on an optically excited microresonator, that measures the total mass of single or multiple adherent cells in culture conditions over days with millisecond time resolution and picogram mass sensitivity. Using our technique, we observe that the mass of living mammalian cells fluctuates intrinsically by around one to four per cent over timescales of seconds throughout the cell cycle. Perturbation experiments link these mass fluctuations to the basic cellular processes of ATP synthesis and water transport. Furthermore, we show that growth and cell cycle progression are arrested in cells infected with vaccinia virus, but mass fluctuations continue until cell death. Our measurements suggest that all living cells show fast and subtle mass fluctuations throughout the cell cycle. As our cell balance is easy to handle and compatible with fluorescence microscopy, we anticipate that our approach will contribute to the understanding of cell mass regulation in various cell states and across timescales, which is important in areas including physiology, cancer research, stem-cell differentiation and drug discovery.

Combining confocal and atomic force microscopy to quantify single-virus binding to mammalian cell surfaces

Over the past five years, atomic force microscopy (AFM)-based approaches have evolved into a powerful multiparametric tool set capable of imaging the surfaces of biological samples ranging from single receptors to membranes and tissues. One of these approaches, force-distance curve-based AFM (FD-based AFM), uses a probing tip functionalized with a ligand to image living cells at high-resolution and simultaneously localize and characterize specific ligand-receptor binding events. Analyzing data from FD-based AFM experiments using appropriate probabilistic models allows quantification of the kinetic and thermodynamic parameters that describe the free-energy landscape of the ligand-receptor bond. We have recently developed an FD-based AFM approach to quantify the binding events of single enveloped viruses to surface receptors of living animal cells while simultaneously observing them by fluorescence microscopy. This approach has provided insights into the early stages of the interaction between a virus and a cell. Applied to a model virus, we probed the specific interaction with cells expressing viral cognate receptors and measured the affinity of the interaction. Furthermore, we observed that the virus rapidly established specific multivalent interactions and found that each bond formed in sequence strengthened the attachment of the virus to the cell. Here we describe detailed procedures for probing the specific interactions of viruses with living cells; these procedures cover tip preparation, cell sample preparation, step-by-step FD-based AFM imaging and data analysis. Experienced microscopists should be able to master the entire set of protocols in 1 month.

HEPES inhibits the conversion of prion protein in cell culture

HEPES is a well-known buffering reagent used in cell-culture medium. Interestingly, this compound is also responsible for significant modifications of biological parameters such as uptake of organic molecules, alteration of oxidative stress mechanisms or inhibition of ion channels. While using cell-culture medium supplemented with HEPES on prion-infected cells, it was noticed that there was a significant concentration-dependent inhibition of accumulation of the abnormal isoform of the prion protein (PrP(Sc)). This effect was present only in live cells and was thought to be related to modification of the PrP environment or biology. These results could modify the interpretation of cell-culture assays of prion therapeutic agents, as well as of previous cell biology results obtained in the field using HEPES buffers. This inhibitory effect of HEPES could also be exploited to prevent contamination or propagation of prions in cell culture.

pH drift of "physiological buffers" and culture media used for cell incubation during in vitro studies

In pharmacological or toxicological studies performed at room atmosphere comparison of various media used for cell incubation revealed discrepancies among results due to pH instability when these media contain bicarbonate. With the classically used protocols, a relatively fast and notable rise of the pH of such media has been observed, and values higher than 8.5 could be reached after 1 h of incubation. A less important rise in pH was also observed for media containing low amounts of sodium bicarbonate, e.g., Hank's formula-derived media. Because Hepes-buffered media or media with abnormal osmolarity cannot always be used for such studies, our choice of media is limited.

In vitro taurine uptake into cell culture influenced by using media with or without CO2

Buffers used to incubate cells for pharmacological or toxicological studies are usually of very simple composition, far from the composition of biological fluids or cell culture media. Comparative studies on taurine uptake levels by cultured cells show that a new CO2-Independent Medium (CIM) is suitable for incubating cells in place of the Krebs-Ringer buffer (KR) usually used. Basal uptake level of taurine was lower for cells incubated in CIM or in other culture media when compared to those incubated whether in KR or in other "physiological buffers." Isoproterenol depressed similarly the taurine uptake in cells incubated in CIM or KR. The same uptake modulation by beta-alanine, GES, GABA, or HEPES was observed for cells incubated in CIM or KR. C6 cells growth in CIM was dependent on the starting cell density when classically vented T-flasks were used, growth being notably reduced at low density. In tightly closed flasks cells grew in CIM similarly to control cultures maintained in M199 medium or DMEM.

