Biomedical subjects

David W Busija

Publications and source records attributed to David W Busija.

At least 37 records · Page 2Linked to original sources

PubMed2005

Effects of ATP-sensitive potassium channel activators diazoxide and BMS-191095 on membrane potential and reactive oxygen species production in isolated piglet mitochondria.

Mitochondrial ATP-sensitive potassium (mitoK(ATP)) channel openers protect the piglet brain against ischemic stress. Effects of mitoK(ATP) channel agonists on isolated mitochondria, however, have not been directly examined. We investigated the effects of K(ATP) channel openers and blockers on membrane potential and on the production of reactive oxygen species (ROS) in isolated piglet mitochondria. Diazoxide and BMS-191095, putative selective openers of mitoK(ATP), decreased the mitochondrial membrane potential (delta psi(m)). On a molar basis, diazoxide was less effective than BMS-191095. In contrast, diazoxide but not BMS-191095 increased ROS production by mitochondria. Since diazoxide also inhibits succinate dehydrogenase (SDH), we examined the effects of 3-nitropropionic acid (3-NPA), an inhibitor of SDH. 3-NPA failed to change the delta psi(m) but increased ROS production. Inhibitors of K(ATP) channels did not affect resting delta psi(m) or ROS production, but glibenclamide and 5-hydroxydecanoate (5-HD) blocked effects of diazoxide and BMS-191095 on delta psi(m) and diazoxide effects on ROS production. We conclude that BMS-191095 has selective effects on mitoK(ATP) channels while diazoxide also increases ROS production probably via inhibition of SDH.

Adenosine Triphosphate↗

PubMed2005

The novel red-fluorescent probe DAR-4M measures reactive nitrogen species rather than NO.

INTRODUCTION: Several fluorescent probes were designed for the measurement of nitric oxide (NO), however, questions arose regarding their specificity and sensitivity in biological samples. In the present study we tested the reaction of a novel rhodamine-based chromophore diaminorhodamine-4M (DAR-4M) with NO and other reactive nitrogen and oxygen species. METHODS: We performed fluorometry in 96-well plates in a cell-free buffer with similar ion concentrations as the cytoplasm. Dose-response curves were generated using various NO donors and reactive nitrogen and oxygen species. The effects were compared between the red-fluorescent DAR-4M and its green-fluorescent counterpart 4-amino-5-methylamino-2',7'-difluorofluorescein (DAF-FM). RESULTS: DAR-4M had a markedly higher fluorescence yield to NO donors than DAF-FM, while both probes had a comparable threshold of sensitivity (in the range of 0.1 mM nitroprusside). Both dyes reacted with various NO donors in a dose-dependent manner, while superoxide, hydrogen peroxide, peroxynitrite, or nitroxyl failed to change the fluorescence intensity of the probes. DAR-4M was potentiated in the presence of peroxynitrite to react with low levels of NO donors in a similar manner to DAF-FM. DISCUSSION: We conclude that DAR-4M is a suitable red-fluorescent probe for the qualitative assessment of reactive nitrogen species production, but not specific for NO. Quantitative comparisons among samples is inappropriate since the fluorescent yield is affected by the presence of other oxidants in the sample.

Artifacts↗

PubMed2005

Diazoxide preconditioning attenuates global cerebral ischemia-induced blood-brain barrier permeability.

