Urodynamic effects of the K+ channel (KCNQ) opener retigabine in freely moving, conscious rats

Anti-seizure medications-associated bladder and urethral symptoms: a pharmacovigilance analysis based on the FAERS database

BACKGROUND

In clinical practice, observations have been made regarding bladder and urethral symptoms (BUS), notably urinary frequency and urgency, among patients prescribed the anti-seizure medication (ASM) lacosamide. However, the precise association between ASMs and BUS events in real-world settings remains elusive.

RESEARCH DESIGN AND METHODS

Data from the FDA Adverse Event Reporting System (FAERS) database were employed and the analysis focused on ASMs-associated BUS events utilizing disproportionality analysis methods, including the reporting odds ratio (ROR) and the proportional reporting ratio (PRR). Furthermore, co-administration, time to onset of ASMs-associated BUS events, and severity assessments were conducted.

RESULTS

Several ASMs demonstrated statistically meaningful associations with BUS signals, notably ezogabine, valproic acid/valproate sodium, and clorazepate (p < 0.05). And ASMs-associated BUS events predominantly occurred within the first week and persisted for more than 180 days afterward. Diazepam, gabapentin, and brivaracetam exhibited distinct risk profiles for severe BUS events compared to valproic acid/sodium valproate (p < 0.05). And the nomogram constructed in this study exhibited robust predictive performance.

CONCLUSION

This study yields valuable insights into the association between ASMs and BUS events, but several limitations warrant consideration. Nonetheless, these findings emphasize the significance of vigilance and proactive management of ASMs-associated BUS events.

Discovery of HN37 as a Potent and Chemically Stable Antiepileptic Drug Candidate

We previously reported that P-retigabine (P-RTG), a retigabine (RTG) analogue bearing a propargyl group at the nitrogen atom in the linker of RTG, displayed moderate anticonvulsant efficacy. Recently, our further efforts led to the discovery of HN37 (pynegabine), which demonstrated satisfactory chemical stability upon deleting the ortho liable -NH₂ group and installing two adjacent methyl groups to the carbamate motif. HN37 exhibited enhanced activation potency toward neuronal Kv7 channels and high in vivo efficacy in a range of pre-clinical seizure models, including the maximal electroshock test and a 6 Hz model of pharmacoresistant limbic seizures. With its improved chemical stability, strong efficacy, and better safety margin, HN37 has progressed to clinical trial in China for epilepsy treatment.

Detrusor Smooth Muscle KV7 Channels: Emerging New Regulators of Urinary Bladder Function

Relaxation and contraction of the urinary bladder smooth muscle, also known as the detrusor smooth muscle (DSM), facilitate the micturition cycle. DSM contractility depends on cell excitability, which is established by the synchronized activity of multiple diverse ion channels. K+ channels, the largest family of channels, control DSM excitability by maintaining the resting membrane potential and shaping the action potentials that cause the phasic contractions. Among the members of the voltage-gated K+ (KV) channel superfamily, KV type 7 (KV7) channels - KV7.1-KV7.5 members encoded by KCNQ1-KCNQ5 genes - have been recently identified as functional regulators in various cell types including vascular, cardiac, and neuronal cells. Their regulatory roles in DSM, however, are just now emerging and remain to be elucidated. To address this gap, our research group has initiated the systematic investigation of human DSM KV7 channels in collaboration with clinical urologists. In this comprehensive review, we summarize the current understanding of DSM Kv7 channels and highlight recent discoveries in the field. We describe KV7 channel expression profiles at the mRNA and protein levels, and further elaborate on functional effects of KV7 channel selective modulators on DSM excitability, contractility, and intracellular Ca2+ dynamics in animal species along with in vivo studies and the limited data on human DSM. Within each topic, we highlight the main observations, current gaps in knowledge, and most pressing questions and concepts in need of resolution. We emphasize the lack of systematic studies on human DSM KV7 channels that are now actively ongoing in our laboratory.

Urinary bladder smooth muscle ion channels: expression, function, and regulation in health and disease

Urinary bladder smooth muscle (UBSM), also known as detrusor smooth muscle, forms the bladder wall and ultimately determines the two main attributes of the organ: urine storage and voiding. The two functions are facilitated by UBSM relaxation and contraction, respectively, which depend on UBSM excitability shaped by multiple ion channels. In this review, we summarize the current understanding of key ion channels establishing and regulating UBSM excitability and contractility. They include excitation-enhancing voltage-gated Ca2+ (Cav) and transient receptor potential channels, excitation-reducing K+ channels, and still poorly understood Cl- channels. Dynamic interplay among UBSM ion channels determines the overall level of Cav channel activity. The net Ca2+ influx via Cav channels increases global intracellular Ca2+ concentration, which subsequently triggers UBSM contractility. Here, for each ion channel type, we describe UBSM tissue/cell expression (mRNA and protein) profiles and their role in regulating excitability and contractility of UBSM in various animal species, including the mouse, rat, and guinea pig, and, most importantly, humans. The currently available data reveal certain interspecies differences, which complicate the translational value of published animal research results to humans. This review highlights recent developments, findings on genetic knockout models, pharmacological data, reports on UBSM ion channel dysfunction in animal bladder disease models, and the very limited human studies currently available. Among all gaps in present-day knowledge, the unknowns on expression and functional roles for ion channels determined directly in human UBSM tissues and cells under both normal and disease conditions remain key hurdles in the field.

Cyclic AMP-Dependent Regulation of Kv7 Voltage-Gated Potassium Channels

Voltage-gated Kv7 potassium channels, encoded by KCNQ genes, have major physiological impacts cardiac myocytes, neurons, epithelial cells, and smooth muscle cells. Cyclic adenosine monophosphate (cAMP), a well-known intracellular secondary messenger, can activate numerous downstream effector proteins, generating downstream signaling pathways that regulate many functions in cells. A role for cAMP in ion channel regulation has been established, and recent findings show that cAMP signaling plays a role in Kv7 channel regulation. Although cAMP signaling is recognized to regulate Kv7 channels, the precise molecular mechanism behind the cAMP-dependent regulation of Kv7 channels is complex. This review will summarize recent research findings that support the mechanisms of cAMP-dependent regulation of Kv7 channels.

Safety of retigabine in adults with partial-onset seizures after long-term exposure: focus on unexpected ophthalmological and dermatological events

BACKGROUND

Retigabine is an antiepileptic drug developed for the adjunctive treatment of adults with epilepsy and partial-onset seizures (POS). Following its approval in 2011, reports of ophthalmological/dermatological pigmentation/discoloration led to a restriction of the indication in 2013, and in 2017, retigabine was voluntarily withdrawn from the market because of its limited usage. Here, data are reported from four open-label extension studies focusing on long-term safety with particular emphasis on ophthalmological and dermatological events.