Effects of systemic administration of 2-(4-phenyl-piperidino)-cyclohexanol (vesamicol) and an organophosphate DDVP on the cholinergic system in brain regions of rats

Vesamicol is known to inhibit the transport of acetylcholine (ACh) into synaptic vesicles in vitro, but much less is known about its effects in the brain in vivo. To assess the effect of vesamicol in vivo, we examined cholinergic parameters, such as the subcellular distribution of ACh, activities of enzymes, uptake of choline, and muscarinic receptor binding in the striatum, hippocampus, and cerebral cortex of rats 30 and 60 min after intraperitoneal injection of vesamicol (3 mg/kg) or of vesamicol in combination with DDVP (5 mg/kg), which was administered 10 min before vasamicol. The levels of cytosolic ACh increased in all regions of the brain after injection of vesamicol, while those of vesicular ACh decreased in all regions except for the striatum. The increase in the levels of extracellular ACh and cytosolic ACh in the striatum induced by DDVP was generally enhanced after injection of vesamicol, Vesamicol did not reduce the level of vesicular ACh when DDVP had been injected previously. Vesamicol did not induce any significant changes in the activities of enzymes, choline uptake, or binding of [6H]quinuclidinyl benzilate to the muscarinic ACh receptors in the three regions. Changes in the cholinergic parameters caused by DDVP were not reversed by the combined administration of DDVP with vesamicol. The present results indicate that vesamicol can inhibit the transport of ACh into synaptic vesicles in the brain tissue in vivo, although it cannot reverse the effects of DDVP that has been injected prior to vesamicol.

Vesamicol, an inhibitor of acetylcholine vesicle packaging, increases synaptophysin phosphorylation in rat cortical synaptosomes

Vesamicol (AH5183) is an inhibitor (IC50, 50 nM) of acetylcholine (ACh) vesicle packaging. Vesamicol increases the phosphorylation pattern of synaptophysin (p38), identified as a vesicle-specific phosphoprotein involved in vesicle-mediated neurotransmitter release. Percoll fractionation of the rat cortex yielded a cholinergic-enriched synaptosomal Fraction 4. Fraction 4 contained the highest enrichment of cholineacetyl-transferase activity (86 +/- 4.6 mumole AcCh/g protein/hr.) in the Percoll gradient. Fraction 4 demonstrated oxygen consumption (108 +/- 23.4 nmole/mg protein), levels of adenosine triphosphate, ATP, (10.29 +/- 0.45 nmole/mg protein) and adenosine diphosphate, ADP, (10.54 +/- 2.72 nmole/mg protein), energy potential (ATP/[ADP] [Pi], (0.49) phosphate uptake (65-80 nmoles phosphate/mg tissue), 32Pi labelling (130 +/- 12 x 10(5) DPM/mg tissue; 74 +/- 9.8 x 10(2) nmoles phosphate/mg tissue). Synaptophysin was identified by Western blotting and confirmed by qualitative immunoprecipitation. Synaptophysin phosphorylation was confirmed by autoradiograph. Synaptophysin phosphorylation increased (225%) in the presence of vesamicol (ED50, 1 nM) in Fraction 4. Vesamicol (50 nM) and vanadate (54 microM) were compared for their effects on synaptophysin. This study suggests that during the inhibition of acetylcholine packaging by vesamicol that synaptophysin is phosphorylated. Therefore, the phosphorylation and dephosphorylation of synaptophysin may be involved in the transport of acetylcholine in or out of the synaptic vesicle.

Acetylcholine transport, storage, and release

ACh is released from cholinergic nerve terminals under both resting and stimulated conditions. Stimulated release is mediated by exocytosis of synaptic vesicle contents. The structure and function of cholinergic vesicles are becoming known. The concentration of ACh in vesicles is about 100-fold greater than the concentration in the cytoplasm. The AChT exhibits the lowest binding specificity among known ACh-binding proteins. It is driven by efflux of protons pumped into the vesicle by the V-type ATPase. A potent pharmacology of the AChT based on the allosteric VR has been developed. It has promise for clinical applications that include in vivo evaluation of the density of cholinergic innervation in organs based on PET and SPECT. The microscopic kinetics model that has been developed and the very low transport specificity of the vesicular AChT-VR suggest that the transporter has a channel-like or multidrug resistance protein-like structure. The AChT-VR has been shown to be tightly associated with proteoglycan, which is an unexpected macromolecular relationship. Vesamicol and its analogs block evoked release of ACh from cholinergic nerve terminals after a lag period that depends on the rate of release. Recycling quanta of ACh that are sensitive to vesamicol have been identified electrophysiologically, and they constitute a functional correlate of the biochemically identified VP2 synaptic vesicles. The concept of transmitter mobilization, including the observation that the most recently synthesized ACh is the first to be released, has been greatly clarified because of the availability of vesamicol. Differences among different cholinergic nerve terminal types in the sensitivity to vesamicol, the relative amounts of readily and less releasable ACh, and other aspects of the intracellular metabolism of ACh probably are more apparent than real. They easily could arise from differences in the relative rates of competing or sequential steps in the complicated intraterminal metabolism of ACh rather than from fundamental differences among the terminals. Nonquantal release of ACh from motor nerve terminals arises at least in part from the movement of cytoplasmic ACh through the AChT located in the cytoplasmic membrane, and it is blocked by vesamicol. Possibly, the proteoglycan component of the AChT-VR produces long-term residence of the macromolecular complex in the cytoplasmic membrane through interaction with the synaptic matrix. The preponderance of evidence suggests that a significant fraction of what previously, heretofore, had been considered to be nonquantal release from the motor neuron actually is quantal release from the neuron at sites not detected electrophysiologically.(ABSTRACT TRUNCATED AT 400 WORDS)

