References of "Seutin, Vincent"
     in
Bookmark and Share    
See detailBases neurobiologiques et psychopharmacologiques
Scuvée-Moreau, Jacqueline ULg; Seutin, Vincent ULg; Van den Berghe, Marc

in Dierick, Michel; Ansseau, Marc; D'Haenen, Hugo (Eds.) et al Manuel de Psychopharmacothérapie (2003)

Detailed reference viewed: 15 (8 ULg)
Full Text
See detailEffets de la nicotine et du cannabis sur le systeme nerveux central.
Seutin, Vincent ULg

in Revue Médicale de Liège (2003), 58(1), 19-21

We describe the molecular mechanisms of action of nicotine and delta 9-tetrahydrocannabinol, the most potent component of cannabis. Like other drugs of abuse, these compounds enhance dopamine release in a ... [more ▼]

We describe the molecular mechanisms of action of nicotine and delta 9-tetrahydrocannabinol, the most potent component of cannabis. Like other drugs of abuse, these compounds enhance dopamine release in a precise area of the limbic system when administered acutely. It has recently been shown that the cannabinoid receptors on which delta 9-tetrahydrocannabinol acts are also activated by endogenous ligands such as anandamide. This unconventional neurotransmitter appears to have important physiological effects in the central nervous system. Both preclinical and clinical evidence suggests that nicotine is more addictive than delta 9-tetrahydrocannabinol. However, the intimate interactions that exist between cannabinoid and opioid systems within the brain suggest that cannabinoids should not be considered as harmless drugs of abuse. [less ▲]

Detailed reference viewed: 139 (31 ULg)
Full Text
Peer Reviewed
See detailModulation of small conductance calcium-activated potassium (SK) channels: a new challenge in medicinal chemistry.
Liégeois, Jean-François ULg; Mercier, Frédéric ULg; Graulich, Amaury et al

in Current Medicinal Chemistry (2003), 10(8), 625-47

Small conductance calcium-activated potassium (SK) channels are found in many types of neurons as well as in some other cell types. These channels are selective for K(+) and open when intracellular Ca(2 ... [more ▼]

Small conductance calcium-activated potassium (SK) channels are found in many types of neurons as well as in some other cell types. These channels are selective for K(+) and open when intracellular Ca(2+) rises to omega 500 nM. In neurons, this occurs during and after an action potential. Activation of SK channels hyperpolarizes the membrane, thus reducing cell excitability for several tens or hundreds of milliseconds. This phenomenon is called a afterhyperpolarization (AHP). Three subtypes of SK channels (SK1, SK2, SK3) have been cloned and exhibit a differential localization in the brain. SK channels may play a role in physiological and pathological conditions. They may be involved in the control of memory and cognition. Moreover, they are heavily expressed in the basal ganglia (in particular in the substantia nigra, pars compacta) and in the limbic system, suggesting that they may modulate motricity and emotional behaviour. Based on these facts, SK channel subtypes may be a suitable target for developing novel therapeutic agents, but more work is needed to validate these targets. Hence, there is a great need for selective ligands. Moreover, although the risk of peripheral side-effects for SK channel modulators appears to be low, some questions remain to be investigated. Currently, different molecules are known as SK channel modulators. Apamin is a very potent peptidic agent; it produces a strong blockade of these targets which is only very slowly reversible and it has limited selectivity. Dequalinium was found to be an effective blocker. Different chemical modulations on the dequalinium structure led to the discovery of highly potent bis-quinolinium derivatives such as UCL 1684. Other bis-(2-amino-benzimidazole) derivatives are in development. On the other hand, quaternary salts of bicuculline were reported to be effective in inhibiting AHPs. More recent developments on structurally-related molecules revealed that methyl-laudanosine is a new interesting tool for exploring SK channel pharmacology. Finally, a family of compounds has been shown to facilitate SK channel opening. Such compounds may be useful in treating disorders involving neuronal hyperexcitability. [less ▲]

