Direct interaction of the ATP-sensitive K+ channel by the tyrosine kinase inhibitors imatinib, sunitinib and nilotinib.

The ATP-regulated K+ channel (KATP) plays an essential role in the control of many physiological processes, and contains a ATP-binding site. Tyrosine kinase inhibitors (TKI) are commonly used drugs, that primarily target ATP-binding sites in tyrosine kinases. Herein, we used the patch-clamp technique to examine the effects of three clinically established TKIs on KATP channel activity in isolated membrane patches, using a pancreatic ß-cell line as a KATP channel source. In excised inside-out patches, the activity of the KATP channel was dose-dependently inhibited by imatinib with half-maximal concentration of approximately 9.4 µM. The blocking effect of imatinib was slow and reversible. No effect of imatinib was observed on either the large (KBK) or the small (KSK) conductance, Ca2+-regulated K+ channel. In the presence of ATP/ADP (ratio 1) addition of imatinib increased channel activity approximately 1.5-fold. Sunitinib and nilotinib were also found to decrease KATP channel activity. These findings are compatible with the view that TKIs, designed to interact at the ATP-binding pocket on the tyrosine receptor, also interact at the ATP-binding site on the KATP channel. Possibly, this might explain some of the side effects seen with TKIs.

Penehyclidine hydrochloride protects against anoxia/reoxygenation injury in cardiomyocytes through ATP-sensitive potassium channels, and the Akt/GSK-3ß and Akt/mTOR signaling pathways.

Penehyclidine hydrochloride (PHC) can protect against myocardial ischemia/reperfusion (I/R) injury. However, the possible mechanisms of PHC in anoxia/reoxygenation (A/R)-induced injury in H9c2 cells remain unclear. In the present study, H9c2 cells were pretreated with PI3K/Akt inhibitor LY294002, ATP-sensitive K+ (KATP) channel blocker 5-hydroxydecanoate (5-HD), PHC, or KATP channel opener diazoxide (DZ) before subjecting to A/R injury. Cell viability and cell apoptosis were determined by cell counting kit-8 assay and annexin V/PI assay, respectively. Myocardial injury was evaluated by measuring creatine kinase (CK) and lactate dehydrogenase (LDH) activities. Intracellular Ca2+ levels, reactive oxygen species (ROS) generation, mitochondrial membrane potential (ΔΨm ), and mitochondrial permeability transition pore (mPTP) were measured. The levels of cytoplasmic/mitochondrial cytochrome c (Cyt-C), Bax, Bcl-2, cleaved caspase-3, KATP channel subunits (Kir6.2 and SUR2A), and the members of the Akt/GSK-3ß and Akt/mTOR signaling pathways were determined by western blotting. We found that PHC preconditioning alleviated A/R-induced cell injury by increasing cell viability, reducing CK and LDH activities, and inhibiting cell apoptosis. In addition, PHC preconditioning ameliorated intracellular Ca2+ overload and ROS production, accompanied by inhibition of both mPTP opening and Cyt-C release into cytoplasm, and maintenance of ΔΨm . Moreover, PHC preconditioning activated mitochondrial KATP channels, and modulated the Akt/GSK-3ß and Akt/mTOR signaling pathways. Similar effects were observed upon treatment with DZ. Pretreatment with LY294002 or 5-HD blocked the beneficial effects of PHC. These results suggest that the protective effects of PHC preconditioning on A/R injury may be related to mitochondrial KATP channels, as well as the Akt/GSK-3ß and Akt/mTOR signaling pathways.

Effects of Chaihu-Shugan-San on Small Intestinal Interstitial Cells of Cajal in Mice.