The pharmacology of vesamicol: an inhibitor of the vesicular acetylcholine transporter

1. Vesamicol (2-[4-phenylpiperidino] cyclohexanol) inhibits the transport of acetylcholine into synaptic vesicles in cholinergic nerve terminals. 2. Recent pharmacological studies of the effects of vesamicol on skeletal neuromuscular transmission have revealed a pattern of activity for the compound consistent with the neurochemical observation of the mechanism of action of the compound. 3. Pharmacological manipulation of vesicular acetylcholine transport has been used to investigate the recycling and mobilization of synaptic vesicles within cholinergic nerve terminals. 4. In addition to its effects on vesicular acetylcholine transport, vesamicol also possesses some sodium channel and alpha-adrenoceptor blocking activity. 5. Vesamicol clearly represents a unique tool for investigating presynaptic mechanisms in cholinergic nerve terminals.

Parameters not influenced by vesamicol: membrane potential, calcium uptake, and internal calcium concentration of synaptosomes

In our previous study vesamicol, an inhibitor of the acetylcholine transporter of the cholinergic vesicles, inhibited veratridine-evoked external Ca(2+)-dependent acetylcholine release from striatal slices but did not influence acetylcholine release observed in Ca(2+)-free medium (4). Here we examined if the effect of veratridine on membrane potential, Ca(2+)-uptake, and intracellular Ca2+ concentration of synaptosomes was altered by vesamicol in parallel with the inhibition of acetylcholine release. The depolarizing effect of 10 microM veratridine (from 67 +/- 2.3 mV resting membrane potential to 50.7 +/- 2.5 mV) was not significantly influenced by vesamicol (1-20 microM). Vesamicol (1-20 microM) had no effect on either the overall curve of the veratridine-evoked 45Ca2+ uptake or the amount of Ca2+ taken up by synaptosomes. Veratridine caused a rise in intrasynaptosomal Ca2+ concentration as measured by Fura2 fluorescence, and the same increase both in characteristics and in magnitude was observed in the presence of vesamicol (20 microM). The K(+)-evoked (40 mM) increase of Ca2+ uptake and of intracellular calcium concentration were also unaltered by vesamicol. In high concentration (50 microM) vesamicol inhibited both the fall in membrane potential and the elevated Ca2+ uptake by veratridine, indicating a possible nonspecific effect on potential-dependent Na+ channels at this concentration. Vesamicol, in lower concentration (20 microM) when neither of the above parameters was changed, completely prevented veratridine-evoked increase of [14C]acetylcholine release. This was observed only when vesamicol was present in the media throughout the experiment after loading the preparation with [14C]choline.(ABSTRACT TRUNCATED AT 250 WORDS)

Suppression of in vivo neostriatal acetylcholine release by vesamicol: evidence for a functional role of vesamicol receptors in brain

Experiments examined the effects of peripheral and central administration of the vesicular acetylcholine transport blocker vesamicol (AH5183) on the content, synthesis, and release of acetylcholine in the rat brain in vivo. In time course studies, a single intraperitoneal dose of DL-vesamicol (5 mg/kg) rapidly and reversibly (within 2 h) doubled the content of acetylcholine in the striatum and hippocampus, without affecting choline levels or the rate of transmitter synthesis. In microdialysis experiments, the same peripheral dose of drug produced a reversible 55% reduction in endogenous striatal acetylcholine release. A similar inhibitory effect was produced by direct intrastriatal perfusion with vesamicol. Moreover, this effect of vesamicol was (a) concentration-dependent and saturable (EC50 = 68 nM), (b) rapidly reversible, (c) stereospecific for the L-isomer, and (d) poorly mimicked by a vesamicol analog with lower plasma membrane permeability. This profile of effects is consistent with an interaction with a specific vesamicol receptor as defined by previous in vitro binding studies. These results support a functional role for vesamicol receptors in modulating central cholinergic transmission in vivo.

Effect of AH5183 (vesamicol) on cholinergic transmission in intact airway smooth muscle

The effect of the vesicular acetylcholine (ACh) transport blocker trans-2-(4- phenyl-piperidino)-cyclohexanol (AH5183) was studied in bronchial smooth muscle during activation of the vagus nerve. AH5183 inhibited in a dose-dependent manner the Ca(2+)-sensitive electrically induced smooth muscle contractions in vitro with a half-inhibitory concentration (IC50) of 1.6 +/- 0.4 microM. The inhibition was complete within 68 +/- 1 min (n = 8) at approximately 20 microM AH5183 and was partly reversible after washing of the preparations. AH5183 (20 microM) reduced the level of endogenous ACh by 47.4 +/- 7.6% (n = 4) during this time period. The effect of AH5183 is most likely prejunctional, since the contractions induced post-junctionally by carbachol were not altered by AH5183. The irreversible anticholinesterase, soman, increased the tonus of airway smooth muscle as a result of accumulation of spontaneously released ACh from prejunctional leakage. AH5183 had no effect on this increase of muscle contraction. The present results show that the nerve-evoked release of ACh comes from an AH5183-sensitive pool, probably a vesicular pool, whereas leakage of ACh presumably comes from the cytoplasmic pool in airway smooth muscle.