METHODS

Studies 113413 (NCT01336621), 114873 (NCT01777139), 115097 (NCT00310388), and 115098 (NCT00310375) were multicenter, open-label extension studies of retigabine (300-1200 mg/day) for the adjunctive treatment of adults with POS. Safety assessments included monitoring treatment-emergent adverse events (TEAEs) and serious adverse events (SAEs). When new safety issues were identified, protocols were amended to include additional on-treatment safety evaluations, including ophthalmological and dermatological examinations. Patients who had abnormal retinal pigmentation, unexplained vision change, pigmentation of nonretinal ocular tissue, or abnormal discoloration of skin, lips, nails, and/or mucosa at the end of the treatment phase were asked to enter a safety follow-up continuation phase comprising 6-monthly ophthalmological/dermatological assessments.

RESULTS

The safety population (patients receiving ≥1 dose of retigabine in the open-label phase) comprised 98, 30, 376, and 181 patients for studies 113413, 114873, 115097, and 115098, respectively. Mean (standard deviation) treatment exposure ranged from 529 (424) to 1129 (999) days. In total, 68%-96% and 4%-27% of patients across the studies experienced TEAEs and TE SAEs, respectively. There were seven on-treatment deaths and two after discontinuation. Overall, 14%-73% of patients had an on-treatment eye examination, of whom 8/53, 4/22, 17/54, and 14/36 had abnormal retinal pigmentation and 15/53, 7/22, 15/54, and 11/36 had nonretinal ocular pigmentation in studies 113413, 114873, 115097, and 115098, respectively. Four patients had confirmed acquired vitelliform maculopathy. In patients with unresolved events at discontinuation and ≥1 posttreatment follow-up, retinal pigmentation resolved completely in 1/3, 0/3, 0/10, and 1/7 patients and nonretinal ocular pigmentation in 1/4, 0/3, 8/10, and 4/6 patients, respectively. Overall, 12%-83% of patients had an on-treatment dermatological examination, of whom 11/58, 0/25, 23/46, and 23/37 had any-tissue discoloration, respectively. In patients with unresolved events at discontinuation and ≥1 posttreatment follow-up, discoloration of skin, lips, nails, and/or mucosa resolved completely in 2/3, 0/0, 7/13, and 1/11 patients, respectively.

CONCLUSIONS

The safety profile of retigabine in adults with POS across four open-label studies was generally consistent with data from previous placebo-controlled studies. Discoloration of various tissues occurred in a proportion of patients treated with retigabine and resolved completely in a small number of these patients following treatment discontinuation. In addition, comprehensive eye examination identified a new adverse reaction of acquired vitelliform maculopathy in a limited number of patients.

Effects of the Kv7 voltage-activated potassium channel inhibitor linopirdine in rat models of haemorrhagic shock

Recently, we demonstrated that Kv7 voltage-activated potassium channel inhibitors reduce fluid resuscitation requirements in short-term rat models of haemorrhagic shock. The aim of the present study was to further delineate the therapeutic potential and side effect profile of the Kv7 channel blocker linopirdine in various rat models of severe haemorrhagic shock over clinically relevant time periods. Intravenous administration of linopirdine, either before (1 or 3 mg/kg) or after (3 mg/kg) a 40% blood volume haemorrhage, did not affect blood pressure and survival in lethal haemorrhage models without fluid resuscitation. A single bolus of linopirdine (3 mg/kg) at the beginning of fluid resuscitation after haemorrhagic shock transiently reduced early fluid requirements in spontaneously breathing animals that were resuscitated for 3.5 hours. When mechanically ventilated rats were resuscitated after haemorrhagic shock with normal saline (NS) or with linopirdine-supplemented (10, 25 or 50 μg/mL) NS for 4.5 hours, linopirdine significantly and dose-dependently reduced fluid requirements by 14%, 45% and 55%, respectively. Lung and colon wet/dry weight ratios were reduced with linopirdine (25/50 μg/mL). There was no evidence for toxicity or adverse effects based on measurements of routine laboratory parameters and inflammation markers in plasma and tissue homogenates. Our findings support the concept that linopirdine-supplementation of resuscitation fluids is a safe and effective approach to reduce fluid requirements and tissue oedema formation during resuscitation from haemorrhagic shock.

Investigational Drug Therapies for Overactive Bladder Syndrome: The Potential Alternatives to Anticolinergics

Background

Overactive bladder is a high prevalent and quality of life affecting disease. The mainstay of the medical therapy is represented by antimuscarinic drugs, but their side effects markedly affect patient compliance and prompt studies on novel investigational drugs.

Methods

A systematic literature search of peer-reviewed papers and meeting abstracts published by December 2008 was performed. PubMed databank was searched for original English articles, by using the following search terms: “overactive bladder” or “detrusor overactivity” or “urinary incontinence” and “treatment”, alone and linked to any potential molecular target or novel drug cited in the literature.

Results

Effective alternative pharmacological treatments are currently scarce, but many new promising compounds are emerging which target key molecular pathways involved in micturition control. The most promising potential therapeutic targets include central nervous system GABAergic inhibitory pathway, dopaminergic and serotoninergic systems, b-adrenoceptors and cAMP metabolism, nonadrenergic-noncholinergic mechanisms such as purinergic and neuropeptidergic systems, vanilloid receptor, bladder sensory nervous terminals, nonneuronal bladder signalling systems including urothelium and interstitial cells, prostanoids, Rho-kinase and different subtypes of potassium and calcium channels.

Conclusions

Despite the enormous amount of new biologic insight, very few novel pharmacological therapies seems to have passed the proof-of-concept clinical stage. The ultimate clinical utility of new drugs will depend on the ability to exploit tissue-specific differences and disease-related changes in molecular expression/function and to improve storage phase dysfunctions without interfering with the emptying phase. Further preclinical investigations and controlled clinical trials are urgently needed in this challenging field.

KV7 Channel Pharmacological Activation by the Novel Activator ML213: Role for Heteromeric KV7.4/KV7.5 Channels in Guinea Pig Detrusor Smooth Muscle Function

Voltage-gated K_V7 channels (K_V7.1 to K_V7.5) are important regulators of the cell membrane potential in detrusor smooth muscle (DSM) of the urinary bladder. This study sought to further the current knowledge of K_V7 channel function at the molecular, cellular, and tissue levels in combination with pharmacological tools. We used isometric DSM tension recordings, ratiometric fluorescence Ca²⁺ imaging, amphotericin-B perforated patch-clamp electrophysiology, and in situ proximity ligation assay (PLA) in combination with the novel compound N-(2,4,6-trimethylphenyl)-bicyclo[2.2.1]heptane-2-carboxamide (ML213), an activator of K_V7.2, K_V7.4, and K_V7.5 channels, to examine their physiologic roles in guinea pig DSM function. ML213 caused a concentration-dependent (0.1-30 µM) inhibition of spontaneous phasic contractions in DSM isolated strips; effects blocked by the K_V7 channel inhibitor XE991 (10 µM). ML213 (0.1-30 µM) also reduced pharmacologically induced and nerve-evoked contractions in DSM strips. Consistently, ML213 (10 µM) decreased global intracellular Ca²⁺ concentrations in Fura-2-loaded DSM isolated strips. Perforated patch-clamp electrophysiology revealed that ML213 (10 µM) caused an increase in the amplitude of whole-cell K_V7 currents. Further, in current-clamp mode of the perforated patch clamp, ML213 hyperpolarized DSM cell membrane potential in a manner reversible by washout or XE991 (10 µM), consistent with ML213 activation of K_V7 channel currents. Preapplication of XE991 (10 µM) not only depolarized the DSM cells, but also blocked ML213-induced hyperpolarization, confirming ML213 selectivity for K_V7 channel subtypes. In situ PLA revealed colocalization and expression of heteromeric K_V7.4/K_V7.5 channels in DSM isolated cells. These combined results suggest that ML213-sensitive K_V7.4- and K_V7.5-containing channels are essential regulators of DSM excitability and contractility.