Detailed reference viewed: 110 (30 ULg)
Full Text
Peer Reviewed
See detailDopamine activates noradrenergic receptors in the preoptic area
Cornil, Charlotte ULg; Balthazart, Jacques ULg; Motte, Patrick ULg et al

in Journal of Neuroscience (2002), 22(21), 9320-9330

Dopamine (DA) facilitates male sexual behavior and modulates aromatase activity in the quail preoptic area (POA). Aromatase neurons in the POA receive dopaminergic inputs, but the anatomical substrate ... [more ▼]

Dopamine (DA) facilitates male sexual behavior and modulates aromatase activity in the quail preoptic area (POA). Aromatase neurons in the POA receive dopaminergic inputs, but the anatomical substrate that mediates the behavioral and endocrine effects of DA is poorly understood. Intracellular recordings showed that 100 muM DA hyperpolarizes most neurons in the medial preoptic nucleus (80%) by a direct effect, but depolarizes a few others (10%). DA-induced hyperpolarizations were not blocked by D1 or D2 antagonists (SCH-23390 and sulpiride). Extracellular recordings confirmed that DA inhibits the firing of most cells (52%) but excites a few others (24%). These effects also were not affected by DA antagonists (SCH-23390 and sulpiride) but were blocked by alpha(2)-(yohimbine) and alpha(1)-(prazosin) noradrenergic receptor antagonists, respectively. Two dopamine-beta-hydroxylase (DBH) inhibitors (cysteine and fusaric acid) did not block the DA-induced effects, indicating that DA is not converted into norepinephrine (NE) to produce its effects. The pK(B) of yohimbine for the receptor involved in the DA- and NE-induced inhibitions was similar, indicating that the two monoamines interact with the same receptor. Together, these results demonstrate that the effects of DA in the POA are mediated mostly by the activation of alpha(2) (inhibition) and alpha(1) (excitation) adrenoreceptors. This may explain why DA affects the expression of male sexual behavior through its action in the POA, which contains high densities of alpha(2)-noradrenergic but limited amounts of DA receptors. This study thus clearly demonstrates the existence of a cross talk within CNS catecholaminergic systems between a neurotransmitter and heterologous receptors. [less ▲]

Detailed reference viewed: 41 (26 ULg)
Full Text
Peer Reviewed
See detailMethyl-laudanosine: A new pharmacological tool to investigate the function of small-conductance Ca2+-activated K+ channels
Scuvée-Moreau, Jacqueline ULg; Liégeois, Jean-François ULg; Massotte, Laurent ULg et al

in Journal of Pharmacology and Experimental Therapeutics (The) (2002), 302(3), 1176-1183

Small-conductance Ca(2+)-activated K(+) channels (SK channels) underlie the prolonged postspike afterhyperpolarization (AHP) observed in many central neurons and play an important role in modulating ... [more ▼]

Small-conductance Ca(2+)-activated K(+) channels (SK channels) underlie the prolonged postspike afterhyperpolarization (AHP) observed in many central neurons and play an important role in modulating neuronal activity. However, a lack of specific and reversible blockers of these channels hampers their study in various experimental conditions. Because previous work has shown that bicuculline salts block these channels, we examined whether related alkaloids, namely laudanosine quaternary derivatives, would produce similar effects. Intracellular recordings were performed on rat midbrain dopaminergic neurons and hippocampus CA1 pyramidal cells. Binding experiments were performed on rat cerebral cortex membranes. Laudanosine, methyl-laudanosine, and ethyl-laudanosine blocked the apamin-sensitive AHP of dopaminergic neurons with mean IC(50) values of 152, 15, and 47 microM, respectively. The benzyl and butyl derivatives were less potent. Methyl-laudanosine had no effect on the I(h) current, action potential parameters, or membrane resistance of dopaminergic cells, or on the decrease in input resistance induced by muscimol, indicating a lack of antagonism at GABA(A) receptors. Interestingly, 100 microM methyl-laudanosine induced a significant increase in spiking frequency of dopaminergic neurons but not of CA1 pyramidal cells, suggesting the possibility of regional selectivity. Binding experiments on laudanosine derivatives were in good agreement with electrophysiological data. Moreover, methyl-laudanosine has no affinity for voltage-gated potassium channels, and its affinity for SK channels (IC(50) 4 microM) is superior to its affinity for muscarinic (IC(50) 114 microM) and neuronal nicotinic (IC(50) > or =367 microM) receptors. Methyl-laudanosine may be a valuable pharmacological tool to investigate the role of SK channels in various experimental models. [less ▲]