Chaihu-Shugan-San (CSS) has been widely used as an alternative treatment for gastrointestinal (GI) diseases in East Asia. Interstitial cells of Cajal (ICCs) are pacemakers in the GI tract. In the present study, we examined the action of CSS on pacemaker potentials in cultured ICCs from the mouse small intestine in vitro and on GI motility in vivo. We used the electrophysiological methods to measure the pacemaker potentials in ICCs. GI motility was investigated by measuring intestinal transit rates (ITR). CSS inhibited the pacemaker potentials in a dose-dependent manner. The capsazepine did not block the effect of CSS. However, the effects of CSS were blocked by glibenclamide. In addition, NG-nitro-L-arginine methyl ester (L-NAME) also blocked the CSS-induced effects. Pretreatment with SQ-22536 or with KT-5720 did not suppress the effects of CSS; however, pretreatment with ODQ or KT-5823 did. Furthermore, CSS significantly suppressed murine ITR enhancement by neostigmine in vivo. These results suggest that CSS exerts inhibitory effects on the pacemaker potentials of ICCs via nitric oxide (NO)/cGMP and ATP-sensitive K+ channel dependent and transient receptor potential vanilloid 1 (TRPV1) channel independent pathways. Accordingly, CSS could provide the basis for the development of new treatments for GI motility dysfunction.

4-Aminopyridine, a Voltage-Gated K+ Channel Inhibitor, Attenuates Nitric Oxide-Mediated Vasodilation of Retinal Arterioles in Rats.

Nitric oxide (NO) is an important regulator of the retinal blood flow. The present study aimed to determine the role of voltage-gated K+ (KV) channels and ATP-sensitive K+ (KATP) channels in NO-mediated vasodilation of retinal arterioles in rats. In vivo, the retinal vasodilator responses were assessed by measuring changes in the diameter of retinal arterioles from ocular fundus images. Intravitreal injection of 4-aminopyridine (a KV channel inhibitor), but not glibenclamide (a KATP channel blocker), significantly attenuated the retinal vasodilator response to the NO donor (±)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (NOR3). Intravitreal injection of indomethacin (a non-selective cyclooxygenase inhibitor) also reduced the NOR3-induced retinal vasodilator response. The combination of 4-aminopyridine and indomethacin produced a greater reduction in the NOR3-induced response than either agent alone. 4-Aminopyridine had no significant effect on pinacidil (a KATP channel opener)-induced response. These results suggest that the vasodilatory effects of NO are mediated, at least in part, through the activation of 4-aminopyridine-sensitive KV channels in the retinal arterioles of rats. NO exerts its dilatory effect on the retinal vasculature of rats through at least two mechanisms, activation of the KV channels and enhancement of prostaglandin production.

Resistance of Fetal Guinea Pig Ventricular Myocardium to Hypoxia: Maintained Intracellular ATP Prevents the Opening of ATP-Sensitive Potassium Channels.

The presence and function of the ATP-sensitive potassium channel current (IKATP) were examined in the guinea pig myocardium to clarify the mechanisms for the resistance of the fetal myocardium to hypoxia. Experimental hypoxia markedly reduced the action potential duration and contractile force in isolated ventricular myocardium from the adult, but only moderately in those from the fetus. In isolated ventricular cardiomyocytes, the density of the IKATP activated by cromakalim, as well as their sensitivity to intracellular ATP concentration, were not different between the fetus and adult. The tissue ATP content was similar between the fetal and adult myocardium under normal condition, but the hypoxia-induced decrease was smaller in the fetus. Confocal microscopic analysis revealed that the mitochondria in the fetal cardiomyocyte is less in quantity than that in the adult and is more localized to the cell center. These results indicate that IKATP in the fetal guinea pig myocardium has a current density and ATP sensitivity similar to those of the adult, but is not activated under hypoxic conditions because the energy metabolism of the fetal myocardium is less dependent on oxidative phosphorylation.

Antinociceptive activities of Artocarpus lacucha Buch-ham (Moraceae) and its isolated phenolic compound, catechin, in mice.

