Application of near infra-red laser light increases current threshold in optic nerve consistent with increased Na+-dependent transport

Increases in the current threshold occur in optic nerve axons with the application of infra-red laser light, whose mechanism is only partly understood. In isolated rat optic nerve, laser light was applied near the site of electrical stimulation, via a flexible fibre optic. Paired applications of light produced increases in threshold that were reduced on the second application, the response recovering with increasing delays, with a time constant of 24 s. 3-min duration single applications of laser light gave rise to a rapid increase in threshold followed by a fade, whose time-constant was between 40 and 50 s. After-effects were sometimes apparent following the light application, where the resting threshold was reduced. The increase in threshold was partially blocked by 38.6 mM Li+ in combination with 5  μ M bumetanide, a manoeuvre increasing refractoriness and consistent with axonal depolarization. Assessing the effect of laser light on the nerve input resistance ruled out a previously suggested fall in myelin resistance as contributing to threshold changes. These data appear consistent with an axonal membrane potential that partly relies on temperature-dependent electroneutral Na+ influx, and where fade in the response to the laser may be caused by a gradually diminishing Na+ pump-induced hyperpolarization, in response to falling intracellular [Na+].

Crossover randomized controlled trial of bumetanide to rescue an attack of exercise induced hand weakness in hypokalaemic periodic paralysis

The aim of this study was to establish whether bumetanide can abort an acute attack of weakness in patients with HypoPP. This was a randomised, double-blind, cross-over, placebo-controlled phase II clinical trial. Focal attack of weakness was induced by isometric exercise of ADM followed by rest (McManis protocol). Participants had two study visits and received either placebo or 2 mg bumetanide at attack onset (defined as 40 % decrement in the abductor digiti minimi CMAP amplitude from peak). CMAP measurements assessed attack severity and duration. Nine participants completed both visits. CMAP percentage of peak amplitudes in the bumetanide (40.6 %) versus placebo (34.9 %) group at 1hr following treatment did not differ significantly (estimated effect difference 5.9 % (95 % CI: (-5.7 %; 17.5 %), p = 0.27, primary outcome). CMAP amplitudes assessed by the area under the curve for early (0-2hr post-treatment) and late (2-4 h post-treatment) efficacy were not statistically different between bumetanide and placebo (early effect estimate 0.043, p = 0.3; late effect estimate 0.085, p = 0.1). Two participants recovered from the attack following bumetanide intake; none recovered following placebo. Bumetanide was well tolerated but not efficacious to rescue a focal attack in an immobilised hand in the majority of patients, although data supports further studies of this agent.

γ-Aminobutyric Acid-Ergic Development Contributes to the Enhancement of Electroencephalogram Slow-Delta Oscillations Under Volatile Anesthesia in Neonatal Rats

BACKGROUND

General anesthetics (eg, propofol and volatile anesthetics) enhance the slow-delta oscillations of the cortical electroencephalogram (EEG), which partly results from the enhancement of (γ-aminobutyric acid [GABA]) γ-aminobutyric acid-ergic (GABAergic) transmission. There is a GABAergic excitatory-inhibitory shift during postnatal development. Whether general anesthetics can enhance slow-delta oscillations in the immature brain has not yet been unequivocally determined.

METHODS

Perforated patch-clamp recording was used to confirm the reversal potential of GABAergic currents throughout GABAergic development in acute brain slices of neonatal rats. The power density of the electrocorticogram and the minimum alveolar concentrations (MAC) of isoflurane and/or sevoflurane were measured in P4-P21 rats. Then, the effects of bumetanide, an inhibitor of the Na + -K + -2Cl - cotransporter (NKCC1) and K + -Cl - cotransporter (KCC2) knockdown on the potency of volatile anesthetics and the power density of the EEG were determined in vivo.

