Cigarette smoke alters non-neuronal cholinergic system components inducing MUC5AC production in the H292 cell line

Cigarette smoke extract (CSE) affects the expression of Choline Acetyl-Transferase (ChAT), muscarinic acetylcholine receptors, and mucin production in bronchial epithelial cells. Mucin 5AC (MUC5AC), muscarinic acetylcholine receptor M3, ChAT expression, acetylcholine levels and acetylcholine binding were measured in a human pulmonary mucoepidermoid carcinoma cell line (H292) stimulated with CSE. We performed ChAT/RNA interference experiments in H292 cells stimulated with CSE to study the role of ChAT/acetylcholine in MUC5AC production. The effects of Hemicholinium-3 (HCh-3) (50 μM) (a potent and selective choline uptake blocker) and Tiotropium bromide (Spiriva(®)) (100 nM), alone or in combination with Salmeterol (SL) and Fluticasone propionate (FP), were tested in this model. MUC5AC, muscarinic acetylcholine receptor M3, ChAT, acetylcholine expression and acetylcholine binding significantly increased in H292 cells stimulated with CSE (5%) compared to untreated cells. HCh-3 reduced acetylcholine binding and MUC5AC production in H292 cells stimulated with CSE. ChAT/RNA interference eliminated the effect of CSE on MUC5AC production. FP reduced ChAT and acetylcholine binding in unstimulated cells, while showing a partial effect in CSE stimulated cells. SL increased the ChAT expression and acetylcholine binding in H292 cells stimulated with or without CSE. Tiotropium, alone or together with FP and SL, reduced acetylcholine binding and MUC5AC production in H292 cells stimulated with CSE. CSE affects the ChAT/acetylcholine expression, increasing MUC5AC production in H292 cells. Pharmacological treatment with anticholinergic drugs reduces the secretion of MUC5AC generated by autocrine acetylcholine activity in airway epithelial cells.

Choline promotes nicotinic receptor alpha4 + beta2 up-regulation

Neuronal nicotinic acetylcholine receptors (nAChR) composed of alpha4 + beta2 subunits, the high affinity nicotine-binding site in the mammalian brain, up-regulate in response to chronic nicotine exposure. The identities of endogenous mediators of this process are unknown. We find that choline also up-regulates alpha4 + beta2 nAChRs stably expressed by HEK293 cells as measured by increased [(3)H]epibatidine density. Choline-mediated up-regulation is dose-dependent and corresponds with an increase in beta2 subunit protein expression. The choline kinase inhibitor hemicholinium-3 inhibits approximately 60% of choline-mediated up-regulation revealing both an HC3-dependent and -independent pathway. Furthermore, choline-mediated up-regulation is not additive with up-regulation agents such as nicotine, but it is additive with weaker promoters of the up-regulation process. When co-applied with the pro-inflammatory cytokine tumor necrosis factor alpha, choline-mediated up-regulation is increased further through a mechanism that includes an increase in both alpha4 and beta2 protein expression, and this is inhibited by the p38 MAPK inhibitor SB202190. These findings extend the view that up-regulation of alpha4 + beta2 nAChRs is a normal physiological response to altered metabolic and inflammatory conditions.

Increase of plasma insulin by racecadotril, an inhibitor of enkephalinase, in Wistar rats

Racecadotril is known as an inhibitor of enkephalinase. Increase of plasma insulin by racecadotril has been observed in rats while the mechanism of the action remains obscure. In the present study, intravenous injection of male Wistar rats with racecadotril significantly decreased blood glucose levels. However, this effect of racecadotril was not modified by naloxone at the dose sufficient to block opioid receptors. Thus, the blood glucose-lowering action of racecadotril might be through an endogenous opioid independent mechanism. Otherwise, we found that C-peptide content was also raised by racecadotril in parallel with the increase of insulin in Wistar rats. Thus, the blood glucose-lowering action of racecadotril was related to insulin secretion, but not through the inhibition of plasma insulin degradation. In addition, racecadotril showed no direct effect on insulin secretion in isolated islets or cultured HIT-T15 beta cells. The increase of plasma insulin and blood glucose-lowering action induced by racecadotril were reduced by pretreatment with atropine and enhanced by physotigmine. Direct inhibition of cholinesterase was not observed in brain homogenates treated with racecadotril. Moreover, actions of racecadotril were significantly reduced in rats receiving hemicholinium-3 at a sufficient dose to decrease endogenous acetylcholine. Activation of cholinergic tone is possibly involved in the blood glucose-lowering effect of racecadotril. Our results suggested that racecadotril increased insulin secretion to lower blood glucose mainly via regulation of parasympathetic tone in Wistar rats.

Determination of high-affinity choline uptake (HACU) and choline acetyltransferase (ChAT) activity in the same population of cultured cells

Cholinergic neurons are a major constituent of the mammalian central nervous system. Acetylcholine, the neurotransmitter used by cholinergic neurons, is synthesized from choline and acetyl CoA by the enzymatic action of choline acetyltransferase (ChAT). The transport of choline into the cholinergic neurons, which results in synthesis of ACh, is hemicholinium-sensitive and is referred to as high-affinity choline uptake (HACU). Thus, the formation of acetylcholine in cholinergic neurons largely depends on both the levels of choline being transported into the cells from the extracellular space and the activity of ChAT. Several methods were described previously to measure HACU and ChAT simultaneously in synaptosomes, but the same for cultured cells is lacking. We describe a procedure to measure HACU and ChAT at the same time in cultured cells by simple techniques employing radionuclides. In this procedure, we determined quantitatively hemicholinium-sensitive choline uptake and ChAT enzyme activity in a small number of differentiated human neuroblastoma (SK-N-SH) cells. We also determined the kinetics of choline uptake in the SK-N-SH cells. We believe that these simple methods can be used for neurochemical and drug discovery studies in several models of neurodegenerative disorders including Alzheimer's disease.

Complex of Amyloid β Peptides with 24-Hydroxycholesterol and Its Effect on Hemicholinium-3 Sensitive Carriers

Brains of Alzheimer disease patients in early stages of dementia contain an increased 24(S)-hydroxycholesterol (cerebrosterol)/cholesterol ratio when compared to controls. In this study, effects of amyloid beta peptides and of racemic 24-hydroxycholesterol were evaluated in vitro on undepleted or cholesterol-depleted hippocampal synaptosomes of young and old rats via a high-affinity choline transport and membrane anisotropy measurements. Depletion of membrane cholesterol decreased the transport of [3H]choline, increased the specific binding of [3H]hemicholinium-3 and decreased membrane anisotropy. However, less alterations were found in old when compared to young brains. 500 nM nonaggregated peptides were ineffective but aggregated fragment 1-42 evoked marked drops in the transport and anisotropy values on depleted synaptosomes. 50 microM 24-hydroxycholesterol inhibited choline transport on depleted synaptosomes but it did not influence membrane anisotropy. Peptides eliminated the actions of oxysterol on choline carriers in young but not in old rats. On the other hand, oxysterol eliminated the effects of peptides on membrane anisotropy. Our study suggests a possible role of membrane cholesterol in the regulation of choline carriers and supports data reporting a protective role of membrane cholesterol against toxic effects of amyloid beta peptides. Moreover, via Raman spectroscopy we demonstrate for the first time that peptides form a complex with 24-hydroxycholesterol.

The involvement of the central cholinergic system in the pressor and bradycardic effects of centrally administrated melittin in normotensive conscious rats

Recently we demonstrated that centrally administrated melittin, a phospholipase A(2) (PLA(2)) activator, caused pressor and bradycardic effect in the normotensive conscious rats. In the current study we aimed to determine the mediation of central cholinergic system in the pressor and bradycardic effect of centrally administrated melittin. Studies were performed in normotensive male Sprague-Dawley rats. 1.5, 3.0 or 6.0microg/5.0microl doses of melittin were injected intracerebroventricularly (i.c.v.). Melittin caused dose- and time-dependent increases in mean arterial pressure (MAP) and decrease in heart rate (HR). In order to test the mediation of central cholinergic system on the pressor and bradycardic effect of melittin, the rats were pretreated with mecamylamine (50microg; i.c.v.), cholinergic nonselective nicotinic receptor antagonist, atropine sulfate (10microg; i.c.v.), a cholinergic nonselective muscarinic receptor antagonist, hemicholinium-3 (20microg; i.c.v.), a high affinity neuronal choline uptake inhibitor, methyllycaconitine (10 and 25microg; i.c.v.) or alpha-bungarotoxin (10 and 25microg; i.c.v.), selective antagonists of alpha-7 subtype nicotinic acetylcholine receptors (alpha7nAChRs), 15min prior to melittin (3.0microg) injection. Pretreatment with mecamylamine, hemicholinium-3, methyllycaconitine or alpha-bungarotoxin partially attenuated the pressor and bradicardia effect of elicited by melittin in the normotensive conscious rats whereas pretreatment with atropine had no effect. In conclusion, i.c.v. administration of melittin increases MAP and decreases HR in conscious rats. The activation of central nicotinic cholinergic receptors, predominantly alpha7nAChRs, partially acts as a mediator in the pressor responses to i.c.v. injection of melittin in the normotensive conscious rats. Moreover, decreased uptake of choline to the cholinergic terminals may consider that melittin activates central choline and acetylcholine release, as well.

