Inhibition of mTOR prevents glucotoxicity-mediated increase of SA-beta-gal, p16INK4a, and insulin hypersecretion, without restoring electrical features of mouse pancreatic islets.

An over-activation of the mechanistic target of rapamycin (mTOR) pathway promotes senescence and age-related diseases like type 2 diabetes. Besides, the regenerative potential of pancreatic islets deteriorates with aging. Nevertheless, the role of mTOR on senescence promoted by metabolic stress in islet cells as well as its relevance for electrophysiological aspects is not yet known. Here, we investigated whether parameters suggested to be indicative for senescence are induced in vitro in mouse islet cells by glucotoxicity and if mTOR inhibition plays a protective role against this. Islet cells exhibit a significant increase (~ 76%) in senescence-associated beta-galactosidase (SA-beta-gal) activity after exposure to glucotoxicity for 72 h. Glucotoxicity does not markedly influence p16INK4a protein within 72 h, but p16INK4a levels increase significantly after a 7-days incubation period. mTOR inhibition with a low rapamycin concentration (1 nM) entirely prevents the glucotoxicity-mediated increase of SA-beta-gal and p16INK4a. At the functional level, reactive oxygen species, calcium homeostasis, and electrical activity are disturbed by glucotoxicity, and rapamycin fails to prevent this. In contrast, rapamycin significantly attenuates the insulin hypersecretion promoted by glucotoxicity by modifying the mRNA levels of Vamp2 and Snap25 genes, related to insulin exocytosis. Our data indicate an influence of glucotoxicity on pancreatic islet-cell senescence and a reduction of the senescence markers by mTOR inhibition, which is relevant to preserve the regenerative potential of the islets. Decreasing the influence of mTOR on islet cells exposed to glucotoxicity attenuates insulin hypersecretion, but is not sufficient to prevent electrophysiological disturbances, indicating the involvement of mTOR-independent mechanisms.

FGF-23 protects cell function and viability in murine pancreatic islets challenged by glucolipotoxicity.

The fibroblast growth factor FGF-23 is a member of the FGF-15/19 subfamily with hormonal functions. Besides its well-known role for bone mineralization, FGF-23 is discussed as a marker for cardiovascular disease. We investigated whether FGF-23 has any effects on the endocrine pancreas of mice by determining insulin secretion, electrical activity, intracellular Ca2+, and apoptosis. Acute application of FGF-23 (10 to 500 ng/ml, i.e., 0.4 to 20 nM) does not affect insulin release of murine islets, while prolonged exposure leads to a 21% decrease in glucose-stimulated secretion. The present study shows for the first time that FGF-23 (100 or 500 ng/ml) partially protects against impairment of insulin secretion and apoptotic cell death induced by glucolipotoxicity. The reduction of apoptosis by FGF-23 is approximately twofold higher compared to FGF-21 or FGF-15/19. In contrast to FGF-23 and FGF-21, FGF-15/19 is clearly pro-apoptotic under control conditions. The beneficial effect of FGF-23 against glucolipotoxicity involves interactions with the stimulus-secretion cascade of beta-cells. Electrical activity and the rise in the cytosolic Ca2+ concentration of islets in response to acute glucose stimulation increase after glucolipotoxic culture (48 h). Co-culture with FGF-23 further elevates the glucose-mediated effects on both parameters. Protection against apoptosis and glucolipotoxic impairment of insulin release by FGF-23 is prevented, when calcineurin is inhibited by tacrolimus or when c-Jun N-terminal kinase (JNK) is blocked by SP600125. In conclusion, our data suggest that FGF-23 can activate compensatory mechanisms to maintain beta-cell function and integrity of islets of Langerhans during excessive glucose and lipid supply.

NMDA receptors - regulatory function and pathophysiological significance for pancreatic beta cells.

Due to its unique features amongst ionotropic glutamate receptors, the NMDA receptor is of special interest in the physiological context but even more as a drug target. In the pathophysiology of metabolic disorders, particularly type 2 diabetes mellitus, there is evidence that NMDA receptor activation contributes to disease progression by impairing beta cell function. Consequently, channel inhibitors are suggested for treatment, but up to now there are many unanswered questions about the signaling pathways NMDA receptors are interfering with in the islets of Langerhans. In this review we give an overview about channel structure and function with special regard to the pancreatic beta cells and the regulation of insulin secretion. We sum up which signaling pathways from brain research have already been transferred to the beta cell, and what still needs to be proven. The main focus is on the relationship between an over-stimulated NMDA receptor and the production of reactive oxygen species, the amount of which is crucial for beta cell function. Finally, pilot studies using NMDA receptor blockers to protect the islet from dysfunction are reviewed and future perspectives for the use of such compounds in the context of impaired glucose homeostasis are discussed.