Brain edema formation due to blood-brain barrier (BBB) disruption is a major consequence of cerebral ischemia. Previously, we demonstrated that targeting mitochondrial ATP-sensitive potassium channels (mitoK(ATP)) protects neuronal tissues in vivo and in vitro, however, the effects of mitoK(ATP) openers on cerebral endothelial cells and on BBB functions have never been examined. We investigated the effects of mitoK(ATP) channel opener diazoxide on BBB functions during ischemia/reperfusion injury (I/R). Rats were treated with 6, 20 or 40 mg/kg diazoxide ip for 3 days then exposed to global cerebral ischemia for 30 min. BBB permeability was assessed by administering Evan's-blue (EB) and Na-fluorescein (NaF) at the beginning of the 30 min reperfusion. I/R increased BBB permeability for the large molecular weight EB (ng/mg) in the cortex (control: 146 +/- 12, n = 7; I/R: 1049 +/- 152, n = 11) which was significantly attenuated in diazoxide-treated rats (575 +/- 99, n = 9; 582 +/- 104, n = 8; 20 and 40 mg/kg doses). Diazoxide pretreatment also significantly inhibited the extravasation of the low molecular weight NaF. Edema formation in the cortex was also decreased after diazoxide pretreatment. In cultured cerebral endothelial cells, diazoxide depolarized the mitochondrial membrane, suggesting a direct diazoxide effect on the endothelial mitochondria. Our results demonstrate that preconditioning of cerebral endothelium with diazoxide protects the BBB against ischemic stress.

Animals↗

PubMed2005

Mitochondrial NO and reactive nitrogen species production: does mtNOS exist?

It is more than 10 years now that mitochondria are suspected to be sources of nitric oxide (NO). This hypothesis is intriguing since NO has multiple targets within the organelle and it is even suggested that mitochondria are the primary targets of NO in the cell. Most remarkably, nanomolar concentrations of NO can inhibit mitochondrial respiration, so even a small amount of NO in the mitochondrial matrix may regulate ATP synthesis. Therefore, the idea that mitochondria themselves are capable of NO production is an important concept in several physiological and pathological mechanisms. However, this field of research generates surprisingly few original papers and the published studies contain conflicting results. The reliability of the results is frequently questioned since they are seldom reproduced by independent investigators. Until 2003, all papers published in this field showed affirmative results but since then several studies directly challenged the existence of a mitochondrial nitric oxide synthase. The present review aims to summarize the most recent developments in mitochondrial NO production, highlights a few unsolved questions, and proposes new directions for future work in this research area.

Animals↗

PubMed2005

Piglet pial arteries respond to N-methyl-D-aspartate in vivo but not in vitro.

Controversy exists concerning whether activation of N-methyl-D-aspartate (NMDA) receptors exerts direct dilator effects on cerebral arteries. The purpose of this study was to examine the responses of isolated piglet arteries to NMDA to determine whether isolated arteries, apart from surrounding neuronal tissue, are capable of responding to NMDA. Piglet arteries (100-200 microm) were isolated from branches of the middle cerebral artery and carefully dissected free of adherent tissue. Arteries were then mounted in an arteriograph system and pressurized to either 30 mm Hg (n=8), 60 mm Hg (n=10), 80 mm Hg (n=6), or 100 mm Hg (n=5). After development of spontaneous tone, NMDA (10(-5) to 10(-3) M) was administered abluminally to the vessels, and no appreciable response was noted (for example; 10(-4) M, 30 mm Hg: 3+/-3% change in active diameter; 60 mm Hg: -4+/-3% change in active diameter). Following a thorough washout, vessels were treated with bradykinin (10(-9) to 10(-7) M), and the arteries did respond (10(-7) M, 30 mm Hg: 26+/-3% change in active diameter; 60 mm Hg: 65+/-10% change in active diameter). In contrast, 10(-5) M and 10(-4) M NMDA dilated arteries in vivo by 9+/-2% and 29+/-6% change in active diameter, respectively (n=6). These results demonstrate that isolated cerebral arteries do not respond directly to NMDA receptor activation. This work confirms our previous in vivo data and is consistent with the hypothesis that cerebral arteries respond to NMDA through a secondary interaction mediated by neuronal release of NO and not to NMDA directly.

Animals↗

PubMed2005

Acetaminophen and the cyclooxygenase-3 puzzle: sorting out facts, fictions, and uncertainties.