Detailed reference viewed: 40 (20 ULg)
Full Text
Peer Reviewed
See detailPirlindole and dehydropirlindole protect rat cultured neuronal cells against oxidative stress-induced cell death through a mechanism unrelated to MAO-A inhibition
Boland, André ULg; Gerardy, J.; Breeur, Danielle ULg et al

in British Journal of Pharmacology (2002), 135(3), 713-720

1 It has been shown that the MAO (monoamine oxidase)-B inhibitor deprenyl (DPR, selegiline) protects some cell types against oxidative stress. By decreasing H2O2 production, MAO-A inhibitors could also ... [more ▼]

1 It has been shown that the MAO (monoamine oxidase)-B inhibitor deprenyl (DPR, selegiline) protects some cell types against oxidative stress. By decreasing H2O2 production, MAO-A inhibitors could also reduce oxidative stress. 2 This study reports the effect of the MAO-A inhibitors, pirlindole (PIR), dehydropirlindole (DHP), brofaromine (BRO) and moclobemide (MCL) on primary-cultured brain cells exposed to iron-mediated toxicity. A comparison with trolox (TRO), a hydrosoluble vitamin-E analogue that protects against such an induced stress, was performed. 3 Rat hippocampal or cortical cultured cells were exposed either to 2 mum FeSO4 alone or in the presence of PIR, DHP, BRO, DPR, MCL or TRO. Cell survival (lactate-dehydrogenase measurements, 16 h incubation), intracellular peroxide production (DCF-fluorescence. I h incubation), lipoperoxidation (TBARS-fluorescence, 6 h incubation) and mitochondrial function (MTT-test, 16 h incubation) were assessed. 4 PIR, DHP and TRO significantly protected cultures (P<0.05) against Fe2+-induced toxicity in a concentration-dependent manner. The EC50s of these compounds were 6, 12 and 19 muM, respectively, in hippocampal cells. For cortical cell cultures incubated in the presence of iron and PIR or DHP, EC50s were 5 and 6 muM respectively. All Hill coefficients were close to unity. BRO, MCL and DPR were not protective in any type of culture. The IC50s for the inhibition of MAO-A were 2, 2 and 0.2 muM for PIR, DHP and BRO, respectively. PIR, DHP and TRO, but not DPR, induced a significant decrease in both intracellular peroxide production and lipoperoxidation. They also improved mitochondrial function. 5 These experiments show that PIR and DHP can protect hippocampal and cortical neurons against oxidative stress at pharmacologically relevant concentrations. This protective effect seems unrelated to inhibition of MAO-A, but possibly involves free radical scavenging. [less ▲]

Detailed reference viewed: 49 (17 ULg)
Full Text
See detailEffect of intermittent and continuous exposure to electromagnetic fields on cultured hippocampal cells
Boland, André ULg; Gabriel, Danielle ULg; Breeur, Danielle ULg et al

in Bioelectromagnetics (2002), 23(2), 97-105

This study was designed to assess the effect of 50 Hz electromagnetic fields (EMFs) on hippocampal cell cultures in the presence or absence of either sodium nitroprusside (SNP, a NO donor) or Fe2+ induced ... [more ▼]