Pancreatic KCa3.1 channels in health and disease.

Ion channels play an important role for regulation of the exocrine and the endocrine pancreas. This review focuses on the Ca2+-regulated K+ channel KCa3.1, encoded by the KCNN4 gene, which is present in both parts of the pancreas. In the islets of Langerhans, KCa3.1 channels are involved in the regulation of membrane potential oscillations characterizing nutrient-stimulated islet activity. Channel upregulation is induced by gluco- or lipotoxic conditions and might contribute to micro-inflammation and impaired insulin release in type 2 diabetes mellitus as well as to diabetes-associated renal and vascular complications. In the exocrine pancreas KCa3.1 channels are expressed in acinar and ductal cells. They are thought to play a role for anion secretion during digestion but their physiological role has not been fully elucidated yet. Pancreatic carcinoma, especially pancreatic ductal adenocarcinoma (PDAC), is associated with drastic overexpression of KCa3.1. For pharmacological targeting of KCa3.1 channels, we are discussing the possible benefits KCa3.1 channel inhibitors might provide in the context of diabetes mellitus and pancreatic cancer, respectively. We are also giving a perspective for the use of a fluorescently labeled derivative of the KCa3.1 blocker senicapoc as a tool to monitor channel distribution in pancreatic tissue. In summary, modulating KCa3.1 channel activity is a useful strategy for exo-and endocrine pancreatic disease but further studies are needed to evaluate its clinical suitability.

The Special One: Architecture, Physiology and Pharmacology of the TRESK Channel.

The TWIK-related spinal cord K+ channel (TRESK) is part of the two-pore domain K+ channel family (K2P), which are also called leak potassium channels. As indicated by the channel family name, TRESK conducts K+ ions along the concentration gradient in a nearly voltage-independent manner leading to lowered membrane potentials. Although functional and pharmacological similarities exist, TRESK shows low sequence identity with other K2P channels. Moreover, the channel possesses several unique features such as its sensitivity to intracellular Ca2+ ions, that are not found in other K2P channels. High expression rates are found in immune-associated and neuronal cells, especially in sensory neurons of the dorsal root and trigeminal ganglia. As a consequence of the induced hyperpolarization, TRESK influences neuronal firing, the release of inflammatory mediators and the proliferation of distinct immune cells. Consequently, this channel might be a suitable target for pharmacological intervention in migraine, epilepsy, neuropathic pain or distinct immune diseases. In this review, we summarize the biochemical and biophysical properties of TRESK channels as well as their sensitivity to different known compounds. Furthermore, we give a structured overview about the physiological and pathophysiological impact of TRESK, that render the channel as an interesting target for specific drug development.

Alkaloids from Lime Flower (Tiliae flos) Exert Spasmodic Activity on Murine Airway Smooth Muscle Involving Acetylcholinesterase.

Lime flower (Tiliae flos) is traditionally used either for treatment of the common cold or to relieve symptoms of mental stress. Recently, the presence of a new class of piperidine and dihydro-pyrrole alkaloids from lime flower has been described. The present study aimed to investigate the pharmacological activity of hydroacetonic lime flower extracts, alkaloid-enriched lime flower fractions, and isolated alkaloids on the murine airway smooth muscle and the cholinergic system. While a hydroacetonic lime flower extract did not show any pharmacological activity, enriched Tilia alkaloid fractions potentiated acetylcholine-induced contractions of the trachea by ~ 30%, showing characteristics comparable to galanthamine. Effects were abrogated by atropine, indicating an involvement of muscarinic receptors. The dihydro-pyrrole alkaloid tiliine A, the piperidine alkaloid tiliamine B, and the acetylated piperidine alkaloid tilacetine A were characterized as acetylcholinesterase inhibitors. The positive control galanthamine (IC50 = 2.0 µM, 95% CI 1.7 to 2.2 µM) was approximately 100 times more potent compared to tiliine A (IC50 = 237 µM, 95% CI 207 to 258 µM) and tiliamine B (IC50 = 172 µM, 95% CI 158 to 187 µM). Neither DNA synthesis of HepG2 liver cells, HaCaT keratinocytes, and Caco-2 intestinal epithelial cells nor cell viability of primary human fibroblasts was reduced by the alkaloids. The indirect cholinergic activity of the alkaloids might explain some aspects of the traditional use of lime flowers and may extend the portfolio of compounds with regard to diseases involving parasympathetic malfunction or central cholinergic imbalance.