Reduction in CHT1-mediated choline uptake in primary neurons from presenilin-1 M146V mutant knock-in mice

The memory loss in Alzheimer's disease (AD) has been linked to cholinergic hypoactivity. Mutations in presenilin-1 (PS-1) may regulate cholinergic signaling, although their precise roles in cholinergic neurotransmission in AD are unsettled. Neuronal uptake of choline via the high affinity choline transporter (CHT1) is essential for cholinergic neurotransmission. CHT1 is a Na+-dependent, hemicholinium-3 (HC-3)-sensitive choline transporter. Although cholinergic neurons in the nucleus basalis of Meynert are a major source of cholinergic projections for the cerebral cortex, it is unclear whether cortical neurons exhibit intrinsic CHT1 activity that is altered in AD. We now report that primary cortical neurons express intrinsic and biologically active CHT1, and that, in these neurons, CHT1-mediated choline uptake activity is significantly reduced in PS-1 M146V mutant knock-in mice. Further kinetic studies using HC-3 binding and cell surface biotinylation assays showed that the PS-1 mutation inhibits CHT1 mediated choline uptake by reducing the ligand binding affinity of CHT1 without significantly altering levels of CHT1 expression in the plasma membrane. Since human neocortex has recently been shown to possess intrinsic cholinergic innervation, our results indicate that alterations in CHT1-mediated high affinity choline uptake in cortical neurons may contribute to Alzheimer's dementia.

Na+, Cl-, and pH dependence of the human choline transporter (hCHT) in Xenopus oocytes: the proton inactivation hypothesis of hCHT in synaptic vesicles

The recent cloning of the human choline transporter (hCHT) has allowed its expression in Xenopus laevis oocytes and the simultaneous measurement of choline transport and choline-induced current under voltage clamp. hCHT currents and choline transport are evident in cRNA-injected oocytes and significantly enhanced by the hCHT trafficking mutant L530A/V531A. The charge/choline ratio of hCHT varies from 10e/choline at -80 mV to 3e/choline at -20 mV, in contrast with the reported fixed stoichiometry of the Na+-coupled glucose transporter in the same gene family. Ion substitution shows that the choline uptake and choline-induced current are Na+ and Cl- dependent; however, the reversal potential of the induced current suggests a Na+-selective mechanism, consigning Cl- to a regulatory role rather than a coupled, cotransported-ion role. The hCHT-specific inhibitor hemicholinium-3 (HC-3) blocks choline uptake and choline-induced current; in addition, HC-3 alone reveals a constitutive, depolarizing leak current through hCHT. We show that external protons reduce hCHT current, transport, and binding with a similar pKa of 7.4, suggesting proton titration of residue(s) that support choline binding and transport. Given the localization of the choline transporter to synaptic vesicles, we propose that proton inactivation of hCHT prevents acetylcholine and proton leakage from the acidic interior of cholinergic synaptic vesicles. This mechanism would allow cholinergic, activity-triggered delivery of silent choline transporters to the plasma membrane, in which normal pH would reactivate the transporters for choline uptake and subsequent acetylcholine synthesis.

Deficits in acetylcholine homeostasis, receptors and behaviors in choline transporter heterozygous mice

Cholinergic neurons elaborate a hemicholinium-3 (HC-3) sensitive choline transporter (CHT) that mediates presynaptic, high-affinity choline uptake (HACU) in support of acetylcholine (ACh) synthesis and release. Homozygous deletion of CHT (-/-) is lethal shortly after birth (Ferguson et al. 2004), consistent with CHT as an essential component of cholinergic signaling, but precluding functional analyses of CHT contributions in adult animals. In contrast, CHT+/- mice are viable, fertile and display normal levels of synaptosomal HACU, yet demonstrate reduced CHT protein and increased sensitivity to HC-3, suggestive of underlying cholinergic hypofunction. We find that CHT+/- mice are equivalent to CHT+/+ siblings on measures of motor co-ordination (rotarod), general activity (open field), anxiety (elevated plus maze, light/dark paradigms) and spatial learning and memory (Morris water maze). However, CHT+/- mice display impaired performance as a result of physical challenge in the treadmill paradigm, as well as reduced sensitivity to challenge with the muscarinic receptor antagonist scopolamine in the open field paradigm. These behavioral alterations are accompanied by significantly reduced brain ACh levels, elevated choline levels and brain region-specific decreased expression of M1 and M2 muscarinic acetylcholine receptors. Our studies suggest that CHT hemizygosity results in adequate baseline ACh stores, sufficient to sustain many phenotypes, but normal sensitivities to physical and/or pharmacological challenge require full cholinergic signaling capacity.

The Caenorhabditis elegans choline transporter CHO-1 sustains acetylcholine synthesis and motor function in an activity-dependent manner

Cholinergic neurotransmission supports motor, autonomic, and cognitive function and is compromised in myasthenias, cardiovascular diseases, and neurodegenerative disorders. Presynaptic uptake of choline via the sodium-dependent, hemicholinium-3-sensitive choline transporter (CHT) is believed to sustain acetylcholine (ACh) synthesis and release. Analysis of this hypothesis in vivo is limited in mammals because of the toxicity of CHT antagonists and the early postnatal lethality of CHT-/- mice (Ferguson et al., 2004). In Caenorhabditis elegans, in which cholinergic signaling supports motor activity and mutant alleles impacting ACh secretion and response can be propagated, we investigated the contribution of CHT (CHO-1) to facets of cholinergic neurobiology. Using the cho-1 promoter to drive expression of a translational, green fluorescent protein-CHO-1 fusion (CHO-1:GFP) in wild-type and kinesin (unc-104) mutant backgrounds, we establish in the living nematode that the transporter localizes to cholinergic synapses, and likely traffics on synaptic vesicles. Using embryonic primary cultures, we demonstrate that CHO-1 mediates hemicholinium-3-sensitive, high-affinity choline uptake that can be enhanced with depolarization in a Ca(2+)-dependent manner supporting ACh synthesis. Although homozygous cho-1 null mutants are viable, they possess 40% less ACh than wild-type animals and display stress-dependent defects in motor activity. In a choline-free liquid environment, cho-1 mutants demonstrate premature paralysis relative to wild-type animals. Our findings establish a requirement for presynaptic choline transport activity in vivo in a model amenable to a genetic dissection of CHO-1 regulation.

Acetyl-l-carnitine protects striatal neurons against in vitro ischemia: The role of endogenous acetylcholine

The neuronal death after ischemia is closely linked to the essential role of mitochondrial metabolism. Inhibition of mitochondrial respiratory chain reduces ATP generation leading to a dysregulation of ion metabolism. Acetyl-L-carnitine (ALC) influences the maintenance of key mitochondrial proteins for maximum energy production and it may play a neuroprotective role in some pathological conditions. In this study we have analyzed ALC-mediated neuroprotection on an in vitro model of brain ischemia. Field potential recordings were obtained from a rat corticostriatal slice preparation. In vitro ischemia (oxygen and glucose deprivation) was delivered by switching to a solution in which glucose was omitted and oxygen was replaced with N2. Ten minutes of in vitro ischemia caused an irreversible loss of the field potential amplitude. Pretreatment with ALC produced a progressive and dose-dependent recovery of the field potential amplitude following in vitro ischemia. The neuroprotective effect of ALC was stereospecific since the pretreatment with two different carnitine-related compounds did not cause neuroprotection. The choline transporter inhibitor hemicholinium-3 blocked the neuroprotective effect of ALC. ALC-mediated neuroprotection was also prevented either by the non-selective muscarinic antagonist scopolamine, or by the putative M2-like receptor antagonist methoctramine. Conversely, the effect of ALC was not altered by the M1-like receptor antagonist pirenzepine. These findings show that ALC exert a neuroprotective action against in vitro ischemia. This neuroprotective effect requires the activity of choline uptake system and the activation of M2 muscarinic receptors.

Reduced expression and capacity of the striatal high-affinity choline transporter in hyperdopaminergic mice

Behavioral and neuronal abnormalities observed in mice exhibiting a reduced expression of the dopamine transporter model important aspects of schizophrenia, addiction, and attentional disorders. As the consequences of a chronic hyperdopaminergic tone for striatal output regulation have remained poorly understood, the present experiments were designed to determine the status of striatal interneuronal cholinergic neurotransmission in dopamine transporter knockdown animals. The high-affinity choline transporter represents the rate-limiting step of acetylcholine synthesis and release. Compared with wild type mice, striatal high-affinity choline transporter expression in dopamine transporter knockdown mice was significantly decreased. As in vivo basal striatal acetylcholine release did not differ between the strains, reduced high-affinity choline transporter expression in dopamine transporter knockdown mice was not due to reduced basal cholinergic activity. Furthermore, the proportion of high-affinity choline transporters expressed in plasma membrane-enriched versus vesicular membrane-enriched fractions did not differ from wild type animals, suggesting that changes in intracellular high-affinity choline transporter trafficking were not associated with lower overall levels of striatal high-affinity choline transporters. Synaptosomal choline uptake assays indicated a reduced capacity of striatal high-affinity choline transporters in dopamine transporter knockdown mice, and thus the functional significance of the reduced level of high-affinity choline transporter expression. Likewise, in vivo measures of the capacity of striatal high-affinity choline transporters to clear increases in extracellular choline concentrations, using choline-sensitive microelectrodes, revealed a 37-41% reduction in hemicholinium-sensitive clearance of exogenous choline in dopamine transporter knockdown mice. Furthermore, clearance of potassium-evoked choline signals was reduced in dopamine transporter knockdown mice (1.63+/-0.15 microM/s) compared with wild type animals (2.29+/-0.21 microM/s). Dysregulated striatal cholinergic neurotransmission is hypothesized to disrupt the integration of thalamic and cortical information at spiny projection neurons and thus to contribute to abnormal striatal information processing in dopamine transporter knockdown mice.

