Voltage-independent KCNQ4 currents induced by (+/-)BMS-204352

A Novel Role of Uricosuric Agent Benzbromarone in BK Channel Activation and Reduction of Airway Smooth Muscle Contraction

The uricosuric drug benzbromarone, widely used for treatment of gout, hyperpolarizes the membrane potential of airway smooth muscle cells, but how it works remains unknown. Here we show a novel role of benzbromarone in activation of large conductance calcium-activated K⁺ channels. Benzbromarone results in dose-dependent activation of macroscopic big potassium (BK) currents about 1.7- to 14.5-fold with an EC₅₀ of 111 μM and shifts the voltage-dependent channel activation to a more hyperpolarizing direction about 10 to 54 mV in whole-cell patch clamp recordings. In single-channel recordings, benzbromarone decreases single BKα channel closed dwell time and increases the channel open probability. Coexpressing β1 subunit also enhances BK activation by benzbromarone with an EC₅₀ of 67 μM and a leftward shift of conductance-voltage (G-V) curve about 44 to 138 mV. Site-directed mutagenesis reveals that a motif of three amino acids ³²⁹RKK³³¹ in the cytoplasmic linker between S6 and C-terminal regulator of potassium conductance (RCK) gating ring mediates the pharmacological activation of BK channels by benzbromarone. Further ex vivo assay shows that benzbromarone causes reduction of tracheal strip contraction. Taken together, our findings demonstrate that uricosuric benzbromarone activates BK channels through molecular mechanism of action involving the channel RKK motif of S6-RCK linker. Pharmacological activation of BK channel by benzbromarone causes reduction of tracheal strip contraction, holding a repurposing potential for asthma and pulmonary arterial hypertension or BK channelopathies. SIGNIFICANCE STATEMENT: We describe a novel role of uricosuric agent benzbromarone in big potassium (BK) channel activation and relaxation of airway smooth muscle contraction. In this study, we find that benzbromarone is an activator of the large-conductance Ca²⁺- and voltage-activated K⁺ channel (BK channel), which serves numerous cellular functions, including control of smooth muscle contraction. Pharmacological activation of BK channel by the FDA-approved drug benzbromarone may hold repurposing potential for treatment of asthma and pulmonary arterial hypertension or BK channelopathies.

Evidence for Dual Activation of IK(M) and IK(Ca) Caused by QO-58 (5-(2,6-Dichloro-5-fluoropyridin-3-yl)-3-phenyl-2-(trifluoromethyl)-1H-pyrazolol[1,5-a]pyrimidin-7-one)

QO-58 (5-(2,6-dichloro-5-fluoropyridin-3-yl)-3-phenyl-2-(trifluoromethyl)-1H-pyrazolol[1,5-a]pyrimidin-7-one) has been regarded to be an activator of K_V7 channels with analgesic properties. However, whether and how the presence of this compound can result in any modifications of other types of membrane ion channels in native cells are not thoroughly investigated. In this study, we investigated its perturbations on M-type K⁺ current (I_K(M)), Ca²⁺-activated K⁺ current (I_K(Ca)), large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels, and erg-mediated K⁺ current (I_K(erg)) identified from pituitary tumor (GH₃) cells. Addition of QO-58 can increase the amplitude of I_K(M) and I_K(Ca) in a concentration-dependent fashion, with effective EC₅₀ of 3.1 and 4.2 μM, respectively. This compound could shift the activation curve of I_K(M) toward a leftward direction with being void of changes in the gating charge. The strength in voltage-dependent hysteresis (V_hys) of I_K(M) evoked by upright triangular ramp pulse (V_ramp) was enhanced by adding QO-58. The probabilities of M-type K⁺ (K_M) channels that will be open increased upon the exposure to QO-58, although no modification in single-channel conductance was seen. Furthermore, GH₃-cell exposure to QO-58 effectively increased the amplitude of I_K(Ca) as well as enhanced the activity of BK_Ca channels. Under inside-out configuration, QO-58, applied at the cytosolic leaflet of the channel, activated BK_Ca-channel activity, and its increase could be attenuated by further addition of verruculogen, but not by linopirdine (10 μM). The application of QO-58 could lead to a leftward shift in the activation curve of BK_Ca channels with neither change in the gating charge nor in single-channel conductance. Moreover, cell exposure of QO-58 (10 μM) resulted in a minor suppression of I_K(erg) amplitude in response to membrane hyperpolarization. The docking results also revealed that there are possible interactions of the QO-58 molecule with the KCNQ or K_Ca1.1 channel. Overall, dual activation of I_K(M) and I_K(Ca) caused by the presence of QO-58 eventually may have high impacts on the functional activity (e.g., anti-nociceptive effect) residing in electrically excitable cells. Care must be exercised when interpreting data generated with QO-58 as it is not entirely KCNQ/K_V7 selective.

