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PubMed1997

Potassium channel blocker dofetilide does not abolish ischaemic preconditioning.

Ischaemic preconditioning (IP) is a powerful mechanism for infarct reduction. Enhanced K+ conductance and shortening of action potential duration in the early phase of the sustained ischaemic episode have been proposed as important factors in the IP mechanism for infarct reduction. We have investigated whether the potassium channel-blocking class III anti-arrhythmic agent dofetilide could abolish IP in an in situ rabbit heart infarct model. Dofetilide is a specific blocker of the delayed rectifier potassium channel and thus lengthens the action potential duration by reducing potassium conductance during repolarization. Anaesthetized, open-chest rabbits were subjected to 30 min of regional ischaemia and 180 min of reperfusion. The ischaemic risk zone was determined by fluorescent particles, and infarct size was determined by TTC staining. Three groups were investigated: control, ischaemic preconditioned (IP) and IP plus dofetilide-treated (IPdof). The preconditioning protocol was 5 min regional ischaemia and 10 min reperfusion. The IPdof group underwent the same preconditioning protocol but additionally received dofetilide 20 micrograms kg-1 i.v. during the first 2 min of the first reperfusion period. Compared to pre-drug values dofetilide increased monophasic action potential duration from 149.2 +/- 11.5 ms (n = 4) to 215.8 +/- 12.4 ms, supporting blockade of the delayed rectifier potassium channel. At the same time heart rate was decreased from 255.5 +/- 12.5 to 230.3 +/- 8.2. The results expressed as percent infarction of the risk zone +/- SEM for the different groups were as follows: control (n = 11), 42.4 +/- 7.1; IP (n = 6), 7.6 +/- 4.3 [symbol: see text]; IPdof (n = 7), 12.3 +/- 4.1 [symbol: see text] (*p < or = 0.05 vs. control). These results show that the potassium channel-blocking agent dofetilide given after the preconditioning ischaemia but before the sustained ischaemia does not abolish ischaemic preconditioning.

Animals↗
PubMed1993

An ATP-sensitive potassium channel blocker abolishes the potentiating effect of morphine on the bicuculline-induced convulsion in mice.

ICV bicuculline, a selective GABAA antagonist, dose-dependently induced clonic-tonic convulsions in mice. Coadministration of ICV morphine (mu opioid agonist) significantly potentiated ICV bicuculline-induced convulsions, and this effect of morphine was completely blocked by pretreatment with beta-funaltrexamine (beta-FNA), a mu antagonist. ICV glibenclamide, a selective ATP-sensitive potassium (KATP) channel blocker, at a dose which alone did not affect the convulsive threshold of bicuculline, was capable of blocking the exacerbation of ICV bicuculline-induced convulsions by morphine. The present data further suggest that KATP channels may play a tonic regulatory role in the potentiative effect of morphine on ICV bicuculline-induced convulsions.

Adenosine Triphosphate↗
PubMed1994

[3H]histamine uptake and release by astrocytes from rat brain: effects of sodium deprivation, high potassium, and potassium channel blockers.

Histamine transport has been characterized in cultured astroglial cells of rat brain. The kinetics of [3H]-histamine uptake yielded a Km of 0.19 +/- 0.03 microM and a Vmax of 3.12 +/- 0.75 pmol X mg protein-1 X min-1. Transport system revealed high affinity for histamine and an approximately ten times higher capacity than that shown in cultured glial cells of chick embryonic brain. Ouabain which interferes with utilization of ATP to generate ion gradients, and the replacement of Na+ with choline inhibited the initial rate of uptake showing a strong Na(+)-dependency and suggesting the presence of a tightly coupled sodium/histamine symporter. Dissipation of K(+)-gradient (in > out) by high K+ or by K(+)-channel blockers, BaCl2, (100 microM), quinine (100 microM) or Sparteine (20 microM) produced also remarkable inhibitions in the uptake of [3H]-histamine. Impromidine, a structural histamine-analogue could inhibit the uptake non-competitively in a range of concentrations of 1 to 10 microM with a Ki value of 2.8 microM, indicating the specificity of the uptake. [3H]histamine uptake measurements carried out by using a suspension of dissociated hypothalamic cells, of rat brain showed a strong gliotoxin-sensitivity and yielded a Km of 0.33 +/- 0.08 microM; and a Vmax of 2.65 +/- 0.35 pmoles x mg protein-1 x min-1. The uptake could be reversed by incubating the cells in histamine-free Krebs medium. The [3H]histamine efflux was sensitive to Na+ omission, ouabain treatment and high K+ or K+ channel blockers, resulting in marked elevations in the efflux.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2004