Effects of Extracts and Flavonoids from Drosera rotundifolia L. on Ciliary Beat Frequency and Murine Airway Smooth Muscle.

Extracts from Drosera rotundifolia are traditionally used to treat cough symptoms during a common cold. The present study aimed to investigate the impact of extracts from D. rotundifolia and active compounds on the respiratory tract. Tracheal slices of C57BL/6N mice were used ex vivo to examine effects on airway smooth muscle (ASM) and ciliary beat frequency (CBF). Phosphodiesterase (PDE) inhibition assays were carried out to test whether PDE1 or PDE4 are targeted by the active compounds. An ethanol-water extract, as well as an aqueous fraction of this extract, exerted antispasmodic properties against acetylcholine-induced contractions. In addition, contractions induced by 60 mM K+ were abrogated by the aqueous fraction. Effects on ASM could be attributed to the flavonoids quercetin, 2″-O-galloylhyperoside and hyperoside. Moreover, the Drosera extract and the aqueous fraction increased the CBF of murine tracheal slices. Quercetin and 2″-O-galloylhyperoside were identified as active compounds involved in the elevation of CBF. Both compounds inhibited PDE1A and PDE4D. The elevation of CBF was mimicked by the subtype-selective PDE inhibitor rolipram (PDE4) and by 8-methoxymethyl-IBMX. In summary, our study shows, for the first time, that a Drosera extract and its flavonoid compounds increase the CBF of murine airways while antispasmodic effects were transferred to ASM.

Selective Inhibition of N-Methyl-d-aspartate Receptors with GluN2B Subunit Protects ß Cells against Stress-Induced Apoptotic Cell Death.

Participation of N-methyl-d-aspartate (NMDA) receptors (NMDARs) in the failure of pancreatic ß cells during development of type 2 diabetes mellitus is discussed. Our study investigates whether ß cell mass and function can be preserved by selectively addressing the GluN2B subunit of the NMDAR. NMDAR activation by NMDA and its coagonist glycine moderately influenced electrical activity and Ca2+ handling in islet cells at a threshold glucose concentration (4-5 mM) without affecting glucose-mediated insulin secretion. Exposure of islet cells to NMDA/glycine or a glucolipotoxic milieu increased apoptosis by 5% and 8%, respectively. The GluN2B-specific NMDAR antagonist WMS-1410 (0.1 and 1 µM) partly protected against this. In addition, WMS-1410 completely prevented the decrease in insulin secretion of about 32% provoked by a 24-hour-treatment with NMDA/glycine. WMS-1410 eliminated NMDA-induced changes in the oxidation status of the islet cells and elevated the sensitivity of intracellular calcium to 15 mM glucose. By contrast, WMS-1410 did not prevent the decline in glucose-stimulated insulin secretion occurring after glucolipotoxic culture. This lack of effect was due to a decrease in insulin content to 18% that obviously could not be compensated by the preservation of cell mass or the higher percentage of insulin release in relation to insulin content. In conclusion, the negative effects of permanent NMDAR activation were effectively counteracted by WMS-1410 as well as the apoptotic cell death induced by high glucose and lipid concentrations. Modulation of NMDARs containing the GluN2B subunit is suggested to preserve ß cell mass during development of type 2 diabetes mellitus. SIGNIFICANCE STATEMENT: Addressing NMDA receptors containing the GluN2B subunit in pancreatic islet cells has the potential to protect the ß cell mass that progressively declines during the development of type 2 diabetes. Furthermore, this study shows that harmful effects of permanent NMDAR activation can be effectively counteracted by the compound WMS-1410, a selective modulator for NMDARs containing the GluN2B subunit.

Novel Piperidine and 3,4-dihydro-2H-pyrrole Alkaloids from Tilia platyphyllos and Tilia cordata Flowers.