This study was designed to assess the effect of 50 Hz electromagnetic fields (EMFs) on hippocampal cell cultures in the presence or absence of either sodium nitroprusside (SNP, a NO donor) or Fe2+ induced oxidative stress. One week old cultured rat hippocampal cells were exposed to either intermittent EMFs (IEMFs, 50 Hz, 0-5 mT, 1 min ON/OFF cycles, repeated 10 times every 2 h, 6 times/day during 48 h) or continuous EMFs (CEMFs, 50 Hz, 0-5 mT for 48 h). In a second set of experiments, the effect on such EMFs applied in combination with oxidative stress induced by 0.5 microM Fe2+ or SNP was estimated. At the end of both sets of experiments, cell mortality was assessed by lactate dehydrogenase measurements (LDH). Neither type of exposure to EMFs was observed to modify the basal rate of cell mortality. The exposure to CEMFs in presence of either NO or Fe2+ did not induce any significant increase in cell death. However, when cells were exposed to EMFs in the presence of NO, we observed a significant increase in cell death of 11 and 23% (P<0.001) at 2.5 and 5 mT, respectively. This effect had some specificity because IEMFs did not modify the effect of Fe2+ on cell mortality. Although the effects of IEMFs reported in this study were only observed at very high intensities, our model may prove valuable in trying to identify one cellular target of EMFs. [less ▲]

Detailed reference viewed: 26 (6 ULg)
Full Text
See detailProgres recents dans la pharmacologie des hypnotiques et anxiolytiques
Scuvée-Moreau, Jacqueline ULg; Seutin, Vincent ULg

in Revue Médicale de Liège (2001), 56(3), 159-64

Recent studies on the respective contribution of GABAA receptor subunits in the various pharmacological effects of benzodiazepines suggest that the sedative and amnesic properties of diazepam are mediated ... [more ▼]

Recent studies on the respective contribution of GABAA receptor subunits in the various pharmacological effects of benzodiazepines suggest that the sedative and amnesic properties of diazepam are mediated by enhancement of gabaergic transmission in neurons expressing the alpha 1 subunit while the anxiolytic effect is selectively mediated by alpha 2 subunit. These findings suggest that a separation of the pharmacological properties of benzodiazepines is possible and that drugs with increased clinical specificity could be developed. [less ▲]

Detailed reference viewed: 36 (3 ULg)
Full Text
Peer Reviewed
See detailEvidence for a Modulatory Role of Ih on the Firing of a Subgroup of Midbrain Dopamine Neurons
Seutin, Vincent ULg; Massotte, Laurent ULg; Renette, M. F. et al

in Neuroreport (2001), 12(2), 255-8

A previous investigation has suggested that the hyperpolarization-activated cation current Ih does not contribute to the spontaneous firing of midbrain dopaminergic neurons. This conclusion was reached ... [more ▼]

A previous investigation has suggested that the hyperpolarization-activated cation current Ih does not contribute to the spontaneous firing of midbrain dopaminergic neurons. This conclusion was reached using Cs(-1). We have re-examined this question with extracellular recordings in slices using the more specific blocker ZD7288. In two-thirds of the cells, low concentrations of ZD7288 induced a decrease of the spontaneous firing. The maximal inhibition was about 40% and the mean IC50 was 1.6 microM. This effect was probably direct because it persisted in the presence of antagonists of various receptors. These concentrations of ZD7288 had no effect in the remaining one third of the examined cells. However, the highest concentration of ZD7288 (300 microM) abolished the firing of all dopaminergic neurons, probably by a mechanism unrelated to the blockade of Ih. We conclude that Ih controls to a certain extent the firing of a majority of midbrain dopaminergic neurons. [less ▲]

Detailed reference viewed: 6 (2 ULg)
Full Text
Peer Reviewed
See detailCalcium Release from Internal Stores Is Required for the Generation of Spontaneous Hyperpolarizations in Dopaminergic Neurons of Neonatal Rats
Seutin, Vincent ULg; Mkahli, F.; Massotte, Laurent ULg et al

in Journal of Neurophysiology (2000), 83(1), 192-7

We recently have demonstrated the existence of spontaneous hyperpolarizations in midbrain dopaminergic neurons of neonatal but not adult rats. These events are mediated by the opening of apamin-sensitive ... [more ▼]