Purification, characterization and sequence determination of BmKK4, a novel potassium channel blocker from Chinese scorpion Buthus martensi Karsch.

The scorpion neurotoxin BmKK4 was purified from the venom of the Chinese scorpion Buthus martensi Karsch by a combination of gel-filtration, ion exchange and reversed phase chromatography. The primary sequence of BmKK4 was determined using the tandem MS/MS technique and the cDNA database searching as followings: ZTQCQ SVRDC QQYCL TPDRC SYGTC YCKTT (NH(2)). BmKK4 is the first isolated member of a new subfamily alpha-KTx17 of scorpion K(+) toxins.

Amino Acid Sequence↗
PubMed1998

Potassium channel blockers have minimal effect on repolarization of spontaneous action potentials in rat pituitary lactotropes.

Patch-clamp techniques were used in primary cultures of rat lactotropes and the rat pituitary clonal cell line GH3 to determine the population characteristics of spontaneous action potentials and the nature of the currents responsible for repolarization of spontaneous action potentials. Spontaneous action potentials were observed in 75% of lactotropes (74/99) and 80% of GH3 cells (42/51). Lactotropes exhibited broad and shallow action potentials (average duration 460 ms, peak -17 mV, slope of upstroke 0.5 mV/ms) compared to the GH3 cells which displayed narrow and tall action potentials (average duration 177 ms, peak -10 mV, slope of upstroke 1.6 mV/ms). Blockers of potassium currents were used to determine the role of specific potassium currents in the repolarization process. Spontaneous action potentials in lactotropes were largely unaffected by 4-aminopyridine (4AP), charybdotoxin, and apamin. Tetraethylammonium (TEA) caused only an small increase in peak amplitude and, in a subset of cells, a small increase in duration. In contrast, in GH3 cells, TEA, 4AP, charybdotoxin, and apamin all caused a significant increase in duration, while TEA and charybdotoxin also caused an increase in peak amplitude. Further, apamin caused a positive shift in the afterhyperpolarization voltage. In lactotropes, strong buffering of intracellular calcium with calcium chelators (EGTA or BAPTA) caused a profound increase in action potential duration. Thus, repolarization of action potentials in lactotropes is a calcium-dependent process, but unlike GH3 cells, is not mediated by calcium-dependent potassium currents, nor is it strongly influenced by voltage-dependent potassium currents.

4-Aminopyridine↗
PubMed1997

Effects of aranidipine, a novel calcium channel blocker, on mechanical responses of the isolated rat portal vein: comparison with typical calcium channel blockers and potassium channel openers.