High ability of zileuton ((±)-1-(1-benzo[b]thien-2-ylethyl)-1-hydroxyurea) to stimulate IK(Ca) but suppress IK(DR) and IK(M) independently of 5-lipoxygenase inhibition

Zileuton (Zyflo®) is regarded to be an inhibitor of 5-lipoxygenase. Although its effect on Ca²⁺-activated K⁺ currents has been reported, its overall ionic effects on neurons are uncertain. In whole-cell current recordings, zileuton increased the amplitude of Ca²⁺-activated K⁺ currents with an EC₅₀ of 3.2 μM in pituitary GH₃ lactotrophs. Furthermore, zileuton decreased the amplitudes of both delayed-rectifier K⁺ current (I_K(DR)) and M-type K⁺ current (I_K(M)). Conversely, no modification of hyperpolarization-activated cation current (I_h) was demonstrated in its presence of zileuton, although the subsequent addition of cilobradine effectively suppressed the current. In inside-out current recordings, the addition of zileuton to the bath increased the probability of large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels; however, the subsequent addition of GAL-021 effectively reversed the stimulation of channel activity. The kinetic analyses showed an evident shortening in the slow component of mean closed time of BK_Ca channels in the presence of zileuton, with minimal change in mean open time or that in the fast component of mean closed time. The elevation of BK_Ca channels caused by zileuton was also observed in hippocampal mHippoE-14 neurons, without any modification of single-channel amplitude. In conclusion, except for its suppression of 5-lipoxygenase, our results indicate that zileuton does not exclusively act on BK_Ca channels, and its inhibitory effects on I_K(DR) and I_K(M) may combine to exert strong influence on the functional activities of electrically excitable cells in vivo.

Vasodilation of rat skeletal muscle arteries by the novel BK channel opener GoSlo is mediated by the simultaneous activation of BK and Kv 7 channels

Background and Purpose

BK channels play important roles in various physiological and pathophysiological processes and thus have been the target of several drug development programmes focused on creating new efficacious BK channel openers, such as the GoSlo‐SR compounds. However, the effect of GoSlo‐SR compounds on vascular smooth muscle has not been studied. Therefore, we tested the hypothesis that GoSlo‐SR compounds dilate arteries exclusively by activating BK channels.

Experimental Approach

Experiments were performed on rat Gracilis muscle, saphenous, mesenteric and tail arteries using isobaric and isometric myography, sharp microelectrodes, digital droplet PCR and the patch‐clamp technique.

Key Results

GoSlo‐SR compounds dilated isobaric and relaxed and hyperpolarised isometric vessel preparations and their effects were abolished after (a) functionally eliminating K⁺ channels by pre‐constriction with 50 mM KCl or (b) blocking all K⁺ channels known to be expressed in vascular smooth muscle. However, these effects were not blocked when BK channels were inhibited. Surprisingly, the K_v7 channel inhibitor XE991 reduced their effects considerably, but neither K_v1 nor K_v2 channel blockers altered the inhibitory effects of GoSlo‐SR. However, the combined blockade of BK and K_v7 channels abolished the GoSlo‐SR‐induced relaxation. GoSlo‐SR compounds also activated K_v7.4 and K_v7.5 channels expressed in HEK 293 cells.

Conclusion and Implications

This study shows that GoSlo‐SR compounds are effective relaxants in vascular smooth muscle and mediate their effects by a combined activation of BK and K_v7.4/K_v7.5 channels. Activation of K_v1, K_v2 or K_v7.1 channels or other vasodilator pathways seems not to be involved.