BACKGROUND: The present study evaluated the antinociceptive effect of the bark of Artocarpus lacucha, which is used for the treatment of stomachache, headache and boils in the traditional system of medicine. METHODS: The antinociceptive activity was investigated by the tail immersion, hot plate, acetic acid- & formalin-induced nociception and carrageenan-induced paw edema tests using a hydro-methanolic extract of A. lacucha bark. The plant extract was found to contain a substantial amount of phenolic compounds according to the total phenolic and flavonoid content assay. A phenolic metabolite, (+)-catechin, has been isolated using different chromatographic techniques. The compound was characterized with 1D and 2D NMR spectroscopic data. (+)-catechin, isolated from A. lacucha was assessed for antinociceptive effects swiss albino mice. Furthermore, the possible involvement of opioid receptors and ATP-sensitive K+ channel for the effect of the plant extract and (+)-catechin has been justified using naloxone and glibenclamide, respectively. RESULTS: Oral administration (p.o) of the plant extract (50-200 mg/Kg b.w.) resulted in significant thermal pain protection in the hot plate and tail immersion tests. The action of the plant extract was significantly antagonized by naloxone, a non-selective opioid antagonist, in the hot plate and tail immersion tests, which supports the involvement of opioid receptors. Both the plant extract and (+)-catechin, (50-200 mg/Kg b.w., p.o.) significantly diminished the acetic acid- & formalin-induced nociception, and carrageenan-induced paw edema. Glibenclamide, an ATP-sensitive K+ channel blocker, significantly reversed their effect in the acetic acid-induced writhing test which indicates the participation of ATP-sensitive K+ channel system. CONCLUSIONS: The investigation revealed potential central and peripheral antinociceptive effects of A. lacucha bark supports its applications in the traditional system of medicine.

Muscarinic suppression of ATP-sensitive K+ channels mediated by the M3/Gq/11/phospholipase C pathway contributes to mouse ileal smooth muscle contractions.

ATP-sensitive K+ (KATP) channels are expressed in gastrointestinal smooth muscles, and their activity is regulated by muscarinic receptor stimulation. However, the physiological significance and mechanisms of muscarinic regulation of KATP channels are not fully understood. We examined the effects of the KATP channel opener cromakalim and the KATP channel blocker glibenclamide on electrical activity of single mouse ileal myocytes and on mechanical activity in ileal segment preparations. To explore muscarinic regulation of KATP channel activity and its underlying mechanisms, the effect of carbachol (CCh) on cromakalim-induced KATP channel currents ( IKATP) was studied in myocytes of M2 or M3 muscarinic receptor-knockout (KO) and wild-type (WT) mice. Cromakalim (10 µM) induced membrane hyperpolarization in single myocytes and relaxation in segment preparations from WT mice, whereas glibenclamide (10 µM) caused membrane depolarization and contraction. CCh (100 µM) induced sustained suppression of IKATP in cells from both WT and M2KO mice. However, CCh had a minimal effect on IKATP in M3KO and M2/M3 double-KO cells. The Gq/11 inhibitor YM-254890 (10 µM) and PLC inhibitor U73122 (1 µM), but not the PKC inhibitor calphostin C (1 µM), markedly decreased CCh-induced suppression of IKATP in WT cells. These results indicated that KATP channels are constitutively active and contribute to the setting of resting membrane potential in mouse ileal smooth muscles. M3 receptors inhibit the activity of these channels via a Gq/11/PLC-dependent but PKC-independent pathways, thereby contributing to membrane depolarization and contraction of smooth muscles. NEW & NOTEWORTHY We systematically investigated the regulation of ATP-sensitive K+ channels by muscarinic receptors expressed on mouse ileal smooth muscles. We found that M3 receptors inhibit the activity of ATP-sensitive K+ channels via a Gq/11/PLC-dependent, but PKC-independent, pathway. This muscarinic suppression of ATP-sensitive K+ channels contributes to membrane depolarization and contraction of smooth muscles.

Minoxidil improves vascular compliance, restores cerebral blood flow, and alters extracellular matrix gene expression in a model of chronic vascular stiffness.