Cyclooxygenase (COX)-3, a novel COX splice variant, was suggested as the key to unlocking the mystery of the mechanism of action of acetaminophen. Although COX-3 might have COX activity in canines, and this activity might be inhibited by acetaminophen, its low expression level and the kinetics indicate unlikely clinical relevance. In rodents and humans, COX-3 encodes proteins with completely different amino acid sequences than COX-1 or COX-2 and without COX activity; therefore, it is improbable that COX-3 in these species plays a role in prostaglandin-mediated fever and pain. The aim of this review is to evaluate the literature that seeks to point out critical theoretical and methodological limitations of the COX-3 studies that led several investigators to scientifically questionable conclusions.

Acetaminophen↗

PubMed2005

The role of nitric oxide in the development of cortical spreading depression-induced tolerance to transient focal cerebral ischemia in rats.

Cortical spreading depression (CSD) has been documented to confer ischemic tolerance on brain. Although nitric oxide (NO) is a crucial mediator in preconditioning under certain circumstances, the role of NO in CSD-induced neuroprotection is unclear. We examined the effect of L-NAME, an inhibitor of NO synthase, on CSD-induced tolerance against transient focal cerebral ischemia. A solution of 0.5 M KCl was applied for 2 h on the right hemisphere to induce CSD. Animals received either vehicle or L-NAME (4 mg/kg, iv) 30 min before CSD. Temporary occlusion (120 min) of the right middle cerebral artery was induced 4 days after preconditioning and the infarct volume was measured. Additionally, ERK 1/2 activation and cyclooxygenase-2 (COX-2) expression in the cerebral cortex were examined by Western blotting analysis immediately after cessation of CSD, or at 1, 2, 4, 8, and 24 h after CSD. CSD reduced infarct volume from 275 +/- 15 mm3 (mean +/- SEM) in the non-CSD group to 155 +/- 14 mm3 in the CSD group (P < 0.05). L-NAME abolished this protection (281 +/- 14 mm3; P < 0.05 vs. CSD group). Elevated ERK activation and COX-2 expression were observed immediately after or 8 h after preconditioning, respectively. Those responses are significantly augmented by L-NAME (3-fold for ERK and 4-fold for COX-2). These results suggest a crucial role of NO in the establishment of preconditioning with CSD.

Animals↗

PubMed2005

Diazoxide preserves hypercapnia-induced arteriolar vasodilation after global cerebral ischemia in piglets.

Diazoxide (Diaz), an activator of mitochondrial ATP-sensitive K+ (mitoKATP) channels, is neuroprotective, but the mechanism of action is unclear. We tested whether Diaz preserves endothelium-dependent (hypercapnia) or -independent [iloprost (Ilo)] cerebrovascular dilator responses after ischemia-reperfusion (I/R) in newborn pigs and whether the effect of Diaz is sensitive to 5-hydroxydecanoate (5-HD), an inhibitor of mitoKATP channels. Anesthetized, ventilated piglets (n = 48) were equipped with closed cranial windows. Changes in diameter of pial arterioles were determined with intravital microscopy in response to graded hypercapnia (5-10% CO2 - 21% O2-balance N2, n = 25) or Ilo (0.1-1 microg/ml, n = 18) before and 1 h after 10 min of global I/R. Experimental groups were pretreated with vehicle, NS-398 (a selective cyclooxygenase-2 inhibitor, 1 mg/kg), Diaz (3 mg/kg), or 5-HD (20 mg/kg) + Diaz. Potential direct effects of Diaz and 5-HD on hypercapnic vasodilation were also tested in the absence of I/R (n = 5). To confirm the direct effect of Diaz on mitochondria, mitochondrial membrane potential in cultured piglet cerebrovascular endothelial cells was monitored using Mito Tracker Red. Hypercapnia resulted in dose-dependent pial arteriolar vasodilation, which was attenuated by approximately 70% after I/R in vehicle- and NS-398-treated animals. Diaz and 5-HD did not affect the CO2 response. Diaz significantly preserved the postischemic vasodilation response to hypercapnia, but not to Ilo. Diaz depolarized mitochondria in cultured piglet cerebrovascular endothelial cells, and 5-HD completely abolished the protective effect of Diaz, both findings indicate a role for mitoKATP channels. In summary, preservation of arteriolar dilator responsiveness by Diaz may contribute to neuroprotection.