We recently have demonstrated the existence of spontaneous hyperpolarizations in midbrain dopaminergic neurons of neonatal but not adult rats. These events are mediated by the opening of apamin-sensitive K(+) channels after a rise in the intracellular concentration of Ca(2+). They are resistant to tetrodotoxin in most cases and are probably endogenous (i.e., not synaptically activated). Here their mechanism was investigated. Cyclopiazonic acid (10 microM), a specific inhibitor of endoplasmic reticulum Ca(2+) ATPases, reversibly abolished the events. Caffeine, which promotes Ca(2+) release from intracellular stores, had concentration-dependent effects. At 1 mM, it markedly and steadily increased the frequency and the amplitude of the hyperpolarizations. At 10 mM, it induced a transient increase in their frequency followed by their cessation. All these effects were quickly reversible. Ryanodine (10 microM), which decreases the conductance of Ca(2+) release channels, irreversibly blocked the spontaneous hyperpolarizations. Dantrolene (100 microM), a blocker of Ca(2+) release from sarcoplasmic reticulum of striated muscle, did not affect the events. On the other hand, Cd(2+) (100-300 microM), a broad antagonist of membrane voltage-gated Ca(2+) channels, significantly reduced the amplitude and the frequency of the hyperpolarizations. However, when the frequency of the events was increased by 1 mM caffeine, Cd(2+) affected them to a smaller extent, whereas cyclopiazonic acid still abolished them. We conclude that internal stores are the major source of Ca(2+) ions that induce the K(+) channel openings underlying the spontaneous hyperpolarizations of these neurons. [less ▲]

Detailed reference viewed: 7 (3 ULg)
Full Text
Peer Reviewed
See detailRecent Advances in the Pharmacology of Quaternary Salts of Bicuculline
Seutin, Vincent ULg; Johnson, S. W.

in Trends in Pharmacological Sciences (1999), 20(7), 268-270

Detailed reference viewed: 10 (1 ULg)
Full Text
Peer Reviewed
See detailSpontaneous Apamin-Sensitive Hyperpolarizations in Dopaminergic Neurons of Neonatal Rats
Seutin, Vincent ULg; Massotte, Laurent ULg; Scuvée-Moreau, Jacqueline ULg et al

in Journal of Neurophysiology (1998), 80(6), 3361-4

Spontaneous apamin-sensitive hyperpolarizations in dopaminergic neurons of neonatal rats. J. Neurophysiol. 80: 3361-3364, 1998. Intracellular recordings from substantia nigra slices revealed the existence ... [more ▼]

Spontaneous apamin-sensitive hyperpolarizations in dopaminergic neurons of neonatal rats. J. Neurophysiol. 80: 3361-3364, 1998. Intracellular recordings from substantia nigra slices revealed the existence of spontaneous hyperpolarizations (amplitude 2-8 mV, duration 100-400 ms) at -60 mV in most dopaminergic neurons of neonatal (9-15 days) but not adult rats. These events were blocked by apamin (300 nM) and bicuculline methochloride (100-300 microM), which blocks apamin-sensitive currents. They were unaffected by the selective gamma-aminobutyric acid-A (GABAA) antagonists SR95531 (100 microM) and picrotoxin (30-50 microM), the GABAB antagonist CGP35348 (300 microM), the D2 antagonist haloperidol (1 microM), and the metabotropic antagonist MCPG (1 mM). The hyperpolarizations were strongly attenuated or abolished when recording electrodes contained 200 mM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid. They were resistant to tetrodotoxin in the majority of the cells. They had some voltage dependency and were in some cases transiently potentiated when cells were briefly depolarized by current injection. We conclude that dopaminergic neurons have developmentally regulated physiological properties. These spontaneous hyperpolarizations might affect the firing rate of these cells, which was found to be lower in neonates than in adults. [less ▲]

Detailed reference viewed: 23 (18 ULg)
Full Text
Peer Reviewed
See detailEffect of potassium channel openers on the firing rate of hippocampal pyramidal cells and A10 dopaminergic neurons in vitro.
Scuvée-Moreau, Jacqueline ULg; Seutin, Vincent ULg; Vrijens, Bernard ULg et al

in Archives of Physiology & Biochemistry (1997), 105(5), 421-8

The effect of four KATP channel openers (KCOs) on the firing rate of CA1 pyramidal cells and A10 dopaminergic neurons was investigated using extracellular recording techniques in rat brain slices ... [more ▼]