High Efficacy by GAL-021: A Known Intravenous Peripheral Chemoreceptor Modulator that Suppresses BKCa-Channel Activity and Inhibits IK(M) or Ih

GAL-021 has recently been developed as a novel breathing control modulator. However, modifications of ionic currents produced by this agent remain uncertain, although its efficacy in suppressing the activity of big-conductance Ca²⁺-activated K⁺ (BK_Ca) channels has been reported. In pituitary tumor (GH₃) cells, we found that the presence of GAL-021 decreased the amplitude of macroscopic Ca²⁺-activated K⁺ current (I_K(Ca)) in a concentration-dependent manner with an effective IC₅₀ of 2.33 μM. GAL-021-mediated reduction of I_K(Ca) was reversed by subsequent application of verteporfin or ionomycin; however, it was not by that of diazoxide. In inside-out current recordings, the addition of GAL-021 to the bath markedly decreased the open-state probability of BK_Ca channels. This agent also resulted in a rightward shift in voltage dependence of the activation curve of BK_Ca channels; however, neither the gating charge of the curve nor single-channel conductance of the channel was changed. There was an evident lengthening of the mean closed time of BK_Ca channels in the presence of GAL-021, with no change in mean open time. The GAL-021 addition also suppressed M-type K⁺ current with an effective IC₅₀ of 3.75 μM; however, its presence did not alter the amplitude of erg-mediated K⁺ current, or mildly suppressed delayed-rectifier K⁺ current. GAL-021 at a concentration of 30 μM could also suppress hyperpolarization-activated cationic current. In HEK293T cells expressing α-hSlo, the addition of GAL-021 was also able to suppress the BK_Ca-channel open probabilities, and GAL-021-mediated suppression of BK_Ca-channel activity was attenuated by further addition of BMS-191011. Collectively, the GAL-021 effects presented herein do not exclusively act on BK_Ca channels and these modifications on ionic currents exert significant influence on the functional activities of electrically excitable cells occurring in vivo.

Modulation of BK Channels by Small Endogenous Molecules and Pharmaceutical Channel Openers

Voltage- and Ca(2+)-activated K(+) channels of big conductance (BK channels) are abundantly found in various organs and their relevance for smooth muscle tone and neuronal signaling is well documented. Dysfunction of BK channels is implicated in an array of human diseases involving many organs including the nervous, pulmonary, cardiovascular, renal, and urinary systems. In humans a single gene (KCNMA1) encodes the pore-forming α subunit (Slo1) of BK channels, but the channel properties are variable because of alternative splicing, tissue- and subcellular-specific auxiliary subunits (β, γ), posttranslational modifications, and a multitude of endogenous signaling molecules directly affecting the channel function. Initiatives to develop drugs capable of activating BK channels (channel openers) therefore need to consider the tissue-specific variability of BK channel structure and the potential interference with endogenously produced regulatory factors. The atomic structural basis of BK channel function is only beginning to be revealed. However, building on detailed knowledge of BK channel function, including its single-channel characteristics, voltage- and Ca(2+) dependence of channel gating, and modulation by diffusible messengers, a multi-tier allosteric model of BK channel gating (Horrigan and Aldrich (HA) model) has become a valuable tool in studying modulation of the channel. Using the conceptual framework of the HA model, we here review the functional impact of endogenous modulatory factors and select small synthetic compounds that regulate BK channel activity. Furthermore, we devise experimental approaches for studying BK channel-drug interactions with the aim to classify BK-modulating substances according to their molecular mode of action.

Critical role of large-conductance calcium- and voltage-activated potassium channels in leptin-induced neuroprotection of N-methyl-d-aspartate-exposed cortical neurons