Lime flowers, traditionally used for medical purposes for the treatment of symptoms of the common cold and mental stress, consist of the dried inflorescences including the floral bracts of Tilia cordata, Tilia platyphyllos, Tilia × vulgaris, or mixtures thereof. During phytochemical investigations, 6 different alkaloids - not described until now - were detected in T. cordata and T. platyphyllos flowers. They have been isolated and characterized as alkaloids with a dihydro-pyrrole and a piperidine substructure, respectively. Compounds 1A: and 1B: (tiliines A and B) are characterized as 2 diastereomers containing a 2-methyl-3,4-dihydro-2H-pyrrol-3-ol, connected via a C-10 alkyl chain to a O-glucosylated hydroquinone moiety. Compounds 2A: and 2B: (tiliamines A and B) are diastereomers of a 2-methyl-substituted piperidin-3-ol, coupled via a C-9 alkyl chain again to an O-glucosylated hydroquinone moiety. Compounds 3A: and 3B: (tilacetines A and B) are 3-O-acetylated derivatives of tiliamines. Quantification of the 6 alkaloids by HPLC-ESI-qTOF analysis indicated the presence of all alkaloids in T. cordata flowers and T. platyphyllos flowers, bracts, and leaves, with tiliines A and B and tilacetines A and B being the major compounds. Acetone/water turned out be the best extraction solvent for the alkaloids, but ethanol and ethanol/water mixtures also can be used for effective extraction. Furthermore, the alkaloids are found in hot water extracts, which are typically used in the traditional medicine.

Interactions between Atorvastatin and the Farnesoid X Receptor Impair Insulinotropic Effects of Bile Acids and Modulate Diabetogenic Risk.

Bile acids such as chenodeoxycholic acid (CDC) acutely enhance insulin secretion via the farnesoid X receptor (FXR). Statins, which are frequently prescribed for patients with type 2 diabetes who suffer from dyslipidemia, are known for their diabetogenic risk and are reported to interact with the FXR. Our study investigates whether this interaction is relevant for beta cell signaling and plays a role for negative effects of statins on glycemic control. Experiments were performed with islets and islet cells from C57BL/6N wild-type and FXR-knockout (KO) mice. Culturing islets with atorvastatin (15 µM) for 24 hours decreased glucose-stimulated insulin secretion by approximately 30% without affecting ATP synthesis. Prolonged exposure for 7 days lowered the concentration necessary for impairment of insulin release to 150 nM. After 24-hour culture with atorvastatin, the ability of CDC (500 nM) to elevate [Ca2+]c was diminished and the potentiating effect on insulin secretion was completely lost. Mevalonate largely reduced the negative effect of atorvastatin. Nuclear activity of FXR was reduced by atorvastatin in a mouse FXR reporter assay. The atorvastatin-induced decrease in insulin release was also present in FXR-KO mice. Although not a prerequisite, FXR seems to influence the degree of damage caused by atorvastatin depending on its interaction with CDC: Preparations responding to CDC with an increase in insulin secretion under control conditions were less impaired by atorvastatin than preparations that were nonresponsive to CDC. Extended stimulation of FXR by the synthetic agonist GW4064, which is suggested to induce translocation of FXR from the cytosol into the nucleus, increased the inhibitory effect of atorvastatin. In conclusion, atorvastatin inhibits insulin release and prevents positive effects of bile acids on beta cell function. Both interactions may contribute to progression of type 2 diabetes mellitus. SIGNIFICANCE STATEMENT: This study shows that the diabetogenic risk of statins is coupled to the activity of farnesoid X receptor (FXR)-dependent signaling pathways in beta cells. On the one hand, statins abolish the insulinotropic effects of bile acids and on the other hand, FXR determines the level of impairment of islet function by the statin.

Dextromethorphan and Dextrorphan Influence Insulin Secretion by Interacting with KATP and L-type Ca2+ Channels in Pancreatic ß-Cells.