Inhibitory effect of hemicholinium-3 on presynaptic nicotinic acetylcholine receptors located on the terminal region of myenteric motoneurons

Previously we have demonstrated the presence of presynaptic nicotinic acetylcholine receptors on the terminals of myenteric neurons in Auerbach's plexus of guinea-pig ileum. During these studies we observed, that the presence of hemicholinium-3, an inhibitor of the high affinity choline uptake significantly influences the contraction of the longitudinal muscle strip preparation. Our aim was to investigate the neurochemical background of this effect and quantitatively characterize the action of HC-3. We studied the effect of HC-3 on epibatidine- and electrical stimulation-evoked contraction and release of [3H]acetylcholine from the guinea-pig longitudinal muscle strip preparation. We found that in the presence of tetrodotoxin, when the contribution of somatodendritic nicotinic acetylcholine receptors to the response was prevented due to the inhibition of axonal conduction, HC-3 inhibited the epibatidine-evoked contraction and [3H]acetylcholine release in the submicromolar range (IC50 = 897 nM and IC50 = 693 nM, respectively), whereas the electrical stimulation-evoked contraction was not affected by HC-3, and the release of [3H]acetylcholine was apparently enhanced. Our data indicate that HC-3 inhibits the presynaptic nicotinic acetylcholine receptors of myenteric neurons. Since these receptors play an important role in the regulation of cholinergic neurotransmission in the enteric nervous system, the use of HC-3 in [3H]acetylcholine release experiments might bias the interpretation of data.

Increase of insulin secretion by ginsenoside Rh2 to lower plasma glucose in Wistar rats

1. The aim of the present study was to clarify the role of ginsenoside Rh2 as the active compound in Panax ginseng root for lowering plasma glucose in animals. 2. Plasma glucose was assessed using the glucose oxidase method. Changes in the levels of insulin and C-peptide in plasma were measured by ELISA using commercially available kits. 3. After intravenous injection into fasting Wistar rats for 60 min, ginsenoside Rh2 (0.1-1.0 mg/kg) decreased plasma glucose in a dose-dependent manner. In parallel with the decrease in plasma glucose, increases in plasma insulin levels, as well as plasma C-peptide, were observed in rats receiving the same treatment. These effects of Rh2 were reversed by atropine (0.1-1.0 mg/kg), but not affected by the ganglionic nicotinic antagonists pentolinium or hexamethonium (both at 7.5 mg/kg). 4. Disruption of synaptically available acetylcholine (ACh) using an inhibitor of choline uptake (hemicholinium-3; 1-10 microg/kg) or an inhibitor of vesicular ACh transport (vesamicol; 1.5-3.5 mg/kg) abolished the actions of Rh2. In addition, physostigmine (0.1-0.5 mg/kg), at a concentration sufficient to inhibit acetylcholinesterase, enhanced the actions of the ginsenoside Rh2. Thus, mediation of the effects of Rh2 to enhance insulin secretion by ACh released from nerve terminals can be considered. 5. Blockade of the increase in plasma insulin and the plasma glucose-lowering action of Rh2 by 4-diphenylacetoxy-N-methylpiperdine methiodide (4-DAMP; 5-10 microg/kg) indicates the participation of muscarinic M(3) receptors. Increases in plasma C-peptide level induced by Rh2 were also sensitive to 4-DAMP. 6. The results of the present study suggest that ginsenoside Rh2 has the ability to increase insulin secretion as a result of the release of ACh from nerve terminals that then stimulates muscarinic M(3) receptors in pancreatic cells. This finding shows the mechanism for the plasma glucose-lowering action of ginsenoside Rh2, that is one of the major principles contained in P. ginseng root. Thus, ginsenoside Rh2 may be applied as an adjuvant for the management of diabetes.

Cortical choline transporter function measured in vivo using choline-sensitive microelectrodes: clearance of endogenous and exogenous choline and effects of removal of cholinergic terminals

The capacity of the high-affinity choline transporter (CHT) to import choline into presynaptic terminals is essential for acetylcholine synthesis. Ceramic-based microelectrodes, coated at recording sites with choline oxidase to detect extracellular choline concentration changes, were attached to multibarrel glass micropipettes and implanted into the rat frontoparietal cortex. Pressure ejections of hemicholinium-3 (HC-3), a selective CHT blocker, dose-dependently reduced the uptake rate of exogenous choline as well as that of choline generated in response to terminal depolarization. Following the removal of CHTs, choline signal recordings confirmed that the demonstration of potassium-induced choline signals and HC-3-induced decreases in choline clearance require the presence of cholinergic terminals. The results obtained from lesioned animals also confirmed the selectivity of the effects of HC-3 on choline clearance in intact animals. Residual cortical choline clearance correlated significantly with CHT-immunoreactivity in lesioned and intact animals. Finally, synaptosomal choline uptake assays were conducted under conditions reflecting in vivo basal extracellular choline concentrations. Results from these assays confirmed the capacity of CHTs measured in vivo and indicated that diffusion of substrate away from the electrode did not confound the in vivo findings. Collectively, these results indicate that increases in extracellular choline concentrations, irrespective of source, are rapidly cleared by CHTs.

The lateral septal area is involved in the pressor pathway activated by microinjection of norepinephrine into the rat brain cingulate cortex

The cingulate cortex (CC) is involved in cardiovascular regulation. Microinjection of norepinephrine (NE) into the Cg3 area of the CC caused vasopressin release and pressor responses in unanesthetized rats. Microinjection of acetylcholine (ACh) into the lateral septal area (LSA) of unanesthetized rats caused similar vasopressin-related pressor responses. The LSA is anatomically connected to the CC and the paraventricular nucleus (PVN) of the hypothalamus, an important nucleus involved in vasopressin synthesis. Therefore, we attempted to verify if the cholinergic neurotransmission within the LSA is involved in the mediation of the pressor response to the microinjection of NE into the Cg3. Local pretreatment with lidocaine, muscimol, atropine or hemicholinium-3 microinjected into the LSA blocked the pressor response to the microinjection of NE injection into the Cg3. Conversely, pretreatment with physostigmine microinjected into the LSA potentiated the pressor response to NE injection into the Cg3. The present results indicate that the synapses in the LSA are part of the pressor pathway originating at the CC and that cholinergic neurotransmission within the LSA is involved in the mediation of the cardiovascular responses to the microinjection of NE into the Cg3.

Chronic treatment with amyloid β1–42 inhibits non-cholinergic high-affinity choline transport in NG108-15 cells through protein kinase C signaling

We investigated the influence of the amyloid-beta-peptide(1-42) on hemicholinum-3-sensitive high-affinity choline uptake in NG108-15 cells. RT-PCR analysis revealed the presence of mRNA for a choline transporter-like protein but not for cholinergic high-affinity choline transporter. Differentiation of cells increased both hemicholinum-3-sensitive choline uptake and high-affinity hemicholinium-3 binding. This transport was not influenced by tenfold excess of carnitine. Continuous presence of submicromolar concentrations of amyloid-beta-peptide(1-42) during differentiation resulted in a decrease of both choline uptake and hemicholinium-3 binding. These effects were not present when amyloid-beta-peptide(1-42) was added 5 min prior to measurements. Neither differentiation nor amyloid-beta-peptide(1-42) treatment changed levels of choline transporter-like protein mRNA. Protein kinase C inhibition by staurosporine or its inactivation by continuous presence of tetradecanoyl phorbol acetate prevented the inhibitory effect of amyloid-beta-peptide(1-42) treatment on choline uptake. Activation of protein kinase C by tetradecanoyl phorbol acetate during measurement had inhibitory effect on choline uptake in control but not amyloid-beta-peptide(1-42)-treated cells. The concentration of amyloid-beta-peptide(1-42) maximally effective on hemicholinium-3-sensitive choline uptake had no effect on cell growth, oxidative activity, membrane integrity, number of surface muscarinic receptors, caspase-3 and -8 activities, or uptake of deoxyglucose. Results demonstrate that long-term treatment with non-toxic concentrations of amyloid-beta-peptide(1-42) downregulates choline uptake presumably mediated by a choline transporter-like protein through activation of protein kinase C signaling. The decrease of choline uptake may have relevance to the pathogenesis of Alzheimer's disease.

The effects of chemical or surgical deafferentation on [3H]-acetylcholine release from rat spinal cord

Cholinergic modulation of nociceptive transmission through both nicotinic and muscarinic receptors in the spinal cord represents an important mechanism in pain signaling. However, what neuronal elements release acetylcholine and how release might change in response to deafferentation are unclear. The present studies demonstrated Ca++- and K+-dependent release of [3H]-acetylcholine from slices of regional areas of rat spinal cord. That [3H]-acetylcholine was synthesized from [3H]-choline was demonstrated by the lack of [3H]-acetylcholine release following incubation with either the choline uptake inhibitor hemicholinium or the choline acetyltransferase inhibitor bromoacetylcholine. Rats treated neonatally with capsaicin or with spinal nerve ligation as adults showed a significantly decreased K+-stimulated release of [3H]-acetylcholine from dorsal horn but not ventral horn lumbar spinal cord slices. In rats subjected to dorsal rhizotomy, while basal release from lumbar dorsal spinal cord slices was reduced, K+-stimulated [3H]-acetylcholine release, while decreased, was not significantly different compared with controls. The data presented here show that there are regional differences in the release of acetylcholine from spinal cord and that this release can be modulated by chemical or surgical deafferentation. These results also indicate that the source of acetylcholine in the dorsal cord originates mainly from resident somata and their collaterals, interneurons and/or descending terminals, with only very minor contributions coming from primary afferents. The present data help to further elucidate the role of acetylcholine in spinal signaling, particularly with respect to the effects of nerve injury and nociceptive neurotransmission.