Kv7 voltage-activated potassium channel inhibitors reduce fluid resuscitation requirements after hemorrhagic shock in rats

Background

Recent evidence suggests that drugs targeting Kv7 channels could be used to modulate vascular function and blood pressure. Here, we studied whether Kv7 channel inhibitors can be utilized to stabilize hemodynamics and reduce resuscitation fluid requirements after hemorrhagic shock.

Methods

Anesthetized male Sprague-Dawley rats were instrumented with arterial and venous catheters for blood pressure monitoring, hemorrhage and fluid resuscitation. Series 1: Linopirdine (Kv7 channel blocker, 0.1–6 mg/kg) or retigabine (Kv7 channel activator, 0.1–12 mg/kg) were administered to normal animals. Series 2: Animals were hemorrhaged to a MAP of 25 mmHg for 30 min, followed by fluid resuscitation with normal saline (NS) to a MAP of 70 mmHg until t = 75 min. Animals were treated with single bolus injections of vehicle, linopirdine (1–6 mg/kg), XE-991 (structural analogue of linopirdine with higher potency for channel blockade, 1 mg/kg) prior to fluid resuscitation. Series 3: Animals were resuscitated with NS alone or NS supplemented with linopirdine (1.25–200 μg/mL). Data were analyzed with 2-way ANOVA/Bonferroni post-hoc testing.

Results

Series 1: Linopirdine transiently (10–15 min) and dose-dependently increased MAP by up to 15%. Retigabine dose-dependently reduced MAP by up to 60%, which could be reverted with linopirdine. Series 2: Fluid requirements to maintain MAP at 70 mmHg were 65 ± 34 mL/kg with vehicle, and 57 ± 13 mL/kg, 22 ± 8 mL/kg and 22 ± 11 mL/kg with intravenous bolus injection of 1, 3 and 6 mg/kg linopirdine, respectively. XE-991 (1 mg/kg), reduced resuscitation requirements comparable to 3 mg/kg linopirdine.

Series 3: When resuscitation was performed with linopirdine-supplemented normal saline (NS), fluid requirements to stabilize MAP were 73 ± 12 mL/kg with NS alone and 72 ± 24, 61 ± 20, 36 ± 9 and 31 ± 9 mL/kg with NS supplemented with 1.25, 6.25, 12.5 and 200 μg/mL linopirdine, respectively.

Conclusions

Our data suggest that Kv7 channel blockers could be used to stabilize blood pressure and reduce fluid resuscitation requirements after hemorrhagic shock.

Novel treatment strategies for smooth muscle disorders: Targeting Kv7 potassium channels

Smooth muscle cells provide crucial contractile functions in visceral, vascular, and lung tissues. The contractile state of smooth muscle is largely determined by their electrical excitability, which is in turn influenced by the activity of potassium channels. The activity of potassium channels sustains smooth muscle cell membrane hyperpolarization, reducing cellular excitability and thereby promoting smooth muscle relaxation. Research over the past decade has indicated an important role for Kv7 (KCNQ) voltage-gated potassium channels in the regulation of the excitability of smooth muscle cells. Expression of multiple Kv7 channel subtypes has been demonstrated in smooth muscle cells from viscera (gastrointestinal, bladder, myometrial), from the systemic and pulmonary vasculature, and from the airways of the lung, from multiple species, including humans. A number of clinically used drugs, some of which were developed to target Kv7 channels in other tissues, have been found to exert robust effects on smooth muscle Kv7 channels. Functional studies have indicated that Kv7 channel activators and inhibitors have the ability to relax and contact smooth muscle preparations, respectively, suggesting a wide range of novel applications for the pharmacological tool set. This review summarizes recent findings regarding the physiological functions of Kv7 channels in smooth muscle, and highlights potential therapeutic applications based on pharmacological targeting of smooth muscle Kv7 channels throughout the body.

The Novel KV7.2/KV7.3 Channel Opener ICA-069673 Reveals Subtype-Specific Functional Roles in Guinea Pig Detrusor Smooth Muscle Excitability and Contractility

The physiologic roles of voltage-gated KV7 channel subtypes (KV7.1-KV7.5) in detrusor smooth muscle (DSM) are poorly understood. Here, we sought to elucidate the functional roles of KV7.2/KV7.3 channels in guinea pig DSM excitability and contractility using the novel KV7.2/KV7.3 channel activator ICA-069673 [N-(2-chloro-5-pyrimidinyl)-3,4-difluorobenzamide]. We employed a multilevel experimental approach using Western blot analysis, immunocytochemistry, isometric DSM tension recordings, fluorescence Ca(2+) imaging, and perforated whole-cell patch-clamp electrophysiology. Western blot experiments revealed the protein expression of KV7.2 and KV7.3 channel subunits in DSM tissue. In isolated DSM cells, immunocytochemistry with confocal microscopy further confirmed protein expression for KV7.2 and KV7.3 channel subunits, where they localize within the vicinity of the cell membrane. ICA-069673 inhibited spontaneous phasic, pharmacologically induced, and nerve-evoked contractions in DSM isolated strips in a concentration-dependent manner. The inhibitory effects of ICA-069673 on DSM spontaneous phasic and tonic contractions were abolished in the presence of the KV7 channel inhibitor XE991 [10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone dihydrochloride]. Under conditions of elevated extracellular K(+) (60 mM), the effects of ICA-069673 on DSM tonic contractions were significantly attenuated. ICA-069673 decreased the global intracellular Ca(2+) concentration in DSM cells, an effect blocked by the L-type Ca(2+) channel inhibitor nifedipine. ICA-069673 hyperpolarized the membrane potential and inhibited spontaneous action potentials of isolated DSM cells, effects that were blocked in the presence of XE991. In conclusion, using the novel KV7.2/KV7.3 channel activator ICA-069673, this study provides strong evidence for a critical role for the KV7.2- and KV7.3-containing channels in DSM function at both cellular and tissue levels.