We investigated the effects of aranidipine, a dihydropyridine-type Ca2+ channel blocker, on contractile responses to KCl and spontaneous contractions in isolated rat portal veins in comparison with those of the Ca2+ channel blockers, nifedipine, nicardipine, nitrendipine, diltiazem, and verapamil, and of the K+ channel openers, cromakalim and nicorandil. All the Ca2+ channel blockers concentration-dependently inhibited contractions induced by KCl. Interestingly, aranidipine was more potent against the low K+ (20 mM)-induced contraction than the high K+ (80 mM)-induced contraction, whereas the other Ca2+ channel blockers were equally potent against contractions induced by either concentration of KCl. Cromakalim and nicorandil were effective only on the low K(+)-induced contraction. In addition, all the Ca2+ channel blockers and the K+ channel openers tested inhibited the amplitude of spontaneous contractions of isolated rat portal vein. Tetraethylammonium (TEA), a classic K+ channel blocker, significantly attenuated the effect of aranidipine but not of other Ca2+ channel blockers on the spontaneous contractions. The cromakalim-induced inhibition of spontaneous contractions was antagonized by TEA. Thus aranidipine was found to be different from the typical Ca2+ channel blockers and in part similar to the K+ channel openers in inhibiting mechanical responses of isolated rat portal vein, suggesting that activation of K+ channels may in part in part be involved in the aranidipine-induced vasodilation.

Animals↗
PubMed2000

Dispersion of ventricular repolarization and ventricular fibrillation in left ventricular hypertrophy: influence of selective potassium channel blockers.

This study tested the hypothesis that combination ion channel blockers of the transient outward current (I(to)) and the rapid component of the delayed rectifying current (I(Kr)) would produce greater prolongation of the ventricular action potential duration (APD) and increased dispersion of the APD in hypertrophied hearts compared with control hearts. Isolated rabbit hearts were studied 48 +/- 5 days postabdominal aortic banding. Left ventricular endocardial and epicardial APDs were significantly greater at baseline in the hypertrophied group than in controls (P <.05). The magnitude of APD prolongation induced by the I(to) blocker 4-aminopyridine (4-AP) and combination 4-AP and the I(Kr) blocker dofetilide was greater in the hypertrophied hearts than in the normal hearts (P <.01). Mean APD dispersion was significantly greater in the hypertrophied group than in the control hearts at baseline (P <.05). 4-AP increased APD dispersion by a similar magnitude in the hypertrophied hearts (10 +/- 10 ms) and the control hearts (8 +/- 8 ms, P = NS), whereas the combination 4-AP and dofetilide increased APD dispersion by a greater magnitude in the hypertrophied hearts (41 +/- 28 ms) than the control hearts (21 +/- 11 ms, P <.05). Ventricular fibrillation occurred spontaneously in four hypertrophied hearts (40%) during combination drug perfusion and in none of the control hearts (P <.05). Thus, combination I(to) and I(Kr) blockers cause greater prolongation APD and increased APD dispersion in left ventricular hypertrophy, and this is associated with the development of ventricular fibrillation.

4-Aminopyridine↗
PubMed2000

Pharmacological characterization of the discriminative stimulus effects of the potassium channel blocker 4-aminopyridine in rats.

The discriminative stimulus (DS) effects of 4-aminopyridine (4-AP) were evaluated in 36 male Sprague-Dawley rats that were trained to discriminate 4-AP from saline in a standard two-lever food reinforced drug discrimination procedure. 4-AP along with its structural analogs 3-aminopyridine (3-AP), 2-aminopyridine (2-AP), and 2,3-diaminopyridine (2,3-DIAP) produced dose-dependent increases in the percentage of responses on the 4-AP-associated lever with full substitution at one or more doses. 2,6-Diaminopyridine (2, 6-DIAP) and 3,4-diaminopyridine (3,4-DIAP) produced dose-dependent increases in the percentage of responses on the 4-AP-associated lever but only partially substituted for 4-AP. Neither 4-dimethylaminopyridine (4-DMAP) nor pyridine substituted for 4-AP. Substitution studies were also conducted with indirect dopamine, norepinephrine, serotonin, and acetylcholine agonists, and gamma-aminobutyric acid A (GABA(A)) agonists and antagonists. The norepinephrine reuptake inhibitor tomoxetine, but not nisoxetine or imipramine, produced dose-dependent increases in the percentage of responses on the 4-AP-associated lever and partially substituted for 4-AP. In addition, antagonism studies were conducted using indirect dopamine, norepinephrine, serotonin, acetylcholine antagonists, and GABA(A) agonists as pretreatments to the training dose of 4-AP. The benzodiazepine agonists chlordiazepoxide and diazepam dose dependently attenuated the DS effects of 4-AP. The present results demonstrate that the K-channel blocker 4-AP can be trained as a DS in rats and the DS effects of 4-AP are likely mediated through blockade of voltage-dependent K-channels. The results also demonstrate a novel interaction between benzodiazepines and K-channels.