Increased vascular stiffness correlates with a higher risk of cardiovascular complications in aging adults. Elastin (ELN) insufficiency, as observed in patients with Williams-Beuren syndrome or with familial supravalvular aortic stenosis, also increases vascular stiffness and leads to arterial narrowing. We used Eln+/- mice to test the hypothesis that pathologically increased vascular stiffness with concomitant arterial narrowing leads to decreased blood flow to end organs such as the brain. We also hypothesized that drugs that remodel arteries and increase lumen diameter would improve flow. To test these hypotheses, we compared carotid blood flow using ultrasound and cerebral blood flow using MRI-based arterial spin labeling in wild-type (WT) and Eln+/- mice. We then studied how minoxidil, an ATP-sensitive K+ channel opener and vasodilator, affects vessel mechanics, blood flow, and gene expression. Both carotid and cerebral blood flows were lower in Eln+/- mice than in WT mice. Treatment of Eln+/- mice with minoxidil lowered blood pressure and reduced functional arterial stiffness to WT levels. Minoxidil also improved arterial diameter and restored carotid and cerebral blood flows in Eln+/- mice. The beneficial effects persisted for weeks after drug removal. RNA-Seq analysis revealed differential expression of 127 extracellular matrix-related genes among the treatment groups. These results indicate that ELN insufficiency impairs end-organ perfusion, which may contribute to the increased cardiovascular risk. Minoxidil, despite lowering blood pressure, improves end-organ perfusion. Changes in matrix gene expression and persistence of treatment effects after drug withdrawal suggest arterial remodeling. Such remodeling may benefit patients with genetic or age-dependent ELN insufficiency. NEW & NOTEWORTHY Our work with a model of chronic vascular stiffness, the elastin ( Eln)+/- mouse, shows reduced brain perfusion as measured by carotid ultrasound and MRI arterial spin labeling. Vessel caliber, functional stiffness, and blood flow improved with minoxidil. The ATP-sensitive K+ channel opener increased Eln gene expression and altered 126 other matrix-associated genes.

Multiple Actions of Rotenone, an Inhibitor of Mitochondrial Respiratory Chain, on Ionic Currents and Miniature End-Plate Potential in Mouse Hippocampal (mHippoE-14) Neurons.

BACKGROUND/AIMS: Rotenone (Rot) is known to suppress the activity of complex I in the mitochondrial chain reaction; however, whether this compound has effects on ion currents in neurons remains largely unexplored. METHODS: With the aid of patch-clamp technology and simulation modeling, the effects of Rot on membrane ion currents present in mHippoE-14 cells were investigated. RESULTS: Addition of Rot produced an inhibitory action on the peak amplitude of INa with an IC50 value of 39.3 µM; however, neither activation nor inactivation kinetics of INa was changed during cell exposure to this compound. Addition of Rot produced little or no modifications in the steady-state inactivation curve of INa. Rot increased the amplitude of Ca2+-activated Cl- current in response to membrane depolarization with an EC50 value of 35.4 µM; further addition of niflumic acid reversed Rot-mediated stimulation of this current. Moreover, when these cells were exposed to 10 µM Rot, a specific population of ATP-sensitive K+ channels with a single-channel conductance of 18.1 pS was measured, despite its inability to alter single-channel conductance. Under current clamp condition, the frequency of miniature end-plate potentials in mHippoE-14 cells was significantly raised in the presence of Rot (10 µM) with no changes in their amplitude and time course of rise and decay. In simulated model of hippocampal neurons incorporated with chemical autaptic connection, increased autaptic strength to mimic the action of Rot was noted to change the bursting pattern with emergence of subthreshold potentials. CONCLUSIONS: The Rot effects presented herein might exert a significant action on functional activities of hippocampal neurons occurring in vivo.

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.

Opening of KATP Channel Regulates Tonic Currents From Pyramidal Neurons in Rat Brain.

BACKGROUND: ATP-sensitive K+ (KATP) channels couple metabolic state to cellular excitability. Activation of neuronal and astrocytic mitochondrial KATP (mitoKATP) channels regulates a variety of neuronal functions. However, less is known about the impact of mitoKATP on tonic γ-aminobutyric acid (GABA) inhibition. Tonic GABA inhibition is mediated by the binding of ambient GABA on extrasynaptic GABA A-type receptors (GABAARs) and is involved in regulating neuronal excitability. METHODS: We determined the impact of activation of KATP channels with diazoxide (DIZ) on tonic inhibition and recorded tonic current from rat cortical layer 5 pyramidal cells by patch-clamp recordings. RESULTS: We found that neonatal tonic current increased with an increase in GABA concentration, which was partially mediated by the GABA A-type receptor (GABAAR) α5, and likely the δ subunits. Activation of KATP channels resulted in decreased tonic current in newborns, but there was increased tonic current during the second postnatal week. CONCLUSIONS: These findings suggest that activation of KATP channels with DIZ regulates GABAergic transmission in neocortical pyramidal cells during development.

Mechanism of Mitochondrial Connexin43's Protection of the Neurovascular Unit under Acute Cerebral Ischemia-Reperfusion Injury.