Efficacy and safety of ezogabine/retigabine as adjunctive therapy to specified single antiepileptic medications in an open-label study of adults with partial-onset seizures

PURPOSE

To assess efficacy/tolerability of ezogabine (EZG)/retigabine (RTG) in combination with specified monotherapy antiepileptic drug (AED) treatments in adults with uncontrolled partial-onset seizures using a flexible dosing regimen.

METHODS

NCT01227902 was an open-label, uncontrolled study of flexibly dosed EZG/RTG. Adults with partial-onset seizures must have been taking either carbamazepine/oxcarbazepine (CBZ/OXC), lamotrigine (LTG), levetiracetam (LEV), or valproic acid (VPA). The study comprised a screening/baseline phase, a 4-week titration phase (initiation on 150mg/day [50mg three times daily (TID)] with weekly increases of 150mg/day [50mg TID] over 4 weeks to 600mg/day), and a flexible dose evaluation (FDE) phase (optional weekly dose changes of 50-150mg/day, to an optimal daily dosage [300-1200mg/day]). The primary efficacy endpoint was percentage of patients experiencing a ≥50% reduction from baseline in partial seizure frequency (responder rate) during the treatment phase (titration and FDE phases). Safety and tolerability were also assessed.

RESULTS

Patients (N=203) were enrolled and received ≥1 dose of EZG/RTG. The dose of EZG/RTG prescribed most frequently during the treatment phase was 600mg/day for all AED groups. Responder rates during the treatment phase were: 40.0% (CBZ/OXC), 32.0% (LTG), 50.0% (LEV), and 56.9% (VPA). Treatment-emergent adverse events occurred in 82% (CBZ/OXC), 76% (LTG), 73% (LEV), and 67% (VPA) of patients; most were of mild-to-moderate intensity.

CONCLUSIONS

EZG/RTG was effective as adjunctive therapy to CBZ/OXC, LTG, LEV, and VPA, using a flexible dosing regimen, in adults with partial-onset seizures; safety and tolerability were consistent with that previously observed.

Pioneering drugs for overactive bladder and detrusor overactivity: Ongoing research and future directions

The ongoing research on pioneering drug candidates for the overactive bladder (OAB) aimed to overcome the limitations of currently licensed pharmacotherapies, such as antimuscarinics, β3-adrenergic agents, and botulinum neurotoxin, has been reviewed performing a systematic literature review and web search. The review covers the exploratory agents alternative to available medications for OAB and that may ultimately prove to be therapeutically useful in the future management of OAB patients based on preclinical and early clinical data. It emerges that many alternative pharmacological strategies have been discovered or are under investigation in disease-oriented studies. Several potential therapeutics are known for years but still find obstacles to pass the clinical stages of development, while other completely novel compounds, targeting new pharmacological targets, have been recently discovered and show potential to translate into clinical therapeutic agents for idiopathic and neurogenic OAB syndrome. The global scenario of investigational drugs for OAB gives promise for the development of innovative therapeutics that may ultimately prove effective as first, combined or second-line treatments within a realistic timescale of ten years.

Functional and molecular evidence for Kv7 channel subtypes in human detrusor from patients with and without bladder outflow obstruction

The aim of the study was to investigate whether Kv7 channels and their ancillary β-subunits, KCNE, are functionally expressed in the human urinary bladder. Kv7 channels were examined at the molecular level and by functional studies using RT-qPCR and myography, respectively. We found mRNA expression of KCNQ1, KCNQ3-KCNQ5 and KCNE1-5 in the human urinary bladder from patients with normal bladder function (n = 7) and in patients with bladder outflow obstruction (n = 3). Interestingly, a 3.4-fold up-regulation of KCNQ1 was observed in the latter. The Kv7 channel subtype selective modulators, ML277 (activator of Kv7.1 channels, 10 μM) and ML213 (activator of Kv7.2, Kv7.4, Kv7.4/7.5 and Kv7.5 channels, 10 μM), reduced the tone of 1 μM carbachol pre-constricted bladder strips. XE991 (blocker of Kv7.1-7.5 channels, 10 μM) had opposing effects as it increased contractions achieved with 20 mM KPSS. Furthermore, we investigated if there is interplay between Kv7 channels and β-adrenoceptors. Using cumulative additions of isoprenaline (β-adrenoceptor agonist) and forskolin (adenylyl cyclase activator) in combination with the Kv7 channel activator and blocker, retigabine and XE991, we did not find interplay between Kv7 channels and β-adrenoceptors in the human urinary bladder. The performed gene expression analysis combined with the organ bath studies imply that compounds that activate Kv7 channels could be useful for treatment of overactive bladder syndrome.

New antiepileptic medication linked to blue discoloration of the skin and eyes

Ezogabine is an antiepileptic medication approved in June 2011 by the US Food and Drug Administration (FDA) as an adjunctive treatment for partial seizures. Minimal drug interactions and a novel mechanism of action made ezogabine an appealing new treatment option. However, adverse effects reported during clinical trials and following drug approval have been alarming. A Risk Evaluation Mitigation Strategy (REMS) program has been established for urinary retention. A safety alert was published in April 2013 warning ezogabine may cause retinal pigment abnormalities and/or blue-gray discoloration, most notably on or near the lips, nail beds, sclera and conjunctiva with long-term use. In October 2013, the FDA announced a formal label change to ezogabine to include a black boxed warning emphasizing the previously reported warnings of eye and skin discoloration and permanent vision changes. Given the unknown nature of the pathophysiology, consequences and potential for reversibility of these effects, GlaxoSmithKline and the FDA have published recommendations for patients currently receiving ezogabine. Further data from published case reports and long-term safety trials in the future may lend additional insight into these concerning effects.

P-retigabine: an N-propargyled retigabine with improved brain distribution and enhanced antiepileptic activity

Retigabine (RTG, [ethyl N-[2-amino-4-[(4-fluorophenyl)methyl]amino] phenyl] carbamate]) is a first-in-class antiepileptic drug that acts by potentiating neuronal KCNQ potassium channels; however, it has less than optimal brain distribution. In this study, we report that P-RTG (ethyl N-[2-amino-4-((4-fluorobenzyl)(prop-2-ynyl)amino)phenyl]carbamate), an RTG derivative that incorporates a propargyl group at the N position of the RTG linker, exhibits an inverted brain distribution compared with RTG. The brain-to-plasma concentration ratio of P-RTG increased to 2.30 compared with 0.16 for RTG. However, the structural modification did not change the drug's potentiation potency, subtype selectivity, or RTG molecular determinants on KCNQ channels. In addition, in cultured hippocampal neurons, P-RTG exhibited a similar capability as RTG for suppressing both induced and spontaneous action potential firing. Notably, P-RTG antiepileptic activity in the maximal electroshock (MES)-induced mouse seizure model was significantly enhanced to a value 2.5 times greater than that of RTG. Additionally, the neurotoxicity of P-RTG in the rotarod test was comparable with that of RTG. Collectively, our results indicate that the incorporation of a propargyl group significantly improves the RTG brain distribution, supporting P-RTG as a promising antiepileptic drug candidate. The strategy for improving brain-to-plasma distribution of RTG might be applicable for the drug development of other central nervous system diseases.