The stimulant cathartic, emodin, contracts the rat isolated ileum by triggering release of endogenous acetylcholine

Anthraquinone stimulant cathartics, such as emodin, are believed to increase the rate of contraction of ileum tissue in vitro via multiple mechanisms. The aim of this study was to probe the effects of emodin on acetylcholine (ACh)-induced contraction of the rat isolated ileum preparation. 2 Ileal sections were incubated in Tyrode's solution and responses to methacholine, ACh and emodin obtained in the absence and presence of the muscarinic antagonist atropine and the choline uptake inhibitor hemicholinium (HC-3). Depletion of endogenous ACh in the presence of HC-3 was achieved by construction of an ACh dose-response curve, using exogenous ACh, prior to re-testing the effects of emodin in the presence of HC-3. 3 Emodin caused dose-dependent tissue contraction that was abolished by inclusion of atropine (1 microM) in the buffer. Atropine (1 microM) antagonized the response caused by methacholine. Incubation of tissues with HC-3 (1 and 10 microM) reduced the maximum response caused by emodin by 45% and 71% respectively, but had no effect on ACh-induced tissue contraction. These data suggest that, emodin causes contraction of the ileum by triggering the release of endogenous ACh which acts on muscarinic receptors to cause contraction of the rat isolated ileum preparation.

Nicotine therapy in adulthood reverses the synaptic and behavioral deficits elicited by prenatal exposure to phenobarbital

A major objective in identifying the mechanisms underlying neurobehavioral teratogenicity is the possibility of designing therapies that reverse or offset drug- or toxicant-induced neural damage. In our previous studies, we identified deficits in hippocampal muscarinic cholinergic receptor-induced membrane translocation of protein kinase C (PKC)gamma as the likely mechanism responsible for adverse behavioral effects of prenatal phenobarbital exposure. We therefore explored whether behavioral and synaptic defects could be reversed in adulthood by nicotine administration. Pregnant mice were given milled food containing phenobarbital to achieve a daily dose of 0.5-0.6 g/kg from gestational days 9-18. In adulthood, offspring showed deficits in the Morris maze, a behavior dependent on the integrity of septohippocampal cholinergic synaptic function, along with the loss of the PKCgamma response. Phenobarbital-exposed and control mice then received nicotine (10 mg/kg/day) for 14 days via osmotic minipumps. Nicotine reversed the behavioral deficits and restored the normal response of hippocampal PKCgamma to cholinergic receptor stimulation. The effects were regionally specific, as PKCgamma in the cerebellum was unaffected by either phenobarbital or nicotine; furthermore, in the hippocampus, PKC isoforms unrelated to the behavioral deficits showed no changes. Nicotine administration thus offers a potential therapy for reversing neurobehavioral deficits originating in septohippocampal cholinergic defects elicited by prenatal drug or toxicant exposures.

Centrally injected CDP-choline increases plasma vasopressin levels by central cholinergic activation

In the present study, both the effects of intracerebroventricular (i.c.v.) injection of cytidine-5'-diphosphate choline (CDP-choline) on plasma vasopressin levels and the choline involvement of these effects were investigated. I.c.v. administration of CDP-choline (0.5, 1.0 and 2.0 micromol) increased plasma vasopressin levels dose- and time-dependently. I.c.v. injection of equimolar dose of choline (1 micromol) produced similar vasopressin response. However equimolar dose of cytidine (1 micromol; i.c.v.), the other hydrolysis product of CDP-choline, did not affect plasma vasopressin levels. Pretreatment of rats with hemicholinium-3, neuronal high affinity choline uptake inhibitor (20 microg; i.c.v.) blocked the vasopressin response to i.c.v. CDP-choline (1 micromol). Pretreatment of rats with mecamylamine (50 microg; i.c.v.), a nonselective nicotinic receptor antagonist, abolished the increase in plasma vasopressin induced by CDP-choline while atropine (10 microg; i.c.v.), nonselective muscarinic receptor antagonist, failed to change the response. In conclusion, intracerebroventricularly injected CDP-choline can increase plasma vasopressin levels by activating central nicotinic cholinergic receptors through the activation of presynaptic cholinergic mechanisms.

The Importance of Brainstem Cholinergic Neurons in the Pressor Response to Cocaine

After intracisternal injection, 140 nmol (48 microg) of cocaine (but not lidocaine or procaine) evoked an increase in mean arterial pressure (MAP) of 41 mm Hg. The increase in MAP began within 1 min after injection and lasted 10 to 15 min. The pressor response to intracisternal injection of cocaine was not mediated through central alpha-adrenergic receptors, but intracisternal pretreatment with D1 or D2 dopamine receptor antagonists shortened the duration of the response. Pretreatment with intracisternal injection of hemicholinium-3 to deplete medullary acetylcholine produced a dose-dependent inhibition of the pressor and tachycardic responses to intracisternal injection of cocaine. Central pretreatment with hemicholinium-3 also inhibited the pressor response to intravenous injection of 0.5 mg/kg cocaine. Atropine pretreatment was only partly effective in blocking the pressor and tachycardic responses to intracisternal injection of cocaine. However, a single intracisternal injection of the nicotinic ganglionic receptor blocker hexamethonium inhibited the pressor response to cocaine administered intracisternally 24 h later, and on each of the following 4 days. The blocking effect of hexamethonium was not mimicked by the alpha7 selective antagonist methyllycaconitine or by the alpha4beta2 subtype-preferring antagonist dihydro-beta-erythroidine. The data suggest that the pressor response to cocaine is mediated by medullary acetylcholine release on to nicotinic receptors of the ganglionic type, enhancing the output of bulbospinal sympathetic premotor neurons. Our results provide new evidence for the prolonged inactivation of relevant central nicotinic receptors by nicotinic receptor antagonists, and suggest that such compounds might be used safely for cocaine overdose, as well as for antiabuse issues without the concern for autonomic side effects.

Antinociceptive effects of bethanechol or dimethylphenylpiperazinium in models of phasic or incisional pain in rats

The mechanism by which muscarinic or nicotinic agonists produce antinociception has been the subject of several studies. In the present investigation, we used intrathecal administration of drugs to rats to show that muscarinic or nicotinic agonists such as bethanechol (BCh) and dimethylphenylpiperazinium (DM), respectively, dose-dependently increased the tail flick latency and reduced the pain produced by a surgical incision performed on the plantar aspect of a hind paw. The effects of BCh in both tests were inhibited by the previous intrathecal administration of atropine, but not mecamylamine (muscarinic and nicotinic antagonists, respectively). Mecamylamine significantly reduced the effects of DM in both tests. Atropine significantly reduced the effect of DM in the tail flick test and inhibited the effect of DM against the incisional pain. Intrathecal hemicholinium-3 (HC-3), a reversible inhibitor of choline transporter, did not change the effect of BCh in the tail flick test but produced a non-significant reduction of the effect of BCh against incisional pain. In contrast, HC-3 produced a non-significant reduction of the effect of DM in the tail flick test but fully inhibited the effect of DM against incisional pain. Therefore, the BCh-induced antinociception depends on a direct activation of muscarinic receptors, whereas DM-induced antinociception results in drug interaction with nicotinic receptors to activate the further release of acetylcholine from intrinsic spinal cholinergic terminals. The acetylcholine released by DM in turn induces antinociception via activation of muscarinic receptors.

Hypothalamic regulation of pancreatic secretion is mediated by central cholinergic pathways in the rat

The vago-vagal reflex plays an important role in mediating pancreatic secretion evoked by cholecystokinin and non-cholecystokinin-dependent luminal factors. We hypothesize that the vago-vagal reflex mediating pancreatic secretion in the rat is under central control and regulated by cholinergic pathways in the hypothalamus. To test this hypothesis, we demonstrated that chronic decerebration decreased basal pancreatic enzyme secretion from 318 +/- 12 to 233 +/- 9 mg h-1 and reduced the net increase in pancreatic secretion stimulated by intraduodenal infusion of 5 % peptone and hypertonic NaCl by 54 % and 45 %, respectively. Intracerebroventricular administration of methscopolamine (MSCP, 50 nmol (5 mul)-1), a blood-brain barrier-impermeant cholinergic muscarinic receptor antagonist, evoked results similar to those achieved by chronic decerebration. To localize the sites of action, we demonstrated that microinjection of MSCP (20 nmol) into the lateral hypothalamic nucleus or the paraventricular nucleus resulted in inhibition of both basal pancreatic protein secretion and luminally stimulated pancreatic secretion by 48 % and 52 %, respectively. Intracerebroventricular injection of hemicholinium-3 at doses known to deplete the endogenous ACh store produced similar inhibitory results. In addition, microinjection of ACh (5 pmol) or the muscarinic M1 receptor agonist McN-A-343 (30 ng) into the lateral hypothalamic nucleus increased pancreatic secretion over basal levels by 46 % and 40 %, respectively. Selective lesions of lateral septal cholinergic neurons decreased basal pancreatic secretion and inhibited peptone-induced pancreatic secretion by 30 %. Destruction of the lateral parabrachial nucleus produced a 44 % inhibition of peptone-induced pancreatic section. Finally, microinjection of glutamate into the lateral septum or the lateral parabrachial nucleus stimulated vagal pancreatic efferent nerve firings from a basal level of 0 +/- 0.5 impulses (30 s)-1 to 4.5 +/- 0.5 and 14 +/- 2 impulses (30 s)-1, respectively, and pancreatic protein output increased 50 % and 84 % over basal levels. Administration of MSCP to the paraventricular nucleus eliminated these effects. These observations suggest that cholinergic neurons of the lateral septum and lateral parabrachial nucleus regulate pancreatic secretion. Further, cholinergic input from the lateral parabrachial nucleus to the hypothalamus plays a major role in the modulation of vagal pancreatic efferent nerve activity and pancreatic secretion evoked by the vago-vagal reflex.