Local anaesthetic activity of vesamicol in the electric organ of Torpedo

Synaptic transmission in intact pieces of the Torpedo electric organ treated with vesamicol (2-(4-phenylpiperidino)cyclohexanol, formerly AH5183) was elicited by trains of repetitive electrical stimulation at different frequencies. When the frequency of stimulation was increased from 10 to 50 or 100 Hz, micromolar concentrations of vesamicol enhanced the tetanic rundown of the successive tissue responses. This effect was already detectable with 10 microM vesamicol. It was dramatically potentiated with concentrations of 50 or 100 microM vesamicol, which caused complete failure of transmission after usually less than 10 responses. The drug was unequivocally demonstrated to act by depressing the evoked release of acetylcholine as a consequence of a highly frequency- and concentration-dependent impairment of Na+ channel function in afferent axons. It is concluded that, in the electric organ, vesamicol blocks transmission by acting as a local anaesthetic. This action of micromolar concentrations of vesamicol must be taken into account especially during high-rate nerve activity.

Ca2+o-independent veratridine-evoked acetylcholine release from striatal slices is not inhibited by vesamicol (AH5183): mobilization of distinct transmitter pools

The effect of 2-(4-phenylpiperidino)cyclohexanol (AH5183 or vesamicol), a compound known to block the uptake of acetylcholine (ACh) into cholinergic synaptic vesicles, on the release of endogenous and [14C]ACh from slices of rat striatum was investigated. ACh release was evoked either by electrical stimulation or by veratridine. The effect of electrical stimulation was entirely dependent on external Ca2+. By contrast, veratridine (40 microM) also enhanced ACh release in the absence of Ca2+. Indeed, with veratridine two components were clearly distinguished: one dependent on external Ca2+ and the other not. Vesamicol inhibited [14C]ACh release evoked by both veratridine and electrical stimulation in the presence of external Ca2+, provided it was added to the tissue prior to loading with [14C]choline. With the same treatment vesamicol only slightly affected the release of endogenous ACh. Under the same conditions the Ca2(+)-independent [14C]ACh release evoked by veratridine was not prevented by vesamicol. The differential responsiveness to vesamicol suggests that ACh pools involved in Ca2+o-dependent ACh release are different from those mobilized during Ca2+o-independent ACh release.

Decrease of acetylcholine release from cortical slices in aged rats: investigations into its reversal by phosphatidylserine

The release of total acetylcholine (ACh) and [3H]ACh was investigated in electrically stimulated cortical slices prepared from 4- and 18-month-old male Wistar rats. The slices were prelabeled with [3H]choline ([3H]Ch) and perfused with Krebs solution containing physostigmine. Total ACh was measured and the nature of the tritium efflux identified by HPLC. The total tritium content in the slices at the end of the incubation period was half as great in the old as in young rats. A linear relationship was found between stimulation frequencies (2, 5, and 10 Hz) and fractional [3H]ACh release in both young and old rats. In the latter the release was significantly smaller. At 10 Hz stimulation frequency the ratio between the two 2-min stimulation periods, S2/S1, was higher in the 18-month-old rats than in the young rats. Specific activity of the evoked ACh release was significantly smaller in S2 than in S1 in 4-month-old rats only. These findings indicate that the young synthetize ACh from endogenous unlabeled Ch more than older rats. In 18-month-old rats both the evoked total ACh and [3H]ACh release, expressed as picograms per minute, showed an approximately 50% decrease in both S1 and S2 stimulation periods, with no significant difference in specific activity. Phosphatidylserine (PtdSer) administration (15 mg/kg, i.p. daily) for 1 week to 18-month-old rats prevented the reduction in total evoked ACh release but not the reduction in evoked [3H]ACh release. The specific activity of ACh release was therefore significantly smaller than that of the young and untreated old rats.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of L-vesamicol, an inhibitor of vesicular acetylcholine uptake, on two populations of miniature endplate currents at the snake neuromuscular junction