Functional expression of KCNQ (Kv7) channels in guinea pig bladder smooth muscle and their contribution to spontaneous activity

Background and Purpose

The aim of the study was to determine whether KCNQ channels are functionally expressed in bladder smooth muscle cells (SMC) and to investigate their physiological significance in bladder contractility.

Experimental Approach

KCNQ channels were examined at the genetic, protein, cellular and tissue level in guinea pig bladder smooth muscle using RT-PCR, immunofluorescence, patch-clamp electrophysiology, calcium imaging, detrusor strip myography, and a panel of KCNQ activators and inhibitors.

Key Results

KCNQ subtypes 1–5 are expressed in bladder detrusor smooth muscle. Detrusor strips typically displayed TTX-insensitive myogenic spontaneous contractions that were increased in amplitude by the KCNQ channel inhibitors XE991, linopirdine or chromanol 293B. Contractility was inhibited by the KCNQ channel activators flupirtine or meclofenamic acid (MFA). The frequency of Ca²⁺-oscillations in SMC contained within bladder tissue sheets was increased by XE991. Outward currents in dispersed bladder SMC, recorded under conditions where BK and K_ATP currents were minimal, were significantly reduced by XE991, linopirdine, or chromanol, and enhanced by flupirtine or MFA. XE991 depolarized the cell membrane and could evoke transient depolarizations in quiescent cells. Flupirtine (20 μM) hyperpolarized the cell membrane with a simultaneous cessation of any spontaneous electrical activity.

Conclusions and Implications

These novel findings reveal the role of KCNQ currents in the regulation of the resting membrane potential of detrusor SMC and their important physiological function in the control of spontaneous contractility in the guinea pig bladder.

Cardiovascular responses to retigabine in conscious rats--under normotensive and hypertensive conditions

BACKGROUND AND PURPOSE

Retigabine is a recently approved antiepileptic agent which activates Kv7.2-7.5 potassium channels. It is emerging that these channels have an important role in vascular regulation, but the vascular effects of retigabine in the conscious state are unknown. Hence, in the present study we assessed the regional haemodynamic responses to retigabine in conscious rats.

EXPERIMENTAL APPROACH

Male Sprague Dawley rats were chronically instrumented with pulsed Doppler flow probes to measure regional haemodynamic responses to retigabine under control conditions and during acute hypertension induced by infusion of angiotensin II and arginine vasopressin. Further experiments were performed, using the β-adrenoceptor antagonists CGP 20712A, ICI 118551 and propranolol, to elucidate the roles of β-adrenoceptors in the responses to retigabine in vivo and in vitro.

KEY RESULTS

Under normotensive conditions, retigabine induced dose-dependent hypotension and hindquarters vasodilatation, with small, transient renal and mesenteric vasodilatations. In the acutely hypertensive state, the renal and mesenteric, but not hindquarters, vasodilatations were enhanced. The response of the hindquarters vascular bed to retigabine was mediated, in part, by β₂-adrenoceptors. However, in vitro experiments confirmed that retigabine did not act as a β-adrenoceptor agonist.

CONCLUSIONS AND IMPLICATIONS

We demonstrated that retigabine causes regionally specific vasodilatations, which are different under normotensive and hypertensive conditions, and are, in part, mediated by β₂-adrenoceptors in some vascular beds but not in others. These results broadly support previous findings and further indicate that Kv7 channels are a potential therapeutic target for the treatment of vascular diseases associated with inappropriate vasoconstriction.

Vasorelaxant effects of novel Kv 7.4 channel enhancers ML213 and NS15370

BACKGROUND AND PURPOSE

The KCNQ-encoded voltage-gated potassium channel family (Kv 7.1-Kv 7.5) are established regulators of smooth muscle contractility, where Kv 7.4 and Kv 7.5 predominate. Various Kv 7.2-7.5 channel enhancers have been developed that have been shown to cause a vasorelaxation in both rodent and human blood vessels. Recently, two novel Kv 7 channel enhancers have been identified, ML213 and NS15370, that show increased potency, particularly on Kv 7.4 channels. The aim of this study was to characterize the effects of these novel enhancers in different rat blood vessels and compare them with Kv 7 enhancers (S-1, BMS204352, retigabine) described previously. We also sought to determine the binding sites of the new Kv 7 enhancers.

KEY RESULTS

Both ML213 and NS15370 relaxed segments of rat thoracic aorta, renal artery and mesenteric artery in a concentration-dependent manner. In the mesenteric artery ML213 and NS15370 displayed EC50 s that were far lower than other Kv 7 enhancers tested. Current-clamp experiments revealed that both novel enhancers, at low concentrations, caused significant hyperpolarization in mesenteric artery smooth muscle cells. In addition, we determined that the stimulatory effect of these enhancers relied on a tryptophan residue located in the S5 domain, which is the same binding site for the other Kv 7 enhancers tested in this study.

CONCLUSIONS AND IMPLICATIONS

This study has identified and characterized ML213 and NS15370 as potent vasorelaxants in different blood vessels, thereby highlighting these new compounds as potential therapeutics for various smooth muscle disorders.

Diabetes attenuates urothelial modulation of detrusor contractility and spontaneous activity

OBJECTIVES

To investigate the effect of diabetes on urothelial modulation of bladder contractility.

METHODS

Bladder strips (urothelium intact or denuded) were prepared from 8-week-old streptozotocin-induced diabetic (n = 19) and non-diabetic control rats (n = 10). The effect of modulators of MaxiK (iberiotoxin and tetraethylammonium) and Kv7 (XE991 and retigabine) potassium channel activity were investigated for their effects on both carbachol-induced force generation and spontaneous contractile activity.

RESULTS

In bladder strips from non-diabetic animals, the presence of the urothelium resulted in marked sensitivity to carbachol-induced force generation by modulators of MaxiK and Kv7 channel activity, whereas in the diabetic animal urothelial sensitivity to these agents was significantly diminished. Urothelial-intact bladder strips from non-diabetic animals were more sensitive to modulators of Kv7 activity in reducing the amplitude of spontaneous phasic contractions than urothelial-denuded bladder strips, whereas in diabetic animals the presence or absence of the urothelium did not alter the sensitivity to modulators of Kv7 activity. Spontaneous activity in the presence of tetraethylammonium was not affected by the urothelium in bladder strips from either diabetic or non-diabetic animals.

CONCLUSIONS

The presence of the urothelium in bladders from non-diabetic animals modulates the activity of potassium blockers to affect bladder contractility, whereas in the diabetic bladder this effect is attenuated. These findings could help to explain the lack of success of pharmaceutical treatments targeting potassium channels to treat bladder pathology in patients with diseases imparing urothelial function.

