Electrophysiology, molecular modelling, and functional analysis of the effects of dietary quercetin and flavonoid analogues on Kir6.1 channels in rat stomach fundus smooth muscle

Flavonoids, ubiquitously distributed in the plant world, are regularly ingested with diets rich in fruit, vegetables, wine, and tea. During digestion, they are partially absorbed in the stomach. The present work aimed to assess the in vitro effects of quercetin and ten structurally related flavonoids on the rat gastric fundus smooth muscle, focussing on ATP-dependent K+ (Kir6.1) channels, which play a central role in the regulation of resting membrane potential, membrane excitability and, consequently, of gastric motility. Whole-cell currents through Kir6.1 channels (IKir6.1) were recorded with the patch-clamp technique and the mechanical activity of gastric fundus smooth muscle strips was studied under isometric conditions. Galangin ≈ tamarixetin > quercetin > kaempferol > isorhamnetin ≈ luteolin ≈ fisetin > (±)-taxifolin inhibited pinacidil-evoked, glibenclamide-sensitive IKir6.1 in a concentration-dependent manner. Morin, rutin, and myricetin were ineffective. The steric hindrance of the molecule and the number and position of hydroxyl groups on the B ring played an important role in the activity of the molecule. Molecular docking simulations revealed a possible binding site for flavonoids in the C-terminal domain of the Kir6.1 channel subunit SUR2B, in a flexible loop formed by residues 251 to 254 of chains C and D. Galangin and tamarixetin, but not rutin relaxed both high K+- and carbachol-induced contraction of fundus strips in a concentration-dependent manner. Furthermore, both flavonoids shifted to the right the concentration-relaxation curves to either pinacidil or L-cysteine constructed in strips pre-contracted by high K+, rutin being ineffective. In conclusion, IKir6.1 inhibition exerted by dietary flavonoids might counterbalance their myorelaxant activity, affect gastric accommodation or, at least, some stages of digestion.

Rapid Characterization of the Functional and Pharmacological Consequences of Cantú Syndrome KATP Channel Mutations in Intact Cells

Gain-of-function of KATP channels, resulting from mutations in either KCNJ8 (encoding inward rectifier sub-family 6 [Kir6.1]) or ABCC9 (encoding sulphonylurea receptor [SUR2]), cause Cantú syndrome (CS), a channelopathy characterized by excess hair growth, coarse facial appearance, cardiomegaly, and lymphedema. Here, we established a pipeline for rapid analysis of CS mutation consequences in Landing pad HEK 293 cell lines stably expressing wild type (WT) and mutant human Kir6.1 and SUR2B. Thallium-influx and cell membrane potential, reported by fluorescent Tl-sensitive Fluozin-2 and voltage-sensitive bis-(1,3-dibutylbarbituric acid)trimethine oxonol (DiBAC4(3)) dyes, respectively, were used to assess channel activity. In the Tl-influx assay, CS-associated Kir6.1 mutations increased sensitivity to the ATP-sensitive potassium (KATP) channel activator, pinacidil, but there was strikingly little effect of pinacidil for any SUR2B mutations, reflecting unexpected differences in the molecular mechanisms of Kir6.1 versus SUR2B mutations. Compared with the Tl-influx assay, the DiBAC4(3) assay presents more significant signal changes in response to subtle KATP channel activity changes, and all CS mutants (both Kir6.1 and SUR2B), but not WT channels, caused marked hyperpolarization, demonstrating that all mutants were activated under ambient conditions in intact cells. Most SUR2 CS mutations were markedly inhibited by <100 nM glibenclamide, but sensitivity to inhibition by glibenclamide, repaglinide, and PNU37883A was markedly reduced for Kir6.1 CS mutations. Understanding functional consequences of mutations can help with disease diagnosis and treatment. The analysis pipeline we have developed has the potential to rapidly identify mutational consequences, aiding future CS diagnosis, drug discovery, and individualization of treatment. SIGNIFICANCE STATEMENT: We have developed new fluorescence-based assays of channel activities and drug sensitivities of Cantú syndrome (CS) mutations in human Kir6.1/SUR2B-dependent KATP channels, showing that Kir6.1 mutations increase sensitivity to potassium channel openers, while SUR2B mutations markedly reduce K channel opener (KCO) sensitivity. However, both Kir6.1 and SUR2B CS mutations are both more hyperpolarized than WT cells under basal conditions, confirming pathophysiologically relevant gain-of-function, validating DiBAC4(3) fluorescence to characterize hyperpolarization induced by KATP channel activity under basal, non KCO-activated conditions.

Prenatal exposure to alcohol impairs responses of cerebral arterioles to activation of potassium channels: Role of oxidative stress

BACKGROUND

Potassium channels play an important role in the basal tone and dilation of cerebral resistance arterioles in response to many stimuli. However, the effect of prenatal alcohol exposure (PAE) on specific potassium channel function remains unknown. The first goal of this study was to determine the influence of PAE on the reactivity of cerebral arterioles to activation of ATP-sensitive potassium (KATP ) and BK channels. Our second goal was to determine whether oxidative stress contributed to potassium channel dysfunction of cerebral arterioles following PAE.

METHODS

We fed Sprague-Dawley dams a liquid diet with or without alcohol (3% EtOH) for the duration of their pregnancy (21 to 23 days). We examined in vivo responses of cerebral arterioles in control and PAE male and female offspring (14 to 16 weeks after birth) to activators of potassium channels (Iloprost [BK channels] and pinacidil [KATP channels]), before and following inhibition of oxidative stress with apocynin.

RESULTS

We found that PAE impaired dilation of cerebral arterioles in response to activation of potassium channels with iloprost and pinacidil, and this impairment was similar in male and female rats. In addition, treatment with apocynin reversed the impaired vasodilation to iloprost and pinacidil in PAE rats to levels observed in control rats. This effect of apocynin also was similar in male and female rats.

CONCLUSIONS

PAE induces dysfunction in the ability of specific potassium channels to dilate cerebral arterioles which appears to be mediated by an increase in oxidative stress. We suggest that these alterations in potassium channel function may contribute to the pathogenesis of cerebral vascular abnormalities and/or behavioral/cognitive deficits observed in fetal alcohol spectrum disorders.

[Impact of late sodium current inhibition on cardiac electrophysiology parameters and ventricular arrhythmias in isolated Langendorff perfused rabbit hearts with short QT interval]

Objective: To determine the electrophysiological effects and related mechanisms of late sodium current inhibitors on hearts with short QT intervals. Methods: The electrophysiological study was performed on isolated Langendorff perfused rabbit hearts. A total of 80 New Zealand White rabbits were used and 34 hearts without drug treatment were defined as control group A, these hearts were then treated with I_KATP opener pinacidil, defined as pinacidil group A. Then, 27 hearts from pinacidil group A were selected to receive combined perfusion with sodium channel inhibitors or quinidine, a traditional drug used to treat short QT syndrome, including ranolazine combined group (n=9), mexiletine combined group (n=9), and quinidine combined group (n=9). Nineteen out of the remaining 46 New Zealand rabbits were selected as control group B (no drug treatments, n=19), and then treated with pinacidil, defined as pinacidil group B (n=19). The remaining 27 rabbits were treated with sodium inhibitors or quinidine alone, including ranolazine alone group (n=9), mexiletine alone group (n=9), and quinidine alone group (n=9). Electrocardiogram (ECG) physiological parameters of control group A and pinacidil group A were collected. In control group B and pinacidil group B, programmed electrical stimulation was used to induce ventricular arrhythmias and ECG was collected. ECG physiological parameters and ventricular arrhythmia status of various groups were analyzed. The concentrations of pinacidil, ranolazine, mexiletine and quinidine used in this study were 30, 10, 30 and 1 μmol/L, respectively. Results: Compared with control group A, the QT interval, 90% of the repolarization in epicardial and endocardial monophasic action potential duration (MAPD₉₀-Epi, MAPD₉₀-Endo) was shortened, the transmural dispersion of repolarization (TDR) was increased, and the effective refractor period (ERP) and post-repolarization refractoriness (PRR) were reduced in pinacidil group A (all P<0.05). Compared with the pinacidil group A, MAPD₉₀-Epi, MAPD₉₀-Endo, QT interval changes were reversed in quinidine combined group and mexiletine combined group (all P<0.05), but not in ranolazine combined group. All these three drugs reversed the pinacidil-induced increases of TDR and the decreases of ERP and PRR. The induced ventricular arrhythmia rate was 0 in control group B, and increased to 10/19 (χ²=13.6, P<0.05) in pinacidil group B during programmed electrical stimulation. Compared with the pinacidil group B, incidences of ventricular arrhythmia decreased to 11% (1/9), 11% (1/9) and 0 (0/9) (χ²=4.5, 4.5, 7.4, P<0.05) respectively in ranolazine group, mexiletine group and quinidine group. Conclusions: Inhibition of late sodium current does not increase but even decreases the risk of malignant arrhythmia in hearts with a shortened QT interval. The antiarrhythmic mechanism might be associated with the reversal of the increase of TDR and the decrease of refractoriness (including both ERP and PRR) of hearts with shortened QT interval.

Endothelial ATP-Sensitive Potassium Channel Protects Against the Development of Hypertension and Atherosclerosis

In the endothelium, ATP-sensitive potassium (KATP) channels are thought to couple cellular metabolism with membrane excitability, calcium entry, and endothelial mediator release. We hypothesized that endothelial KATP channels have a broad role protecting against high blood pressure and atherosclerosis. Endothelial-specific Kir6.1 KO mice (eKO) and eKO mice on an apolipoprotein E KO background were generated (A-eKO) to investigate the role of KATP channels in the endothelium. Basal blood pressure was not elevated in eKO mice. However, when challenged with a high-salt diet and the eNOS inhibitor L-NAME, eKO mice became more hypertensive than their littermate controls. In aorta, NO release at least partly contributes to the endothelium-dependent vasorelaxation induced by pinacidil. In A-eKO mice atherosclerotic plaque density was significantly greater than in their littermate controls when challenged with a high-fat diet, particularly in the aortic arch region. Levels of endothelial dysfunction markers were higher in eKO compared with WT mice; however, these were not significant for A-eKO mice compared with their littermate controls. Furthermore, decreased vascular reactivity was observed in the mesenteric arteries of A-eKO mice, but not in aorta when on a high-fat diet. Our data support a role for endothelial Kir6.1-containing KATP channels in the endothelial protection against environmental stressors: the maintenance of blood pressure homeostasis in response to high salt and endothelial integrity when challenged with a high-fat diet.