Animals↗

PubMed2005

Cloning and characterization of cyclooxygenase-1b (putative cyclooxygenase-3) in rat.

A splice variant of cyclooxygenase-1 (COX-1), COX-1b (previously termed as COX-3), has been identified in canine tissues as an acetaminophen-sensitive isoform, but the sequence of COX-1b mRNA and the encoded protein are not known in rats. We cloned and sequenced rat COX-1b mRNA from cerebral endothelial cells. Sequence analysis indicated that the 98-base pair intron-1 of COX-1 gene remains unprocessed in the COX-1b mRNA, causing a frameshift mutation and a 127-amino acid open reading frame with no sequence similarity with known cyclooxygenases. Transient and permanent transfection of COS-7 cells with a vector containing the rat COX-1b cDNA resulted in synthesis of a protein of the expected size. We generated an affinity-purified polyclonal antibody against the rat COX-1b protein. Western blot analysis of rat tissues using this antibody demonstrated the likely existence of rat COX-1b protein in vivo with the highest expression in heart, kidney, and neuronal tissues. Our results on both stable and on transiently transfected COS-7 cells suggest that rat COX-1b does not have cyclooxygenase activity and does not have any effect on the inhibition of prostaglandin production by acetaminophen. Because this protein has a completely different amino acid sequence than COX-1 and COX-2 and it does not have cyclooxygenase activity, we suggest a name cyclooxygenase variant protein to distinguish it from the known prostaglandin-synthesizing cyclooxygenase isoforms.

Amino Acid Sequence↗

PubMed2005

Impaired insulin-induced vasodilation in small coronary arteries of Zucker obese rats is mediated by reactive oxygen species.

Insulin resistance (IR) and associated hyperinsulinemia are major risk factors for coronary artery disease. Mechanisms linking hyperinsulinemia to coronary vascular dysfunction in IR are unclear. We evaluated insulin-induced vasodilation in isolated small coronary arteries (SCA; approximately 225 microm) of Zucker obese (ZO) and control Zucker lean (ZL) rats. Vascular responses to insulin (0.1-100 ng/ml), ACh (10(-9)-10(-5) mol/l), and sodium nitroprusside (10(-8)-10(-4) mol/l) were assessed in SCA by measurement of intraluminal diameter using videomicroscopy. Insulin-induced dilation was decreased in ZO compared with ZL rats, whereas ACh and sodium nitroprusside elicited similar vasodilations. Pretreatment of arteries with SOD (200 U/ml), a scavenger of reactive oxygen species (ROS), restored the vasorelaxation response to insulin in ZO arteries, whereas ZL arteries were unaffected. Pretreatment of SCA with N-nitro-L-arginine methyl ester (100 micromol/l), an inhibitor of endothelial nitric oxide (NO) synthase (eNOS), elicited a vasoconstrictor response to insulin that was greater in ZO than in ZL rats. This vasoconstrictor response was reversed to vasodilation in ZO and ZL rats by cotreatment of the SCA with SOD or apocynin (10 micromol/l), a specific inhibitor of vascular NADPH oxidase. Lucigenin-enhanced chemiluminescence showed increased basal ROS levels as well as insulin (330 ng/ml)-stimulated production of ROS in ZO arteries that was sensitive to inhibition by apocynin. Western blot analysis revealed increased eNOS expression in ZO rats, whereas Mn SOD and Cu,Zn SOD expression were similar to ZL rats. Thus IR in ZO rats leads to decreased insulin-induced vasodilation, probably as a result of increased production of ROS by vascular NADPH oxidase, leading to decreased NO bioavailability, despite a compensatory increase in eNOS expression.