Lethal impairment of cholinergic neurotransmission in hemicholinium-3-sensitive choline transporter knockout mice

Presynaptic acetylcholine (ACh) synthesis and release is thought to be sustained by a hemicholinium-3-sensitive choline transporter (CHT). We disrupted the murine CHT gene and examined CHT-/- and +/- animals for evidence of impaired cholinergic neurotransmission. Although morphologically normal at birth, CHT-/- mice become immobile, breathe irregularly, appear cyanotic, and die within an hour. Hemicholinium-3-sensitive choline uptake and subsequent ACh synthesis are specifically lost in CHT-/- mouse brains. Moreover, we observe a time-dependent loss of spontaneous and evoked responses at CHT-/- neuromuscular junctions. Consistent with deficits in synaptic ACh availability, we also observe developmental alterations in neuromuscular junction morphology reminiscent of changes in mutants lacking ACh synthesis. Adult CHT+/- mice overcome reductions in CHT protein levels and sustain choline uptake activity at wild-type levels through posttranslational mechanisms. Our results demonstrate that CHT is an essential and regulated presynaptic component of cholinergic signaling and indicate that CHT warrants consideration as a candidate gene for disorders characterized by cholinergic hypofunction.

The sea urchin embryo as a model for mammalian developmental neurotoxicity: ontogenesis of the high-affinity choline transporter and its role in cholinergic trophic activity

Embryonic development in the sea urchin requires trophic actions of the same neurotransmitters that participate in mammalian brain assembly. We evaluated the development of the high-affinity choline transporter, which controls acetylcholine synthesis. A variety of developmental neurotoxicants affect this transporter in mammalian brain. [3H]Hemicholinium-3 binding to the transporter was found in the cell membrane fraction at stages from the unfertilized egg to pluteus, with a binding affinity comparable with that seen in mammalian brain. Over the course of development, the concentration of transporter sites rose more than 3-fold, achieving concentrations comparable with those of cholinergically enriched mammalian brain regions. Dimethylaminoethanol (DMAE), a competitive inhibitor of choline transport, elicited dysmorphology beginning at the mid-blastula stage, with anomalies beginning progressively later as the concentration of DMAE was lowered. Pretreatment, cotreatment, or delayed treatment with acetylcholine or choline prevented the adverse effects of DMAE. Because acetylcholine was protective at a lower threshold, the DMAE-induced defects were most likely mediated by its effects on acetylcholine synthesis. Transient removal of the hyaline layer enabled a charged transport inhibitor, hemicholinium-3, to penetrate sufficiently to elicit similar anomalies, which were again prevented by acetylcholine or choline. These results indicate that the developing sea urchin possesses a high-affinity choline transporter analogous to that found in the mammalian brain, and, as in mammals, the functioning of this transporter plays a key role in the developmental, trophic activity of acetylcholine. The sea urchin model may thus be useful in high-throughput screening of suspected developmental neurotoxicants.

The hemicholinium-3 sensitive high affinity choline transporter is internalized by clathrin-mediated endocytosis and is present in endosomes and synaptic vesicles

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.

QSAR-derived choline kinase inhibitors: how rational can antiproliferative drug design be?

This review presents an overview of Choline Kinase (ChoK) inhibitors with antiproliferative activity. The consideration of ChoK as a novel target for the development of new anticancer drugs is justified. The synthesis of several derivatives based on structural modifications of hemicholinium-3 (HC-3) is not accompanied by potentiation of the neurological toxicity of HC-3. The increment of both ChoK inhibitory and antiproliferative activities was successfully obtained by the two following changes: a) substitution of the oxazonium moiety of HC-3 by several aromatic heterocycles, and b) using the 1,2-ethylene(bisbenzyl) moiety instead of the 4,4'-biphenyl fragment. In an attempt to understand the ChoK inhibitory activity, a quantitative structure-activity relationship was developed. The QSAR equations have described the forces involved in quantitative terms. The electron characteristic of the substituent at position 4 of the heterocycle and the lipophilic character of the whole molecule were found to significantly affect the antitumour activity in compounds 17-95. Trispyridinium compounds 91-95 are more potent than the bispyridinium ones 87-89 as ChoK inhibitors. Nevertheless, 91-95 are less active than 87-89 as antiproliferative agents because the latter show better lipophilicities to cross the cytosolic membranes. Inhibition of the growth of human tumours in nude mice has been demonstrated: Antitumour activity of compound 64 against human HT-29 produced a decrease of up to 70% in the size of the tumour in nude mice. These results indicate that ChoK can be used as a general target for anticancer drug design against Ras-dependent tumourigenesis.

High potassium-induced activation of choline-acetyltransferase in human neocortex: implications and species differences

The role of electrical and potassium (K(+))-induced depolarisation on choline-acetyltransferase (ChAT) activity in human and mouse neocortical slices was studied. When [3H]-ACh release was evoked by two K(+) stimulations in human neocortex, the mean S(2)/S(1) ratio was significantly below unity. ChAT inhibitors, like bromo-acetylcholine and ocadaic acid, raised this ratio by 79 and 63%, respectively, suggesting that the diminished S(2)/S(1) value in the absence of ChAT inhibitors reflected an increased ChAT activity at S(2) following K(+) depolarisation at S(1). When stimulated electrically, however, the S(2)/S(1) ratio in human neocortex was near unity and ocadaic acid remained without effect. In parallel experiments on mouse neocortical slices, the S(2)/S(1) ratio was near unity in both electrically or K(+)-evoked [3H]-ACh release and was not altered by ChAT inhibition. ChAT activity following K(+) depolarisation was also determined directly. ChAT activation in human neocortical slices was highest at 10 and 20mM K(+). ChAT activity in mouse neocortical tissue was not altered by K(+) depolarisation. These results suggest that in human, but not in mouse, neocortex ChAT activity may be increased due to ongoing K(+) depolarisation. This increase of ChAT activity supports a cholinergic degeneration hypothesis which has been entitled "autocannibalism" by Wurtman [TINS 15 (1992) 177].

Detection of the high-affinity choline transporter in the MOLT-3 human leukemic T-cell line

We previously showed that lymphocytes possess the necessary components to constitute an independent, non-neuronal cholinergic system; these include acetylcholine (ACh) itself, choline acetyltransferase (the ACh-synthesizing enzyme), and both muscarinic and nicotinic ACh receptors (AChRs). In addition, we showed that stimulation of AChRs with their respective agonists elicits a variety of biochemical and functional effects, suggesting that lymphocytic cholinergic system is involved in the regulation of immune function. In nerve terminals, choline taken up via the high-affinity choline transporter (CHT1) is exclusively utilized for ACh synthesis. In the present study, therefore, we investigated the expression of CHT1 in T-lymphocytes. Reverse transcription-polymerase chain reaction analysis revealed that MOLT-3 cells, a human leukemic T-cell line used as a T-lymphocyte model, expressed CHT1 mRNA, but that the CEM and Jurkat T-cell lines did not. Consistent with that finding, specific binding of [3H]hemicholinium-3 (HC-3), an inhibitor of CHT1, and HC-3-sensitive [3H]choline uptake were also detected in MOLT-3 cells. These results suggest that CHT1 plays a role in mediating choline uptake in T-lymphocytes and provides further evidence for the presence of an independent lymphocytic cholinergic system.

Release of acetylcholine by Die-Huang-Wan to enhance insulin secretion for lowering plasma glucose in Wistar rats

We have recently observed that Die-Huang-Wan has an ability to stimulate the secretion of insulin to decrease the plasma glucose levels in normal rats. In the present study, this effect of Die-Huang-Wan was reversed by the general muscarinic antagonists atropine and scopolamine, but not affected by the ganglionic nicotinic antagonist pentolinium or hexamethonium. Moreover, disruption of synaptically available acetylcholine using an inhibitor of choline uptake, hemicholinium-3, or vesicular acetylcholine transport, vesamicol, abolished the actions induced by Die-Huang-Wan. Mediation of acetylcholine released from nerve terminals by this product can thus be considered. Also, physostigmine at concentration sufficient to inhibit acetylcholinesterase enhanced the effect of Die-Huang-Wan. Blockade of the increase of plasma insulin and plasma glucose lowering action of Die-Huang-Wan by 4-diphenylacetoxy-N-methylpiperdine methiodide (4-DAMP) indicated the mediation of muscarinic M3 receptors. The results suggest that Die-Huang-Wan may enhance the release of acetylcholine from nerve terminals to stimulate the muscarinic M3 receptors for augmenting insulin release to produce plasma glucose lowering action.