4-Aminopyridine↗
PubMed1999

Effects of potassium channel blockers on CO2-induced slowly adapting pulmonary stretch receptor inhibition.

In anesthetized, artificially ventilated rabbits with vagus nerve section, inhalation of CO(2) gas mixtures (tracheal CO(2) concentration ranging from 8.0 to 10.2%) for 60 s decreased slowly adapting pulmonary stretch receptor (SAR) activity during both inflation and deflation. The magnitude of decreased receptor activity during deflation had a more pronounced effect than that seen during inflation. CO(2) inhalation did not cause any significant change in tracheal pressure (P(T)) as an index of bronchomotor tone. Intravenous administration of 4-aminopyridine (0. 7 and 2.0 mg/kg i.v.), a K(+) channel blocker, which dose-dependently increased SAR activity during deflation and had no effect on P(T), abolished or attenuated the decrease in SAR activities induced by CO(2) inhalation in a dose-dependent manner. The K(+) channel blocker tetraethylammonium (2.0 and 6.0 mg/kg i.v.) that did not significantly alter either basal SAR discharge or P(T) had no effect on the inhibitory responses of receptor activity to CO(2) inhalation. These results suggest that the inhibitory mechanism of CO(2) inhalation on SARs may be involved in the activation of 4-aminopyridine-sensitive K(+) channels in the nerve terminals of SARs.

4-Aminopyridine↗
PubMed2006

Pulmonary vasoconstrictor action of KCNQ potassium channel blockers.

BACKGROUND: KCNQ channels have been widely studied in the nervous system, heart and inner ear, where they have important physiological functions. Recent reports indicate that KCNQ channels may also be expressed in portal vein where they are suggested to influence spontaneous contractile activity. The biophysical properties of K+ currents mediated by KCNQ channels resemble a current underlying the resting K+ conductance and resting potential of pulmonary artery smooth muscle cells. We therefore investigated a possible role of KCNQ channels in regulating the function of pulmonary arteries by determining the ability of the selective KCNQ channel blockers, linopirdine and XE991, to promote pulmonary vasoconstriction. METHODS: The tension developed by rat and mouse intrapulmonary or mesenteric arteries was measured using small vessel myography. Contractile responses to linopirdine and XE991 were measured in intact and endothelium denuded vessels. Experiments were also carried out under conditions that prevent the contractile effects of nerve released noradrenaline or ATP, or block various Ca2+ influx pathways, in order to investigate the mechanisms underlying contraction. RESULTS: Linopirdine and XE991 both contracted rat and mouse pulmonary arteries but had little effect on mesenteric arteries. In each case the maximum contraction was almost as large as the response to 50 mM K+. Linopirdine had an EC50 of around 1 microM and XE991 was almost 10-fold more potent. Neither removal of the endothelium nor exposure to phentolamine or alpha,beta-methylene ATP, to block alpha1-adrenoceptors or P2X receptors, respectively, affected the contraction. Contraction was abolished in Ca2+-free solution and in the presence of 1 microM nifedipine or 10 microM levcromakalim. CONCLUSION: The KCNQ channel blockers are potent and powerful constrictors of pulmonary arteries. This action may be selective for the pulmonary circulation as mesenteric arteries showed little response. The results imply that the drugs act directly on smooth muscle cells and contraction requires voltage-dependent Ca2+ influx. It is concluded that the drugs probably act by blocking KCNQ channels in pulmonary artery myocytes, leading to membrane depolarization and Ca2+ influx through L-type Ca2+ channels. This implies a functional role for KCNQ channels in regulating the resting membrane potential of pulmonary artery myocytes.