The NMDA receptor antagonist dextromethorphan (DXM) and its metabolite dextrorphan (DXO) have been recommended for treatment of type 2 diabetes mellitus because of their beneficial effects on insulin secretion. This study investigates how different key points of the stimulus-secretion coupling in mouse islets and ß-cells are influenced by DXM or DXO. Both compounds elevated insulin secretion, electrical activity, and [Ca2+]c in islets at a concentration of 100 µM along with a stimulating glucose concentration. DXO and DXM increased insulin secretion approximately 30-fold at a substimulatory glucose concentration (3 mM). Patch-clamp experiments revealed that 100 µM DXM directly inhibited KATP channels by about 70%. Of note, DXM decreased the current through L-type Ca2+ channels about 25%, leading to a transient reduction in Ca2+ action potentials. This interaction might explain why elevating DXM to 500 µM drastically decreased insulin release. DXO inhibited KATP channels almost equally. In islets of KATP channel-deficient sulfonylurea receptor 1 knockout mice, the elevating effects of 100 µM DXM on [Ca2+]c and insulin release were completely lost. By contrast, 100 µM DXO still increased glucose-stimulated insulin release around 60%. In summary, DXM-induced alterations in stimulus-secretion coupling of wild-type islets result from a direct block of KATP channels and are partly counteracted by inhibition of L-type Ca2+ channels. The stimulatory effect of DXO seems to be based on a combined antagonism on KATP channels and NMDA receptors and already occurs under resting conditions. Consequently, both compounds seem not to be suitable candidates for treatment of type 2 diabetes mellitus. SIGNIFICANCE STATEMENT: This study shows that the use of dextromethorphan as an antidiabetic drug can cause unpredictable alterations in insulin secretion by direct interaction with KATP and L-type Ca2+ channels besides its actual target, the NMDA receptor.

Mitochondrial succinate dehydrogenase is involved in stimulus-secretion coupling and endogenous ROS formation in murine beta cells.

AIMS/HYPOTHESIS: Generation of reduction equivalents is a prerequisite for nutrient-stimulated insulin secretion. Mitochondrial succinate dehydrogenase (SDH) fulfils a dual function with respect to mitochondrial energy supply: (1) the enzyme is part of mitochondrial respiratory chains; and (2) it catalyses oxidation of succinate to fumarate in the Krebs cycle. The aim of our study was to elucidate the significance of SDH for beta cell stimulus-secretion coupling (SSC). METHODS: Mitochondrial variables, reactive oxygen species (ROS) and cytosolic Ca(2+) concentration ([Ca(2+)]c) were measured by fluorescence techniques and insulin release by radioimmunoassay in islets or islet cells of C57Bl/6N mice. RESULTS: Inhibition of SDH with 3-nitropropionic acid (3-NPA) or monoethyl fumarate (MEF) reduced glucose-stimulated insulin secretion. Inhibition of the ATP-sensitive K(+) channel (KATP channel) partly prevented this effect, whereas potentiation of antioxidant defence by superoxide dismutase mimetics (TEMPOL and mito-TEMPO) or by nuclear factor erythroid 2-related factor 2 (Nrf-2)-mediated upregulation of antioxidant enzymes (oltipraz, tert-butylhydroxyquinone) did not diminish the inhibitory influence of 3-NPA. Blocking SDH decreased glucose-stimulated increase in intracellular FADH2 concentration without alterations in NAD(P)H. In addition, 3-NPA and MEF drastically reduced glucose-induced hyperpolarisation of mitochondrial membrane potential, indicative of decreased ATP production. As a consequence, the glucose-stimulated rise in [Ca(2+)]c was significantly delayed and reduced. Acute application of 3-NPA interrupted glucose-driven oscillations of [Ca(2+)]c. 3-NPA per se did not elevate intracellular ROS, but instead prevented glucose-induced ROS accumulation. CONCLUSIONS/INTERPRETATION: SDH is an important regulator of insulin secretion and ROS production. Inhibition of SDH interrupts membrane-potential-dependent SSC, pointing to a pivotal role of mitochondrial FAD/FADH2 homeostasis for the maintenance of glycaemic control.

Evidence against a Ca(2+)-induced potentiation of dehydrogenase activity in pancreatic beta-cells.