We observed mitochondrial connexin43 (mtCx43) expression under cerebral ischemia-reperfusion (I/R) injury, analyzed its regulation, and explored its protective mechanisms. Wistar rats were divided into groups based on injections received before middle cerebral artery occlusion (MCAO). Cerebral infarction volume was detected by 2,3,5-triphenyltetrazolim chloride staining, and cell apoptosis was observed by transferase dUTP nick end labeling. We used transmission electron microscopy to observe mitochondrial morphology and determined superoxide dismutase (SOD) activity and malondialdehyde (MDA) content. MtCx43, p-mtCx43, protein kinase C (PKC), and p-PKC expression were detected by Western blot. Compared with those in the IR group, cerebral infarction volumes in the carbenoxolone (CBX) and diazoxide (DZX) groups were obviously smaller, and the apoptosis indices were down-regulated. Mitochondrial morphology was damaged after I/R, especially in the IR and 5-hydroxydecanoic acid (5-HD) groups. Similarly, decreased SOD activity and increased MDA were observed after MCAO; CBX, DZX, and phorbol-12-myristate-13-acetate (PMA) reduced mitochondrial functional injury. Expression of mtCx43 and p-mtCx43 and the p-Cx43/Cx43 ratio were significantly lower in the IR group than in the sham group. These abnormalities were ameliorated by CBX, DZX, and PMA. MtCx43 may protect the neurovascular unit from acute cerebral IR injury via PKC activation induced by mitoKATP channel agonists.

Acute exposure of beta-cells to troglitazone decreases insulin hypersecretion via activating AMPK.

BACKGROUND: It has been recognized that insulin hypersecretion can lead to the development of insulin resistance and type 2 diabetes mellitus. There is substantial evidence demonstrating that thiazolidinediones are able to delay and prevent the progression of pancreatic ß-cell dysfunction. However, the mechanism underlying the protective effect of thiazolidinediones on ß-cell function remains elusive. METHODS: We synchronously detected the effects of troglitazone on insulin secretion and AMP-activated protein kinase (AMPK) activity under various conditions in isolated rat islets and MIN6 cells. RESULTS: Long-term exposure to high glucose stimulated insulin hypersecretion and inhibited AMPK activity in rat islets. Troglitazone-suppressed insulin hypersecretion was closely related to the activation of AMPK. This action was most prominent at the moderate concentration of glucose. Glucose-stimulated insulin secretion was decreased by long-term troglitazone treatment, but significantly increased after the drug withdrawal. Compound C, an AMPK inhibitor, reversed troglitazone-suppressed insulin secretion in MIN6 cells and rat islets. Knockdown of AMPKα2 showed a similar result. In MIN6 cells, troglitazone blocked high glucose-closed ATP-sensitive K(+) (KATP) channel and decreased membrane potential, along with increased voltage-dependent potassium channel currents. Troglitazone suppressed intracellular Ca(2+) response to high glucose, which was abolished by treatment with compound C. CONCLUSION: Our results suggest that troglitazone provides ß-cell "a rest" through activating AMPK and inhibiting insulin hypersecretion, and thus restores its response to glucose. GENERAL SIGNIFICANCE: These data support that AMPK activation may be an important mechanism for thiazolidinediones preserving ß-cell function.

Expression levels of KATP channel subunits and morphological changes in the mouse liver after exposure to radiation.

BACKGROUND: ATP sensitive K+ (KATP) channels are ubiquitously distributed in various of cells and tissues, including the liver. They play a role in the pathogenesis of myocardial and liver ischemia. AIM: To evaluate the radiation-induced changes in the expression of KATP channel subunits in the mouse liver to understand the potential role of KATP channels in radiation injury. METHODS: Adult C57BL/6 mice were randomly exposed to γ-rays at 0 Gy (control, n = 2), 0.2 Gy (n = 6), 1 Gy (n = 6), or 5 Gy (n = 6). The livers were removed 3 and 24 h after radiation exposure. Hematoxylin and eosin staining was used for morphological observation; immunohistochemical staining was applied to determine the expression of KATP channel subunits in the liver tissue. RESULTS: Compared with the control group, the livers exposed to 0.2 Gy γ-ray showed an initial increase in the expression of Kir6.1 at 3 h, followed by recovery at 24 h after exposure. Exposure to a high dose of 5.0 Gy resulted in decreased expression of Kir6.1 and increased expression of SUR2B at 24 h. However, the expression of Kir6.2, SUR1, or SUR2A had no remarkable changes at 3 and 24 h after exposure to any of these doses. CONCLUSION: The expression levels of Kir6.1 and SUR2B in mouse liver changed differently in response to different radiation doses, suggesting a potential role for them in radiation-induced liver injury.