The actions of the active L-isomer of vesamicol, an inhibitor of the vesicular storage of acetylcholine, has been studied on spontaneous and evoked acetylcholine release at the snake neuromuscular junction. Miniature endplate currents and endplate currents were recorded from cut muscle fibres of the garter snake, Thamnophis sirtalis. In controls, prolonged periods of high frequency nerve stimulation produced a bimodal distribution of miniature endplate current amplitudes. The stimulation induced "small-mode" miniature endplate currents had a mean amplitude of around 40-55% of the pre-stimulation miniature endplate current. Relative to the normal-sized post-stimulation miniature endplate current, the proportion and, to a lesser extent, amplitude of the small-mode miniature endplate currents was related to both the frequency and duration of nerve stimulation and to the extracellular calcium ion concentration. In unstimulated preparations, L-vesamicol (2-5 microM) did not affect either endplate current quantal content or miniature endplate current amplitude or frequency. However, at these doses, the mean amplitude of the stimulation-induced, small-mode miniature endplate current was reduced by L-vesamicol in a concentration-dependent manner such that they were not visible at the highest dose. L-Vesamicol had no affect on the mean or coefficient of variance of amplitude of the larger, normal-sized miniature endplate current. Additionally, the stimulation-induced increase in overall miniature endplate current frequency seen in controls was abolished by 5 microM L-vesamicol. After prolonged 10 Hz nerve stimulation endplate current amplitude was markedly reduced in both controls (by 94%) and in the presence of 5 microM L-vesamicol (by 98%). Analysis of endplate current amplitude variance showed that in control the decrease was due to reductions in both quantal content and quantal size while in L-vesamicol the decrease was due entirely to a change in quantal content with no change in quantal size. Thus, we have observed that L-vesamicol selectively reduces the amplitude of a population of stimulation-induced small-mode quanta both as miniature endplate currents and as constituents of endplate currents. We suggest that these quanta are derived from a highly active, readily releasable pool. An action of L-vesamicol on this labile pool is consistent with previous observations on its ability to inhibit the vesicular storage of acetylcholine.

Compared effects of two vesicular acetylcholine uptake blockers, AH5183 and cetiedil, on cholinergic functions in Torpedo synaptosomes: acetylcholine synthesis, choline transport, vesicular uptake, and evoked acetylcholine release

We examined the effects of two drugs, AH5183 and cetiedil, demonstrated to be potent inhibitors of acetylcholine (ACh) transport by isolated synaptic vesicles on cholinergic functions in Torpedo synaptosomes. AH5183 exhibited a high specificity toward vesicular ACh transport, whereas cetiedil was shown to inhibit both high-affinity choline uptake and vesicular ACh transport. Choline acetyltransferase was not affected by either drug. High external choline concentrations permitted us to overcome cetiedil inhibition of high-affinity choline transport, and thus synthesis of [14C]ACh in treated preparations was similar to that in controls. We then tested evoked ACh release in drug-treated synaptosomes under conditions where ACh translocation into the vesicles was blocked. We observed that ACh release was impaired only in cetiedil-treated preparations; synaptosomes treated with AH5183 behaved like the controls. Thus, this comparative study on isolated nerve endings allowed us to dissociate two steps in drug action: upstream, where both AH5183 and cetiedil are efficient blockers of the vesicular ACh translocation, and downstream, where only cetiedil is able to block the ACh release process.

Effects of an inhibitor of the synaptic vesicle acetylcholine transport system on quantal neurotransmitter release: an electrophysiological study

The drug 2-(4-phenylpiperidino)cyclohexanol (AH5183), which potently inhibits the active transport of acetylcholine (ACh) into synaptic vesicles, was used as a pharmacological tool to study the functional role of synaptic vesicles in quantal transmitter release. Using microelectrode recording techniques, miniature endplate potentials (mepps) and nerve-evoked endplate potentials (epps) were recorded from frog cutaneous pectoris neuromuscular junctions in low Ca2+/high Mg2+ Ringer solution, and in normal Ringer with added D-tubocurarine (D-TC). Stimulation in the presence of AH5183 caused a 40% reduction in quantal size (mepp amplitude), depressed tetanic potentiation, and decreased the number of quanta released with each nerve impulse in the presence of D-TC. All of these effects appeared gradually and only after extended stimulation of the nerve, during which several hundred thousand quanta were released. Consequently, these findings suggest a serial one-time usage of vesicles, with little or no re-entry of recycled vesicles until after a large fraction of the original vesicles has been exhausted. The results primarily show that filling of synaptic vesicles with ACh is crucial for sustaining synaptic transmission, and gives further evidence that the ACh released by nerve impulses originates from these organelles.

Effect of 2-(4-phenylpiperidino)cyclohexanol (AH 5183) on the veratridine-induced increase in acetylcholine synthesis by rat hippocampal tissue

The intent of this study was to determine whether the drug 2-(4-phenylpiperidino)cyclohexanol (AH 5183 or vesamicol) might inhibit the veratridine-induced increase in acetylcholine (ACh) synthesis by reducing the veratridine-induced activation of a detergent-soluble choline-O-acetyltransferase (EC 2.3.1.6; ChAT) fraction associated with a vesicle-bound store of ACh. When minces of rat hippocampal tissue were loaded with [14C]choline and subsequently depolarized with veratridine, an increase in the synthesis of [14C]ACh occurred that could be abolished by L-AH 5183 (75 nM). When minces were depolarized with veratridine in the presence of L-AH 5183 (75 nM), the depolarization-induced activation of a detergent-soluble ChAT fraction associated with a vesicle-bound store of ACh was blocked. Conversely, the veratridine-induced activation of a water-soluble ChAT fraction believed to be cytosolic was not. AH 5183 also blocked the repletion of the vesicle-bound store with newly synthesized ACh following veratridine-induced depletion of ACh, a result that appeared to be mediated by an effect on the synthesis of ACh at the vesicular surface. These results suggest that veratridine depolarization of rat hippocampal nerve terminals stimulates the synthesis of ACh by activating a detergent-soluble fraction of ChAT closely associated with synaptic vesicle release sites. ACh synthesis and transport at the vesicular surface may be influenced by a common AH 5183-sensitive regulatory protein.