Pancreatic beta-cells respond to an unchanging stimulatory glucose concentration with oscillations in membrane potential (Vm), cytosolic Ca(2+) concentration ([Ca(2+)]c), and insulin secretion. The underlying mechanisms are largely ascertained. Some particular details, however, are still in debate. Stimulus-secretion coupling (SSC) of beta-cells comprises glucose-induced Ca(2+) influx into the cytosol and thus into mitochondria. It is suggested that this activates (mitochondrial) dehydrogenases leading to an increase in reduction equivalents and ATP production. According to SSC, a glucose-induced increase in ATP production would thus further augment ATP production, i.e. induce a feed-forward loop that is hardly compatible with oscillations. Consistently, other studies favour a feedback mechanism that drives oscillatory mitochondrial ATP production. If Ca(2+) influx activates dehydrogenases, a change in [Ca(2+)]c should increase the concentration of reduction equivalents. We measured changes in flavin adenine dinucleotide (FAD) and nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) autofluorescence in response to changes in glucose concentration or glucose-independent changes in [Ca(2+)]c. The FAD signal was altered by glucose but not by alterations in [Ca(2+)]c. NAD(P)H was increased by glucose but even decreased by Ca(2+) influx evoked by tolbutamide. The mitochondrial membrane potential ΔΨ was hyperpolarized by 4 mM glucose. As adding tolbutamide then depolarized ΔΨ, we deduce that Ca(2+) does not activate mitochondrial activity but by contrast even inhibits it by reducing the driving force for ATP production. Inhibition of Ca(2+) influx reversed the Ca(2+)-induced changes in ΔΨ and NAD(P)H. The results are consistent with a feedback mechanism which transiently and repeatedly reduces ATP production and explain the oscillatory activity of pancreatic beta-cells at increased glucose concentrations.

Lupanine Improves Glucose Homeostasis by Influencing KATP Channels and Insulin Gene Expression.

The glucose-lowering effects of lupin seeds involve the combined action of several components. The present study investigates the influence of one of the main quinolizidine alkaloids, lupanine, on pancreatic beta cells and in an animal model of type-2 diabetes mellitus. In vitro studies were performed with insulin-secreting INS-1E cells or islets of C57BL/6 mice. In the in vivo experiments, hyperglycemia was induced in rats by injecting streptozotocin (65 mg/kg body weight). In the presence of 15 mmol/L glucose, insulin secretion was significantly elevated by 0.5 mmol/L lupanine, whereas the alkaloid did not stimulate insulin release with lower glucose concentrations. In islets treated with l-arginine, the potentiating effect of lupanine already occurred at 8 mmol/L glucose. Lupanine increased the expression of the Ins-1 gene. The potentiating effect on secretion was correlated to membrane depolarization and an increase in the frequency of Ca(2+) action potentials. Determination of the current through ATP-dependent K⁺ channels (KATP channels) revealed that lupanine directly inhibited the channel. The effect was dose-dependent but, even with a high lupanine concentration of 1 mmol/L or after a prolonged exposure time (12 h), the KATP channel block was incomplete. Oral administration of lupanine did not induce hypoglycemia. By contrast, lupanine improved glycemic control in response to an oral glucose tolerance test in streptozotocin-diabetic rats. In summary, lupanine acts as a positive modulator of insulin release obviously without a risk for hypoglycemic episodes.

Targeting KCa3.1 channels to overcome erlotinib resistance in non-small cell lung cancer cells.

Almost all non-small cell lung cancer (NSCLC) patients initially responding to EGFR tyrosine kinase inhibitors (TKIs) develop acquired resistance. Since KCa3.1 channels, expressed in mitochondria and plasma membrane, regulate similar behavioral traits of NSCLC cells as EGFR, we hypothesized that their blockade contributes to overcoming EGFR-TKI resistance. Meta-analysis of microarray data revealed that KCa3.1 channel expression in erlotinib-resistant NSCLC cells correlates with that of genes of integrin and apoptosis pathways. Using erlotinib-sensitive and -resistant NSCLC cells we monitored the role of mitochondrial KCa3.1 channels in integrin signaling by studying cell-matrix adhesion with single-cell force spectroscopy. Apoptosis was quantified with fluorescence-based assays. The function of mitochondrial KCa3.1 channels in these processes was assessed by measuring the mitochondrial membrane potential and by quantifying ROS production. Functional assays were supplemented by biochemical analyses. We show that KCa3.1 channel inhibition with senicapoc in erlotinib-resistant NSCLC cells increases cell adhesion by increasing ß1-integrin expression, that in turn depends on mitochondrial ROS release. Increased adhesion impairs migration of NSCLC cells in a 3D matrix. At the same time, the senicapoc-dependent ROS production induces cytochrome C release and triggers apoptosis of erlotinib-resistant NSCLC cells. Thus, KCa3.1 channel blockade overcomes EGFR-TKI resistance by inhibiting NSCLC motility and inducing apoptosis.