One man's side effect is another man's therapeutic opportunity: targeting Kv7 channels in smooth muscle disorders

Retigabine is a first in class anticonvulsant that has recently undergone clinical trials to test its efficacy in epileptic patients. Retigabine's novel mechanism of action - activating Kv7 channels - suppresses neuronal activity to prevent seizure generation by hyperpolarizing the membrane potential and suppressing depolarizing surges. However, Kv7 channels are not expressed exclusively in neurones and data generated over the last decade have shown that Kv7 channels play a key role in various smooth muscle systems of the body. This review discusses the potential of targeting Kv7 channels in the smooth muscle to treat diseases such as hypertension, bladder instability, constipation and preterm labour.

Molecular expression and pharmacological evidence for a functional role of kv7 channel subtypes in Guinea pig urinary bladder smooth muscle

Voltage-gated Kv7 (KCNQ) channels are emerging as essential regulators of smooth muscle excitability and contractility. However, their physiological role in detrusor smooth muscle (DSM) remains to be elucidated. Here, we explored the molecular expression and function of Kv7 channel subtypes in guinea pig DSM by RT-PCR, qRT-PCR, immunohistochemistry, electrophysiology, and isometric tension recordings. In whole DSM tissue, mRNAs for all Kv7 channel subtypes were detected in a rank order: Kv7.1~Kv7.2Kv7.3~Kv7.5Kv7.4. In contrast, freshly-isolated DSM cells showed mRNA expression of: Kv7.1~Kv7.2Kv7.5Kv7.3~Kv7.4. Immunohistochemical confocal microscopy analyses of DSM, conducted by using co-labeling of Kv7 channel subtype-specific antibodies and α-smooth muscle actin, detected protein expression for all Kv7 channel subtypes, except for the Kv7.4, in DSM cells. L-364373 (R-L3), a Kv7.1 channel activator, and retigabine, a Kv7.2-7.5 channel activator, inhibited spontaneous phasic contractions and the 10-Hz electrical field stimulation (EFS)-induced contractions of DSM isolated strips. Linopiridine and XE991, two pan-Kv7 (effective at Kv7.1-Kv7.5 subtypes) channel inhibitors, had opposite effects increasing DSM spontaneous phasic and 10 Hz EFS-induced contractions. EFS-induced DSM contractions generated by a wide range of stimulation frequencies were decreased by L-364373 (10 µM) or retigabine (10 µM), and increased by XE991 (10 µM). Retigabine (10 µM) induced hyperpolarization and inhibited spontaneous action potentials in freshly-isolated DSM cells. In summary, Kv7 channel subtypes are expressed at mRNA and protein levels in guinea pig DSM cells. Their pharmacological modulation can control DSM contractility and excitability; therefore, Kv7 channel subtypes provide potential novel therapeutic targets for urinary bladder dysfunction.

Bladder contractility is modulated by Kv7 channels in pig detrusor

Kv7 channels are involved in smooth muscle relaxation, and accordingly we believe that they constitute potential targets for the treatment of overactive bladder syndrome. We have therefore used myography to examine the function of Kv7 channels in detrusor, i.e. pig bladder, with a view to determining the effects of the following potassium channel activators: ML213 (Kv7.2/Kv7.4 channels) and retigabine (Kv7.2-7.5 channels). Retigabine produced a concentration-dependent relaxation of carbachol- and electric field-induced contractions. The potency was similar in magnitude to that of ML213-induced relaxation, suggesting that Kv7.2 and/or Kv7.4 channels constitute the subtypes that are relevant to bladder contractility. The effects of retigabine and ML213 were attenuated by pre-incubation with 10µM XE991 (Kv7.1-7.5 channel blocker) (P<0.05), which in turn confirmed Kv7 channel selectivity. Subtype-selective effects were further investigated by incubating the detrusor with 10µM chromanol 293B (Kv7.1 channel blocker). Regardless of the experimental protocol, this did not cause a further increase in the evoked contraction. In contrast, the addition of XE991 potentiated the KCl-induced contractions, but not those induced by carbachol or electric field, indicating the presence of a phosphatidyl-inositol-4,5-biphosphate-dependent mechanism amongst the Kv7 channels in detrusor. qRT-PCR studies of the mRNA transcript level of Kv7.3-7.5 channels displayed a higher level of Kv7.4 transcript in detrusor compared to that present in brain cortex and heart tissues. Thus, we have shown that Kv7.4 channels are expressed and functionally active in pig detrusor, and that the use of selective Kv7.4 channel modulators in the treatment of detrusor overactivity seems promising.

Investigation of the impact of urine handling procedures on interpretation of urinalysis findings and product safety in subjects treated with ezogabine

Background

Ezogabine (also known by the international nonproprietary name of retigabine) is an antiepileptic drug codeveloped and comarketed by Valeant Pharmaceuticals North America and GlaxoSmithKline, which reduces neuronal excitability by enhancing the activity of potassium channels and has the potential to have effects on the urinary system through a pharmacologic action on bladder smooth muscle. In a single post-herpetic neuralgia trial, but not in an extensive epilepsy development program, proteinuria was unexpectedly reported in patients receiving ezogabine. Consequently, investigations were conducted to determine whether the reported proteinuria represented a true or false-positive finding.

Methods

Patients receiving ezogabine 900–1200 mg/day in an open-label extension (Study 303) of a Phase III epilepsy trial voluntarily provided urine samples. Fresh samples were analyzed immediately at the study site, and stabilized aliquots were analyzed 1–3 days after collection at two central laboratories. In an open-label study in healthy volunteers receiving ezogabine 600–900 mg/day (Study RTG114137), urine samples were analyzed fresh (<2 hours after collection) and, using two different stabilizers and storage at room temperature, after 24 and 72 hours. Fluid intake was restricted prior to one sample point. Albumin:creatinine ratios were assessed in both studies.

Results

In Study 303, there was notable variation in clarity, color, and proteinuria between fresh and stored urine samples, and between samples analyzed at different laboratories. In RTG114137, reporting rates of proteinuria were elevated following storage using one stabilizer, and the frequency of color change from fresh to stored samples differed between the stabilizers and between 24 and 72 hours with one stabilizer. Following fluid restriction, proteinuria rates were elevated with both stabilizers. Poor tolerability of ezogabine 750–900 mg/day resulted in limited titration beyond 750 mg/day and early termination of RTG114137.

Conclusion

Hydration status, interval between urine collection and analysis, and the type of stabilizer used are all factors that may lead to false-positive proteinuria findings in patients receiving ezogabine and should be borne in mind if abnormalities are reported.

Ezogabine: An Evaluation of Its Efficacy and Safety as Adjunctive Therapy for Partial-Onset Seizures in Adults

Objective:

To evaluate the safety, efficacy, pharmacokinetics, pharmacodynamic properties, and clinical application of ezogabine (retigabine. INN), an antiepileptic drug approved in 2011.