In the present study, the neuroprotective effects of the adipokine leptin, and the molecular mechanism involved, have been studied in rat and mice cortical neurons exposed to N-methyl-d-aspartate (NMDA) in vitro. In rat cortical neurons, leptin elicited neuroprotective effects against NMDA-induced cell death, which were concentration-dependent (10-100 ng/ml) and largest when the adipokine was preincubated for 2h before the neurotoxic stimulus. In both rat and mouse cortical neurons, leptin-induced neuroprotection was fully antagonized by paxilline (Pax, 0.01-1 μM) and iberiotoxin (Ibtx, 1-100 nM), with EC50s of 38 ± 10 nM and 5 ± 2 nM for Pax and Ibtx, respectively, close to those reported for Pax- and Ibtx-induced Ca(2+)- and voltage-activated K(+) channels (Slo1 BK channels) blockade; the BK channel opener NS1619 (1-30 μM) induced a concentration-dependent protection against NMDA-induced excitotoxicity. Moreover, cortical neurons from mice lacking one or both alleles coding for Slo1 BK channel pore-forming subunits were insensitive to leptin-induced neuroprotection. Finally, leptin exposure dose-dependently (10-100 ng/ml) increased intracellular Ca(2+) levels in rat cortical neurons. In conclusion, our results suggest that Slo1 BK channel activation following increases in intracellular Ca(2+) levels is a critical step for leptin-induced neuroprotection in NMDA-exposed cortical neurons in vitro, thus highlighting leptin-based intervention via BK channel activation as a potential strategy to counteract neurodegenerative diseases.

Stretch-activation of angiotensin II type 1a receptors contributes to the myogenic response of mouse mesenteric and renal arteries

RATIONALE

Vascular wall stretch is the major stimulus for the myogenic response of small arteries to pressure. The molecular mechanisms are elusive, but recent findings suggest that G protein-coupled receptors can elicit a stretch response.

OBJECTIVE

To determine whether angiotensin II type 1 receptors (AT1R) in vascular smooth muscle cells exert mechanosensitivity and identify the downstream ion channel mediators of myogenic vasoconstriction.

METHODS AND RESULTS

We used mice deficient in AT1R signaling molecules and putative ion channel targets, namely AT1R, angiotensinogen, transient receptor potential channel 6 (TRPC6) channels, or several subtypes of the voltage-gated K+ (Kv7) gene family (KCNQ3, 4, or 5). We identified a mechanosensing mechanism in isolated mesenteric arteries and in the renal circulation that relies on coupling of the AT1R subtype a to a Gq/11 protein as a critical event to accomplish the myogenic response. Arterial mechanoactivation occurs after pharmacological block of AT1R and in the absence of angiotensinogen or TRPC6 channels. Activation of AT1R subtype a by osmotically induced membrane stretch suppresses an XE991-sensitive Kv channel current in patch-clamped vascular smooth muscle cells, and similar concentrations of XE991 enhance mesenteric and renal myogenic tone. Although XE991-sensitive KCNQ3, 4, and 5 channels are expressed in vascular smooth muscle cells, XE991-sensitive K+ current and myogenic contractions persist in arteries deficient in these channels.

CONCLUSIONS

Our results provide definitive evidence that myogenic responses of mouse mesenteric and renal arteries rely on ligand-independent, mechanoactivation of AT1R subtype a. The AT1R subtype a signal relies on an ion channel distinct from TRPC6 or KCNQ3, 4, or 5 to enact vascular smooth muscle cell activation and elevated vascular resistance.

Kv7 channels as targets for anti-epileptic and psychiatric drug-development

The Kv7 channels, a family of voltage-dependent K(+) channels (Kv7.1-Kv7.5), have gained much attention in drug discovery especially because four members are genetically linked to diseases. For disorders of the CNS focus was originally on epilepsy and pain, but it is becoming increasingly evident that Kv7 channels can also be valid targets for psychiatric disorders, such as anxiety and mania. The common denominator is probably neuronal hyperexcitability in different brain areas, which can be successfully attenuated by pharmacological increment of Kv7 channel activity. This perspective attempts to review the current status and challenges for CNS drug discovery based on Kv7 channels as targets for neurological and psychiatric indications with special focus on selectivity and mode-of-actions.