Evidence to suggest that the spontaneous release of acetylcholine from rat hippocampal tissue is carrier-mediated

The effect of L- and D-stereoisomers of 2-(4-phenylpiperidino) cyclohexanol (AH 5183) on the spontaneous release of acetylcholine (ACh) from rat hippocampal tissue was studied. L-AH 5183 was approximately 100 times more potent than was D-AH 5183 in reducing spontaneous ACh release. Spontaneous ACh release was also temperature dependent. These results may suggest that the spontaneous release of ACh from brain tissue is carrier-mediated.

Acetylcholine mobilization in a sympathetic ganglion in the presence and absence of 2-(4-phenylpiperidino)cyclohexanol (AH5183)

The present experiments measured the release of acetylcholine (ACh) by the cat superior cervical ganglia in the presence of, and after exposure to, 2-(4-phenylpiperidino)cyclohexanol (AH5183), a compound known to block the uptake of ACh by cholinergic synaptic vesicles. We confirmed that AH5183 blocks evoked ACh release during preganglionic nerve stimulation when approximately 13-14% of the initial ganglial ACh stores had been released; periods of rest in the presence of the drug did not promote recovery from the block, but ACh release recovered following the washout of AH5183. ACh was synthesized in AH5183-treated ganglia, as determined by the synthesis of [3H]ACh from [3H]choline, and this [3H]ACh could be released by stimulation following drug washout. The specific activity of the released ACh matched that of the tissue's ACh, and thus we conclude that ACh synthesized in the presence of AH5183 is a releasable as pre-existing ACh stores once the drug is removed. We tested the relative releasability of ACh synthesized during AH5183 exposure (perfusion with [3H]choline) and that synthesized during recovery from the drug's effects (perfusion with [14C]choline: the ratio of [3H]ACh to [14C]ACh released by stimulation was similar to the ratio in the tissue. These results suggest that the mobilization of ACh for release by ganglia during recovery from an AH5183-induced block is independent of the conditions under which the ACh was synthesized. Unlike nerve impulses, black widow spider venom (BWSV) induced the release of ACh from AH5183-blocked ganglia, even in the drug's continued presence. Venom-induced release of ACh from AH5183-treated ganglia was not less than the venom-induced release from tissues not exposed to AH5183. This effect of BWSV was attributed to the action of the protein, alpha-latrotoxin, because an anti-alpha-latrotoxin antiserum blocked the venom's action. ACh synthesized during AH5183 exposure was labelled from [3H]choline, and subsequent treatment with BWSV released [3H]ACh with the same temporal pattern as the release of total ACh. To exclude a nonexocytotic origin for the [3H]ACh released by BWSV, ganglia were preloaded with [3H]diethylhomocholine to form [3H]acetyldiethylhomocholine, an ACh analogue excluded from vesicles; the venom did not increase the rate of [3H]acetyldiethylhomocholine efflux. It is concluded that a vesicular ACh pool insensitive to the inhibitory action of AH5183 might exist and that this vesicular pool is not mobilized by electrical stimulation to exocytose in the presence of AH5183, but it is by BWSV.

[3H]vesamicol binding in brain: autoradiographic distribution, pharmacology, and effects of cholinergic lesions

An autoradiographic analysis of high-affinity binding sites for the vesicular acetylcholine transport blocker [3H]vesamicol (2-(4-phenylpiperidino) cyclohexanol; AH 5183) was conducted in rat brain. [3H]Vesamicol binding was displaced 52-99% by DPPN [( 2,3,4,8]-decahydro-3-(4-phenyl-1-piperidinyl)-2-napthalenol) (IC50 = 14 nM) and by ketanserin (500 nM), haloperidol (43 nM), and vesamicol analogs, but not by drugs selective for adenosine, adrenergic, amino acid, calcium channel, monoaminergic, opioid, PCP, sigma, or several other receptor classes. [3H]Vesamicol binding was most concentrated in the interpeduncular nucleus and fifth and seventh cranial nerve nuclei. Moderate binding was found in the lateral caudate-putamen, medial nucleus accumbens, olfactory tubercle, vertical and horizontal diagonal bands of Broca, and basolateral amygdala. The distribution of [3H]vesamicol binding was similar to distributions of acetylcholine (r = 0.88), acetylcholine esterase (r = 0.97), choline acetyltransferase (ChAT) (r = 0.97), and [3H]hemicholinium-3 binding sites (r = 0.95-0.99). Lower correlations were obtained between [3H]vesamicol and muscarinic receptor densities (r = 0.50-0.70). Few exceptions to the match between binding and cholinergic neuronal markers were found, e.g., the molecular layer of the cerebellum and the thalamus. Lesions of cholinergic neuronal projections to the neocortex or hippocampus reduced [3H]vesamicol binding in each of these regions, but to a lesser extent than reductions in ChAT. [3H]Vesamicol binding sites appear to be anatomically associated with brain cholinergic neurons, a locus that is consistent with the control by this site of vesicular acetylcholine uptake.