Data Sources:

Published data from in vitro, animal, and clinical studies were obtained from PubMed and CINAHL searches, from January 1980 to March 31, 2012. Other relevant data regarding the safety and efficacy of ezogabine were obtained from the Food and Drug Administration and the European Medication Agency Web sites.

Study Selection and Data Extraction:

Selected articles were prospective in vitro, animal, and controlled clinical studies of ezogabine. Non-English-language articles were excluded.

Data Synthesis:

In vitro and animal studies show that ezogabine activates voltage-gated potassium channels, leading to reduction of seizure frequency by inhibiting hyperexcitability activity in the central nervous system. Additionally, ezogabine enhances γ-aminobutyric acid (GABA) activity and de novo GABA synthesis. Eight clinical studies of ezogabine have been published, 5 being Phase 1 clinical trials in healthy subjects and 3 being Phase 3 clinical trials in patients with pharmacoresistant partial-onset seizures. Phase 3 clinical trials demonstrated the safety and efficacy of ezogabine in patients with partial-onset seizures.

Conclusions:

Clinical trials have shown that ezogabine is efficacious as an adjunctive agent in patients with pharmacoresistant partial seizures. Careful monitoring of drug interactions and adverse reactions is necessary. While ezogabine is efficacious (or partial seizures, its precise role in the management of patients with epilepsy is yet to be determined.

Clinical utility, safety, and tolerability of ezogabine (retigabine) in the treatment of epilepsy

One-third of patients with epilepsy continue to have seizures despite current treatments, indicating the need for better antiseizure medications with novel mechanisms of action. Ezogabine (retigabine) has recently been approved for adjunctive treatment of partial-onset seizures in adult patients with epilepsy. Ezogabine utilizes a novel mechanism of action, involving activation of specific potassium channels. The most common side effects of ezogabine are shared by most antiseizure medications and primarily consist of central nervous system (CNS) symptoms, such as somnolence, dizziness, confusion, and fatigue. In addition, a small percentage of patients on ezogabine experience a unique adverse effect affecting the bladder, which results in urinary hesitancy; thus, patients on ezogabine should be monitored carefully for potential urological symptoms. Overall, ezogabine appears to be well tolerated and represents a reasonable new option for treating patients with intractable epilepsy.

Pharmacotherapy of the third-generation AEDs: lacosamide, retigabine and eslicarbazepine acetate

INTRODUCTION

The search for new, more effective antiepileptic drugs (AEDs) continues. The three most recently approved drugs, the so-called third-generation AEDs, include lacosamide, retigabine and eslicarbazepine acetate and are licensed as adjunctive treatment of partial epilepsy in adults.

AREAS COVERED

For the above three AEDs, their mechanisms of action, pharmacokinetic characteristics, drug-drug interactions, pharmacotherapeutics, dose and administration and therapeutic drug monitoring are reviewed in this paper.

EXPERT OPINION

Lacosamide and retigabine act through novel mechanisms, while eslicarbazepine acetate, a pro-drug for eslicarbazepine, acts in a similar manner to several other AEDs. All three AEDs are associated with linear pharmacokinetic and rapid absorption and undergo metabolism. Their drug-drug interaction profile is low (lacosamide and retigabine) to modest (eslicarbazepine) in propensity. At the highest approved doses for the three AEDs, responder rates were similar. The most commonly observed adverse effects compared with placebo were dizziness, headache, diplopia and nausea for lacosamide; dizziness, somnolence and fatigue for retigabine and dizziness and somnolence for eslicarbazepine acetate. The precise role that these new AEDs will have in the treatment of epilepsy and whether they will make a significant impact on the prognosis of intractable epilepsy is not yet known and will have to await further clinical experience.

Role of potassium ion channels in detrusor smooth muscle function and dysfunction

Contraction and relaxation of the detrusor smooth muscle (DSM), which makes up the wall of the urinary bladder, facilitates the storage and voiding of urine. Several families of K(+) channels, including voltage-gated K(+) (K(V)) channels, Ca(2+)-activated K(+) (K(Ca)) channels, inward-rectifying ATP-sensitive K(+) (K(ir), K(ATP)) channels, and two-pore-domain K(+) (K(2P)) channels, are expressed and functional in DSM. They control DSM excitability and contractility by maintaining the resting membrane potential and shaping the action potentials that determine the phasic nature of contractility in this tissue. Defects in DSM K(+) channel proteins or in the molecules involved in their regulatory pathways may underlie certain forms of bladder dysfunction, such as overactive bladder. K(+) channels represent an opportunity for novel pharmacological manipulation and therapeutic intervention in human DSM. Modulation of DSM K(+) channels directly or indirectly by targeting their regulatory mechanisms has the potential to control urinary bladder function. This Review summarizes our current state of knowledge of the functional role of K(+) channels in DSM in health and disease, with special emphasis on current advancements in the field.

Ezogabine: a new angle on potassium gates

Ezogabine is a new drug for adjunctive therapy of partial-onset seizures with a novel mechanism of action. As a potassium-channel facilitator, it promotes membrane repolarization and thus opposes rapid repetitive discharges. Side effects are typical for antiepileptic drugs and the safety profile is good. Occasional instances of urinary difficulty may require surveillance.

Profile of ezogabine (retigabine) and its potential as an adjunctive treatment for patients with partial-onset seizures

Epilepsy is a common disease with significant morbidity and mortality. Approximately one-third of patients with epilepsy are refractory to available seizure medications, emphasizing the need to develop better drugs with novel mechanisms of action. Ezogabine, also known as retigabine, is a new potential adjunctive treatment for adults with intractable partial seizures. Ezogabine has a unique mechanism of action consisting of activating KCNQ2/3 (Kv7) potassium channels. Ezogabine has undergone a number of Phase II and III trials demonstrating efficacy at 600,900 and 1200 mg/day in a dose-dependent fashion. The most common adverse events with ezogabine are central nervous system effects, particularly dizziness and somnolence. Urologic symptoms, particularly urinary retention, represent a rare but unique side effect of ezogabine. Ezogabine is predominantly metabolized via glucuronidation. Its half-life is 8 hours, suggesting a need for three-times-a-day administration. Ezogabine exhibits minimal interactions with other seizure medications, except possibly lamotrigine. Ezogabine has potential for clinical applications in other medical conditions beyond epilepsy, such as neuropathic pain, neuromyotonia, and bipolar disease, but these are based primarily on experimental models.

Activation of voltage-gated KCNQ/Kv7 channels by anticonvulsant retigabine attenuates mechanical allodynia of inflammatory temporomandibular joint in rats

BACKGROUND

Temporomandibular disorders (TMDs) are characterized by persistent orofacial pain and have diverse etiologic factors that are not well understood. It is thought that central sensitization leads to neuronal hyperexcitability and contributes to hyperalgesia and spontaneous pain. Nonsteroidal anti-inflammatory drugs (NSAIDs) are currently the first choice of drug to relieve TMD pain. NSAIDS were shown to exhibit anticonvulsant properties and suppress cortical neuron activities by enhancing neuronal voltage-gated potassium KCNQ/Kv7 channels (M-current), suggesting that specific activation of M-current might be beneficial for TMD pain.