Neuronal Ca2+-activated K+ channels limit brain infarction and promote survival

Neuronal calcium-activated potassium channels of the BK type are activated by membrane depolarization and intracellular Ca(2+) ions. It has been suggested that these channels may play a key neuroprotective role during and after brain ischemia, but this hypothesis has so far not been tested by selective BK-channel manipulations in vivo. To elucidate the in vivo contribution of neuronal BK channels in acute focal cerebral ischemia, we performed middle cerebral artery occlusion (MCAO) in mice lacking BK channels (homozygous mice lacking the BK channel alpha subunit, BK(-/-)). MCAO was performed in BK(-/-) and WT mice for 90 minutes followed by a 7-hour-reperfusion period. Coronal 1 mm thick sections were stained with 2,3,5-triphenyltetrazolium chloride to reveal the infarction area. We found that transient focal cerebral ischemia by MCAO produced larger infarct volume, more severe neurological deficits, and higher post-ischemic mortality in BK(-/-) mice compared to WT littermates. However, the regional cerebral blood flow was not significantly different between genotypes as measured by Laser Doppler (LD) flowmetry pre-ischemically, intra-ischemically, and post-ischemically, suggesting that the different impact of MCAO in BK(-/-) vs. WT was not due to vascular BK channels. Furthermore, when NMDA was injected intracerebrally in non-ischemic mice, NMDA-induced neurotoxicity was found to be larger in BK(-/-) mice compared to WT. Whole-cell patch clamp recordings from CA1 pyramidal cells in organotypic hippocampal slice cultures revealed that BK channels contribute to rapid action potential repolarization, as previously found in acute slices. When these cultures were exposed to ischemia-like conditions this induced significantly more neuronal death in BK(-/-) than in WT cultures. These results indicate that neuronal BK channels are important for protection against ischemic brain damage.

The therapeutic potential of neuronal K V 7 (KCNQ) channel modulators: an update

BACKGROUND

Neuronal KCNQ channels (K(V)7.2-5) represent attractive targets for the development of therapeutics for chronic and neuropathic pain, migraine, epilepsy and other neuronal hyperexcitability disorders, although there has been only modest progress in translating this potential into useful therapeutics.

OBJECTIVE

Compelling evidence of the importance of K(V)7 channels as neuronal regulatory elements, readily amenable to pharmacological modulation, has sustained widespread interest in these channels as drug targets. This review will update readers on key aspects of the characterization of these important ion channel targets, and will discuss possible current barriers to their exploitation for CNS therapeutics.

METHODS

This article is based on a review of recent literature, with a focus on data pertaining to the roles of these channels in neurophysiology. In addition, I review some of the regulatory elements that influence the channels and how these may relate to channel pharmacology, and present a review of recent advances in neuronal K(V)7 channel pharmacology.

CONCLUSIONS

These channels continue to be valid and approachable targets for CNS therapeutics. However, we may need to understand more about the roles of neuronal K(V)7 channels during the development of disease states, as well as to pay more attention to a detailed analysis of the molecular pharmacology of the different channel subfamily members and the modes of interaction of individual modulators, in order to successfully target these channels for therapeutic development.

Validation of a medium-throughput electrophysiological assay for KCNQ2/3 channel enhancers using IonWorks HT

Enhancers of KCNQ channels are known to be effective in chronic pain models. To discover novel enhancers of KCNQ channels, the authors developed a medium-throughput electrophysiological assay by using the IonWorks platform. Screening of 20 CHO-K1 clones stably expressing KCNQ2/3 was performed on the IonWorks HT until the best clone (judged from seal rate, current level, and stability) was obtained. The KCNQ2/3 current amplitude in the cells was found to increase from 60 +/- 15 pA to 473 +/- 80 pA (at -10 mV), and the expression rate was increased by 56% when the cells were incubated at 27 degrees C overnight. The clone used for compound screening had a seal rate of greater than 90% and an overall success rate of greater than 70%. The voltage step protocol (hold cells at -80 mV and depolarize to -10 mV for 1 s) was designed to provide moderate current but still allow for pharmacological current enhancement. EC(50)s were generated from 8-point concentration-response curves with a control compound on each plate using compounds that were also tested with conventional patch clamp. The authors found that there was a very good correlation (R(2) > 0.9) between the 2 assays, thus demonstrating the highly predictive nature of the IonWorks assay.