Acetylcholine↗

PubMed2004

Acetaminophen-sensitive prostaglandin production in rat cerebral endothelial cells.

Acetaminophen is a widely used antipyretic and analgesic drug whose mechanism of action has recently been suggested to involve inhibitory effects on prostaglandin synthesis via a newly discovered cyclooxygenase variant (COX-3). Because COX-3 expression is high in cerebral endothelium, we investigated the effect of acetaminophen on the prostaglandin production of cultured rat cerebral endothelial cells (CECs). Acetaminophen dose-dependently inhibited both basal and LPS-induced PGE(2) production in CECs with IC(50) values of 15.5 and 6.9 microM, respectively. Acetaminophen also similarly inhibited the synthesis of 6-keto-PGF(1alpha) and thromboxane B(2). LPS stimulation increased the expression of COX-2 but not COX-1 or COX-3. In addition, the selective COX-2 inhibitor NS398 (1 microM) was equally as effective as acetaminophen in blocking LPS-induced PGE(2) production. Acetaminophen did not influence the expression of the three COX isoforms and the inducible nitric oxide synthase. In LPS-stimulated isolated cerebral microvessels, acetaminophen also significantly inhibited PGE(2) production. Our results show that prostaglandin production in CECs during basal and stimulated conditions is very sensitive to inhibition by acetaminophen and suggest that acetaminophen acts against COX-2 and not COX-1 or COX-3. Furthermore, our findings support a critical role for cerebral endothelium in the therapeutic actions of acetaminophen in the central nervous system.

6-Ketoprostaglandin F1 alpha↗

PubMed2004

Diazoxide prevents mitochondrial swelling and Ca2+ accumulation in CA1 pyramidal cells after cerebral ischemia in newborn pigs.

Diazoxide (DIAZ), an opener of mitochondrial ATP-sensitive K(+) channels (mK(ATP)), protects neurons against hypoxic/ischemic stress in vivo, however, direct evidence showing mitochondrial effects of DIAZ in postischemic neurons is lacking. We investigated if DIAZ affects mitochondrial alterations after global ischemia/reperfusion (I/R) in CA1 pyramidal neurons by using oxalate-pyroantimonate electron cytochemistry. Anesthetized piglets were either non-treated, or treated with DIAZ (3 mg/kg, iv), I/R, DIAZ+I/R, or 5-hydroxy-decanoate (5HD)+DIAZ+I/R (n=6, 6, 11, 5, 7, respectively). Ischemia (10 min) was induced by intracranial pressure (ICP) elevation. After 5-30 min of reperfusion, the brains were fixed for ultrastructural studies. Relative volumes of Ca(2+)-containing deposits and mitochondria in CA1 pyramidal cells were determined by point counting on electron micrographs. I/R resulted in maximal increases in mitochondrial volume (from 7.14+/-0.63% to 9.74+/-0.57%*), and Ca(2+) levels (from 5.86+/-1.11% to 11.39+/-1.35%*; mean+/-S.E.M., *p<0.05) at 10-15-min reperfusion time. In this interval, pretreatment with DIAZ virtually abolished mitochondrial swelling (6.88+/-0.49%) and Ca(2+) accumulation (5.15+/-0.82%) evoked by I/R. The protective effect of DIAZ was reduced by 5HD, an inhibitor of mK(ATP), resulting in a calcium accumulation similar to that after IR (10.44+/-1.98%). Thus, DIAZ might preserve mitochondrial integrity in CA1 pyramidal cells after I/R, at least in part mediated by mK(ATP).

Animals↗

PubMed2004

Vasoconstrictor mechanisms in the cerebral circulation are unaffected by insulin resistance.