RESULTS

Reversal potential of GABAergic currents were gradually hyperpolarized from P4 to P21 in cortical pyramidal neurons. Bumetanide enhanced the hypnotic effects of volatile anesthetics at P5 (for MAC LORR , isoflurane: 0.63% ± 0.07% vs 0.81% ± 0.05%, 95% confidence interval [CI], -0.257 to -0.103, P < .001; sevoflurane: 1.46% ± 0.12% vs 1.66% ± 0.09%, 95% CI, -0.319 to -0.081, P < .001); while knockdown of KCC2 weakened their hypnotic effects at P21 in rats (for MAC LORR , isoflurane: 0.58% ± 0.05% to 0.77% ± 0.20%, 95% CI, 0.013-0.357, P = .003; sevoflurane: 1.17% ± 0.04% to 1.33% ± 0.04%, 95% CI, 0.078-0.244, P < .001). For cortical EEG, slow-delta oscillations were the predominant components of the EEG spectrum in neonatal rats. Isoflurane and/or sevoflurane suppressed the power density of slow-delta oscillations rather than enhancement of it until GABAergic maturity. Enhancement of slow-delta oscillations under volatile anesthetics was simulated by preinjection of bumetanide at P5 (isoflurane: slow-delta changed ratio from -0.31 ± 0.22 to 1.57 ± 1.15, 95% CI, 0.67-3.08, P = .007; sevoflurane: slow-delta changed ratio from -0.46 ± 0.25 to 0.95 ± 0.97, 95% CI, 0.38-2.45, P = .014); and suppressed by KCC2-siRNA at P21 (isoflurane: slow-delta changed ratio from 16.13 ± 5.69 to 3.98 ± 2.35, 95% CI, -18.50 to -5.80, P = .002; sevoflurane: slow-delta changed ratio from 0.13 ± 2.82 to 3.23 ± 2.49, 95% CI, 3.02-10.79, P = .003).

CONCLUSIONS

Enhancement of cortical EEG slow-delta oscillations by volatile anesthetics may require mature GABAergic inhibitory transmission during neonatal development.

Astrocytic NKCC1 inhibits seizures by buffering Cl- and antagonizing neuronal NKCC1 at GABAergic synapses

OBJECTIVE

A pathological excitatory action of the major inhibitory neurotransmitter γ-aminobutyric acid (GABA) has been observed in epilepsy. Blocking the Cl- importer NKCC1 with bumetanide is expected to reduce the neuronal intracellular Cl- concentration ([Cl- ]i ) and thereby attenuate the excitatory GABA response. Accordingly, several clinical trials of bumetanide for epilepsy were conducted. Although NKCC1 is expressed in both neurons and glial cells, an involvement of glial NKCC1 in seizures has not yet been reported. Astrocytes maintain high [Cl- ]i with NKCC1, and this gradient promotes Cl- efflux via the astrocytic GABAA receptor (GABAA R). This Cl- efflux buffers the synaptic cleft Cl- concentration to maintain the postsynaptic Cl- gradient during intense firing of GABAergic neurons, thereby sustaining its inhibitory action during seizure. In this study, we investigated the function of astrocytic NKCC1 in modulating the postsynaptic action of GABA in acute seizure models.

METHODS

We used the astrocyte-specific conditional NKCC1 knockout (AstroNKCC1KO) mice. The seizurelike events (SLEs) in CA1 pyramidal neurons were triggered by tetanic stimulation of stratum radiatum in acute hippocampus slices. The SLE underlying GABAA R-mediated depolarization was evaluated by applying the GABAA R antagonist bicuculline. The pilocarpine-induced seizure in vivo was monitored in adult mice by the Racine scale. The SLE duration and tetanus stimulation intensity threshold and seizure behavior in AstroNKCC1KO mice and wild-type (WT) mice were compared.

RESULTS

The AstroNKCC1KO mice were prone to seizures with lower threshold and longer duration of SLEs and larger GABAA R-mediated depolarization underlying the SLEs, accompanied by higher Racine-scored seizures. Bumetanide reduced these indicators of seizure in AstroNKCC1KO mice (which still express neuronal NKCC1), but not in the WT, both in vitro and in vivo.

SIGNIFICANCE

Astrocytic NKCC1 inhibits GABA-mediated excitatory action during seizures, whereas neuronal NKCC1 has the converse effect, suggesting opposing actions of bumetanide on these cells.