RESULTS

In this study, we selected a new anticonvulsant drug retigabine that specifically activates M-current, and investigated the effect of retigabine on inflammation of the temporomandibular joint (TMJ) induced by complete Freund's adjuvant (CFA) in rats. The results show that the head withdrawal threshold for escape from mechanical stimulation applied to facial skin over the TMJ in inflamed rats was significantly lower than that in control rats. Administration of centrally acting M-channel opener retigabine (2.5 and 7.5 mg/kg) can dose-dependently raise the head withdrawal threshold of mechanical allodynia, and this analgesic effect can be reversed by the specific KCNQ channel blocker XE991 (3 mg/kg). Food intake is known to be negatively associated with TMJ inflammation. Food intake was increased significantly by the administration of retigabine (2.5 and 7.5 mg/kg), and this effect was reversed by XE991 (3 mg/kg). Furthermore, intracerebralventricular injection of retigabine further confirmed the analgesic effect of central retigabine on inflammatory TMJ.

CONCLUSIONS

Our findings indicate that central sensitization is involved in inflammatory TMJ pain and pharmacological intervention for controlling central hyperexcitability by activation of neuronal KCNQ/M-channels may have therapeutic potential for TMDs.

Voltage-gated K(+) channels sensitive to stromatoxin-1 regulate myogenic and neurogenic contractions of rat urinary bladder smooth muscle

Members of the voltage-gated K(+) (K(V)) channel family are suggested to control the resting membrane potential and the repolarization phase of the action potential in urinary bladder smooth muscle (UBSM). Recent studies report that stromatoxin-1, a peptide isolated from tarantulas, selectively inhibits K(V)2.1, K(V)2.2, K(V)4.2, and K(V)2.1/9.3 channels. The objective of this study was to investigate whether K(V) channels sensitive to stromatoxin-1 participate in the regulation of rat UBSM contractility and to identify their molecular fingerprints. Stromatoxin-1 (100 nM) increased the spontaneous phasic contraction amplitude, muscle force, and tone in isolated UBSM strips. However, stromatoxin-1 (100 nM) had no effect on the UBSM contractions induced by depolarizing agents such as KCl (20 mM) or carbachol (1 microM). This indicates that, under conditions of sustained membrane depolarization, the K(V) channels sensitive to stromatoxin-1 have no further contribution to the membrane excitability and contractility. Stromatoxin-1 (100 nM) increased the amplitude of the electrical field stimulation-induced contractions, suggesting also a role for these channels in neurogenic contractions. RT-PCR experiments on freshly isolated UBSM cells showed mRNA expression of K(V)2.1, K(V)2.2, and K(V)9.3, but not K(V)4.2 channel subunits. Protein expression of K(V)2.1 and K(V)2.2 channels was detected using Western blot and was further confirmed by immunocytochemical detection in freshly isolated UBSM cells. These novel findings indicate that K(V)2.1 and K(V)2.2, but not K(V)4.2, channel subunits are expressed in rat UBSM and play a key role in opposing both myogenic and neurogenic UBSM contractions.

Functional effects of the KCNQ modulators retigabine and XE991 in the rat urinary bladder

The anticonvulsant retigabine has previously been reported to inhibit bladder overactivity in rats in vivo but the mechanism and site of action are not known. In the present study we investigated the effect of retigabine in isolated rat bladder tissue. Bladders from Sprague-Dawley rats were cut transversally into rings and mounted on an isometric myograph. The average tension, the amplitude and frequency of bladder muscle twitches were measured. The bladder tissue was stimulated with carbachol, KCl (5, 10 and 60mM), and by electric field stimulation. Dose-response curves were obtained with increasing concentrations of the KCNQ((2-5)) selective positive modulator, retigabine or with the KCNQ((1-5)) negative modulator XE991. Retigabine experiments were repeated in the presence of 10 microM XE991. Retigabine reduced both the contractility and the overall tonus of bladder tissue independent of the mode of stimulation with EC(50) values ranging from 3.3 microM (20mM KCl) to 8.3 microM (0.2 microM carbachol). In support of a KCNQ-specific effect, retigabine had only weak effects after 60mM KCl pre treatment and all retigabine effects could be reversed by XE991. XE991 increased both the amplitude and mean tension of the bladder but was more potent at increasing the number rather than the size of the stimulated twitches. In conclusion, this study demonstrates an efficacious KCNQ dependent effect of retigabine and XE991 on rat bladder contractility.

New tricks for old dogs: KCNQ expression and role in smooth muscle

Ion channels encoded by the KCNQ gene family (K(v)7.1-7.5) are major determinants of neuronal membrane potential and the cardiac action potential. This key physiological role is highlighted by the existence of a number of hereditary disorders caused by mutations to KCNQ genes. Recently, KCNQ gene expression has been identified in vascular and non-vascular smooth muscles. In addition, experiments with an array of pharmacological modulators of KCNQ channels have supported a crucial role for these channels in regulating smooth muscle contractility. This article will provide an overview of present understanding in this nascent area of KCNQ research and will offer guidance as to future directions.

Molecular and functional characterization of Kv7 K+ channel in murine gastrointestinal smooth muscles

Members of the K(v)7 voltage-gated K(+) channel family are important determinants of cardiac and neuronal membrane excitability. Recently, we and others have shown that K(v)7 channels are also crucial regulators of smooth muscle activity. The aim of the present study was to assess the K(v)7 expression in different parts of the murine gastrointestinal (GI) tract and to assess their functional roles by use of pharmacological agents. Of KCNQ/K(v)7 members, both KCNQ4/K(v)7.4 and KCNQ5/K(v)7.5 genes and proteins were the most abundantly expressed K(v)7 channels in smooth muscles throughout the GI tract. Immunohistochemical staining also revealed that K(v)7.4 and K(v)7.5 but not K(v)7.1 were expressed in the circular muscle layer of the colon. In segments of distal colon circular muscle exhibiting spontaneous phasic contractions, the nonselective K(v)7 blockers XE991 and linopirdine increased the integral of tension. Increases in the integral of tension were also observed under conditions of neuronal blockade. Similar effects, although less marked, were observed in the proximal colon. As expected, the K(v)7.1-selective blocker chromanol 293B had no effect in either type of segment. These data show that K(v)7.x especially K(v)7.4 and K(v)7.5 are expressed in different regions of the murine gastrointestinal tract and blockers of K(v)7 channels augment inherent contractile activity. Drugs that selectively block K(v)7.4/7.5 might be promising therapeutics for the treatment of motility disorders such as constipation associated with irritable bowel syndrome.