Glycerophosphocholine metabolism in higher plant cells. Evidence of a new glyceryl-phosphodiester phosphodiesterase

Glycerophosphocholine (GroPCho) is a diester that accumulates in different physiological processes leading to phospholipid remodeling. However, very little is known about its metabolism in higher plant cells. (31)P-Nuclear magnetic resonance spectroscopy and biochemical analyses performed on carrot (Daucus carota) cells fed with GroPCho revealed the existence of an extracellular GroPCho phosphodiesterase. This enzymatic activity splits GroPCho into sn-glycerol-3-phosphate and free choline. In vivo, sn-glycerol-3-phosphate is further hydrolyzed into glycerol and inorganic phosphate by acid phosphatase. We visualized the incorporation and the compartmentation of choline and observed that the major choline pool was phosphorylated and accumulated in the cytosol, whereas a minor fraction was incorporated in the vacuole as free choline. Isolation of plasma membranes, culture medium, and cell wall proteins enabled us to localize this phosphodiesterase activity on the cell wall. We also report the existence of an intracellular glycerophosphodiesterase. This second activity is localized in the vacuole and hydrolyzes GroPCho in a similar fashion to the cell wall phosphodiesterase. Both extra- and intracellular phosphodiesterases are widespread among different plant species and are often enhanced during phosphate deprivation. Finally, competition experiments on the extracellular phosphodiesterase suggested a specificity for glycerophosphodiesters (apparent K(m) of 50 microM), which distinguishes it from other phosphodiesterases previously described in the literature.

Assessment of choline uptake for the synthesis and release of acetylcholine in brain slices by a dynamic autoradiographic technique using [11C]choline

The uptake of choline for the synthesis and release of acetylcholine was investigated in brain slices by dynamic positron autoradiography using [11C]choline. Brain slices (330 microm) were incubated with [11C]choline in oxygenated Krebs-Ringer medium at 34 degrees C and serial two-dimensional time-resolved images of the uptake and release of radioactivity were recorded on Storage Phosphor screens. [11C]choline uptake increased with the period of incubation and was 1.9 times higher in the striatum than cerebral cortex. The uptake in the striatum was significantly diminished by hemicholinium-3 (HC-3), an inhibitor of high-affinity choline uptake. Pretreatment of brain slices with 50 mM K(+) for 20 min enhanced the uptake in striatum. The uptake of [11C]choline in brain slices was saturable using nonlabeled choline. Two uptake systems, a high-affinity and a low-affinity system, were confirmed to exist by kinetic analysis using Lineweaver-Burk plots. The 11C radioactivity that had accumulated in the striatum disappeared on treatment with veratridine, a depolarization agent, in the presence of HC-3. This pattern of disappearance was consistent with that of the appearance of unlabeled and labeled acetylcholine in the medium. These results indicate that this method is useful for obtaining information regarding the uptake of choline for the synthesis and release of acetylcholine in live brain tissues.

Intracerebroventricular choline increases plasma vasopressin and augments plasma vasopressin response to osmotic stimulation and hemorrhage

Intracerebroventricular (i.c.v.) injection of choline (50-150 microg), a precursor of the neurotransmitter acetylcholine, produced a time-and dose-dependent increase in plasma vasopressin levels in conscious, freely moving rats. The increase in plasma vasopressin in response to i.c.v. choline (150 microg) was inhibited by pretreatment with the nicotinic receptor antagonist, mecamylamine (50 microg; i.c.v.), but not by the muscarinic receptor antagonist, atropine (10 microg; i.c.v). The choline-induced rise in plasma vasopressin levels was greatly attenuated by hemicholinium-3 (HC-3; 20 microg; i.c.v.), a neuronal choline uptake inhibitor. Choline (50 or 150 microg; i.c.v.) produced a much greater increase in plasma vasopressin levels in osmotically stimulated or hemorrhaged rats than in normal rats. Choline (150 microg; i.c.v.) also enhanced plasma vasopressin response to graded hemorrhage; the enhancing effect of choline was also attenuated by HC-3 (20 microg; i.c.v.). Choline and acetylcholine concentrations in hypothalamic dialysates increased significantly following i.c.v. injection of choline (150 microg). It is concluded that choline increases plasma vasopressin levels by stimulating central nicotinic receptors indirectly, through the enhancement of acetylcholine synthesis and release, and augments the ability of osmotic stimulations or hemorrhage to stimulate vasopressin release.

Hyperglycemia induced by intracerebroventricular choline: involvement of the sympatho-adrenal system

Intracerebroventricular (i.c.v.) injection of choline (75-300 microg) produced a dose-dependent increase in blood glucose levels. Pre-treatment with the nicotinic acetylcholine receptor antagonist, mecamylamine (50 microg, i.c.v.) blocked the hyperglycemia induced by choline (150 microg, i.c.v.), but the response was not affected by pre-treatment with the muscarinic acetylcholine receptor antagonist, atropine (10 microg, i.c.v.). Pre-treatment with the neuronal choline uptake inhibitor, hemicholinium-3 (20 microg, i.c.v.), attenuated the hyperglycemia induced by choline. The hyperglycemic response to choline was associated increased plasma levels of adrenaline and noradrenaline. The hyperglycemia elicited by choline was greatly attenuated by bilateral adrenalectomy, and entirely blocked by either surgical transection of the splanchnic nerves or by pre-treatment with the alpha-adrenoceptor antagonist, phentolamine. These data show that choline, a precursor of acetylcholine, increases blood glucose and this effect is mediated by central nicotinic acetylcholine receptor activation. An increase in sympatho-adrenal activity appears to be involved in the hyperglycemic effect of choline.

A homeostatic mechanism counteracting K(+) -evoked choline release in adult brain

Choline (Ch) is an essential nutrient as the biosynthetic precursor of acetylcholine (ACh) and phospholipids. Under resting conditions, the intracellular accumulation of Ch (above 10-fold), which is positively charged, is governed by the membrane potential and follows the Nernst equation. Accordingly, in synaptosomes from adult rats during depolarization, we observed a linear relationship between release of free cytoplasmic Ch and KCl concentration (2.7-120 mm). The K(+) -evoked Ch release was Ca(2+) -independent and did not originate from ACh or phospholipid hydrolysis. In superfused brain slices of adult rats, however, a K(+) -induced Ch efflux was absent. Also, under in vivo conditions, 30-60 mm KCl failed to increase the extracellular Ch level as shown by microdialysis in adult rat hippocampus. On the contrary, in brain slices from 1-week-old rats, high K(+) as well as 4-aminopyridine evoked a marked Ch efflux in a concentration-dependent fashion. This phenomenon faded within 1 week. Hemicholinium-3 (HC-3, 1 and 10 microm), a blocker of cellular choline uptake, caused a marked efflux of choline from adult rat slices but no or significantly less release from immature slices. We conclude that depolarization of synaptic endings causes a Ca(2+) -independent release of free cytoplasmic Ch into the extracellular space. In adult rat brain, this elevation of Ch is counteracted by a homeostatic mechanism such as uptake into brain cells.

Role of the choline exchanger in Na(+)-independent Mg(2+) efflux from rat erythrocytes

Two types of Na(+)-independent Mg(2+) efflux exist in erythrocytes: (1) Mg(2+) efflux in sucrose medium and (2) Mg(2+) efflux in high Cl(-) media such as KCl-, LiCl- or choline Cl-medium. The mechanism of Na(+)-independent Mg(2+) efflux in choline Cl medium was investigated in this study. Non-selective transport by the following transport mechanisms has been excluded: K(+),Cl(-)- and Na(+),K(+),Cl(-)-symport, Na(+)/H(+)-, Na(+)/Mg(2+)-, Na(+)/Ca(2+)- and K(+)(Na(+))/H(+) antiport, Ca(2+)-activated K(+) channel and Mg(2+) leak flux. We suggest that, in choline Cl medium, Na(+)-independent Mg(2+) efflux can be performed by non-selective transport via the choline exchanger. This was supported through inhibition of Mg(2+) efflux by hemicholinum-3 (HC-3), dodecyltrimethylammonium bromide (DoTMA) and cinchona alkaloids, which are inhibitors of the choline exchanger. Increasing concentrations of HC-3 inhibited the efflux of choline and efflux of Mg(2+) to the same degree. The K(d) value for inhibition of [(14)C]choline efflux and for inhibition of Mg(2+) efflux by HC-3 were the same within the experimental error. Inhibition of choline efflux and of Mg(2+) efflux in choline medium occurred as follows: quinine>cinchonine>HC-3>DoTMA. Mg(2+) efflux was reduced to the same degree by these inhibitors as was the [(14)C]choline efflux.

Molecular cloning and characterization of a murine hemicholinium-3-sensitive choline transporter

In cholinergic neurons, a specific requirement for precursor choline in the biosynthesis of acetylcholine (ACh) is thought to be sustained by a presynaptic, hemicholinium-3 (HC-3)-sensitive choline transporter (CHT). This transporter exhibits micromolar affinity for choline and transport activity is Na(+)- and Cl(-)-dependent. Based on the sequence information available with the recent cloning of rat and human CHTs [Okuda, Haga, Kanai, Endou, Ishihara and Katsura (2000) Nat. Neurosci. 3, 120-125; Apparsundaram, Ferguson, George Jr and Blakely (2000) Biochem. Biophys. Res. Commun. 276, 862-867; Okuda and Haga (2000) FEBS Lett. 484, 92-97], we have identified a murine CHT orthologue (mCHT) by reverse transcriptase-PCR of spinal cord mRNA and confirmed this sequence using assembled mouse genomic DNA. Inferred splice junctions for mCHT exons are conserved with those of hCHT. The mCHT cDNA encodes a protein of 580 amino acids with 93% and 98% amino acid identity to human CHT and rat CHT1, respectively. Hydropathy analysis of the predicted amino acid sequence of mCHT indicates a protein containing 13 transmembrane domains (TMDs), with the N-terminus oriented extracellularly and the C-terminus oriented intracellularly. Northern blot analysis of mouse tissues reveals the expression of mCHT as a single transcript of approximately 5 kb with highest expression in regions that are rich in cholinergic cell bodies, e.g. the spinal cord, brainstem, mid-brain and striatum, whereas hybridization signals are absent in regions lacking cholinergic soma, e.g. the cerebellum and kidney. Expression of mCHT in COS-7 cells results in high-affinity [(3)H]HC-3-binding sites (K(d)=5 nM), and Na(+)- and Cl(-)-dependent HC-3-sensitive choline uptake (K(m)=2 microM), assessed in resealed membrane vesicles. The availability of cloned, functional mCHT and its cognate genomic DNA should prove useful for studies of mCHT regulation and should open possibilities for evaluation of CHT dysfunction in murine models.