Inhibition of martentoxin on neuronal BK channel subtype (alpha+beta4): implications for a novel interaction model

Martentoxin as a 37-residue peptide was capable of blocking large-conductance Ca(2+)-activated K(+) (BK) channels in adrenal medulla chromaffin cells. This study investigated the pharmacological discrimination of martentoxin on BK channel subtypes. The results showed that the iberiotoxin-insensitive neuronal BK channels (alpha+beta4) could be potently blocked by martentoxin (IC(50) = approximately 80 nM). In contrast, the iberiotoxin-sensitive BK channel consisting of only alpha-subunit was less sensitive to martentoxin. Distinctively, martentoxin inhibited neuronal BK channels (alpha+beta4) with a novel interaction mode. Two possible interaction sites of neuronal BK channels (alpha+beta4) might be responsible for the binding with martentoxin: one for trapping and the other located at the pore region for blocking. In addition, the inhibition of martentoxin on neuronal BK channels (alpha+beta4) depended on cytoplasmic Ca(2+) concentration. On the other hand, in vivo experiments from EEG recordings suggested that neuronal BK channels (alpha+beta4) were the primary target of martentoxin. Therefore, this research not only sheds light on a unique ligand for neuronal BK channels (alpha+beta4), but also highlights a novel model approach for the interaction between K(+) channels and specific-ligands.

Inactivation as a new regulatory mechanism for neuronal Kv7 channels

Voltage-gated K(+) channels of the Kv7 (KCNQ) family have important physiological functions in both excitable and nonexcitable tissue. The family encompasses five genes encoding the channel subunits Kv7.1-5. Kv7.1 is found in epithelial and cardiac tissue. Kv7.2-5 channels are predominantly neuronal channels and are important for controlling excitability. Kv7.1 channels have been considered the only Kv7 channels to undergo inactivation upon depolarization. However, here we demonstrate that inactivation is also an intrinsic property of Kv7.4 and Kv7.5 channels, which inactivate to a larger extent than Kv7.1 channels at all potentials. We demonstrate that at least 30% of these channels are inactivated at physiologically relevant potentials. The onset of inactivation is voltage dependent and occurs on the order of seconds. Both time- and voltage-dependent recovery from inactivation was investigated for Kv7.4 channels. A time constant of 1.47 +/- 0.21 s and a voltage constant of 54.9 +/- 3.4 mV were determined. It was further demonstrated that heteromeric Kv7.3/Kv7.4 channels had inactivation properties different from homomeric Kv7.4 channels. Finally, the Kv7 channel activator BMS-204352 was in contrast to retigabine found to abolish inactivation of Kv7.4. In conclusion, this work demonstrates that inactivation is a key regulatory mechanism of Kv7.4 and Kv7.5 channels.

Molecular Mechanisms for Large Conductance Ca2+-Activated K+ Channel Activation by a Novel Opener, 12,14-Dichlorodehydroabietic Acid

Our recent study has revealed that 12,14-dichlorodehydroabietic acid (diCl-DHAA), which is synthetically derived from a natural product, abietic acid, is a potent opener of large conductance Ca(2+)-activated K(+) (BK) channel. Here, we examined, by using a channel expression system in human embryonic kidney 293 cells, the mechanisms underlying the BK channel opening action of diCl-DHAA and which subunit of the BK channel (alpha or beta1) is the site of action for diCl-DHAA. BK channel activity was significantly enhanced by diCl-DHAA at concentrations of 0.1 microM and higher in a concentration-dependent manner. diCl-DHAA enhanced the activity of BKalpha by increasing sensitivity to both Ca(2+) and membrane potential without changing the single channel conductance. It is notable that the increase in BK channel open probability by diCl-DHAA showed significant inverse voltage dependence, i.e., larger potentiation at lower potentials. Since coexpression of beta1 subunit with BKalpha did not affect the potency of diCl-DHAA, the site of action for diCl-DHAA is suggested to be BKalpha subunit. Moreover, kinetic analysis of single channel currents indicates that diCl-DHAA opens BKalpha mainly by decreasing the time staying in a long closed state. Although reconstituted voltage-dependent Ca(2+) channel current was significantly reduced by 1 microM diCl-DHAA, BK channels were selectively activated at lower concentrations. These results indicate that diCl-DHAA is one of the most potent BK channel openers acting on BKalpha and a useful prototype compound to develop a novel BK channel opener.