Concurrent increases in post-pacing action potential duration and contractility predict occurrence of ventricular arrhythmia

Excitation-contraction coupling from the integration of action potential duration (APD) and muscle contractility plays an important role in arrhythmogenesis. We aimed to determine whether distinctive excitation-contraction coupling contributes to the genesis of ventricular tachycardias (VTs). Action potential (AP) and mechanical activity were simultaneously recorded under electrical pacing (cycle lengths from 1000 to 100 ms) in the tissue model created from isolated rabbit right ventricular outflow tracts treated with NS 5806 (10 μM, transient outward potassium current enhancer), pinacidil (2 μM, ATP-sensitive potassium channel opener), and pilsicainide (5 μM, sodium channel blocker). There were 15 (9.9%) inducible VT episodes (group 1) and 136 (90.1%) non-inducible VT episodes (group 2) in our tissue model. Group 1 had greater post-pacing increases of the first occurrence of AP at 90% repolarization (ΔAPD₉₀, p < 0.001) and contractility (ΔContractility, p = 0.003) compared with group 2. Triggered VT episodes were common (72.7%) in cases with a ΔAPD₉₀ > 15% and a ΔContractility > 270%, but were undetectable in those with a ΔAPD₉₀ < 15% and a ΔContractility < 270%. In those with pacing-induced VTs, KB-R7943 (10 μM, a Na⁺-Ca²⁺ exchanger inhibitor, NCX inhibitor) significantly reduced the occurrence of VTs from 100.0 to 20.0% (15/15 to 3/15 episodes, p < 0.001). Concurrent increases in both post-pacing APD and contractility resulted in the occurrence of ventricular arrhythmias. NCX inhibition may be a potential therapeutic strategy for ventricular arrhythmias.

Hypoxia augments NaHS-induced ANP secretion via KATP channel, HIF-1α and PPAR-γ pathway

It has been reported that sodium hydrosulfide (NaHS) stimulated high stretch induced-atrial natriuretic peptide (ANP) secretion via ATP sensitive potassium (K_ATP) channel. K_ATP channel is activated during hypoxic condition as a compensatory mechanism. However, whether NaHS affects ANP secretion during hypoxia remains obscure. The purpose of the present study is to discover the impact of NaHS on ANP secretion during hypoxia and to unravel its signaling pathway. Isolated beating rat atria were perfused with buffer exposed to different O₂ tension (to 100% O₂, normoxia; to 20% O₂, hypoxia). The ANP secretion increased negatively correlated with O₂ tension. NaHS (50 μM) did not show any significant effect on low stretch induced-ANP secretion in normoxic condition but augmented low stretch induced-ANP secretion in hypoxic condition. The augmentation of NaHS-induced ANP secretion during hypoxia was blocked by the pretreatment with K_ATP channel blocker (glibenclamide) and was enhanced by the pretreatment with K_ATP channel activator (pinacidil). Hypoxia increased the expression of PPAR-γ protein but did not change the expression of HIF-1α protein and eNOS phosphorylation. The NaHS-induced ANP secretion during hypoxia was also blocked by the pretreatment with HIF-1α inhibitor (2-methoxy- estradiol), PPAR-γ inhibitor (GW9662) but not by NOS inhibitor (L-NAME) and endothelin receptor inhibitor (bosentan). The intravenous infusion of NaHS increased plasma ANP level in monocrotaline-treated rats but not in sham rats. These results suggest that hypoxia augmented NaHS-induced ANP secretion partly through K_ATP channel, HIF-1α, and PPAR-γ pathway.

Inactivation of p66Shc Decreases Afferent Arteriolar KATP Channel Activity and Decreases Renal Damage in Diabetic Dahl SS Rats

Increased expression of adaptor protein p66Shc has been associated with progression of diabetic nephropathy. Afferent arteriolar dilation and glomerular hyperfiltration in diabetes are due to increased K_ATP channel availability and activity. Hyperglycemia was induced in Dahl salt-sensitive (SS) rats in a model of diabetes induced by streptozotocin (STZ). Renal injury was evaluated in SS rats and genetically modified SS rats either lacking p66Shc (p66Shc knockout [p66ShcKO]) or expressing p66Shc mutant (p66Shc-S36A). Afferent arteriolar diameter responses during STZ-induced hyperfiltration were determined by using the juxtamedullary nephron technique. Albuminuria and glomerular injury were mitigated in p66ShcKO and p66Shc-S36A rats with STZ-induced diabetes. SS rats with STZ-induced diabetes had significantly increased afferent arteriolar diameter, whereas p66ShcKO and p66Shc-S36A rats did not. SS rats with STZ-induced diabetes, but not p66ShcKO or p66Shc-S36A rats with STZ-induced diabetes, had an increased vasodilator response to the K_ATP channel activator pinacidil. Likewise, the K_ATP inhibitor glibenclamide resulted in a greater decrease in afferent arteriolar diameter in SS rats with STZ-induced diabetes than in STZ-treated SS p66ShcKO and p66Shc-S36A rats. Using patch-clamp electrophysiology, we demonstrated that p66ShcKO decreases K_ATP channel activity. These results indicate that inactivation of the adaptor protein p66Shc decreases afferent arteriolar K_ATP channel activity and decreases renal damage in diabetic SS rats.

ATP-sensitive inwardly rectifying potassium channel modulators alter cardiac function in honey bees

ATP-sensitive inwardly rectifying potassium (K_ATP) channels couple cellular metabolism to the membrane potential of the cell and play an important role in a variety of tissue types, including the insect dorsal vessel, making them a subject of interest not only for understanding invertebrate physiology, but also as a potential target for novel insecticides. Most of what is known about these ion channels is the result of work performed in mammalian systems, with insect studies being limited to only a few species and physiological systems. The goal of this study was to investigate the role that K_ATP channels play in regulating cardiac function in a model social insect, the honey bee (Apis mellifera), by examining the effects that modulators of these ion channels have on heart rate. Heart rate decreased in a concentration-dependent manner, relative to controls, with the application of the K_ATP channel antagonist tolbutamide and K_ATP channel blockers barium and magnesium, whereas heart rate increased with the application of a low concentration of the K_ATP channel agonist pinacidil, but decreased at higher concentrations. Furthermore, pretreatment with barium magnified the effects of tolbutamide treatment and eliminated the effects of pinacidil treatment at select concentrations. The data presented here confirm a role for K_ATP channels in the regulation of honey bee dorsal vessel contractions and provide insight into the underlying physiology that governs the regulation of bee cardiac function.

The Opening of ATP-Sensitive K+ Channels Protects H9c2 Cardiac Cells Against the High Glucose-Induced Injury and Inflammation by Inhibiting the ROS-TLR4-Necroptosis Pathway

BACKGROUND/AIMS

Hyperglycemia activates multiple signaling molecules, including reactive oxygen species (ROS), toll-like receptor 4 (TLR4), receptor-interacting protein 3 (RIP3, a kinase promoting necroptosis), which mediate hyperglycemia-induced cardiac injury. This study explored whether inhibition of ROS-TLR4-necroptosis pathway contributed to the protection of ATP-sensitive K+ (KATP) channel opening against high glucose-induced cardiac injury and inflammation.

METHODS

H9c2 cardiac cells were treated with 35 mM glucose (HG) to establish a model of HG-induced insults. The expression of RIP3 and TLR4 were tested by western blot. Generation of ROS, cell viability, mitochondrial membrane potential (MMP) and secretion of inflammatory cytokines were measured as injury indexes.

RESULTS

HG increased the expression of TLR4 and RIP3. Necrostatin-1 (Nec-1, an inhibitor of necroptosis) or TAK-242 (an inhibitor of TLR4) co-treatment attenuated HG-induced up-regulation of RIP3. Diazoxide (DZ, a mitochondrial KATP channel opener) or pinacidil (Pin, a non-selective KATP channel opener) or N-acetyl-L-cysteine (NAC, a ROS scavenger) pre-treatment blocked the up-regulation of TLR4 and RIP3. Furthermore, pre-treatment with DZ or Pin or NAC, or co-treatment with TAK-242 or Nec-1 attenuated HG-induced a decrease in cell viability, and increases in ROS generation, MMP loss and inflammatory cytokines secretion. However, 5-hydroxy decanoic acid (5-HD, a mitochondrial KATP channel blocker) or glibenclamide (Gli, a non-selective KATP channel blocker) pre-treatment did not aggravate HG-induced injury and inflammation.

CONCLUSION

KATP channel opening protects H9c2 cells against HG-induced injury and inflammation by inhibiting ROS-TLR4-necroptosis pathway.

Role of KATPChannels in the Regulation of Rat Dura and Pia Artery Diameter

The aim of the present study was to examine the effect of KATPchannel openers pinacidil and levcromakalim on rat dural and pial arteries as well as their inhibition by glibenclamide. We used an in-vivo genuine closed cranial window model and an in-vitro organ bath. Glibenclamide alone reduced the dural but not the pial artery diameter compared with controls. Intravenous pinacidil and levcro-makalim induced dural and pial artery dilation that was significantly attenuated by glibenclamide. In the organ bath pinacidil and levcromakalim induced dural and middle cerebral artery relaxation that was significantly attenuated by glibenclamide. In conclusion, KATPchannel openers induce increasing diameter/relaxation of dural and pial arteries after intravenous infusion in vivo and on isolated arteries in vitro. Furthermore, dural arteries were more sensitive to KATPchannel openers than pial arteries.