Muscarinic stimulation and pinacidil produce similar facilitation of tachyarrhythmia induction in rat isolated atria.

Atrial tachyarrhythmias, the most common type of cardiac arrhythmias, are associated with greater stroke risk. Muscarinic cholinergic agonists have been shown to facilitate atrial tachyarrhythmia maintenance in the absence of cardiac disease. This has been attributed to action potential shortening, which enhances myocardial electrical anisotropy, and thus creates a substrate for reentrant excitation. In this study, we describe a similar effect of the ATP-sensitive K(+) channel (KATP) opener pinacidil on tachyarrhythmia induction in isolated rat atria. Pinacidil, which activates a weakly inwardly-rectifying current in isolated atrial myocytes, enhanced arrhythmia induction in the right and left atria. This effect was abolished by the KATP blocker glibenclamide, but not by atropine, which rules out a possible indirect effect due to stimulation of acetylcholine release. However, pinacidil attenuated carbachol-induced tachyarrhythmia facilitation, which may indicate that the action of these agonists converges to a common cellular mechanism. Both agonists caused marked action potential shortening in isolated atrial myocytes. Moreover, during arrhythmia in the presence of pinacidil and carbachol, the atrial vectorelectrographic patterns were similar and consistent with reentrant propagation of the electrical activity. From these results, we conclude that the KATP channel opening is pro-arrhythmic in atrial tissue, which may pose as an additional risk in the scenario of myocardial hypoxia. Moreover, the similarity of the electrophysiological effects of pinacidil and carbachol is suggestive that the sole increase in background K(+) conductance is sufficient for atrial tachyarrhythmia facilitation.

Wnt/ß-catenin antagonist pyrvinium rescues high dose isoproterenol induced cardiotoxicity in rats: Biochemical and immunohistological evidences.

The up-regulation of Wnt/ß-catenin pathway induces cardiac function abnormalities, hypertrophy, and fibrosis in diabetic hypertensive and pressure overload models. The present study investigates the cardioprotective effects of Wnt/ß-catenin inhibition on isoproterenol (ISO) induced cardiotoxicity in rats. ISO was administered at a dose of 85 mg/kg (s.c) for 2 days. Wnt/ß-catenin inhibitor pyrvinium (60 µg/kg, p.o) was given 2h prior and glibenclamide at a dose of 5 mg/kg; p.o, 2 h after ISO injection. Cardiac function parameters were assessed on isolated hearts by using automated Biopac apparatus. The ß-catenin transcription and expression was detected by RT-PCR technique and immunohistochemical method. Serum and cardiac tissue biochemical changes including cardiac troponin-I, CK-MB, LDH, anti-oxidant enzyme levels, inflammatory cytokines, and membrane associated Na+/K + ATPase and Ca2+ATPase and caspase-3 activity, collagen content, fibronectin protein levels were evaluated in various study groups. Histological studies were also carried out to analyze the cardiomyocyte damage, hypertrophy, fibrosis, and necrosis, while α-SMA, TGF-ß expression was checked by immunostaining. ISO administration enhanced ß-catenin gene expression and transcription which promoted oxidative and nitrosative stress, inflammatory cytokine release, reduced ATP levels, induced over-expression of fibrotic proteins resulting in cardiac hypertrophy, myocardial necrosis, functional and histological changes. However, antagonism of Wnt/ß-catenin pathway attenuated these ISO induced pathological manifestations. Notably, the co-treatment with ATP-sensitive K+ channel inhibitor partially, reduced the cardioprotective effects of Wnt/ß-catenin blocker pyrvinium in ISO rats. Thus Wnt/ß-catenin inhibition exhibits cardioprotective in ISO model by anti-oxidant, anti-inflammatory, anti-fibrotic properties and by possible involvement of ATP-sensitive potassium channel activation.