Bumetanide Attenuates Cognitive Deficits and Brain Damage in Rats Subjected to Hypoxia-Ischemia at Two Time Points of the Early Postnatal Period

Neonatal hypoxia-ischemia (HI) is one of the main causes of tissue damage, cell death, and imbalance between neuronal excitation and inhibition and synaptic loss in newborns. GABA, the major inhibitory neurotransmitter of the central nervous system (CNS) in adults, is excitatory at the onset of neurodevelopment and its action depends on the chloride (Cl-) cotransporters NKCC1 (imports Cl-) and KCC2 (exports Cl-) expression. Under basal conditions, the NKCC1/KCC2 ratio decreases over neurodevelopment. Thus, changes in this ratio caused by HI may be related to neurological disorders. The present study evaluated the effects of bumetanide (NKCC cotransporters inhibitor) on HI impairments in two neurodevelopmental periods. Male Wistar rat pups, 3 (PND3) and 11 (PND11) days old, were submitted to the Rice-Vannucci model. Animals were divided into 3 groups: SHAM, HI-SAL, and HI-BUM, considering each age. Bumetanide was administered intraperitoneally at 1, 24, 48, and 72 h after HI. NKCC1, KCC2, PSD-95, and synaptophysin proteins were analyzed after the last injection by western blot. Negative geotaxis, righting reflex, open field, object recognition test, and Morris water maze task were performed to assess neurological reflexes, locomotion, and memory function. Tissue atrophy and cell death were evaluated by histology. Bumetanide prevented neurodevelopmental delay, hyperactivity, and declarative and spatial memory deficits. Furthermore, bumetanide reversed HI-induced brain tissue damage, reduced neuronal death and controlled GABAergic tone, maintained the NKCC1/KCC2 ratio, and synaptogenesis close to normality. Thereby, bumetanide appears to play an important therapeutic role in the CNS, protecting the animals against HI damage and improving functional performance.

Bumetanide induces post-traumatic microglia-interneuron contact to promote neurogenesis and recovery

Although the Na-K-Cl cotransporter (NKCC1) inhibitor bumetanide has prominent positive effects on the pathophysiology of many neurological disorders, the mechanism of action is obscure. Attention paid to elucidating the role of Nkcc1 has mainly been focused on neurons, but recent single cell mRNA sequencing analysis has demonstrated that the major cellular populations expressing NKCC1 in the cortex are non-neuronal. We used a combination of conditional transgenic animals, in vivo electrophysiology, two-photon imaging, cognitive behavioural tests and flow cytometry to investigate the role of Nkcc1 inhibition by bumetanide in a mouse model of controlled cortical impact (CCI). Here, we found that bumetanide rescues parvalbumin-positive interneurons by increasing interneuron-microglia contacts shortly after injury. The longitudinal phenotypic changes in microglia were significantly modified by bumetanide, including an increase in the expression of microglial-derived BDNF. These effects were accompanied by the prevention of CCI-induced decrease in hippocampal neurogenesis. Treatment with bumetanide during the first week post-CCI resulted in significant recovery of working and episodic memory as well as changes in theta band oscillations 1 month later. These results disclose a novel mechanism for the neuroprotective action of bumetanide mediated by an acceleration of microglial activation dynamics that leads to an increase in parvalbumin interneuron survival following CCI, possibly resulting from increased microglial BDNF expression and contact with interneurons. Salvage of interneurons may normalize ambient GABA, resulting in the preservation of adult neurogenesis processes as well as contributing to bumetanide-mediated improvement of cognitive performance.

Dietary Na+ depletion up-regulates NKCC1 expression and enhances electrogenic Cl- secretion in rat proximal colon

The corticosteroid hormone, aldosterone, markedly enhances K+ secretion throughout the colon, a mechanism critical to its role in maintaining overall K+ balance. Previous studies demonstrated that basolateral NKCC1 was up-regulated by aldosterone in the distal colon specifically to support K+ secretion-which is distinct from the more well-established role of NKCC1 in supporting luminal Cl- secretion. However, considerable segmental variability exists between proximal and distal colonic ion transport processes, especially concerning their regulation by aldosterone. Furthermore, delineating such region-specific effects has important implications for the management of various gastrointestinal pathologies. Experiments were therefore designed to determine whether aldosterone similarly up-regulates NKCC1 in the proximal colon to support K+ secretion. Using dietary Na+ depletion as a model of secondary hyperaldosteronism in rats, we found that proximal colon NKCC1 expression was indeed enhanced in Na+-depleted (i.e., hyperaldosteronemic) rats. Surprisingly, electrogenic K+ secretion was not detectable by short-circuit current (ISC) measurements in response to either basolateral bumetanide (NKCC1 inhibitor) or luminal Ba2+ (non-selective K+ channel blocker), despite enhanced K+ secretion in Na+-depleted rats, as measured by 86Rb+ fluxes. Expression of BK and IK channels was also found to be unaltered by dietary Na+ depletion. However, bumetanide-sensitive basal and agonist-stimulated Cl- secretion (ISC) were significantly enhanced by Na+ depletion, as was CFTR Cl- channel expression. These data suggest that NKCC1-dependent secretory pathways are differentially regulated by aldosterone in proximal and distal colon. Development of therapeutic strategies in treating pathologies related to aberrant colonic K+/Cl- transport-such as pseudo-obstruction or ulcerative colitis-may benefit from these findings.