Animals↗
PubMed2003

Preserved effects of potassium channel blockers in the pacing-induced remodeled canine atrium: a comparison between E4031 and azimilide.

This study was designed to evaluate the electrophysiologic effects of E4031 (a pure IKr blocker) and azimilide (AZ: a combined Ikr + IKs blocker) at various stages of atrial electrical remodeling. Twelve dogs underwent continuous rapid atrial pacing (400/min) for 14 days. The electrophysiologic study was performed on the day before as well as after 2, 7, and 14 days of rapid atrial pacing both before and after the administration of either E4031 (n = 6) or AZ (n = 6). In response to rapid atrial pacing, the atrial effective refractory period (ERP), conduction velocity, and wavelength decreased significantly at pacing cycle lengths (PCLs) of 200 and 400 ms (P < 0.05). E4031 prolonged ERP in a reverse use-dependent manner throughout the study period. AZ also prolonged ERP during the 14 days of rapid pacing. ERP prolongation at a PCL of 200 ms was significantly greater with AZ than with E4031 (P < 0.05). The effects of blocking IKr by E4031 and IKr + IKs by AZ were well preserved at various stages of atrial electrical remodeling. However, the effect of prolonging ERP at a shorter PCL was more prominent by AZ than by E4031. Thus, IKs blockade may add a favorable anti-fibrillatory effect to IKr blockade even in the remodeled atrium.

Animals↗
PubMed2003

Potassium channel blockers attenuate hypoxia- and ischemia-induced neuronal death in vitro and in vivo.

BACKGROUND AND PURPOSE: In light of recent evidence suggesting that an upregulation of K+ efflux mediated by outward delayed rectifier (I(K)) channels promotes central neuronal apoptosis, we sought to test the possibility that blockers of I(K) channels might be neuroprotective against hypoxia/ischemia-induced neuronal death. METHODS: Membrane currents were recorded with the use of patch clamp recordings in cultured murine cortical neurons. Protective effects of K+ channel blockers were examined in rats subjected to transient middle cerebral artery occlusion followed by 14-day reperfusion. RESULTS: The K+ channel blocker tetraethylammonium (TEA) (5 mmol/L) selectively blocked I(K) without affecting N-methyl-D-aspartate receptor-mediated current or voltage-gated Ca2+ currents. Both TEA and a lipophilic K+ channel blocker, clofilium, attenuated neuronal apoptosis induced by hypoxia in vitro and infarct volume induced by ischemia in vivo. CONCLUSIONS: These data are consistent with the idea that K+ channel-mediated K+ efflux may contribute to ischemia-triggered apoptosis and suggest that preventing excessive K+ efflux through K+ channels may constitute a therapeutic approach for the treatment of stroke.

Animals↗
PubMed1995

Effect of almokalant, a selective potassium channel blocker, on the termination and inducibility of paroxysmal supraventricular tachycardias: a study in patients with Wolff-Parkinson-White syndrome and atrioventricular nodal reentrant tachycardia. Almokalant PSVT Study Group.