Compartmentalization of choline and acetylcholine metabolism in cultured sympathetic neurons

To determine the relative contribution of cell bodies and distal axons to the production of acetylcholine, we used retinoic acid to induce a cholinergic phenotype in compartmented cultures of rat sympathetic neurons. When [3H]choline was given to cell bodies/proximal axons for 24 h, 98% of the radiolabel was recovered as choline, phosphocholine, CDP-choline and phosphatidylcholine, whereas only 1 to 2% of the radiolabel was incorporated into acetylcholine. Choline taken up by cell bodies and transported to axons is poorly utilized for acetylcholine biosynthesis. In contrast, when distal axons were supplied with [3H]choline, 11% of the radiolabel was recovered in acetylcholine after 24 h, the remainder being incorporated into precursors/metabolites of phosphatidylcholine. The lack of acetylcholine synthesis in cell bodies/proximal axons could not be ascribed to an absence of choline acetyltransferase activity in this region of the neurons, since the specific activity of this enzyme was similar in cell bodies/proximal axons and distal axons. The rate of choline uptake by distal axons (15.3 4.4 nmol/5 min/mg protein) was approximately 10-fold greater than by cell bodies/proximal axons (1.6 0.8 nmol/5 min/mg protein). Moreover, choline uptake into distal axons was inhibited by 74.5% by hemicholinium-3, and by 80.1% by removal of Na(+) from the medium. In contrast, choline uptake by cell bodies/proximal axons was not significantly inhibited by hemicholinium-3 or Na(+) removal. These results suggest that the majority of axonal acetylcholine is synthesized in distal axons/axon terminals from choline taken up by a high-affinity choline transporter in distal axons.

Ameliorative effect of vasopressin-(4-9) through vasopressin V(1A) receptor on scopolamine-induced impairments of rat spatial memory in the eight-arm radial maze

In order to clarify the mechanism by which pGlu-Asn-Cys(Cys)-Pro-Arg-Gly-NH(2) (vasopressin-(4-9)), a major metabolite C-terminal fragment of [Arg(8)]-vasopressin (vasopressin-(1-9)), improves learning and memory, we used several different drugs such as an acetylcholine receptor antagonist, a Ca(2+)/calmodulin-dependent protein kinase II inhibitor, vasopressin receptor antagonists and L-type Ca(2+) channel blocker to disrupt spatial memory in rats. Moreover, we examined the effect of vasopressin-(4-9) on acetylcholine release in the ventral hippocampus using microdialysis. Vasopressin-(4-9) (10 fg/brain, i.c.v.) improved the impairment of spatial memory in the eight-arm radial maze induced by scopolamine, pirenzepine and Ca(2+)/calmodulin -dependent protein kinase II inhibitor. Pirenzepine, a vasopressin V(1A) receptor antagonist, and L-type Ca(2+) channel blocker, but not a vasopressin V(2) receptor antagonist, suppressed the effects of vasopressin-(4-9) on scopolamine-induced impairment of spatial memory. Moreover, vasopressin-(4-9) did not affect acetylcholine release in the ventral hippocampus of intact rats or of scopolamine-treated rats as assessed by microdialysis. These results suggest that vasopressin-(4-9) activates vasopressin V(1A) receptors on the postsynaptic membrane of cholinergic neurons, and induces a transient influx of intracellular Ca(2+) through L-type Ca(2+) channels to interact with muscarinic M(1) receptors. The activation of these processes by vasopressin-(4-9) is critically involved in the positive effect of vasopressin-(4-9) on scopolamine-induced impairment of spatial memory.

The effects of continuous and single-dose radiation on choline uptake in organotypic tissue slice cultures of rabbit hippocampus

The objective of the present study was to determine the time-dependent course of choline uptake in mature organotypic slice cultures of rabbit hippocampal formation and to assess the effects of continuous and single high-dose irradiation on choline uptake in cultivated slices in vitro. Transverse slices of hippocampus were dynamically incubated in a cerebrospinal fluid-like culture medium for 72 h. To study the changes in choline uptake longitudinally, the slice cultures were processed with 0.1 microM [3H]-choline, and tritium accumulation was counted. Two different gamma irradiation sources (125I seeds and a clinical 60Co source) were used as representative models of interstitial radiosurgery and other radiosurgical techniques. A total dose of approximately 6000 cGy was delivered to the brain slices in one session or in a continuous, relatively low-dose rate fashion, and their effects on high-affinity choline uptake were examined. In another set of experiments with 125I, 5 microM hemicholinium-3 was used in choline uptake procedures as a competitive high-affinity choline uptake inhibitor. The results can be summarized as follows: (1) in the control group of the hippocampal tissue culture, there was a significant increase in tritium accumulation values from 0 to 48 h and a decrease thereafter; (2) continuous 125I irradiation caused a highly significant depression of the accumulation of tritium compared to that observed in the control group throughout its application for 72 h; (3) there was no significant change in the accumulation of tritium in the slices after single high-dose rate irradiation with a 60Co source; and (4) 5 microM hemicholinium significantly depressed the accumulation of tritium in both the control and the 125I-irradiated groups, and there was no longer a difference between 125I-irradiated and control groups when both groups were treated with hemicholinium. These results demonstrate that the delivery of continuous but relatively low-dose rate gamma irradiation is more efficacious than single high-dose external irradiation on high-affinity choline uptake in hippocampal nervous tissue. The results also indicate that continuous irradiation specifically affected the high-affinity energy-dependent choline uptake mechanism, whereas nonspecific choline uptake did not seem to be disturbed.

Spinal endogenous acetylcholine contributes to the analgesic effect of systemic morphine in rats

BACKGROUND

Systemic morphine is known to cause increased release of acetyicholine in the spinal cord. Intrathecal injection of the cholinergic receptor agonists or acetyicholinesterase inhibitors produces antinociception in both animals and humans. In the present study, we explored the functional importance of spinal endogenous acetylcholine in the analgesic action produced by intravenous morphine.

METHODS

Rats were implanted with intravenous and intrathecal catheters. The antinociceptive effect of morphine was determined by the paw-withdrawal latency in response to a radiant heat stimulus after intrathecal treatment with atropine (a muscarinic receptor antagonist), mecamylamine (a nicotinic receptor antagonist), or cholinergic neurotoxins (ethylcholine mustard aziridinium ion [AF64A] and hemicholinium-3).

RESULTS

Intravenous injection of 2.5 mg/kg morphine increased significantly the paw-withdrawal latency. Intrathecal pretreatment with 30 microg atropine (n = 7) or 50 microg mecamylamine (n = 6) both attenuated significantly the antinociceptive effect of morphine. The inhibitory effect of atropine on the effect of morphine was greater than that of mecamylanilne. Furthermore, the antinociceptive effect of morphine was significantly reduced in rats pretreated with intrathecal AF64A (n = 7) or hemicholinium-3 (n = 6) to inhibit the high-affinity choline transporter and acetylcholine synthesis. We found that intrathecal AF64A reduced significantly the [3H]hemicholinium-3 binding sites but did not affect its affinity in the dorsal spinal cord.

CONCLUSIONS

The data in the current study indicate that spinal endogenous acetylcholine plays an important role in mediating the analgesic effect of systemic morphine through both muscarinic and nicotinic receptors.

In vivo assessment of acetylcholine-releasing function at cardiac vagal nerve terminals

We examined whether the ACh concentration measured by cardiac microdialysis provided information on left ventricular ACh levels under a variety of vagal stimulatory and modulatory conditions in anesthetized cats. Local administration of KCl (n = 5) and ouabain (n = 7) significantly increased the ACh concentration in the dialysate to 4.3 +/- 0.8 and 7.3 +/- 1.3 nmol/l, respectively, from the baseline value of 0.6 +/- 0.5 nmol/l. Intravenous administration of phenylbiguanide (n = 5) and phenylephrine (n = 6) significantly increased the ACh concentration to 5.4 +/- 0.9 and 6.0 +/- 1.5 nmol/l, respectively, suggesting that the Bezold-Jarisch and arterial baroreceptor reflexes affected myocardial ACh levels. Modulation of vagal nerve terminal function by local administration of tetrodotoxin (n = 6), hemicholinium-3 (n = 6), and vesamicol (n = 5) significantly suppressed the electrical stimulation-induced ACh release from 20.4 +/- 3.9 to 0.6 +/- 0.1, 7.2 +/- 1.9, and 2.7 +/- 0.6 nmol/l, respectively. Increasing the heart rate from 120 to 200 beats/min significantly reduced the myocardial ACh levels during electrical vagal stimulation, suggesting a heart rate-dependent washout of ACh. We conclude that ACh concentration measured by cardiac microdialysis provides information regarding ACh release and disposition under a variety of pathophysiological conditions in vivo.