Bumetanide increases postsynaptic inhibition after chronic SCI and decreases presynaptic inhibition with step-training

Current anti-spastic medication significantly compromises motor recovery after spinal cord injury (SCI), indicating a critical need for alternative interventions. Because a shift in chloride homeostasis decreases spinal inhibition and contributes to hyperreflexia after SCI, we investigated the effect of bumetanide, an FDA-approved sodium-potassium-chloride intruder (NKCC1) antagonist, on presynaptic and postsynaptic inhibition. We compared its effect with step-training as it is known to improve spinal inhibition by restoring chloride homeostasis. In SCI rats, a prolonged bumetanide treatment increased postynaptic inhibition but not presynaptic inhibition of the plantar H-reflex evoked by posterior biceps and semitendinosus (PBSt) group I afferents. By using in vivo intracellular recordings of motoneurons, we further show that a prolonged bumetanide increased postsynaptic inhibition by hyperpolarizing the reversal potential for inhibitory postsynaptic potentials (IPSPs) after SCI. However, in step-trained SCI rats an acute delivery of bumetanide decreased presynaptic inhibition of the H-reflex, but not postsynaptic inhibition. These results suggest that bumetanide might be a viable option to improve postsynaptic inhibition after SCI, but it also decreases the recovery of presynaptic inhibition with step-training. We discuss whether the effects of bumetanide are mediated by NKCC1 or by off-target effects. KEY POINTS: After spinal cord injury (SCI), chloride homeostasis is dysregulated over time in parallel with the decrease in presynaptic inhibition of Ia afferents and postsynaptic inhibition of motoneurons, and the development of spasticity. While step-training counteracts these effects, it cannot always be implemented in the clinic because of comorbidities. An alternative intervention is to use pharmacological strategies to decrease spasticity without hindering the recovery of motor function with step-training. Here we found that, after SCI, a prolonged bumetanide (an FDA-approved antagonist of the sodium-potassium-chloride intruder, NKCC1) treatment increases postsynaptic inhibition of the H-reflex, and it hyperpolarizes the reversal potential for inhibitory postsynaptic potentials in motoneurons. However, in step-trained SCI, an acute delivery of bumetanide decreases presynaptic inhibition of the H-reflex, but not postsynaptic inhibition. Our results suggest that bumetanide has the potential to decrease spastic symptoms related to a decrease in postsynaptic but not presynaptic inhibition after SCI.

The loop diuretic torasemide but not azosemide potentiates the anti-seizure and disease-modifying effects of midazolam in a rat model of birth asphyxia

Loop diuretics such as furosemide and bumetanide, which act by inhibiting the Na-K-2Cl cotransporter NKCC2 at the thick ascending limb of the loop of Henle, have been shown to exert anti-seizure effects. However, the exact mechanism of this effect is not known. For bumetanide, it has been suggested that inhibition of the NKCC isoform NKCC1 in the membrane of brain neurons may be involved; however, NKCC1 is expressed by virtually all cell types in the brain, which makes any specific targeting of neuronal NKCC1 by bumetanide impossible. In addition, bumetanide only poorly penetrates the brain. We have previously shown that loop diuretics azosemide and torasemide also potently inhibit NKCC1. In contrast to bumetanide and furosemide, azosemide and torasemide lack a carboxylic group, which should allow them to better penetrate through biomembranes by passive diffusion. Because of the urgent medical need to develop new treatments for neonatal seizures and their adverse outcome, we evaluated the effects of azosemide and torasemide, administered alone or in combination with phenobarbital or midazolam, in a rat model of birth asphyxia and neonatal seizures. Neither diuretic suppressed the seizures when administered alone but torasemide potentiated the anti-seizure effect of midazolam. Brain levels of torasemide were below those needed to inhibit NKCC1. In addition to suppressing seizures, the combination of torasemide and midazolam, but not midazolam alone, prevented the cognitive impairment of the post-asphyxial rats at 3 months after asphyxia. Furthermore, aberrant mossy fiber sprouting in the hippocampus was more effectively prevented by the combination. We assume that either an effect on NKCC1 at the blood-brain barrier and/or cells in the periphery or the NKCC2-mediated diuretic effect of torasemide are involved in the present findings. Our data suggest that torasemide may be a useful option for improving the treatment of neonatal seizures and their adverse outcome.