[The functional state of the kidneys after adenosine triphosphate-sensitive potassium channels activation in experimental acute hypoxia]

In the experiments on non-linear white rats with the model of acute hypoxia we have studied the changes of the functional state of kidneys after a single intraventricular administration of the original fluorine-containing KATP-sensitive potassium channels activator flocalin at the dose of 5 mg/kg on the background of induced water load. It has been shown that under the influence of prohypoxic factors: sodium nitrite (50 mg/kg, subcutaneously) and dinitrophenol (3 mg/kg, intraperitoneal) flocalin activates volume-regulating, ion-regulating and excretory functions of kidneys. Renal effects after activation of KATP-sensitive potassium channels in the rats with histohemic hypoxia were induced by the changes of tubular and predominantly glomerular processes. The increase of glomerular filtration rate, restoration of volatile distal reabsorption of potassium channels, decrease of sodium loss with urine, decrease ofproteinuria after a single administration of flocalin under conditions of acute hypoxia complement the range of protective effects of KATP-sensitive potassium channels activator flocalin.

[Comparative assessment of nephroprotective properties of potassium and calcium channel modulators in experimental renal injury]

The experiments in white laboratory rats have shown that a single intragasrtric administration of the new fluorine-containing potassium channel opener flocalin in a dose of 5 mg/kg in the initial stage of sublimate nephropathy increased the glomerular filtration rate, reduced creatininemia, increased urinary creatinine excretion, and decreased proteinuria. Under similar conditions, the administration of the calcium channel blocker diltiazem in a dose of 5 mg/kg (intragasrtric) showed a less pronounced antiproteinuric effect as compared to that of flocalin. A comparative assessment of the influence of flocalin and diltiazem on the basic renal function markers demonstrated predominant nephroprotective effect of flocalin in the treatment of acute toxic nephropathy.

The effect of resveratrol on contractility of non-pregnant rat uterus: the contribution of K(+) channels

This study was aimed to evaluate resveratrol (1-100 μM) effect on the spontaneous rhythmic contractions (SRC), oxytocin-induced (0.2 nM, POxC) phasic and tonic (20 nM, TOxC) contractions of isolated rat uterus. The SRC and POxC were more sensitive to resveratrol than TOxC (pD2 values: 4.53 and 4.66 versus 4.06). Different blockers of K(+) channels (glibenclamide, tetraethylamonium, iberiotoxin, 4-aminopyridine) antagonized the response to resveratrol on the SRC and phasic contractions, but did not antagonize the effect of resveratrol on the TOxC. In order to compare the relaxant activities of resveratrol on the TOxC with that of potassium channel openers, a separate experiments with NS 1619, a highly specific big Ca(2+)-sensitive K(+) (BKCa) channels opener and pinacidil, a predominant opener of ATP-sensitive K(+) (KATP) channels were done. NS 1619 (10-100 μM) and pinacidil (10-100 μM) produced more potent inhibition of TOxC than resveratrol (pD2 values were 6.00 and 5.29). Iberiotoxin, a highly selective BKCa channels blocker, antagonized the response to NS 1619 and glibenclamide, a highly selective KATP channels blocker, antagonized the response to pinacidil on the TOxC. To test K(+)- and extracellular Ca(2+)- independent mechanism(s) of resveratrol on TOxC, a K(+)-rich, Ca(2+)-free solution was used. Under this condition, only high concentrations (≥30 μM) of resveratrol inhibited TOxC. Western blots analysis confirmed expression of Kir6.1, Kir6.2, KCa1.1, Kv2.1 and Kv4.2. channel proteins in myometrium. Thus, the effect of resveratrol is dependent on the types of contractions. The inhibitory response of resveratrol on the SRC and phasic contractions involves different myometrial K(+)- channels. When applied in high concentrations, resveratrol has an additional K(+)- channels independent mechanism(s) of action. As the effects of NS 1619, pinacidil and resveratrol on the TOxC are different, we can conclud that resveratrol does not behave as a classical potassium channel opener.

Heterogeneity and function of K(ATP) channels in canine hearts

BACKGROUND

The concept that pore-forming Kir6.2 and regulatory SUR2A subunits form cardiac ATP-sensitive potassium (K(ATP)) channels is challenged by recent reports that SUR1 is predominant in mouse atrial K(ATP) channels.

OBJECTIVE

To assess SUR subunit composition of K(ATP) channels and consequence of K(ATP) activation for action potential duration (APD) in dog hearts.

METHODS

Patch-clamp techniques were used on isolated dog cardiomyocytes to investigate K(ATP) channel properties. Dynamic current clamp, by injection of a linear K(+) conductance to simulate activation of the native current, was used to study the consequences of K(ATP) activation on APD.

RESULTS

Metabolic inhibitor (MI)-activated current was not significantly different from pinacidil (SUR2A-specific)-activated current, and both currents were larger than diazoxide (SUR1-specific)-activated current in both the atrium and the ventricle. Mean K(ATP) conductance (activated by MI) did not differ significantly between chambers, although, within the ventricle, both MI-induced and pinacidil-induced currents tended to decrease from the epicardium to the endocardium. Dynamic current-clamp results indicate that myocytes with longer baseline APDs are more susceptible to injected K(ATP) current, a result reproduced in silico by using a canine action potential model (Hund-Rudy) to simulate epicardial and endocardial myocytes.

CONCLUSIONS

Even a small fraction of K(ATP) activation significantly shortens APD in a manner that depends on existing heterogeneity in K(ATP) current and APD.

[Biochemical mechanisms of the cardioprotective effect of the K(ATP) channels opener flocalin (medicinal form) in ischemia-reperfusion of myocardium]

In experiments on the anaesthetized dogs with modeling of experimental ischemia (90 min) and reperfusion (180 min) of myocardium it was investigated changes of biochemical processes in arterial blood at intragastric introduction of medicinal form (tablets) of flocalin (the fluorine-containing opener of ATP-sensitive potassium channels) in a dose 2,2 mg/kg. The data analysis allowed to define a few possible mechanisms of cardioprotective action offlocalin, which prevented the opening of a mitochondrial permeability transition pore (MPTP) and inhibition of apoptosis induced by it. They consist, from one side, in activating of the constitutive de novo biosynthesis of nitric oxide by cNOS, from other side, in suppression of inducible nitric oxide de novo synthesis by iNOS in such way to prevent the formation of toxic peroxynitrite by co-operation of surplus nitric oxide with superoxide anion, thereby limits the generation of toxic active forms of nitrogen (*NO2) and oxygen (*OH). The first effect of flocalin takes place due to limitation the degradation of L-arginine by arginase which keeps substrat for cNOS, second--due to the inhibition of superoxide generation, in particular, by xanthine oxidase (marker uric acid), lipoxigenase (marker LTC4) and cyclooxygenase (marker TxB2). Because LTC4 have coronaroconstrictory, arrhythmogenic and chemoattractory properties in the conditions of myocardial ischemia, inhibition of its production both with superoxide generation (markers H2O2 and diene conjugates) may be the another mechanisms of flocalin's cardioprotection. Powerful antiischemic action of flocalin (marker nitrite anion) as the mechanisms of cardioprotection is possible as well as inhibition of ATP and GTP degradation (marker hypoxanthine+xanthine+inosine levels in the blood) and, possibly, stimulation ofhaem degradation by haem oxygenase (markers total bilirubin and Fe in the blood). Diminishing content of free arachidonic acid in arterial blood can testify inhibition of cellular membranes phospholipides degradation by phospholipase A2 as a result of flocalin cardioprotection.

[New fluorine-containing openers of ATP-sensitive potassium channels flokalin and tioflokalin inhibit calcium-induced mitochondrial pore opening in rat hearts]

In experiments in vitro on the mitochondria isolated from the rat's heart we studied the effects of the openers of ATP-sensitive potassium channels (K(ATP)-channels), flocalin and tioflocalin, on the calcium-induced mitochondrial pore (MPTP) opening. Flocalin and tioflocalin caused moderate Ca(2+)-independent mitochondria swelling, which was prevented by a specific inhibitor of 5-hydroxydecanoate. This allowed to identify these compounds as mitochondrial K(ATP)-channels openers. We found that concentration-dependent inhibitory effects (10(-7) to 10(-4) M) of flocalin (with IC50 = 50 microM) and tioflocalin (with IC50 = 2,7 microM) on Ca(2+)-induced mitochondrial swelling (MPTP opening) in the heart characterized more powerful cardioprotective action of the latter. It was shown that the administration of these compounds in experiments in vivo decreased the sensitivity of the MPTP opening to Ca2+. Thus, under physiological conditions the activators K(ATP)-channels probably provide the membrane-stabilizing effects, thereby effectively increasing the organelles resistance to Ca2+, an inductor of MPTP. The results obtained allowed to characterize the role of the compound studied as cardioprotectors and regulators of the MPTP formation in the heart, indicated their anti-ischemic and anti-apoptotic effects that can be used in order to correct the mitochondrial dysfunction under pathological conditions of the cardiovascular system.

[Influence of flocalin on development of apoptosis and necrosis at anoxia-reoxygenation of culture rats neonatal cardiomyocytes]

The influence of the new cardioprotector flocalin was investigated on the culture of rat's neonatal cardiomyocytes during anoxia-reoxygenation modelling. The mechanisms of apoptosis and necrosis were investigated under influence of ATP-sensitive potassium (K(ATP)) channels activation and in conditions of blocking of the L-type calcium (VGCCs) channels. Flocalin was added in the culture medium in the dose 5 and 20 microM at 2 minutes before anoxia (30 minutes) and following reoxygenation (60 minutes). These doses are near to: the first dose means the opening of K(ATP) channels and the second one means the IC50 block of VGCCs. It is discovered that in dose 5 microM of flocalin drew the change of correlation of living, necrotizing and apoptizing cells drew side-shifting living. The number of live cells was almost the same like in control (experiments without anoxia-reoxygenation modelling). The opening of K(ATP) channels decreases necrosis in two times and fully prevented development of apoptosis which was induced anoxia-reoxygenation modelling. Flocalin depressed the apoptosis of neonatal cardiomyocytes so that he was on to 36% less than in control group (without anoxia-reoxygenation). But in the high dose (20 microM) that provokes not only K(ATP) channels opening but also IC50 block of VGCCs cardioprotection was not detected after modelling of anoxia-reoxygenation. The last can be investigation both enough strong activating of the potassium channels and by investigation of both factors are opening of potassium and inhibition of VGCCs channels and, accordingly, substantial diminishing of level of introcellular Ca2+ and violation of metabolic processes yet to anoxia-reoxygenation. Thus, small doses of flocalin, that induce moderate opening of K(ATP) channels significantly decrease the number of necrotic and apoptotic cells in culture of rat neonatal cardiomyocytes induced by anoxia-reoxygenation.