Contribution of Mitochondria to Insulin Secretion by Various Secretagogues.

Significance: Mitochondria determine glucose-stimulated insulin secretion (GSIS) in pancreatic ß-cells by elevating ATP synthesis. As the metabolic and redox hub, mitochondria provide numerous links to the plasma membrane channels, insulin granule vesicles (IGVs), cell redox, NADH, NADPH, and Ca2+ homeostasis, all affecting insulin secretion. Recent Advances: Mitochondrial redox signaling was implicated in several modes of insulin secretion (branched-chain ketoacid [BCKA]-, fatty acid [FA]-stimulated). Mitochondrial Ca2+ influx was found to enhance GSIS, reflecting cytosolic Ca2+ oscillations induced by action potential spikes (intermittent opening of voltage-dependent Ca2+ and K+ channels) or the superimposed Ca2+ release from the endoplasmic reticulum (ER). The ATPase inhibitory factor 1 (IF1) was reported to tune the glucose sensitivity range for GSIS. Mitochondrial protein kinase A was implicated in preventing the IF1-mediated inhibition of the ATP synthase. Critical Issues: It is unknown how the redox signal spreads up to the plasma membrane and what its targets are, what the differences in metabolic, redox, NADH/NADPH, and Ca2+ signaling, and homeostasis are between the first and second GSIS phase, and whether mitochondria can replace ER in the amplification of IGV exocytosis. Future Directions: Metabolomics studies performed to distinguish between the mitochondrial matrix and cytosolic metabolites will elucidate further details. Identifying the targets of cell signaling into mitochondria and of mitochondrial retrograde metabolic and redox signals to the cell will uncover further molecular mechanisms for insulin secretion stimulated by glucose, BCKAs, and FAs, and the amplification of secretion by glucagon-like peptide (GLP-1) and metabotropic receptors. They will identify the distinction between the hub ß-cells and their followers in intact and diabetic states. Antioxid. Redox Signal. 36, 920-952.

Regulation of capillary hemodynamics by KATP channels in resting skeletal muscle.

ATP-sensitive K+ channels (KATP ) have been implicated in the regulation of resting vascular smooth muscle membrane potential and tone. However, whether KATP channels modulate skeletal muscle microvascular hemodynamics at the capillary level (the primary site for blood-myocyte O2 exchange) remains unknown. We tested the hypothesis that KATP channel inhibition would reduce the proportion of capillaries supporting continuous red blood cell (RBC) flow and impair RBC hemodynamics and distribution in perfused capillaries within resting skeletal muscle. RBC flux (fRBC ), velocity (VRBC ), and capillary tube hematocrit (Hctcap ) were assessed via intravital microscopy of the rat spinotrapezius muscle (n = 6) under control (CON) and glibenclamide (GLI; KATP channel antagonist; 10 µM) superfusion conditions. There were no differences in mean arterial pressure (CON:120 ± 5, GLI:124 ± 5 mmHg; p > 0.05) or heart rate (CON:322 ± 32, GLI:337 ± 33 beats/min; p > 0.05) between conditions. The %RBC-flowing capillaries were not altered between conditions (CON:87 ± 2, GLI:85 ± 1%; p > 0.05). In RBC-perfused capillaries, GLI reduced fRBC (CON:20.1 ± 1.8, GLI:14.6 ± 1.3 cells/s; p < 0.05) and VRBC (CON:240 ± 17, GLI:182 ± 17 µm/s; p < 0.05) but not Hctcap (CON:0.26 ± 0.01, GLI:0.26 ± 0.01; p > 0.05). The absence of GLI effects on the %RBC-flowing capillaries and Hctcap indicates preserved muscle O2 diffusing capacity (DO2 m). In contrast, GLI lowered both fRBC and VRBC thus impairing perfusive microvascular O2 transport (Q̇m) and lengthening RBC capillary transit times, respectively. Given the interdependence between diffusive and perfusive O2 conductances (i.e., %O2 extraction∝DO2 m/Q̇m), such GLI alterations are expected to elevate muscle %O2 extraction to sustain a given metabolic rate. These results support that KATP channels regulate capillary hemodynamics and, therefore, microvascular gas exchange in resting skeletal muscle.