Glitazones exert multiple effects on ß-cell stimulus-secretion coupling.

Earlier studies suggest that glitazones exert beneficial effects in patients with type 2 diabetes by directly affecting insulin secretion of ß-cells, besides improving the effectiveness of insulin in peripheral tissues. The effects of glitazones on stimulus-secretion coupling (SSC) are poorly understood. We tested the influence of troglitazone and pioglitazone on different parameters of SSC, including insulin secretion (radioimmunoassay), cell membrane potential, various ion currents (patch-clamp), mitochondrial membrane potential (ΔΨ), and cytosolic Ca(2+) concentration (fluorescence). Troglitazone exerted stimulatory, inhibitory, or no effects on insulin secretion depending on the drug and glucose concentration. It depolarized the ΔΨ, thus lowering ATP production, which resulted in opening of ATP-dependent K(+) channels (K(ATP) channels) and reduced insulin secretion. However, it also exerted direct inhibitory effects on K(ATP) channels that can explain enhanced insulin secretion. Troglitazone also inhibited the currents through voltage-dependent Ca(2+) and K(+) channels. Pioglitazone was less effective than troglitazone on all parameters tested. The effects of both glitazones were markedly reduced in the presence of bovine serum albumin. Glitazones exert multiple actions on ß-cell SSC that have to be considered as undesired side effects because the influence of these compounds on ß-cells is not controllable. The final effect on insulin secretion depends on many parameters, including the actual glucose and drug concentration, protein binding of the drug, and the drug by itself. Troglitazone and pioglitazone differ in their influence on SSC. It can be assumed that the effects of pioglitazone on ß-cells are negligible under in vivo conditions.

A benzodiazepine activator locks Kv7.1 channels open by electro-mechanical uncoupling.

Loss-of-function mutations in Kv7.1 often lead to long QT syndrome (LQTS), a cardiac repolarization disorder associated with arrhythmia and subsequent sudden cardiac death. The discovery of agonistic IKs modulators may offer a new potential strategy in pharmacological treatment of this disorder. The benzodiazepine derivative (R)-L3 potently activates Kv7.1 channels and shortens action potential duration, thus may represent a starting point for drug development. However, the molecular mechanisms underlying modulation by (R)-L3 are still unknown. By combining alanine scanning mutagenesis, non-canonical amino acid incorporation, voltage-clamp electrophysiology and fluorometry, and in silico protein modelling, we show that (R)-L3 not only stimulates currents by allosteric modulation of the pore domain but also alters the kinetics independently from the pore domain effects. We identify novel (R)-L3-interacting key residues in the lower S4-segment of Kv7.1 and observed an uncoupling of the outer S4 segment with the inner S5, S6 and selectivity filter segments.

Rapid functional evaluation of beta-cells by extracellular recording of membrane potential oscillations with microelectrode arrays.

The membrane potential (V (m)) of beta-cells oscillates at glucose concentrations between ~6 and 25 mM, i.e. burst phases with action potentials alternate with silent interburst phases generating so-called slow waves. The slow waves drive oscillations of the cytosolic Ca(2+) concentration ([Ca(2+)](c)) and insulin secretion. The length of the bursts correlates with the amount of insulin release. Thus, the fraction of plateau phase (FOPP), i.e. the percentage of time with burst activity, is an excellent marker for beta-cell function and metabolic integrity. Extracellular voltage changes of mouse islets were measured using a microelectrode array (MEA) allowing the detection of burst and interburst phases. At a non-stimulating glucose concentration (3 mM) no electrical activity was detectable while bursting was continuous at 30 mM. The glucose concentration-response (determined as FOPP) curve revealed half-maximal stimulation at 12 ± 1 mM (Hill equation fit). The signal was sensitive to K(ATP) channel modulators, e.g. tolbutamide or diazoxide. Simultaneous recordings of electrical activity and [Ca(2+)](c) revealed congruent bursts and peaks, respectively. The extracellular recordings are in perfect agreement with more time-consuming intracellular electrical recordings. The results provide a 'proof-of-principle' for detection of beta-cell slow waves and determination of the FOPP using extracellular electrodes in a MEA-based system. The method is facile and provides the capability to study the effects of modulators of beta-cell function including possible anti-diabetic drugs in real time. Moreover, the method may be useful for checking the metabolic integrity of human donor islets prior to transplantation.