Insulin-resistance (IR) impairs agonist-induced relaxation in cerebral arteries, but little is known about its effect on constrictor mechanisms. We examined the vascular responses of the basilar artery (BA) and its side branches in anesthetized Zucker lean (ZL) and IR Zucker obese (ZO) rats using a cranial window technique. Endothelin-1 (ET-1) constricted the BAs in both the ZL and ZO rats, but there was no significant difference between the two groups (ZL: 36 +/- 8%; ZO: 33 +/- 3% at 10(-8) M). Inhibition of the ET(A) receptors by BQ-123 slightly increased the diameters of the BAs, with no difference shown between the ZL (6 +/- 1%) and ZO (5 +/- 3%) rats. Expressions of the ET(A) receptors and ET-1 mRNA examined by immunoblot analysis and RT-PCR, respectively, were also similar in the ZL and ZO groups. Phorbol 12,13-dibutyrate (PDBu), an activator of protein kinase C (PKC), and the thromboxane A(2) (TxA(2)) mimetic U-46619 constricted the BAs, but similarly to ET-1, there was no significant difference between the ZL and ZO groups (10(-6) M PDBu: ZL: 33 +/- 2%; ZO: 32 +/- 4%; and 10(-7) M U-46619: ZL: 23 +/- 1%; ZO: 19 +/- 2%). Inhibition of Rho-kinase with Y-27632 induced dilation of the BAs, and these responses were also comparable in the ZL and ZO rats (ZL: 39 +/- 4%; ZO: 38 +/- 2% at 10(-5) M). In contrast, nitric oxide-dependent relaxation to bradykinin was significantly reduced in the ZO rats (10(-6) M: 10 +/- 3%) compared with ZLs (29 +/- 7%, P < 0.01). These findings indicate that vasoconstrictor responses of the BA mediated by ET-1, TxA(2), PKC, and Rho-kinase are not affected by IR.

Amides↗

PubMed2004

Regional distribution of cyclooxygenase-3 mRNA in the rat central nervous system.

We determined COX-3 mRNA expression in regions of the rat central nervous system (CNS). On a regional basis, levels were the highest in choroid plexus and spinal chord followed by pituitary gland, hypothalamus, hippocampus, medulla, cerebellum, and cortex. COX-3 mRNA levels were higher in major brain arteries, and dramatically higher in brain microvessels. Our results suggest that the expression pattern of COX-3 mRNA in the rat CNS primarily relates to the vascular density of a given region.

Animals↗

PubMed2004

Diazoxide preconditioning protects against neuronal cell death by attenuation of oxidative stress upon glutamate stimulation.

We examined the effects of diazoxide, the putative mitochondrial adenosine triphosphate-sensitive potassium (mitoK(ATP)) channel opener, against glutamate excitotoxicity in primary cultures of rat cortical neurons. Cells were treated with diazoxide for 24 hr and then exposed to 200 microM glutamate. Cell viability was measured 24 hr after glutamate exposure. We found that treatment 24 hr before glutamate exposure with 250 and 500 microM diazoxide but not with another mitoK(ATP) channel opener, nicorandil, increased neuronal viability from 54 +/- 2% to 84 +/- 2% and 92 +/- 3%, respectively (n = 25-40). These effects were not inhibited by the putative mitoK(ATP) channel blocker 5-hydroxydecanoic acid. Diazoxide application increased production of reactive oxygen species (ROS) and coapplication of M40401, a superoxide dismutase mimetic, prevented delayed preconditioning. The 24 hr preconditioned neurons showed significantly reduced ROS production upon glutamate stimulation compared to that in untreated cells. These results suggest that diazoxide induces delayed preconditioning in cultured cortical neurons via increased ROS production and attenuation of oxidative stress upon glutamate stimulation.

Analysis of Variance↗

PubMed2004

Rosuvastatin treatment reverses impaired coronary artery vasodilation in fructose-fed, insulin-resistant rats.