The effect of four KATP channel openers (KCOs) on the firing rate of CA1 pyramidal cells and A10 dopaminergic neurons was investigated using extracellular recording techniques in rat brain slices. Pinacidil, lemakalim, diazoxide and a new compound, BPDZ44, had an inhibitory effect on the electrical activity of CA1 pyramidal cells. They all had a similar potency. Only BPDZ44 and diazoxide inhibited the firing rate of A10 dopamine neurons. The sulfonylurea glipizide (1 microM) antagonized the effect of BPDZ44 and diazoxide on A10 neurons but failed to antagonize the effect of KCOs on CA1 pyramidal cells. These results show that differences exist among KCOs in their ability to decrease the electrical activity of various populations of central neurons. [less ▲]

Detailed reference viewed: 16 (7 ULg)
Full Text
Peer Reviewed
See detailEvidence for a Non-Gabaergic Action of Quaternary Salts of Bicuculline on Dopaminergic Neurones
Seutin, Vincent ULg; Scuvée-Moreau, Jacqueline ULg; Dresse, Albert ULg

in Neuropharmacology (1997), 36(11-12, Nov-Dec), 1653-7

Intracellular recordings were made from neurones, presumed to be dopaminergic, in the rat midbrain slice preparation. Bicuculline methiodide (BMI) and methochloride (BMC) reversibly blocked the slow ... [more ▼]

Intracellular recordings were made from neurones, presumed to be dopaminergic, in the rat midbrain slice preparation. Bicuculline methiodide (BMI) and methochloride (BMC) reversibly blocked the slow, apamin-sensitive component of the afterhyperpolarization in these cells. The IC50 for this effect was about 26 microM. In comparison, BMC antagonized the input resistance decrease evoked by muscimol (3 microM) with an IC50 of 7 microM. The base of bicuculline was less potent in blocking the slow afterhyperpolarization. SR95531 (2-[carboxy-3'-propyl]-3-amino-6-paramethoxy-phenyl-pyridaziniu m bromide), another competitive GABA(A) antagonist, and picrotoxin, a non-competitive GABA(A) antagonist, also blocked the action of muscimol (IC50s: 2 and 12 microM respectively), but had no effect on the afterhyperpolarization at a concentration of up to 100 microM. Moreover, 100 microM SR95531 did not affect the blockade of the afterhyperpolarization by BMC. This blockade persisted in the presence of tetrodotoxin and was apparently not due to a reduction of calcium entry, suggesting that it involved a direct action on the channels which mediate this afterhyperpolarization. These results strongly suggest that quaternary salts of bicuculline act on more than one target in the central nervous system. Thus, the involvement of GABA(A) receptors in a given effect cannot be proven solely on the basis of its blockade by these agents. [less ▲]

Detailed reference viewed: 32 (23 ULg)
Full Text
Peer Reviewed
See detailBicuculline methiodide potentiates NMDA-dependent burst firing in rat dopamine neurons by blocking apamin-sensitive Ca2+-activated K+ currents.
Johnson, S. W.; Seutin, Vincent ULg

in Neuroscience Letters (1997), 231(1), 13-6

Apamin, a bee venom toxin which blocks a Ca2+-dependent K+ current, potentiates N-methyl-D-aspartate (NMDA)-induced burst firing in dopamine neurons. We now report that burst firing is also potentiated by ... [more ▼]