Potassium channel subtypes as molecular targets for overactive bladder and other urological disorders

Potassium channels have re-emerged as attractive targets for overactive bladder and other urological diseases in recent years, in part due to an enhanced understanding of their molecular heterogeneity, tissue distribution, functional roles and regulation in physiological and pathological states. Cloning and heterologous expression analysis, coupled with the advancement of improved high-throughput screening techniques, have enabled expeditious identification of selective small-molecule openers and blockers for ATP-sensitive K+ channels, Ca2+-activated K+ channels and voltage-dependent K+ channel-KQT-like subfamily (KCNQ) members, and has paved the way in the assessment of efficacy and adverse effects in preclinical models. This review focuses on the rationale for molecular targeting of K+ channels, the current status of target validation, including preclinical proof-of-concept studies, and provides perspectives on the limitations and hurdles to be overcome in realising the potential of these targets for diverse urological indications such as overactive bladder, erectile dysfunction and prostate diseases.

Voltage-gated cation channel modulators for the treatment of stroke

Neuronal voltage-gated cation channels regulate the transmembrane flux of calcium, sodium and potassium. Neuronal ischaemia occurring during acute ischaemic stroke results in the breakdown in the normal function of these ion channels, contributing to a series of pathological events leading to cell death. A dramatic increase in the intracellular concentration of calcium during neuronal ischaemia plays a particularly important role in the neurotoxic cascade resulting in stroke-related acute neurodegeneration. One approach to provide therapeutic benefit following ischaemic stroke has been to target neuronal voltage-gated cation channels, and particularly blockers of calcium and sodium channels, for post-stroke neuroprotection. A recent development has been the identification of openers of large-conductance calcium- and voltage-dependent potassium channels (maxi-K channels), which hyperpolarize ischaemic neurons, reduce excitatory amino acid release, and reduce ischaemic calcium entry. Thus far, targeting these voltage-gated cation channels has not yet yielded significant clinical benefit. The reasons for this may involve the lack of small-molecule blockers of many neuronal members of these ion channel families and the design of preclinical stroke models, which do not adequately emulate the clinical condition and hence lack sufficient rigor to predict efficacy in human stroke. Furthermore, there may be a need for changes in clinical trial designs to optimise the selection of patients and the course of drug treatment to protect neurons during all periods of potential neuronal sensitivity to neuro-protectants. Clinical trials may also have to be powered to detect small effect sizes or be focused on patients more likely to respond to a particular therapy. The development of future solutions to these problems should result in an improved probability of success for the treatment of stroke.

Anxiolytic effects of Maxipost (BMS-204352) and retigabine via activation of neuronal Kv7 channels

Neuronal Kv7 channels are recognized as potential drug targets for treating hyperexcitability disorders such as pain, epilepsy, and mania. Hyperactivity of the amygdala has been described in clinical and preclinical studies of anxiety, and therefore, neuronal Kv7 channels may be a relevant target for this indication. In patch-clamp electrophysiology on cell lines expressing Kv7 channel subtypes, Maxipost (BMS-204352) exerted positive modulation of all neuronal Kv7 channels, whereas its R-enantiomer was a negative modulator. By contrast, at the Kv7.1 and the large conductance Ca2+-activated potassium channels, the two enantiomers showed the same effect, namely, negative and positive modulation at the two channels, respectively. At GABA(A) receptors (alpha1beta2gamma2s and alpha2beta2gamma2s) expressed in Xenopus oocytes, BMS-204352 was a negative modulator, and the R-enantiomer was a positive modulator. The observation that the S- and R-forms exhibited opposing effects on neuronal Kv7 channel subtypes allowed us to assess the potential role of Kv7 channels in anxiety. In vivo, BMS-204352 (3-30 mg/kg) was anxiolytic in the mouse zero maze and marble burying models of anxiety, with the effect in the burying model antagonized by the R-enantiomer (3 mg/kg). Likewise, the positive Kv7 channel modulator retigabine was anxiolytic in both models, and its effect in the burying model was blocked by the Kv7 channel inhibitor 10,10-bis-pyridin-4-ylmethyl-10H-anthracen-9-one (XE-991) (1 mg/kg). Doses at which BMS-204352 and retigabine induce anxiolysis could be dissociated from effects on sedation or memory impairment. In conclusion, these in vitro and in vivo studies provide compelling evidence that neuronal Kv7 channels are a target for developing novel anxiolytics.