Role of Monovalent Ions in the NKCC1 Inhibition Mechanism Revealed through Molecular Simulations

The secondary active Na-K-Cl cotransporter 1 (NKCC1) promotes electroneutral uptake of two chloride ions, one sodium ion and one potassium ion. NKCC1 regulates Cl^- homeostasis, thus being implicated in transepithelial water transport and in neuronal excitability. Aberrant NKCC1 transport is linked to a variety of human diseases. The loop diuretic drugs bumetanide, furosemide, azosemide and ethacrynic acid target NKCC1, but are characterized by poor selectivity leading to severe side effects. Despite its therapeutic importance, the molecular details of the NKCC1 inhibition mechanism remain unclear. Using all-atom simulations, we predict a putative binding mode of these drugs to the zebrafish (z) and human (h) NKCC1 orthologs. Although differing in their specific interactions with NKCC1 and/or monovalent ions, all drugs can fit within the same cavity and engage in hydrophobic interactions with M304/M382 in z/hNKCC1, a proposed ion gating residue demonstrated to be key for bumetanide binding. Consistent with experimental evidence, all drugs take advantage of the K⁺/Na⁺ ions, which plastically respond to their binding. This study not only provides atomic-level insights useful for drug discovery campaigns of more selective/potent NKCC1 inhibitors aimed to tackle diseases related to deregulated Cl^- homeostasis, but it also supplies a paradigmatic example of the key importance of dynamical effects when drug binding is mediated by monovalent ions.

A Wholistic View of How Bumetanide Attenuates Autism Spectrum Disorders

The specific NKCC1 cotransporter antagonist, bumetanide, attenuates the severity of Autism Spectrum Disorders (ASD), and many neurodevelopmental or neurodegenerative disorders in animal models and clinical trials. However, the pervasive expression of NKCC1 in many cell types throughout the body is thought to challenge the therapeutic efficacy of bumetanide. However, many peripheral functions, including intestinal, metabolic, or vascular, etc., are perturbed in brain disorders contributing to the neurological sequels. Alterations of these functions also increase the incidence of the disorder suggesting complex bidirectional links with the clinical manifestations. We suggest that a more holistic view of ASD and other disorders is warranted to account for the multiple sites impacted by the original intra-uterine insult. From this perspective, large-spectrum active repositioned drugs that act centrally and peripherally might constitute a useful approach to treating these disorders.

Nanoformulated Bumetanide Ameliorates Social Deficiency in BTBR Mice Model of Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a prevalent neurodevelopmental disorder with few medication options. Bumetanide, an FDA-approved diuretic, has been proposed as a viable candidate to treat core symptoms of ASD, however, neither the brain region related to its effect nor the cell-specific mechanism(s) is clear. The availability of nanoparticles provides a viable way to identify pharmacological mechanisms for use in ASD. Here, we found that treatment with bumetanide, in a systemic and medial prefrontal cortex (mPFC) region-specific way, attenuated social deficits in BTBR mice. Furthermore, using poly (ethylene glycol)-poly(l-lactide) (PEG-PLA) nanoparticles [NP(bumetanide)], we showed that the administration of NP(bumetanide) in a mPFC region-specific way also alleviated the social deficits of BTBR mice. Mechanistically, the behavioral effect of NP(bumetanide) was dependent on selective microglia-specific targeting in the mPFC. Pharmacological depletion of microglia significantly reduced the effect of nanoencapsulation and depletion of microglia alone did not improve the social deficits in BTBR mice. These findings suggest the potential therapeutic capabilities of nanotechnology for ASD, as well as the relevant link between bumetanide and immune cells.