Apamin, a bee venom toxin which blocks a Ca2+-dependent K+ current, potentiates N-methyl-D-aspartate (NMDA)-induced burst firing in dopamine neurons. We now report that burst firing is also potentiated by an apamin-like effect of bicuculline methiodide (BMI) at the same concentration (30 microM) which blocks GABA(A) receptors in vitro. Using microelectrodes to record intracellularly from rat dopamine neurons in the midbrain slice, BMI reduced the apamin-sensitive afterhyperpolarization in all cells tested. BMI also mimicked apamin (100 nM) by potentiating burst firing produced by a concentration of NMDA (10 microM) which is too low to evoke burst firing when perfused alone. When recording under voltage-clamp, both BMI and apamin reduced a depolarization-activated outward current which was also sensitive to perfusate containing no-added Ca2+. Although picrotoxin (100 microM) and bicuculline free base (30 microM) blocked the inhibition of firing produced by the GABA(A) agonist isoguvacine (100 microM), neither had apamin-like effects. We conclude that BMI potentiates burst firing by blocking an apamin-sensitive Ca2+-activated K+ current. [less ▲]

Detailed reference viewed: 19 (2 ULg)
Full Text
Peer Reviewed
See detailSulfonylurea-sensitive potassium current evoked by sodium-loading in rat midbrain dopamine neurons.
Seutin, Vincent ULg; Shen, K. Z.; North, R. A. et al

in Neuroscience (1996), 71(3), 709-19

In Parkinson's disease, there is evidence of impaired mitochondrial function which reduces the capacity to synthesize ATP in dopamine neurons. This would be expected to reduce the activity of the sodium ... [more ▼]

In Parkinson's disease, there is evidence of impaired mitochondrial function which reduces the capacity to synthesize ATP in dopamine neurons. This would be expected to reduce the activity of the sodium pump (Na+/K+ ATPase), causing increased intracellular levels of Na+. Patch pipettes were used to introduce Na+ (40 mM in pipette solutions) into dopamine neurons in the rat midbrain slice in order to study the electrophysiological effects of increased intracellular Na+. We found that intracellular Na+ loading evoked 100-300 pA of outward current (at -60 mV) and increased whole-cell conductance; these effects developed gradually during the first 10 min after rupture of the membrane patch. Extracellular Ba2+ reduced most of the outward current evoked by Na+ loading; this Ba(2+)-sensitive current reversed direction at the expected reversal potential for K+ (EK), and was also blocked by extracellular tetraethylammonium (30 mM) and intracellular Cs+ (which replaced K+ in pipette solutions). The sulfonylurea drugs glipizide (IC50 = 4.9 nM), tolbutamide (IC50 = 23 microM) and glibenclamide (1 microM) were as effective as 300 microM Ba2+ in reducing the K+ current evoked by Na+ loading. When recording with "control" pipettes containing 15 mM Na+, diazoxide (300 microM) increased chord conductance and evoked outward current at -60 mV, which also reversed direction near EK. Effects of diazoxide were blocked by glibenclamide (1 microM) or glipizide (300 nM). Diazoxide (300 microM) and baclofen (3 microM), which also evoked K(+)-mediated outward currents recorded with control pipettes, caused little additional increases in outward currents during Na+ loading. Raising ATP concentrations to 10 mM in pipette solutions failed to significantly reduce currents evoked by diazoxide or Na+ loading, suggesting that these currents may not be mediated by ATP-sensitive K+ channels. Finally, Na+ loading using pipettes containing Cs+ in place of K+ evoked a relatively small outward current (50-150 pA at -60 mV), which developed gradually over the first 10 min after rupturing the membrane patch. This current was reduced by dihydro-ouabain (3 microM) and a low extracellular concentration of K+ (0.5 mM instead of 2.5 mM), but was not affected by Ba2+. We conclude that intracellular Na+ loading evokes a current generated by Na+/K+ ATPase in addition to sulfonylurea-sensitive K+ current. This Na(+)-dependent K+ current is unusual in its sensitivity to sulfonylureas, and could protect dopamine neurons against toxic effects of intracellular Na+ accumulation. [less ▲]

Detailed reference viewed: 9 (2 ULg)
See detailDéterminants de l'activité des neurones dopaminergiques mésencéphaliques chez le rat
Seutin, Vincent ULg

Thèse d’agrégation de l’enseignement supérieur (1995)

Detailed reference viewed: 9 (2 ULg)