[The influence of activation of the ATP-sensitive potassium channels by flocalin on the function of the cardiovascular system]

In experiments on the anaesthetized dogs the influence of a new fluorine-containing opener of ATP-sensitive potassium (K(ATP)) channels flocalin on the cardiohemodynamic of great animals in vivo was studied. Flocalin introduced intravenously in doses 0.01 - 1.5 mgs/kg. It is shown that it reduces in dose-dependent manner a system arterial pressure, perfusion pressure in coronary artery and general peripheral resistance of vessels with maximal effects on 56.8 +/- 2.7, 22.4 +/- 4.7 and 47.2% +/- 6.5% accordingly at most dose 1.5 mgs/kg. Flocalin causes development of cardiodepressive reactions in heart, that is exhibited in dose-dependent the decrease of pressure in the left ventricle, speed of growth (dP/dt(max)) and reduction (dP/dt(min)) in it's of pressure with maximal effects on 37.1 +/- 5.1, 51.2 +/- 9.4 and 55.6% +/- 6.9% accordingly at introduction of most dose of flocalin. Diminish of the cardiac out put and heart rate with a maximal effects on 23.1% +/-12.7% and 19.2% +/- 1.7% accordingly at a dose 1.0 mgs/kg was shown. It should be noted that considerable reduction of heart rate and general peripheral resistance of vessels takes place only at the large doses of flocalin - 1 and 1.5 mgs/kg. Thus, it is shown that activation of K(ATP) channels by flocalin causes the dose-dependent decrease of pressure in the system of circulation of blood and contraction activity of myocardium.

Combined effects of the ATP-sensitive potassium channel opener pinacidil and simvastatin on pulmonary vascular remodeling in rats with monocrotaline-induced pulmonary arterial hypertension

The drugs that are currently used to treat pulmonary hypertension (PH) lack the ability to inhibit or reverse the pulmonary vascular remodeling that occurs during the course of the disease. We propose a novel method that combines the therapeutic powers of the potassium channel opener pinacidil and the statin drug simvastatin. These two drugs do not share similar mechanisms of treating PH. We used rats with monocrotaline (MCT)-induced pulmonary arterial hypertension (PAH) as a model and examined the combined effects of pinacidil and simvastatin on pulmonary vascular remodeling. A series of indicators, including those for pulmonary vascular obstruction, proliferation, and cell phenotype, pulmonary vascular matrix and pulmonary vascular smooth muscle cell phenotype were used to monitor changes in pulmonary structure over the course of disease and treatment in normal controls, untreated PAH rats, pinacidil-treated subjects, simvastatin-treated subjects, and combination-treated subjects. We found that levels of mPAP, right ventricle Fulton index, pulmonary arteriolar wall thickness and muscularization, cell growth rate, transforming growth factor beta (TGF-beta), lung tissue matrix metalloproteinase-2 (MMP-2), MMP-9 and lung tissue inhibitor of matrix metalloproteinase-1 (TIMP-1), vascular smooth muscle cell (VSMC) contractile protein SM-alpha-actin, and SM-alpha-actin mRNA of these different groups were all significantly lower in the combination-treated group than in the untreated group. Subjects in the combination-treated group also showed lower levels than those in either the pinacidil-treated or simvastatin-treated group. These results support our hypothesis and provide basis for a new, more effective therapeutic methods of treating PAH in human patients.

Inhibition of uterine contractility with various tocolytics with and without progesterone: in vitro studies

OBJECTIVE

Various tocolytics are used to suppress uterine contractility in patients in preterm labor. Progesterone (P4) is used in patients at high risk for preterm delivery. In this study, we evaluated the effects of various tocolytics with and without P4 to examine effects on uterine contractility.

STUDY DESIGN

Uterine tissues (n = 280) from women undergoing cesarean at term were exposed in vitro to various agents (vehicle, magnesium sulfate [MgSO(4)], nifedipine, indomethacin, or pinacidil-all with and without P4). Contractility was measured before and after addition of the various agents.

RESULTS

P4 alone at 10(-5) mol/L concentration has little effect to inhibit contractility (P ≥ .05). MgSO(4) (2-8 × 10(-3) mol/L) inhibits uterine contractility (P < .05) but there is no change when combined with P4 (P > .05). Nifedipine (10(-8) mol/L) and indomethacin (10(-5) mol/L) inhibit contractions alone (P < .05) and to a greater extent when combined with P4 (P < .05). P4 significantly (P < .05) reduced the effects of pinacidil (10(-6.5) mol/L).

CONCLUSION

Combinations of P4 with nifedipine or indomethacin, but not MgSO(4), might be used to effectively suppress preterm labor.

Vasodilation of retinal arterioles induced by activation of BKCa channels is attenuated in diabetic rats

The large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels modulate the retinal vascular tone, but question of whether the impairment of the channel function contributes to abnormalities of retinal circulation has not yet been completely elucidated. The purpose of this study was to examine effects of diabetes on the vasodilation induced by activation of BK(Ca) channels. Male Wistar rats were treated with streptozotocin and experiments were performed 2 weeks later. The streptozotocin-treated animals were given drinking water containing 5% d-glucose to shorten the term in the development of retinal vascular dysfunction. The retinal vascular responses were assessed by measuring diameter of retinal arterioles in the fundus images that were captured with an original fundus camera system. In non-diabetic rats, vasodilator effects of acetylcholine on retinal arterioles were significantly reduced by iberiotoxin, an inhibitor of BK(Ca) channels. However, the inhibitory effect of iberiotoxin was not observed in diabetic rats, and the responses to the BK(Ca) channel opener BMS-191011 were almost completely abolished. The retinal vasodilator response to acetylcholine, possibly an endothelium-derived hyperpolarizing factor-mediated response, observed after treatment with N(G)-nitro-l-arginine methyl ester and indomethacin was markedly reduced in diabetic rats. The responses to pinacidil, an opener of ATP-sensitive K(+) channels, were unchanged. These results suggest that the retinal vasodilator response mediated through mechanisms involving activation of BK(Ca) channels is diminished at the early stage of diabetes in rats. The impairment of BK(Ca) channel function may contribute to abnormal retinal hemodynamics in diabetes and consequently play an important role in the pathogenesis of diabetic retinopathy.

[Ontogeny of sulphonylurea-binding regulatory subunits of K(ATP) channels in the pregnant rat myometrium]

K(ATP) channels are composed of sulphonylurea receptors (SURs) and potassium inward rectifiers (Kir(6.x)) that assemble to form a large octameric channel. This study was designed to examine the expression and role of sulphonylurea-binding regulatory subunits 1 [SUR1 (ABCC8)] and 2 [SUR2 (ABCC9)] of the K(ATP) channels in the pregnant rat myometrium with particular regard to the contractility. RT-PCR and Western blot analysis were performed to detect the presence of SUR1 and SUR2. The SUR1 levels were markedly increased in the early stages of pregnancy. The highest level was detected on day 6 of pregnancy, while in the late stages the levels of SUR1 were significantly decreased. The SUR2 level remained unchanged throughout pregnancy. The SUR-non-selective diazoxide and the SUR2-selective pinacidil inhibited oxytocin-induced contractions. Glibenclamide, a K(ATP) channel blocker, antagonized both pinacidil and diazoxide-induced relaxations. It was established that SURs are responsible for pharmacological reactivity of K(ATP) channel openers. We conclude that, both SURs are involved in the K(ATP) channel in the pregnant rat myometrium. It may further be concluded that "pinacidil-like" K(ATP) channel openers may be of therapeutic relevance as tocolytic agents in the future.

A study of the relationship between pharmacologic preconditioning and adenosine triphosphate-sensitive potassium (KATP) channels on cultured cardiomyocytes using the microelectrode array

The microelectrode array was used to study the pharmacologic preconditioning effect of adenosine triphosphate-sensitive channel activation using potassium channel openers (KCOs) on rat cardiomyocytes over 90 minutes of ischemia. Cell viability and electrophysiological changes between KCOs pretreated and untreated cardiomyocytes were compared. Ischemia caused significant increases in beat frequency, extracellular field potential amplitude, and propagation velocity of spontaneously beating untreated cardiomyocytes. However, these electrophysiological parameters reduced as the duration of ischemia increased. The electrophysiological changes on ischemic cardiomyocytes were abolished by pretreating the cells with KCOs. Pinacidil pretreated cardiomyocytes retained a significantly higher viability than the untreated cardiomyocytes after 90 minutes of ischemia. Because Connexin 43 has a direct correlation with the propagation velocity, the Connexin 43 protein expression was also investigated. Connexin 43 expression levels were lower in KCOs pretreated cardiomyocytes than that of the untreated controls, and this correlated with the propagation velocity results obtained from the microelectrode array. The effect of pinacidil (sarcolemmal adenosine triphosphate-sensitive channel opener) was more prominent than that of diazoxide (mitochondrial K adenosine triphosphate-sensitive channel opener) on ischemic cardiomyocytes as indicated in the present acute ischemia study.