Beta-Amyloid (Aβ1-42) Increases the Expression of NKCC1 in the Mouse Hippocampus

Alzheimer’s disease (AD) is a neurodegenerative disorder with an increasing need for developing disease-modifying treatments as current therapies only provide marginal symptomatic relief. Recent evidence suggests the γ-aminobutyric acid (GABA) neurotransmitter system undergoes remodeling in AD, disrupting the excitatory/inhibitory (E/I) balance in the brain. Altered expression levels of K-Cl-2 (KCC2) and N-K-Cl-1 (NKCC1), which are cation–chloride cotransporters (CCCs), have been implicated in disrupting GABAergic activity by regulating GABA_A receptor signaling polarity in several neurological disorders, but these have not yet been explored in AD. NKCC1 and KCC2 regulate intracellular chloride [Cl⁻]_i by accumulating and extruding Cl⁻, respectively. Increased NKCC1 expression in mature neurons has been reported in these disease conditions, and bumetanide, an NKCC1 inhibitor, is suggested to show potential therapeutic benefits. This study used primary mouse hippocampal neurons to explore if KCC2 and NKCC1 expression levels are altered following beta-amyloid (Aβ_1-42) treatment and the potential neuroprotective effects of bumetanide. KCC2 and NKCC1 expression levels were also examined in 18-months-old male C57BL/6 mice following bilateral hippocampal Aβ_1-42 stereotaxic injection. No change in KCC2 and NKCC1 expression levels were observed in mouse hippocampal neurons treated with 1 nM Aβ_1-42, but NKCC1 expression increased 30-days post-Aβ_1-42-injection in the CA1 region of the mouse hippocampus. Primary mouse hippocampal cultures were treated with 1 nM Aβ_1-42 alone or with various concentrations of bumetanide (1 µM, 10 µM, 100 µM, 1 mM) to investigate the effect of the drug on cell viability. Aβ_1-42 produced 53.1 ± 1.4% cell death after 5 days, and the addition of bumetanide did not reduce this. However, the drug at all concentrations significantly reduced cell viability, suggesting bumetanide is highly neurotoxic. In summary, these results suggest that chronic exposure to Aβ_1-42 alters the balance of KCC2 and NKCC1 expression in a region-and layer-specific manner in mouse hippocampal tissue; therefore, this process most likely contributes to altered hippocampal E/I balance in this model. Furthermore, bumetanide induces hippocampal neurotoxicity, thus questioning its suitability for AD therapy. Further investigations are required to examine the effects of Aβ_1-42 on KCC2 and NKCC1 expression and whether targeting CCCs might offer a therapeutic approach for AD.

Bumetanide lowers acute hydrocephalus in a rat model of subarachnoid hemorrhage

BACKGROUND

Subarachnoid hemorrhage (SAH) can lead to acute hydrocephalus (AH). AH pathophysiology is classically attributed to an obstruction of the arachnoid granulations by blood. Recent findings in rodents suggest that after intraventricular hemorrhage, AH is related to cerebrospinal fluid (CSF) hypersecretion by the choroid plexus (CP), as it can be reduced by intracerebroventricular (ICV) injection of bumetanide.

OBJECTIVE

Here, we investigated if and how CSF hypersecretion and/or CSF outflow disorders contribute to post-SAH hydrocephalus.

METHODS

Ninety-four Wistar rats were used. SAH was induced by the endovascular perforation technique. The presence of AH was confirmed by magnetic resonance imaging (MRI), and rats with AH were randomly assigned to 4 groups: control group, superior sagittal sinus (SSS) thrombosis to block CSF reabsorption, ICV injection of saline, and ICV injection of bumetanide to decrease CSF secretion. Clinical outcome was evaluated with a neuroscore. A second MRI was performed 24 h later to evaluate the ventricular volume.

RESULTS

Fifty percent of rats that survived SAH induction had AH. Their ventricular volume correlated well to the functional outcome after 24 h (r = 0.803). In rats with AH, 24 h later, ventricular volume remained equally increased in the absence of any further procedure. Similarly, ICV injection of saline or SSS thrombosis had no impact on the ventricular volume. However, ICV injection of bumetanide reduced AH by 35.9% (p = 0.002).

CONCLUSION

In rodents, post-SAH hydrocephalus is may be due to hypersecretion of CSF by the CP, as it is limited by ICV injection of bumetanide. However, we cannot exclude other mechanisms involved in post-SAH acute hydrocephalus.