Almokalant is a newly developed selective blocker of the delayed outward K+ current and exhibits the electrophysiological properties of a class III antiarrhythmic agent. In a Scandinavian multicenter, placebo-controlled trial, the antiarrhythmic efficacy of almokalant was investigated in patients with paroxysmal supraventricular tachycardia: 87 patients with mean age of 50 +/- 14 years (range 21-71 years), with reciprocating tachycardia due to either Wolff-Parkinson-White (WPW) syndrome (n = 58) or atrioventricular nodal reentry tachycardia (AVNRT) (n = 29) were studied with transesophageal atrial stimulation. After a baseline procedure, during which sustained tachycardia was induced and overdrive terminated, tachycardia was reinduced and an intravenous (i.v.) infusion of either placebo or almokalant (aiming at a pseudoequilibrium plasma level of 20, 50, 100, or 150 nM) (Cpl 20-Cpl 150), was administered. Each patient was studied at two Cpl. Thirty-nine patients were randomly assigned in a double-blind fashion to either placebo+almokalant at Cpl 20 or Cpl 20 + Cpl 50; 26 patients were studied openly at Cpl 50 + Cpl 100, and 22 were studied openly at Cpl 100 + Cpl 150 almokalant. The antiarrhythmic efficacy was assessed as the ability to terminate induced tachycardia and to suppress inducibility: The proportion of patients in which the tachycardia was terminated was placebo 3 of 20 (15%); Cpl 20, 7 of 36 (19%): Cpl 50, 10 of 36 (28%); Cpl 100, 14 of 35 (40%); and Cpl 150, 5 of 9 (56%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1996

Synthesis and structural characterisation of analogues of the potassium channel blocker charybdotoxin.

Charybdotoxin is a 37-residue polypeptide toxin from scorpion venom, which acts by blocking voltage-gated and Ca(2+)-activated K+ channels. We have synthesized charybdotoxin and three mono-substituted analogues using an Fmoc-tBu protocol. The Phe-2 --> Tyr analogues was chosen to introduce a site for Tyr iodination which was distinct from the K+ channel binding surface, while the Glu-12 --> Gln and Arg-19 --> His analogues were studied to probe the roles of charged residues at these positions in the structure and activity of the toxin. The synthetic native molecule was equipped with natural toxin in inhibiting the human erythrocyte Ca(2+)-dependent K+ channel. The affinities of all three analogues for the erythrocyte K+ channel were slightly reduced, with the Arg-19 --> His analogue showing the greatest increase in IC50 (2.30-fold). Two-dimensional 1H-NMR studies of these analogues showed that the Glu-12 to Gln substitution, which appeared to destabilise the N-terminal half of the alpha-helix, possibly due to the weakening of an N-terminal helix capping interaction which is apparent from our NMR data. His-21 has a pKa more than one unit below the value for a non-interacting histidine. Possible reasons for this are that the imidazolium side chain is partly buried and is located near positively charged moieties. Thus, His-21 would be neutral at physiological pH, where charybdotoxin binds to the potassium channel.

Amino Acid Sequence↗
PubMed2001

Effects of potassium channel blockers on hyperinflation-induced rapidly adapting pulmonary stretch receptor stimulation in the rabbit.

The effects of K+ channel blockers, such as 4-aminoprydine (4-AP) and tetraethylammonium (TEA), on the excitatory responses of rapidly adapting pulmonary stretch receptor (RAR) activity to hyperinflation (inflation volume=3 tidal volumes) were investigated in anesthetized, artificially ventilated rabbits after vagus nerve section. The changes in the RAR adaptation index (AI) produced by constant-pressure (approximately 30 cmH2O, 29.7+/-0.2 cmH2O) inflation of the lungs were also examined before and after pretreatment with 4-AP and TEA. The administration of 4-AP (0.7 and 2.0 mg/kg) potentiated hyperinflation-induced RAR stimulation in a dose-dependent manner. During hyperinflation after 2.0 mg/kg 4-AP administration the discharge of RARs showed a relatively regular firing pattern in both inflation and deflation phases. The RAR AI values during constant-pressure inflation of the lungs were significantly reduced by 4-AP treatment (2.0 mg/kg). TEA treatment (2.0 and 7.0 mg/kg) did not significantly alter either the excitatory response of RAR activity to hyperinflation or the RAR AI values seen during constant-pressure inflation of the lungs. These results suggest that during hyperinflation in in vivo experiments on rabbits, RARs may be maintained at a lower activity by opening the 4-AP-sensitive K+ channels on the receptor endings, which can determine accommodation of the receptor discharge.