Vulnerable windows define susceptibility to alternans and spatial discordance

Electrophysiological alternans is a beat-to-beat alternation of the action potential duration and/or Ca(2+) transient amplitude and is linked to ventricular arrhythmias. We investigated the significance of various rate parameters under different experimental conditions with respect to alternans incidence and the propensity for spiral wave formation. Voltage and Ca(2+) were optically mapped in monolayers of neonatal rat ventricular myocytes. Alternans did not occur at physiological temperature, but its incidence increased significantly at lowered temperatures. Pacing cycle length for spatially concordant alternans onset (PCL(C)), PCL for spatially discordant alternans onset (PCL(D)), and minimum cycle length for loss of 1:1 or 2:2 capture (MCL) also significantly increased with lower temperature but in a way such that the differences between PCL(C) and MCL and between PCL(D) and MCL widened. These results provided the rationale to identify the former difference as the alternans vulnerable window (AVW; in ms) and the latter difference as the discordant alternans vulnerable window (AVW(D); in ms). Computational simulations showed that interventions that widen AVW, including altered Ca(2+) cycling and enhanced K(+) currents, also promote alternans, regardless of whether PCL(C) or MCL increased or decreased. The simulation results were confirmed experimentally by addition of the ATP-sensitive K(+) channel agonist pinacidil. Mathematical analysis provided a theoretical basis linking the size of AVW to the incidence of alternans. Finally, experiments showed that the size of AVW(D) is related to the incidence of spatially discordant alternans and, additionally, to the incidence of spiral wave formation. In conclusion, vulnerable windows can be defined that are strongly correlated with alternans incidence, spatial discordance, and spiral wave formation.

Lipopolysaccharides up-regulate Kir6.1/SUR2B channel expression and enhance vascular KATP channel activity via NF-kappaB-dependent signaling

Sepsis is a severe medical condition causing a large number of deaths worldwide. Recent studies indicate that the septic susceptibility is attributable to the vascular ATP-sensitive K(+) (K(ATP)) channel. However, the mechanisms underlying the channel modulation in sepsis are still unclear. Here we show evidence for the modulation of vascular K(ATP) channel by septic pathogen lipopolysaccharides (LPS). In isolated mesenteric arterial rings, phenylephrine (PE) produced concentration-dependent vasoconstriction that was relaxed by pinacidil, a selective K(ATP) channel opener. The PE response was disrupted with a LPS treatment. In acutely dissociated aortic smooth myocytes the LPS treatment augmented K(ATP) channel activity, and hyperpolarized the cells. Quantitative PCR analysis showed that LPS raised Kir6.1 and SUR2B transcripts in a concentration-dependent manner, which was suppressed by transcriptional inhibition. Consistently, the same LPS treatment did not affect Kir6.1/SUR2B channels in a heterologous expression system. The LPS effect on Kir6.1 and SUR2B expression was abolished in the presence of NF-kappaB inhibitors. Several other Toll-like receptor ligands also stimulated Kir6.1 and SUR2B expression to a similar degree as LPS. Thus, the effect of LPS on vasodilation involves up-regulation of K(ATP) channel expression, in which the NF-kappaB-dependent signaling plays an important role.

[The vasodilation effects of flokalin, a fluorine-containing K(ATP) channel opener]

In experiments on anesthetized dogs it was shown that the amplitude and duration of hypotensive effect of flocalin, a fluorine-containing pinacidil analogue, were dose-dependent and similar to those evoked by the known ATP-sensitive potassium channel opener pinacidil. However, flocalin appeared to be 3.5 times less toxic than pinacidil. Registration of systemic arterial pressure (SAP) has shown that following intravenous introduction of the threshold dose of flocalin (0.05 mg/ kg) the dilatation lasts around three minutes with the amplitude 9.52% +/- 2.01% (n=7, P < 0.05). Introduction of flocalin in a dose 0.5 mg/kg and above reduced SAP on more than 37%. Flocalin at 0.5, 0.75, 1.0 and 1.5 mg/kg reduced SAP by 42.07 +/- 6.18 (n=5, P < 0.05); 44.22 +/- 4.87 (n=3, P < 0.05); 44.3 +/- 4.59 (n=5, P < 0.05) and 66.28 +/- 3.15 mm Hg (n=3, P < 0.05), accordingly. Intravenous introduction of high doses of flocalin (0.75-1.5 mg/kgs) quite often reduced SAP to 40-50 mm Hg. However, such dangerous reduction in arterial pressure was comparatively short and lasted not more than 15 minutes, and then (usually within an hour) SAP gradually restored. Introduction of flocalin in hip artery, while measuring the perfusion pressure, produced practically similar results. In our opinion, the optimal cardioprotective doses of flocalin were 0.1 and 0.2 mg/kg. In experiments with acute ischemia and reperfusion of myocardium, preischemic introduction of flocalin at 0.1 and 0.2 mg/kg reduced an infarct size of myocardium by 37-40% and reduced SAP within first 5 and 25 minutes, accordingly.

Differential K(ATP) channel pharmacology in intact mouse heart

Classically, cardiac sarcolemmal K(ATP) channels have been thought to be composed of Kir6.2 (KCNJ11) and SUR2A (ABCC9) subunits. However, the evidence is strong that SUR1 (sulfonylurea receptor type 1, ABCC8) subunits are also expressed in the heart and that they play a significant functional role in the atria. To examine this further, we have assessed the effects of isotype-specific potassium channel-opening drugs, diazoxide (specific to SUR1>SUR2A) and pinacidil (SUR2A>SUR1), in intact hearts from wild-type mice (WT, n=6), SUR1(-/-) (n=6), and Kir6.2(-/-) mice (n=5). Action potential durations (APDs) in both atria and ventricles were estimated by optical mapping of the posterior surface of Langendorff-perfused hearts. To confirm the atrial effect of both openers, isolated atrial preparations were mapped in both WT (n=4) and SUR1(-/-) (n=3) mice. The glass microelectrode technique was also used to validate optical action potentials. In WT hearts, diazoxide (300 microM) decreased APD in atria (from 33.8+/-1.9 ms to 24.2+/-1.1 ms, p<0.001) but was without effect in ventricles (APD 60.0+/-7.6 ms vs. 60.8+/-7.5 ms, respectively, NS), consistent with an atrial-specific role for SUR1. The absence of SUR1 resulted in loss of efficacy of diazoxide in SUR1(-/-) atria (APD 36.8+/-1.9 ms vs. 36.8+/-2.8 ms, respectively, NS). In contrast, pinacidil (300 microM) significantly decreased ventricular APD in both WT and SUR1(-/-) hearts (from 60.0+/-7.6 ms to 29.8+/-3.5 ms in WT, p<0.001, and from 63.5+/-2.1 ms to 24.8+/-3.8 ms in SUR1(-/-), p<0.001), but did not decrease atrial APD in either WT or SUR1(-/-) hearts. Glibenclamide (10 microM) reversed the effect of pinacidil in ventricles and restored APD to control values. The absence of Kir6.2 subunits in Kir6.2(-/-) hearts resulted in loss of efficacy of both openers (APD 47.2+/-2.2 ms vs. 47.6+/-2.1 ms and 50.8+/-2.4 ms, and 90.6+/-5.7 ms vs. 93.2+/-6.5 ms and 117.3+/-6.4 ms, for atria and ventricle in control versus diazoxide and pinacidil, respectively). Collectively, these results indicate that in the same mouse heart, significant differential K(ATP) pharmacology in atria and ventricles, resulting from SUR1 predominance in forming the atrial channel, leads to differential effects of potassium channel openers on APD in the two chambers.

[Effect of a new activator of adenosine triphosphate-sensitive potassium channels flocalin on the glucose level in blood]

In experiments on the anaesthetized dogs we investigated the influence of a new fluorine-containing opener of ATP-sensitive potassium channels of sarcolemal and mitochondrial membranes flocalin on the level of glucose in arterial blood at physiological conditions and under ischemia (90 min) and reperfusion (180 min) of myocardium. It was shown that intravenous introduction of flocalin in doses 0,1 - 1,0 mg/kg did not change the level of glucose in blood. In experiments with ischemia-reperfusion of myocardium, flocalin also did not increase the level of glucose during all experiment (5,5 hours) after intragastric (with a help of catheter) introduction of drug form (tablets) at cardiorotective dose of 2,2 mg/kg. However, intravenous introduction of flocalin in the dose of 1,5 mg/kg, which 15 times exceeded a cardioprotective dose of 0,1 mg/kg increased the glucose level 1,33 fold. It should be noted that this increase was not sustained and the level of glucose restored to the initial level within 1 hour. Identical changes of indexes of cardiohemodynamic and the level of glucose in arterial blood under introduction of identical doses of flocalin at the beginning and at the end of experiment (total dose of flocalin reached 4 - 4,5 mg/kg) can testify the absence of cumulative effect of flocalin at these experimental conditions. Thus, strong cardioprotective properties, hypotoxicity and the absence of meaningful changes in a carbohydrate exchange allow to consider a new fluorine-containing opener of K(ATP) channels of flocalin as perspective drug for clinical use.

Excitotoxicity in rat's brain induced by exposure of manganese and neuroprotective effects of pinacidil and nimodipine

Manganese (Mn) is an essential trace element for humans. However, manganism would be caused by excessive Mn. The mechanisms underlying excitotoxicity induced by manganism are poorly understood. As it is known to us, glutamate (Glu) is the most prevalent excitatory neurotransmitter. To determine the possible role of dysfunction of Glu transportation and metabolism in Mn-induced excitotoxicity, the rats were ip injected with different dose of MnCl(2) (0, 50, 100, and 200 micromol/kg), the levels of Mn and activities of GS, PAG, Na(+)-K(+)-ATPase, and Ca(2+)-ATPase in striatum were investigated. In addition, effect of 20.38 micromol/kg pinacidil (K(+) channel opener) or 2.4 micromol/kg nimodipine (Ca(2+) channel blocker) were studied at 200 micromol/kg MnCl(2). With dose-dependent inhibition of GS, Na(+)-K(+)-ATPase, and Ca(2+)-ATPase activities, increase of Mn levels and PAG activity were observed. Further investigation indicated that pre-treatment of pinacidil or nimodipine reversed toxic effect of MnCl(2) significantly. These results suggested that MnCl(2) could induce dysfunction of Glu transportation and metabolism by augmenting the excitotoxicity dose-dependently; pinacidil and nimodipine might antagonize manganese neurotoxicity.