Dipalmitoylphosphatidylcholine liposomes inhibit calcium-dependent [3H]acetylcholine release

We examined the effects of small unilamellar vesicles composed of dipalmitoylphosphatidylcholine on rat cerebral cortical [3H]acetylcholine release. Synaptosomes from this region were loaded with the labeled transmitter, and then incubated with the lipid (0-6 mg/ml) for specified intervals before adding various secretagogues. Liposomes (0.4 mg/ml-6 mg/ml) inhibited the calcium-dependent release of [3H]acetylcholine induced by 50 mM K+, A23187 (1-5 micrograms/ml) or 500 microM ouabain; the calcium-independent release induced by ouabain was not affected by the highest liposome concentration studied (6 mg/ml). [3H]Acetylcholine levels were also reduced by the liposomes, but higher concentrations were necessary to do so than to reduce K+-induced release. These reductions occurred in the S3 (cytosol) but not P3 (microsomal) subcellular fraction of the nerve terminals. The 50 mM K+-induced induced release of [3H]norepinephrine and [3H]dopamine from cerebral cortical and striatal synaptosomes, respectively, were not affected by 6 mg/ml lipid. Together, these results suggest that the dipalmitoylphosphatidylcholine liposomes may modulate cholinergic transmission presynaptically at the level of the calcium-dependent transmitter-release process.

Cetiedil, a drug that inhibits acetylcholine release in Torpedo electric organ

The effects of cetiedil, a vasodilatator substance with reported anticholinergic properties, were examined on cholinergic presynaptic functions at the nerve electroplaque junction of Torpedo marmorata using either synaptosomes or slices of intact tissue. Cetiedil abolished the calcium-dependent release of acetylcholine (ACh) triggered by depolarization or by addition of A23187 ionophore, a finding localizing the site of action downstream from the calcium entry step. In addition, a direct effect on the release process itself was indicated by the observation that cetiedil blocks the release of ACh mediated by a recently isolated presynaptic membrane protein, the mediatophore, reconstituted into ACh-containing proteoliposomes. In all three preparations, ACh release was inhibited by cetiedil with a Ki of 5-8 microM. Under the conditions used in these release experiments, the synthesis of ACh and its compartmentation within the nerve terminals were not modified. However, the drug was able to reduce high-affinity choline uptake and vesicular ACh incorporation when it was given together with the radioactive precursor, a result showing that cetiedil has a broad inhibitory action on cholinergic uptake processes.

Effects of ovariectomy and estradiol benzoate on high affinity choline uptake, ACh synthesis, and release from rat cerebral cortical synaptosomes

Several presynaptic processes were studied in cerebral cortical synaptosomes prepared from intact adult female rats or from ovariectomized animals that received 3 subcutaneous injections of either estradiol benzoate (10 micrograms/kg) or vehicle. Injections were given 1/day, every other day, and animals were sacrificed 1 h after the last injection. High affinity choline uptake and coupled acetylcholine (ACh) synthesis were reduced by ovariectomy, and restored to control levels by the estradiol benzoate injections. In contrast, low affinity choline uptake and depolarization-induced [3H]ACh release were unaffected by either ovariectomy or estradiol benzoate injections. These results suggest that changes in estradiol levels may alter the high affinity transport process regulating ACh synthesis in this tissue.

Quantitative autoradiography of brain binding sites for the vesicular acetylcholine transport blocker 2-(4-phenylpiperidino)cyclohexanol (AH5183)