4-Aminopyridine↗
PubMed1996

Changes in pharmacological sensitivity of the spinal cord to potassium channel blockers following acute spinal cord injury.

In this investigation we studied changes in the pharmacological sensitivity of dorsal column white matter to a variety of K+ channel blockers, including 4-aminopyridine (4-AP), following acute spinal cord injury (SCI) in vitro using a modified aneurysm clip. Compound action potentials (CAPs) were recorded extracellularly with microelectrodes and by the sucrose gap recording technique. With acute trauma, injured axons showed significantly enhanced sensitivity to 4-AP in comparison to uninjured controls as early as 10 min following injury. Microelectrode derived field potential recordings showed a significantly greater increase in a delayed positive component (P2) of the CAP at both 1 and 5 mM 4-AP in injured as compared to noninjured axons. Sucrose gap recordings showed an increase in CAP area and amplitude of injured axons with 1 mM 4-AP at 22 degrees C. The relative improvement in CAP area and amplitude with 4-AP was even more pronounced (P < 0.05) at higher temperatures (37 degrees C). As shown by sucrose gap, 4-AP also caused a delay in repolarization of the CAP and depolarization of the resting membrane potential of acutely injured axons. TEA (0.1 mM and 10 mM), when infused alone and with CsCl (10 mM), produced similar effects on injured and intact axons. In conclusion, the results of this study show an altered sensitivity of the spinal cord to 4-AP following acute SCI. In contrast, TEA and CsCl exhibit no difference in their effects on low frequency axonal conduction between injured and noninjured axons. The data suggest that acute traumatic myelin disruption following SCI causes axonal dysfunction partly due to abnormal activation of 4-AP-sensitive 'fast' K+ channels.

4-Aminopyridine↗
PubMed2006

Potentiating effect of the ATP-sensitive potassium channel blocker glibenclamide on complex I inhibitor neurotoxicity in vitro and in vivo.

Previous studies have demonstrated a deficiency in mitochondrial function in Parkinson's disease. We measured the ability of mitochondrial inhibitors of complexes I (rotenone, MPP(+), and HPP(+)), II (amdro), IV (Na cyanide), and an uncoupler (dinoseb) to release preloaded dopamine from murine striatal synaptosomes. These compounds were potent dopamine releasers, and the effect was calcium-dependent. The striatum also contains a significant density of K(ATP)(+) channels, which play a protective role during ATP decline. Blockage of these channels with glibenclamide only potentiated the dopamine release by complex I inhibitors, and a selective potentiating effect of glibenclamide on the toxicity of MPTP was also observed, in vivo, using C57BL/6 mice. Western blots of striatal dopamine transporter (DAT) and tyrosine hydroxylase (TH) proteins demonstrated that 30 mg/kg of glibenclamide alone did not affect the expression of DAT and TH after two weeks of daily treatments, but it significantly enhanced the reduction of DAT and TH by a single dose of 20 mg/kg of MPTP. Amdro or dinoseb alone, or in conjunction with glibenclamide did not alter the expression of DAT and TH. The possible mechanisms underlying dopamine release and the selectivity of glibenclamide were further evaluated, in vitro. (86)Rb efflux assay showed that glibenclamide inhibited rotenone-induced K(+) efflux, but not dinoseb-induced K(+) efflux. Analysis of ATP titers in treated synaptosomes did not support a correlation between mitochondrial inhibition and K(ATP)(+) channel activation. However, assay of reactive oxygen species (ROS) showed that greater amounts of ROS generated by complex I inhibitors was a contributory factor to K(ATP)(+) channel activation and glibenclamide potentiation. Overall, these findings suggest that co-exposure to mitochondrial complex I inhibitors and glibenclamide or a genetic defect in K(ATP)(+) channel function, may increase neurotoxicity in the striatal dopaminergic system.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