[Cardioprotective effects of activation of ATP-sensitive potassium channels in experiments in vivo: influence on blood biochemical parameters following ischemia-reperfusion of the myocardium]

In experiments on the anaesthetized dogs with modeling of experimental ischemia (90 min) and reperfusion (180 min), the participation of biochemical processes in the cardioprotective effect of the preischemic activation of ATP-sensitive potassium (KATP) channels caused by intravenous introduction of flokalin, a new fluorine-containing opener of these channels was shown. Flokalin was introduced in a dose 0.1 mg/kg of animal body weight which practically did not change the parameters of hemodynamic in normoxia. Thus, the experiments investigating the influence offlokalin on changes of biochemical parameters of arterial blood during ischemia-reperfusion of myocardium showed certain features of ischemia-reperfusion syndrome development during stimulation of K(ATP) channels. The analysis of biochemical parameters of blood showed that flokalin suppressed free radical reactions and had antioxidant properties: reduced quantity of H2O2 and NO3- (the last can interpreted as a reduction in peroxynitrites formation), prevented the decline of catalase and superoxide dismutase activity. Practically constant content of low-molecular nitrosothiols in blood during all duration of experiment and increase of NO2-level during reperfusion may indicate on intact functions of the NO system and protective influence of flokalin during ischemia-reperfusion of myocardium. Practically unchanged content of inorganic phosphorus and uric acid in blood during ischemia- reperfusion under conditions of preischemic introduction of flokalin indicates the prevention of ATP degradation and fomation of both superoxide anion by xanthinoxidase and peroxynitrite by it interaction with nitric oxide. All mentioned properties of flokalin related to the changes of biochemical parameters of arterial blood, together with the changes of parameters of hemodynamics, result in diminishment of infarct size of myocardium after ischemia-reperfusion by 37% versus control experiments. K(ATP) channels, flokalin, ischemia-reperfusion, free radikaly, NO system.

[Effect of adenosine triphosphate-dependent potassium channel activators on electrical reactions of intact and cultured endothelial cells]

The influence of pinacidil, an activator of ATP-sensitive K+ channels, on the membrane potential of endothelial cells from intact rat aorta and cultured endothelial cells was investigated. Pinacidil evoked a slowly developing sustained hyperpolarization of endothelial cells from isolated artery with the amplitude of 15 +/- 4 MV from the resting membrane potential of -44 +/- 1 MB. In contrast, in cultured endothelial cells pinacidil was without response. Diazoxide, another activator of ATP-sensitive K+ channels, in half of the cultured cells tested, evoked a slowly developing sustained hyperpolarization with the amplitude of 3 mV. The rest of the cells studied did not respond by membrane potential changes to diazoxide. It was suggested that high sensitivity of the membrane potential of in situ endothelial cells to potassium channels openers may represent a potent signaling mechanism influencing endothelial cell function upon stimulation of vascular KATP channels.

The influence of animal species on the relationship between ATP-sensitive potassium ion channels and defense reflexes of the airways

BACKGROUND

The ATP-sensitive potassium ion channels (K+ATP) are widely expressed on airway sensory nerves that mediate cough and other protective reflexes; dependent on airways smooth muscles (ASM) reactivity.

OBJECTIVE

The study was conducted to determine the involvement of K+ATP in airway sensory nerves activity of different animal species.

METHODS

In this study we have evaluated the cough reflex inhibiting potential and modulation of ASM reactivity in vitro, by K+ATP opener-pinacidil in guinea pig and cats. The cough in guinea pig was induced by administration, in cats by mechanical stimulation of the airways. ASM reactivity was tested by organ tissue both method of 0.3 M citric acid aerosol at 3 min interval.

RESULTS

1) Pinacidil inhibits cough reflex in guinea pigs which was antagonized when pre-treated with K+ATP blocker glibenclamide. 2) Pinacidil exhibited antitussive activity in cats comparable to codeine and was noticeably higher than dropropizine effects. 3) ASM reactivity was significantly abolished by pinacidil and almost completely antagonized by glibenclamide in guinea pigs. 4) Pinacidil significantly attenuated ASM contraction in cats only in highest concentrations of contractile mediators.

CONCLUSION

K+ATP may be involved in mechanisms of cough reflex, likewise in antitussive activity of several more agents and also on defence reflexes dependent on ASM reactivity in different animal species such as guinea pigs and cats (Fig. 8, Ref. 20). Full Text (Free, PDF) www.bmj.sk.

[Cardioprotective effects of fluorine-containing activator of adenosine triphosphate-dependent potassium channels flokalin]

In experiments on isolated Langendorff perfused hearts of guinea pig with modeling of ischemia (20 min) and reperfusion (40 min) the cardioprotective effects of drug form of new fluorine-containing K(ATP) channels opener flokalin were shown. Preliminary preischemic perfusion of isolated heart with new form of flokalin (5 M) for 5 minutes significantly improved the recovery of contractive function of ischemic myocardium at reperfusion. In particular, it considerably reduced time of ischemic heart contract recovery from the beginning of reperfusion. Recovery of systolic and developed pressure was improved and the increasing of end-diastolic pressure in left ventricle of heart was prevented. Vasodilatoric and antiarrhythmic properties of new drug form of flokalin can assist to it's cardioprotective effects. The vasoconstriction of coronary vessels was prevented and number of extrasystoles at reperfusion of ischemic heart was decreased.

Dissection of two Cx37-independent conducted vasodilator mechanisms by deletion of Cx40: electrotonic versus regenerative conduction

Conduction of changes in diameter plays an important role in the coordination of peripheral vascular resistance and, thereby, in the control of arterial blood pressure. It is thought that conduction of vasomotor signals relies on the electrotonic spread of changes in membrane potential from a site of stimulation through gap junctions connecting the cells of the vessel wall. To explore this idea, we stimulated a short segment of mouse cremasteric arterioles with an application, via micropipette, of ACh, an endothelium-dependent vasodilator, or pinacidil, an ATP-sensitive K+ channel opener. Vasodilations were evaluated at the stimulation site (local) and at 500, 1,000, and 2,000 microm upstream. The vasodilator response evoked by direct arteriolar hyperpolarization induced by pinacidil decayed rapidly with distance, as expected for the passive spread of an electrical signal. Deletion of the gap junction proteins connexin37 or connexin40 did not alter the conduction of pinacidil-induced vasodilation. In contrast to pinacidil, the vasodilator response activated by ACh spread along the entire vessel without decrement. Although the ACh-induced conducted vasodilation was similar in wild-type and connexin37 knockout mice, deletion of connexin40 converted the nondecremental conducted response activated by ACh into one similar to that of pinacidil, with a decline in magnitude along the vessel length. These results suggest that ACh activates a mechanism of regenerative conduction of vasodilator responses. Connexin40 is essential for the ACh-activated regenerative vasodilator mechanism. However, neither connexin40 nor connexin37 is indispensable for the electrotonic spread of hyperpolarizing signals.

Altered ATP-sensitive potassium channels may underscore obesity-triggered increase in blood pressure

AIM

To determine whether ATP-sensitive potassium channels are altered in VSMC from arotas and mesenteric arteries of obese rat, and their association with obesity-triggered increase in blood pressure.

METHODS

Obesity was induced by 24 weeks of high-fat diet feeding in male Sprague-Dawley rats. Control rats were fed with standard laboratory rat chow. Blood pressure and body weight of these rats were measured every 4 weeks. At the end of 24 weeks, K(ATP) channelmediated relaxation responses in the aortas and mesenteric arteries, K(ATP) channel current, and gene expression were examined, respectively.

RESULTS

Blood pressure and body weight were increased in rats fed with high-fat diet. K(ATP) channelmediated relaxation responses, currents, and K(ATP) expression in VSMC of both aortas and mesenteric arteries were inhibited in these rats.

CONCLUSION

Altered ATP-sensitive potassium channels in obese rats may underscore obesity-triggered increase in blood pressure.

Activated Rho/Rho kinase and modified calcium sensitivity in cryopreserved human saphenous veins

BACKGROUND

We have shown previously that cryopreservation of human internal mammary arteries activates protein kinase C and enhances intracellular Ca(2+) [Ca(2+)](i). We now present evidence that in human saphenous veins (HSV) cryoinjury is associated with activation of the Rho/Rho kinase signaling pathways and enhanced [Ca(2+)](i).

METHODS

HSV were investigated in vitro either unfrozen within 12h after removal or after storage at -196 degrees C in a cryomedium containing 1.8M dimethyl sulfoxide and 0.1M sucrose as cryoprotectant additives.

RESULTS

Cryostorage diminished responses to receptor-mediated contractile agonists such as noradrenaline, 5-HT and endothelin-1 by up to 30% whereas responses to KCl were attenuated by about 50%. Concentration-response curves for CaCl(2) on unfrozen and cryopreserved HSV revealed similar inhibitory activities of both blocking 1,4-dihydropyridine derivatives nifedipine and the (-)-(R) enantiomer of SDZ 202-791 whereas the Ca(2+) channel activating (+)-(S) enantiomer of SDZ 202-791 was 10 times less effective at enhancing contractions to CaCl(2) when tested after cryostorage. These functional effects were reflected by changes in [Ca(2+)](i) as demonstrated by fluorescence of Fluo-3AM loaded veins. The diminished activity of (+)-(S) SDZ 202-791 in cryopreserved HSV was reversed partially when the potassium channel opener pinacidil (1 microM) was present during the freezing/thawing process. Blockade of Rho kinase by HA-1077 proved to be significantly more effective at attenuating contractile responses to both endothelin-1 and KCl after cryostorage.