Transport of choline and its relationship to the expression of the organic cation transporters in a rat brain microvessel endothelial cell line (RBE4)

The present study was undertaken to elucidate the functional characteristics of choline uptake and deduce the relationship between choline uptake and the expression of organic cation transporters in the rat brain microvessel endothelial cell line RBE4. Confluent RBE4 cells were found to express a high affinity choline uptake system. The system is Na(+)-independent and shows a Michaelis-Menten constant of approx. 20 microM for choline. The choline analogue hemicholinium-3 inhibits choline uptake in these cells with an inhibition constant of approx. 50 microM. The uptake system is also susceptible for inhibition by various organic cations, including 1-methyl-4-phenylpyridinium, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, clonidine, procainamide, and tetramethylammonium. The prototypical organic cation tetraethylammonium shows very little affinity for the choline uptake system in these cells. The inhibition of choline uptake by hemicholinium-3 is competitive. Northern analysis and RT-PCR show that these cells do not express the organic cation transporters OCT2 and OCT3. These cells do express, however, low levels of OCT1, but the functional characteristics of choline uptake in these cells are very different from the known properties of choline uptake via OCT1. The Na(+)-coupled high affinity choline transporter CHT1 is not expressed in these cells as evidenced by RT-PCR. This corroborates the Na(+)-independent nature of choline uptake in these cells. It is concluded that RBE4 cells express an organic cation transporter that is responsible for choline uptake in these cells and that this transporter is not identical to any of the organic cation transporters thus far identified at the molecular level in mammalian cells.

Hemicholinium-3 mustard reveals two populations of cycling choline cotransporters in Limulus

Cholinergic neurons have both a low-affinity and a high-affinity choline transport process. The high-affinity choline transport is sodium dependent and thus it can be referred to as choline cotransport. Choline cotransport has been shown to be up-regulated by neuronal activity. Protein kinase C has also been shown to regulate choline cotransport. Both forms of regulation appear to modulate transport by altering the numbers of choline cotransporters in the nerve terminal membrane. The present study centers on choline cotransporter trafficking in Limulus brain hemi-slice preparations. The competitive, reversible, non-permeant ligand, [3H]hemicholinium-3, was used in binding studies to estimate the relative number of choline cotransporters in plasma membranes. The hemicholinium-3 mustard derivative has been shown to be an irreversible, highly selective, non-permeant ligand for the choline cotransporter, and was also used. Hemicholinium-3 mustard binding to the choline cotransporter blocked [3H]choline transport and [3H]hemicholinium-3 binding. Antecedent elevated potassium exposure of cholinergic tissues has been shown to up-regulate choline transport by the recruitment of additional choline cotransporters to surface membranes. This treatment was also effective in the recruitment of cotransporters following maximal inhibition by hemicholinium-3 mustard of brain hemi-slices. Long-term washout of hemicholinium-3 mustard in hemi-slices resulted in a time-dependent restoration of choline cotransport. Full recovery occurred within 2h. In uninhibited slice preparations, both staurosporine and chelerythrine, protein kinase C inhibitors, stimulated choline uptake. However, within a 1-h washout recovery of uptake following hemicholinium-3 mustard inhibition, the staurosporine responsive but not chelerythrine responsive transport had returned. On the basis of these findings, we hypothesize the existence of two distinct populations of cycling choline cotransporters, which includes inactive or "silent" transporters.

Repetitive nerve stimulation decreases the acetylcholine content of quanta at the frog neuromuscular junction

We investigated how elevated quantal release produced by motor nerve stimulation affects the size of the quanta. The motor nerve was stimulated at 10 Hz in preparations in which excitation-contraction coupling was disrupted. Two hundred stimuli reduced the size of the time integrals of the miniature endplate currents ([integral]MEPCs), measured at the same junction immediately after stimulation, by 16 %. Three thousand stimuli reduced size by 23 %. When the solution contained 10 microM neostigmine (NEO) 3000 stimuli reduced [integral]MEPCs by 60 %, because with acetylcholinesterase (AChE) inhibited, [integral]MEPC size is more sensitive to changes in acetylcholine (ACh) content. Similar decreases in miniature endplate potential size ([integral]MEPP) followed repetitive stimulation of contracting preparations. The depolarization produced by iontophoretic pulses of ACh was scarcely changed by 3000 nerve stimuli at 10 Hz, suggesting that the decreases in miniature sizes are largely due to less ACh released per quantum. Following 3000 stimuli at 10 Hz the sizes of the [integral]MEPCs increased back to pre-stimulus values with a half-time of 8-10 min. Recovery was blocked by (-)-vesamicol (VES), by hemicholinium-3 (HC3) and by nicotinic cholinergic agonists - all of which inhibit ACh loading into synaptic vesicles. The number of quanta in the total store was estimated by releasing them with carbonyl cyanide m-chlorophenylhydrazone (CCCP). CCCP releases fewer quanta after stimulation than from unstimulated controls. After resting for hours following stimulation, the releasable number increased, even when ACh loading inhibitors were present. We conclude that the inhibitors do not block a significant fraction of the ACh loading into reformed reserve vesicles and propose that ACh can be loaded in a series of steps.

Sequential changes of cholinergic and dopaminergic receptors in brains after 6-hydroxydopamine lesions of the medial forebrain bundle in rats

We studied sequential changes in muscarinic cholinergic receptors, high-affinity choline uptake sites and dopamine D2 receptors in the brain after 6-hydroxydopamine lesions of the medial forebrain bundle in rats. The animals were unilaterally lesioned in the medial forebrain bundle and the brains were analyzed at 1, 2, 4 and 8 weeks postlesion. [3H]Quinuclidinylbenzilate (QNB), [3H]hemicholinum-3 (HC-3) and [3H]raclopride were used to label muscarinic cholinergic receptors, high-affinity choline uptake sites and dopamine D2 receptors, respectively. The degeneration of nigrostriatal pathway produced a transient decrease in [3H]QNB binding in the parietal cortex of both ipsilateral and contralateral sides at 2 and 8 weeks postlesion. [3H]QNB binding also showed a mild but insignificant decrease in the ipsilateral striatum throughout the postlesion periods. No significant change was observed in the substantia nigra (SN) of both ipsilateral and contralateral sides throughout the postlesion periods. In contrast, [3H]HC-3 binding showed no significant change in the parietal cortex of both ipsilateral and contralateral sides during the postlesion. However, [3H]HC-3 binding was upregulated in the ipsilateral dorsolateral striatum throughout the postlesion periods. The ventromedial striatum also showed a significant increase in [3H]HC-3 binding at 1 week and 2 weeks postlesion. On the other hand, no significant change in [3H]raclopride binding was found in the parietal cortex of both ipsilateral and contralateral sides during the postlesion. [3H]Raclopride binding showed a conspicuous increase in the ipsilateral striatum (35-52% of the sham-operated values in the lateral part and 39-54% in the medial part) throughout the postlesion periods. In the contralateral side, a mild increase in [3H]raclopride binding was also found in the striatum (10-15% of the sham-operated values in the lateral part and 22% in the medial part) after lesioning. However, a significant decline in [3H]raclopride binding was observed in the ipsilateral SN and ventral tegmental area during the postlesion. The present study indicates that 6-hydroxydopamine injection of medial forebrain bundle in rats can cause functional changes in high-affinity choline uptake site in the striatum, as compared with muscarinic cholinergic receptors. Furthermore, our studies demonstrate an upregulation in dopamine D2 receptors in the striatum and a decrease in the receptors in the SN and ventral tegmental area after the 6-hydroxydopamine injection. Thus, these findings provide further support for neurodegeneration of the nigrostriatal pathway that occurs in Parkinson's disease.

Amyloid beta peptide 1-40 and the function of rat hippocampal hemicholinium-3 sensitive choline carriers: effects of a proteolytic degradation in vitro

Effects of amyloid beta peptide 1-40 (Abeta) and of plant cysteine proteases bromelain and papain on the high-affinity uptake of choline (HACU) and the specific binding of [3H]hemicholinium-3 ([3H]HC-3) have been investigated on hippocampal synaptosomes from young adult male Wistar rats under basal and stimulated conditions (55 mM KCl). Depolarization increased significantly the HACU levels (the changes were predominantly in Vmax) and mildly the [3H]HC-3 binding (the changes especially in K(D)). Nonaggregated Abeta at low nM concentrations suppressed the depolarization effects but was ineffective under basal conditions during a short-term incubation. Higher microM concentrations decreased the HACU and binding under basal conditions in a time-dependent manner. The binding changes were firstly associated with alterations in K(D) and secondarily were accompanied also by a drop in Bmax. The results suggest that Abeta directly influences high-affinity carriers, inhibits their transport activity and enhances their sensitivity to proteoLytic cleavage. Stimulation increases the sensitivity of carriers to the interaction with Abeta.

Characterization of the blood-brain barrier choline transporter using the in situ rat brain perfusion technique

Choline enters brain by saturable transport at the blood-brain barrier (BBB). In separate studies, both sodium-dependent and passive choline transport systems of differing affinity have been reported at brain capillary endothelial cells. In the present study, we re-examined brain choline uptake using the in situ rat brain perfusion technique. Saturable brain choline uptake from perfusion fluid was best described by a model with a single transporter (V:(max) = 2.4-3.1 nmol/min/g; K(m) = 39-42 microM) with an apparent affinity (1/Km)) for choline five to ten-fold greater than previously reported in vivo, but less than neuronal 'high-affinity' brain choline transport (K(m) = 1-5 microM). BBB choline uptake from a sodium-free perfusion fluid using sucrose for osmotic balance was 50% greater than in the presence of sodium suggesting that sodium is not required for transport. Hemicholinium-3 inhibited brain choline uptake with a K(i) (57 +/- 11 microM) greater than that at the neuronal choline system. In summary, BBB choline transport occurs with greater affinity than previously reported, but does not match the properties of the neuronal choline transporter. The V:(max) of this system is appreciable and may provide a mechanism for delivering cationic drugs to brain.