2-(4-Phenylpiperidino)cyclohexanol (AH5183) is a noncompetitive and potent inhibitor of high-affinity acetylcholine transport into cholinergic vesicles. It is reported here that [3H]AH5183 binds specifically and saturably to slide-mounted sections of the rat forebrain (Kd = 1.1 to 2.2 X 10(-8) M; Bmax = 286 to 399 fmol/mg of protein). The association and dissociation rate constants for [3H]AH5183 binding are 8.6 X 10(6) M-1 X min-1 and 0.18 min-1, respectively. Bound [3H]AH5183 can be displaced by nonradioactive AH5183 and by the structural analog (2 alpha,3 beta,4A beta,8A alpha)-decahydro-3-(4-phenyl-1-piperidinyl)-2- naphthalenol but not by 10 microM concentrations of the cholinergic drugs acetylcholine, choline, atropine, hexamethonium, eserine, or hemicholinium-3 or by the structurally related compounds 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, 1-methyl-4-phenylpyridine, (+/-)-N-allylnormetazocine (SKF 10,047), levoxadrol, or dexoxadrol. Quantitative autoradiography reveals that [3H]AH5183 binding sites are distributed heterogenously throughout the rat forebrain and are highly localized to cholinergic nerve terminal regions. At the level of the caudate nucleus-putamen, the highest concentrations of saturable [3H]AH5183 binding (713-751 fmol/mg of protein) are found in the vertical limb of the diagonal band and the olfactory tubercle, with lesser amounts (334-516 fmol/mg of protein) in the caudate-putamen, nucleus accumbens, superficial layers of the cerebral cortex, and the primary olfactory cortex. At day 7 after transsection of the left fimbria, [3H]AH5183 binding and choline acetyltransferase activity in the left hippocampus were reduced by 33 +/- 6% and 61 +/- 7%, respectively. These findings indicate that [3H]AH5183 binds to a unique recognition site in rat brain that is topographically associated with cholinergic nerve terminals.

Effect of 2-(4-phenylpiperidino)cyclohexanol on acetylcholine release and subcellular distribution in rat striatal slices

These experiments measured the effect of 2-(4-phenylpiperidino)cyclohexanol (AH5183) on the release of acetylcholine (ACh) and its subcellular distribution in slices of rat striatum incubated in vitro. The AH5183, a drug that blocks the uptake of ACh by isolated synaptic vesicles, reduced the release of ACh from slices stimulated to release transmitter in response to K+ depolarization. Tissue stimulated in the presence of AH5183 contained more ACh in a nerve terminal cytoplasmic fraction than did tissue stimulated in the drug's absence, but stimulation in AH5183's presence reduced the amount of ACh measured in fractions containing synaptic vesicles. The depletion of ACh caused by stimulating tissue in the presence of AH5183 was more evident in the fraction of nerve terminal ACh occluded within synaptic vesicles as isolated by gradient centrifugation (fraction D) than it was in other nerve terminal occluded stores. It is concluded that the synaptic vesicles isolated as fraction D under the present experimental conditions likely contain releasable transmitter. The AH5183 also depressed the spontaneous release of ACh from incubated slices of striatum and this effect was evident in the presence or the absence of medium Ca2+. It is suggested that this effect might indicate that the process of spontaneous ACh release measured neurochemically results, in part, from an AH5183-sensitive carrier-mediated process.

Storage and release of acetylcholine in rat cortical synaptosomes: effects of D,L-2-(4-phenylpiperidino)cyclohexanol (AH5183)

A post-stimulation synthesis of acetylcholine (ACh), its incorporation into a 'stable-bound' (vesicular) compartment and subsequent release, were compared in K+-stimulated synaptosomes, in the absence and presence of 10 microM AH5183. The drug depressed by 16% the net intrasynaptosomal formation of ACh from 1 microM [3H]choline (Ch) in the medium, by competitively inhibiting (Ki approximately equal to 20 microM) the high-affinity Ch transport, but it had no direct effect on the intraterminal synthesis of ACh per se. The drug reduced incorporation of newly synthesized [3H]ACh into synaptic vesicles by 55% and subsequent K+-depolarization-induced release of [3H]ACh by 83%, although it had no effect on Ca2+ influx into synaptosomes. These results are consistent with the hypothesis that AH5183 blocks cholinergic neurotransmission presynaptically by interfering with recharging of synaptic vesicles with ACh. Since the reduction of ACh release in the presence of AH5183 had no direct effect on ACh synthesis, these results also suggest that the transmitter release is not prerequisite for enhancement of Ch uptake and ACh synthesis in stimulated nerve terminals.

Reduction of quantal size by vesamicol (AH5183), an inhibitor of vesicular acetylcholine storage

Isolated unparalysed mouse phrenic nerve-hemidiaphragm preparations were indirectly stimulated in the presence of 2-(4-phenylpiperidino)cyclohexanol (AH5183, vesamicol). Spontaneous miniature endplate potentials were subsequently studied. They exhibited a large depression of amplitude which was more profound at higher stimulation frequencies and drug concentration. No post-junctional effects of the drug were observed. Since the drug blocks storage of acetylcholine by isolated synaptic vesicles, it is argued that the results support the theory of vesicular release of acetylcholine.

Aging decreases the sensitivity of rat cortical synaptosomes to calcium ionophore-induced acetylcholine release

The capacity of calcium ions to trigger acetylcholine release was studied in cerebral cortical synaptosomes from adult (6-month-old) and senescent (24-month-old) rats, using a calcium ionophore, A23187, that bypasses voltage-sensitive calcium channels. The potency but not the efficacy of the A23187 was reduced with respect to releasing acetylcholine (ACh) in the aged animals. There was no age-related difference in the synthesis of ACh or potency of the ionophore with respect to increasing 45calcium uptake. These results suggest that aging reduces the sensitivity of cerebral cortical nerve terminals to calcium-triggered ACh-release.