CONCLUSIONS

Data suggested that cryopreservation modified [Ca(2+)](i) of venous smooth muscle cells (1) through depolarization-induced changes in Ca(2+) influx and (2) through activation of Rho kinase signaling pathways.

Upregulation of ATP-sensitive potassium channels for estrogen-mediated cell proliferation in human uterine leiomyoma cells

OBJECTIVES

The objectives of the present study were to evaluate the expression level of ATP-sensitive potassium (K(ATP)) channels in smooth muscle cells in human uterine leiomyoma and the involvement of the channel in potentiating effect of estrogen on leiomyoma growth.

METHODS

Reverse transcription-polymerase chain reaction (RT-PCR), real-time PCR and Western blot were used for the identification and quantification of K(ATP)-channel subunits in the control myometrial and leiomyoma cells. Furthermore, we measured the K(ATP)-channel activity in enzymatically isolated single uterine smooth muscle cells by whole-cell patch-clamp recordings. The estrogen-induced cell proliferation in leiomyoma was measured by the MTT assay.

RESULTS

The subunits of K(ATP) channels (Kir6.1, Kir6.2, SUR2B) were more highly expressed in leiomyoma cells than in control cells. The whole-cell currents mainly through K(ATP) channels were also greater in the leiomyoma cells. Estrogen applied in the bath solution could acutely enhance the channel activity. Estrogen-induced proliferation of the leiomyoma cells was inhibited by pretreatment with glibenclamide, a K(ATP)-channel inhibitor.

CONCLUSION

Estrogen may induce the proliferation of leiomyoma cells, at least in part, by activating the K(ATP) channel. Increased expression of the K(ATP) channel may be a causal factor for the high growth rate of uterine leiomyoma.

Protective effect of melatonin on Ca2+ homeostasis and contractility in acute cholecystitis

Impaired Ca2+ homeostasis and smooth muscle contractility co-exist in acute cholecystitis (AC) leading to gallbladder dysfunction. There is no pharmacological treatment for this pathological condition. Our aim was to evaluate the effects of melatonin treatment on Ca2+ signaling pathways and contractility altered by cholecystitis. [Ca2+]i was determined by epifluorescence microscopy in fura-2 loaded isolated gallbladder smooth muscle cells, and isometric tension was recorded from gallbladder muscle strips. Malondialdehyde (MDA) and reduced glutathione (GSH) contents were determined by spectrophotometry and cycloxygenase-2 (COX-2) expression was quantified by western blot. Melatonin was tested in two experimental groups, one of which underwent common bile duct ligation for 2 days and another that was later de-ligated for 2 days. Inflammation-induced impairment of Ca2+ responses to cholecystokinin and caffeine were recovered by melatonin treatment (30 mg/kg). This treatment also ameliorated the detrimental effects of AC on Ca2+ influx through both L-type and capacitative Ca2+ channels, and it was effective in preserving the pharmacological phenotype of these channels. Despite its effects on Ca2+ homeostasis, melatonin did not improve contractility. After de-ligation, Ca2+ influx and contractility were still impaired, but both were recovered by melatonin. These effects of melatonin were associated to a reduction of MDA levels, an increase in GSH content and a decrease in COX-2 expression. These findings indicate that melatonin restores Ca2+ homeostasis during AC and resolves inflammation. In addition, this indoleamine helps in the subsequent recovery of functionality.

The effect of potassium channel opener pinacidil on the non-pregnant rat uterus

The effects of the K(+) channel opener, pinacidil on the spontaneous rhythmic contractions and contractions provoked by electrical field stimulation (50 Hz) or by oxytocin were investigated in the isolated uterus of the non-pregnant rat in oestrus. Pinacidil produced more potent inhibition of oxytocin-elicited contractions than of spontaneous rhythmic contractions or electrical field stimulation-induced contractions. Glibenclamide, a selective blocker of adenosine triphosphate (ATP)-sensitive K(+) (K(ATP)) channels, antagonized the pinacidil-induced inhibition of contractions elicited by oxytocin in a competitive manner. However, the pinacidil-induced inhibition of electrical field stimulation-elicited contractions and spontaneous rhythmic contractions was antagonized non-competitively by glibenclamide. In the uterine strips pre-contracted with 80 mM K(+), the pinacidil-induced maximal relaxation was not affected. The present data show that pinacidil exhibits potent relaxant properties in the rat non-pregnant uterus in oestrus and therefore should be taken into account as a possible agent for treatment of dysmenorrhoea. Based on glibenclamide affinity, it appears that the inhibitory response to pinacidil involves K(ATP )channels. We need further investigations to explain why the interaction between glibenclamide and pinacidil in this experimental model depends on the nature of contractions. The ability of pinacidil to completely relax the rat non-pregnant uterus pre-contracted with K(+)-rich solution suggests that K(+) channel-independent mechanism(s) also play a part in its relaxant effect.

Synthesis of 2-methyl-4-aryl-4,6,7,8-tetrahydro-5(1H)-quinolone derivatives and their effects on potassium channels

In this study, twelve compounds having 2-methyl-4-aryl-4,6,7,8-tetrahydro-5(1H)-quinolone structure have been synthesized by the reaction of 4-aryl-3-butene-2-on derivatives with 1,3-cyclohexanedione analogs in the presence of ammonium acetate in methanol. The structures of the compounds have been elucidated by IR, 1H-NMR, 13C-NMR, mass spectroscopy and elementel analysis. Their potassium channel opener activities have been investigated on isolated rabbit bladder smooth muscle using pinacidil (CAS 85371-64-8) as standard. The test compounds and pinacidil caused concentration-dependent relaxation responses in bladder smooth muscle strips precontracted with 80 mmol/L KCl with the efficacy order: pinacidil > or = 3g > or = 3j > or = 3a > or = 3l = 3i > or = 3c = 3b > or = 3d > or = 3h > or = 3k. In bladder smooth muscle strips precontracted with 15 mmol/L KCl, the efficacy order was: pinacidil > 3h > or = 3c > or = 3j > or = 3g > or = 3l > or = 3i = 3b > or = 3k > or = 3f > or = 3a. The test compounds and pinacidil caused concentration-dependent inhibition of electrical field stimulation-evoked contractile responses in the bladder smooth muscle strips with the efficacy order: 3j > or = 3l pinacidil > or = 3k > or = 3h > or = 3a > or = 3g > or = 3c > or = 3i > or = 3b > or = 3f.

[Cardioprotective effects of flokalin: relative role of activation of sarcolemmal and mitochondrial adenosine triphosphate-dependent potassium channels]

In experiments on isolated Langendorff perfused hearts of guinea pig with modeling of ischemia (20 min) and reperfusion (40 min) the cardioprotective effects of flokalin were shown. Preliminary preischemic perfusion of isolated heart with flokalin (5 mM) for 5 minutes has significantly improved the recovery of contractive function ofischemic myocardium at repcrfusion. Particularly, recovery of systolic and developed pressure was improved and the increasing of end-diastolic pressure in left ventricle was prevented. The vasoconstriction of coronary vessels was prevented and number of extrasystols at reperfusion of ischemic heart was decreased. Morphological studies have shown that flokalin prevents the significant damage of myocardial structure and the development of hypercontraction of myofibrils at ischemia-reperfusion of myocardium. It also preserves the intact sarcolemma and intracellular organelles. The intact structure of mitochondria also was saved by flokalin that maintains the energy potential of myocardium. Using the selective blocker of mitochondrial K(ATP) channels 5-hydroxydecanoate (200 mM) allows to determine the relative role of sarcolemmal and mitochondrial K(ATP) channels activation in these effects. It was shown that mitochondrial as well as sarcolemmal K(ATP) channels play role in the recovery of ischemic myocardium functions: first are responsible for recovery of contractive function and second are responsible for coronary blood flow recovery.

Effect of pravastatin on sympathetic reinnervation in postinfarcted rats

We assessed whether pravastatin attenuates cardiac sympathetic reinnervation after myocardial infarction through the activation of ATP-sensitive K+(KATP) channels. Epidemiological studies have shown that men treated with statins appear to have a lower incidence of sudden death than men without statins. However, the specific factor for this has remained disappointingly elusive. Twenty-four hours after ligation of the anterior descending artery, male Wistar rats were randomized to groups treated with either vehicle, nicorandil (a specific mitochondrial KATPchannel agonist), pinacidil (a nonspecific KATPchannel agonist), pravastatin, glibenclamide (a KATPchannel blocker), or a combination of nicorandil and glibenclamide, pinacidil and glibenclamide, or pravastatin and glibenclamide for 4 wk. Myocardial norepinephrine levels revealed a significant elevation in vehicle-treated rats at the remote zone compared with sham-operated rats (2.54 ± 0.17 vs. 1.26 ± 0.36 μg/g protein, P < 0.0001), consistent with excessive sympathetic reinnervation after infarction. Immunohistochemical analysis for tyrosine hydroxylase, growth-associated factor 43, and neurofilament also confirmed the change of myocardial norepinephrine. This was paralleled by a significant upregulation of tyrosine hydroxylase protein expression and mRNA in vehicle-treated rats, which was reduced after the administration of either nicorandil, pinacidil, or pravastatin. Arrhythmic scores during programmed stimulation in vehicle-treated rats were significantly higher than those treated with pravastatin. In contrast, the beneficial effects of pravastatin were reversed by the addition of glibenclamide, implicating KATPchannels as the relevant target. The sympathetic reinnervation after infarction is modulated by the activation of KATPchannels. Chronic use of pravastatin after infarction, resulting in attenuated sympathetic reinnervation by the activation of KATPchannels, may modify the arrhythomogenic response to programmed electrical stimulation.