Antidiabetic compounds 8a, 8b, 8k, and 9h enhance insulin secretion: activity and mechanism.

PURPOSE: This study primarily investigated the effects of hypoglycemic compounds (Imeglimin derivatives) on insulin secretion in type 2 diabetes mellitus (T2DM), and further explored the possible mechanism underlying these effects. METHODS: Firstly, Metformin was used as the initiating compound to synthesize three sets of derivatives which contained Imeglimin structure core. At the cellular level, we screened compounds with better effect on the activity of insulin receptor tyrosine protein kinase (IFcTPK) after the islet ß cells were treated with the compounds of different concentrations. The insulin secretion was assessed using radioimmunoassay and the cytotoxicity to islet ß cells was evaluated by means of MTT assay following treatment with the compounds. The Ca2+-related mechanism by which these compounds promote insulin secretion was elucidated with whole cell recordings from current-clamp mode. RESULTS: Totally, 48 synthesized compounds were generated, wherein 10 compounds could increase the activity of IFcTPK in HIT-T15 cells better among these compounds. The modified Imeglimin, especially in the structure of hydrophilic hydroxyl or piperidine rings, could improve the activity of the compound to promote insulin secretion. Furthermore, the compounds 8a, 8b, 8k, and 9h revealed high insulin secretion-promoting activity. These compounds enhanced insulin secretion in islet ß cells by repressing the ATP-sensitive K(+) and voltage-gated K+ pathway. CONCLUSIONS: Our findings indicate that the hypoglycemic compounds 8a, 8b, 8k, and 9h confer better promotive effect on insulin secretion, which provides a reference for the development of drugs with better hypoglycemic activity.

Central and peripheral pain intervention by Ophiorrhizarugosa leaves: Potential underlying mechanisms and insight into the role of pain modulators.

ETHNOPHARMACOLOGICAL RELEVANCE: Ophiorrhiza rugosa var. prostrata is a traditional medicinal plant used by the indigenous and local tribes (Chakma, Marma and Tanchangya) of Bangladesh for the management of chest pain, body ache, and earache. However, the knowledge of anti-nociceptive and anti-inflammatory potentials of this plant is scarce. AIM OF THE STUDY: Therefore, we scrutinized the anti-nociceptive and anti-inflammatory properties of O. rugosa leaves along with its possible mechanism(s) of action using chemical and heat-induced pain models. METHODS AND MATERIALS: O. rugosa was extracted using 100% ethanol (EEOR) followed by exploring phytochemicals and assessing acute toxicity. To determine anti-nociceptive potentials, chemical-induced (acetic acid and formalin) and heat-induced (hot plate and tail immersion) nociceptive models were followed. To investigate the possible involvement of opioid receptors during formalin, hot plate, and tail immersion tests, naltrexone was administered whereas methylene blue and glibenclamide were used to explore cGMP involvement and ATP-sensitive K+ channel pathways, respectively. Moreover, the anti-inflammatory potential was assessed using the carrageenan-induced paw edema test model. Motor behaviours of EEOR were assessed by the open-field test. Finally, bioactive constituents (identified by GC-MS) from O. rugosa were subjected to molecular docking and ADME/t analysis to evaluate its potency and safety. RESULTS: During chemical-induced and heat-induced pain models, EEOR exhibited significant and effective nociception suppression at all experimental doses (200 and 400 mg/kg). Also, the administration of naltrexone corroborated the association of opioid receptors with the anti-nociceptive activity by EEOR. Similarly, cGMP and ATP-sensitive K+ channel pathways were also found to be involved in the anti-nociceptive mechanism. Furthermore, significant and dose-dependent inhibition of inflammation induced by carrageenan was recorded for EEOR. Both doses of EEOR did not affect the animal's locomotor capacity in the open-field test. Besides, in silico test identified the key compounds (loliolide, harman, squalene, vitamin E, and gamma-sitosterol) that inhibited some particular receptors regarding pain and inflammation. CONCLUSION: This research exposes central and peripheral pain intervention as well as anti-inflammatory activity of O. rugosa. Also, the identified compounds from this plant support its activities by effectively inhibiting anti-nociceptive and anti-inflammatory receptors. Overall, these outcomes valorize the ethnomedicinal efficacy of O. rugosa in managing various painful conditions.