Insulin resistance (IR) impairs vascular responses in coronary arteries, but mechanisms of dysfunction and approaches to treatment remain unclear. We examined the ability of a new 3-hydroxy-methylglutaryl coenzyme A reductase inhibitor, rosuvastatin, to reverse reduced dilator responses in rats made IR by feeding a fructose-rich diet (FF). Sprague-Dawley rats were randomized to control (normal rat diet) or FF. After 1 wk, rats received rosuvastatin (2 mg/kg) or placebo (saline) subcutaneously for 5 wk. Biochemical measurements and in vitro functional studies of small coronary arteries were performed. Fasting insulin and triglyceride (TG) levels were markedly increased in FF-placebo rats compared with other groups. Rosuvastatin treatment of FF rats normalized TG and modestly decreased insulin levels. ACh-induced dilator responses were depressed in arteries from FF-placebo rats. This impairment was due to decreased responses via calcium-dependent K channels (K(Ca)). Rosuvastatin treatment of FF rats completely reversed the response to ACh to normal levels. Moreover, this recovery in function was due to an improvement in vasodilation via K(Ca). Thus rosuvastatin treatment of IR rats normalizes coronary vascular dilator responses by improving the K(Ca) function.

Acetylcholine↗

PubMed2004

Potassium channel dysfunction in cerebral arteries of insulin-resistant rats is mediated by reactive oxygen species.

BACKGROUND AND PURPOSE: Insulin resistance (IR) increases the risk of stroke in humans. One possible underlying factor is cerebrovascular dysfunction resulting from altered K(+) channel function. Thus, the goal of this study was to examine K+ channel-mediated relaxation in IR cerebral arteries. METHODS: Experiments were performed on pressurized isolated middle cerebral arteries (MCAs) from fructose-fed IR and control rats. RESULTS: Dilator responses to iloprost, which are BK(Ca) channel mediated, were reduced in the IR compared with control arteries (19+/-2% versus 33+/-2% at 10(-6) mol/L). Similarly, relaxation to the K(ATP) opener pinacidil was diminished in the IR MCAs (17+/-2%) compared with controls (38+/-2% at 10(-5) mol/L). IR also reduced the K(ATP) channel-dependent component in calcitonin gene-related peptide-induced dilation; however, the magnitude of the relaxation remained unchanged in IR because of a nonspecified K+ channel-mediated compensatory mechanism. In contrast, K(ir) channel-mediated relaxation elicited by increases in extracellular [K+] (4 to 12 mmol/L) was similar in the control and IR arteries. Blockade of the K(ir) and K(v) channels with Ba2+ and 4-aminopyridine, respectively, constricted the MCAs in both experimental groups with no significant difference. Pretreatment of arteries with superoxide dismutase (200 U/mL) plus catalase (150 U/mL) restored the dilatory responses to iloprost and pinacidil in the IR arteries. Immunoblots showed that the expressions of the pore-forming subunits of the examined K+ channels are not altered by IR. CONCLUSIONS: IR induces a type-specific K+ channel dysfunction mediated by reactive oxygen species. The alteration of K(ATP) and BK(Ca) channel-dependent vascular responses may be responsible for the increased risk of cerebrovascular events in IR.

Animals↗

PubMed2004

The mitochondrial K(ATP) channel opener BMS-191095 induces neuronal preconditioning.

BMS-191095, reportedly a selective mitoK(ATP) channel opener which is free from the known side effects of the prototype mitoK(ATP) channel opener diazoxide, induced acute and delayed preconditioning against glutamate excitotoxicity and delayed preconditioning against oxygen-glucose deprivation in primary cultures of rat cortical neurons. BMS-191095 dose dependently depolarized the mitochondria, increased the phosphorylation of PKC isoforms, but had no detectable effects on the activation of MAP kinases and did not influence the expressions of HSP70 and Mn-SOD. In BMS-191095-preconditioned neurons the glutamate-induced free-radical production was abolished. Our data give the first evidence that selective opening of mitoK(ATP) channels with BMS-191095 leads to remarkable neuroprotection via mechanisms that involve mitochondrial depolarization, PKC activation and attenuated free radical production during neuronal stress.

Animals↗