Brazilein-induced contraction of rat arterial smooth muscle involves activation of Ca2+ entry and ROK, ERK pathways

Brazilein (6a,7-dihydro-3,6a,10-trihydroxy-benz[b]indeno[1,2-d]pyran-9(6H)-one) is a compound isolated from Caesalpinia sappan. The vasoactivities of brazilein were evaluated in isolated rat thoracic aorta. The results showed that brazilein can dose-dependently induce contraction of rat thoracic aorta in the resting and phenylephrine pre-evoked state. The average response to 100 microM of brazilein was 30% of the 50 mM KCl contraction, 26% of the 10 muM phenylephrine and 116% of the 20 mM caffeine contraction in comparison. The effects of vasocontraction were proved not to be endothelial dependent and could not be inhibited by alpha-adrenergic receptor blocker phentolamine, beta-adrenergic receptor blocker propranolol, M-adrenaline receptor blocker atropine, angiotensin II receptor blocker losartan or the non-selective nitric oxide synthase (NOS) inhibitor NG-Nitro-L-Arginine Methyl Ester (L-NAME). However the influx of extracellular calcium seemed to be required for this action, because depletion of extracellular calcium and the addition of L-type calcium ion channel antagonist (nimodipine and diltiazem), calcium ion channel activator (BAY-K8644) and potassium ion channel opener (pinacidil) could significantly affect the contraction induced by brazilein. We also investigated the possible signal mechanisms underlying brazilein-induced contraction using selective inhibitors. The inhibitors of myosin light chain kinase (MLCK), Rho-kinase (ROK) and extracellular signal regulated kinase (ERK) can suppress the effect of brazilein respectively, whereas inhibitors of other signaling or receptor molecules such as protein kinase C (PKC) and inositol 1,4,5-triphosphate (IP3) receptor had no effect. All these results demonstrated that brazilein can induce contraction of rat aorta, that the Ca2+ influx, ROK and ERK signal pathways and MLCK activation must be involved in the contractile processes.

The role of potassium ion channels in cough and other reflexes of the airways

In this study we investigated whether openers of potassium channels, K+ATP--pinacidil and BK+Ca--NS1619, modulate cough reflex and airway smooth muscle (ASM) reactivity in in vivo and in vitro conditions in guinea pigs. The cough reflex was induced by 0.3 M citric acid aerosol given for 3 min during which time a total number of coughs was counted. ASM reactivity in vivo was expressed as the values of specific airway resistance calculated by Pennock. Changes in ASM reactivity in vitro were tested by a tissue bath method. We found that both openers of potassium channels inhibit the citric acid-induced cough. ASM reactivity in vivo was significantly abolished by pinacidil and NS1619, which corresponded with the results of in vitro measurements. Pretreatment by selective blockers, K+ATP--glibenclamide and BK+Ca-tetraethylammonium prevented the above mentioned effects. The results indicate an important role of K+ATP and BK+Ca ion channels in defense reflexes of airways.

Angiotensin II-activated protein kinase C targets caveolae to inhibit aortic ATP-sensitive potassium channels

OBJECTIVE

The vasoconstrictor angiotensin II (Ang II) acts at G(q/11)-coupled receptors to suppress ATP-sensitive potassium (K(ATP)) channel activity via activation of protein kinase C (PKC). The aim of this study was to determine the PKC isoforms involved in the Ang II-induced inhibition of aortic K(ATP) channel activity and to investigate potential mechanisms by which these isoforms specifically target these ion channels.

METHODS AND RESULTS

We show that the inhibitory effect of Ang II on pinacidil-evoked whole-cell rat aortic K(ATP) currents persists in the presence of Gö6976, an inhibitor of the conventional PKC isoforms, but is abolished by intracellular dialysis of a selective PKCepsilon translocation inhibitor peptide. This suggests that PKC-dependent inhibition of aortic K(ATP) channels by Ang II arises exclusively from the activation and translocation of PKCepsilon. Using discontinuous sucrose density gradients and Western blot analysis, we show that Ang II induces the translocation of PKCepsilon to cholesterol-enriched rat aortic smooth muscle membrane fractions containing both caveolin, a protein found exclusively in caveolae, and Kir6.1, the pore-forming subunit of the vascular K(ATP) channel. Immunogold electron microscopy of rat aortic smooth muscle plasma membrane sheets confirms both the presence of Kir6.1 in morphologically identifiable regions of the membrane rich in caveolin and Ang II-evoked migration of PKCepsilon to these membrane compartments.

CONCLUSIONS

Ang II induces the recruitment of the novel PKC isoform, PKCepsilon, to arterial smooth muscle caveolae. This translocation allows PKCepsilon access to K(ATP) channels compartmentalized within these specialized membrane microdomains and highlights a potential role for caveolae in targeting PKC isozymes to an ion channel effector.

Voltage-gated Ca2+ currents are necessary for slow-wave propagation in the canine gastric antrum

Electrical slow waves determine the timing and force of peristaltic contractions in the stomach. Slow waves originate from a dominant pacemaker in the orad corpus and propagate actively around and down the stomach to the pylorus. The mechanism of slow-wave propagation is controversial. We tested whether Ca(2+) entry via a voltage-dependent, dihydropyridine-resistant Ca(2+) conductance is necessary for active propagation in canine gastric antral muscles. Muscle strips cut parallel to the circular muscle were studied with intracellular electrophysiological techniques using a partitioned-chamber apparatus. Slow-wave upstroke velocity and plateau amplitude decreased from the greater to the lesser curvature, and this corresponded to a decrease in the density of interstitial cells of Cajal in the lesser curvature. Slow-wave propagation velocity between electrodes impaling cells in two regions of muscle and slow-wave upstroke and plateau were measured in response to experimental conditions that reduce the driving force for Ca(2+) entry or block voltage-dependent Ca(2+) currents. Nicardipine (0.1-1 microM) did not affect slow-wave upstroke or propagation velocities. Upstroke velocity, amplitude, and propagation velocity were reduced in a concentration-dependent manner by Ni(2+) (1-100 microM), mibefradil (10-30 microM), and reduced extracellular Ca(2+) (0.5-1.5 mM). Depolarization (by 10-15 mM K(+)) or hyperpolarization (10 microM pinacidil) also reduced upstroke and propagation velocities. The higher concentrations (or lowest Ca(2+)) of these drugs and ionic conditions tested blocked slow-wave propagation. Treatment with cyclopiazonic acid to empty Ca(2+) stores did not affect propagation. These experiments show that voltage-dependent Ca(2+) entry is obligatory for the upstroke phase of slow waves and active propagation.

SPONTANEOUS OSCILLATORY CONTRACTIONS IN AORTAS OF RATS WITH ARTERIAL PRESSURE LABILITY CAUSED BY SINOAORTIC DENERVATION

1. The spontaneous variation of blood pressure is defined as arterial pressure lability. Sinoaortic denervation (SAD) is characterized by arterial pressure lability without sustained hypertension. 2. The phenomenon of spontaneous oscillatory contractions (SOCs) occurs more frequently in the vascular beds of hypertensive animals. In large arteries, such as the aorta, SOCs occur only occasionally or they can be initiated by application of chemical stimuli. 3. In the present study, we investigated whether the arterial pressure lability evoked by SAD could be related to the emergence of SOCs in the aorta of rats submitted to SAD compared with sham-operated rats (SO). Three days after surgery (SAD or SO), aortic rings were placed in an organ chamber and the incidence (percentage of rats presenting SOCs), frequency (number of SOCs in 10 min) and amplitude (mN) of SOCs were measured. The participation of external Ca(2+) and K(+) channels in the maintenance of SOCs was also verified. 4. The incidence and frequency of SOCs were higher in endothelium-denuded aortas from SAD rats (82% and 38 +/- 4 SOCs/10 min, respectively) than in aortas from SO rats (40% and 14 +/- 2 SOCs/10 min, respectively). In aortas from SAD rats, verapamil (0.2 micromol/L), pinacidil (0.3 micromol/L) and tetraethylammonium (TEA; 5 mmol/L) totally inhibited SOCs, whereas increasing the CaCl(2) concentration to 2.0 and 2.5 mmol/L increased the frequency of SOCs. Interestingly, increasing the concentration of CaCl(2) to 3.5 mmol/L inhibited these contractions in aortas from SAD rats. 5. These results show that although SAD rats did not become hypertensive, their aortas were capable of initiating SOCs without the application of any chemical stimuli. The SOCs seem to be dependent on Ca(2+) influx sensitive to verapamil and also involve K(+) channels sensitive to pinacidil and TEA.

ATP-sensitive potassium channel: a novel target for protection against UV-induced human skin cell damage

Ultraviolet radiation (UV) induces cell damages leading to skin photoaging and skin cancer. ATP-sensitive potassium (K(ATP)) channel openers (KCOs) have been shown to exert significant myocardial preservation and neuroprotection in vitro and in vivo, and yet the potential role of those KCOs in protection against UV-induced skin cell damage is unknown. We investigated the effects of pinacidil and diazoxide, two classical KCOs, on UV-induced cell death using cultured human keratinocytes (HaCat cells). Here, we demonstrated for the first time that Kir 6.1, Kir 6.2 and SUR2 subunits of K(ATP) channels are functionally expressed in HaCaT cells and both non-selective K(ATP) channel opener pinacidil and mitoK(ATP) (mitochondrial K(ATP)) channel opener diazoxide attenuated UV-induced keratinocytes cell death. The protective effects were abolished by both non-selective K(ATP) channel blocker glibenclamide and selective mitoK(ATP) channel blocker 5-hydroxydecanoate (5-HD). Also, activation of K(ATP) channel with pinacidil or diazoxide resulted in suppressive effects on UV-induced MAPK activation and reactive oxygen species (ROS) production. Unexpectedly, we found that the level of intracellular ROS was slightly elevated in HaCaT cells when treated with pinacidil or diazoxide alone. Furthermore, UV-induced mitochondrial membrane potential loss, cytochrome c release and ultimately apoptotic cell death were also inhibited by preconditioning with pinacidil and diazoxide, and their effects were reversed by glibenclamide and 5-HD. Taken together, we contend that mitoK(ATP) is likely to contribute the protection against UV-induced keratinocytes cell damage. Our findings suggest that K(ATP) openers such as pinacidil and diazoxide may be utilized to prevent from UV-induced skin aging.