The GABA Polarity Shift and Bumetanide Treatment: Making Sense Requires Unbiased and Undogmatic Analysis

GABA depolarizes and often excites immature neurons in all animal species and brain structures investigated due to a developmentally regulated reduction in intracellular chloride concentration ([Cl-]i) levels. The control of [Cl-]i levels is mediated by the chloride cotransporters NKCC1 and KCC2, the former usually importing chloride and the latter exporting it. The GABA polarity shift has been extensively validated in several experimental conditions using often the NKCC1 chloride importer antagonist bumetanide. In spite of an intrinsic heterogeneity, this shift is abolished in many experimental conditions associated with developmental disorders including autism, Rett syndrome, fragile X syndrome, or maternal immune activation. Using bumetanide, an EMA- and FDA-approved agent, many clinical trials have shown promising results with the expected side effects. Kaila et al. have repeatedly challenged these experimental and clinical observations. Here, we reply to the recent reviews by Kaila et al. stressing that the GABA polarity shift is solidly accepted by the scientific community as a major discovery to understand brain development and that bumetanide has shown promising effects in clinical trials.

The NKCC1 ion transporter modulates microglial phenotype and inflammatory response to brain injury in a cell-autonomous manner

The NKCC1 ion transporter contributes to the pathophysiology of common neurological disorders, but its function in microglia, the main inflammatory cells of the brain, has remained unclear to date. Therefore, we generated a novel transgenic mouse line in which microglial NKCC1 was deleted. We show that microglial NKCC1 shapes both baseline and reactive microglia morphology, process recruitment to the site of injury, and adaptation to changes in cellular volume in a cell-autonomous manner via regulating membrane conductance. In addition, microglial NKCC1 deficiency results in NLRP3 inflammasome priming and increased production of interleukin-1β (IL-1β), rendering microglia prone to exaggerated inflammatory responses. In line with this, central (intracortical) administration of the NKCC1 blocker, bumetanide, potentiated intracortical lipopolysaccharide (LPS)-induced cytokine levels. In contrast, systemic bumetanide application decreased inflammation in the brain. Microglial NKCC1 KO animals exposed to experimental stroke showed significantly increased brain injury, inflammation, cerebral edema and worse neurological outcome. Thus, NKCC1 emerges as an important player in controlling microglial ion homeostasis and inflammatory responses through which microglia modulate brain injury. The contribution of microglia to central NKCC1 actions is likely to be relevant for common neurological disorders.

Hippocampal chloride transporter KCC2 contributes to excitatory GABA dysregulation in the developmental rat model of schizophrenia

Recent studies have revealed an altered expression of NKCC1 and KCC2 in prefrontal cortex (PFC) and hippocampus of schizophrenic patients. Despite extensive considerations, the alteration of NKCC1 and KCC2 co-transporters at different stages of development has not been fully studied. Therefore, we evaluated the expression of these transporters in PFC and hippocampus at time points of four, eight, and twelve weeks in post-weaning social isolation rearing rat model. For this purpose, 23-25 days-old rats were classified into social- or isolation-reared groups. The levels of NKCC1 and KCC2 mRNA expression were evaluated at hippocampus or PFC regions at the time-points of four, eight, and twelve weeks following housing. Post-weaning isolation rearing decreased the hippocampal KCC2 mRNA expression level, but does not affect the NKCC1 mRNA expression. However, no significant difference was observed in the PFC mRNA levels of NKCC1 and KCC2 in the isolation-reared group compared to the socially-reared group during the course of modeling. Further, we assessed the therapeutic effect of selective NKCC1 inhibitor bumetanide (10 mg/kg), on improvement of prepulse inhibition (PPI) test on twelve weeks isolation-reared rats. Intraperitoneal administration of bumetanide (10 mg/kg) did not exert beneficial effects on PPI deficit. Our findings show that isolation rearing reduces hippocampal KCC2 expression level and may underlie hippocampal GABA excitatory. In addition, 10 mg/kg bumetanide is not effective in improving the reduced PPI of twelve weeks isolation-reared rats. Collectively, our findings show that hippocampal chloride transporter KCC2 contributes to excitatory GABA dysregulation in the developmental rat model of schizophrenia.

Bumetanide prevents diazepam-modified anxiety-like behavior in lipopolysaccharide-treated mice

Benzodiazepine receptor agonists are widely prescribed therapeutic agents that alter gamma-aminobutyric acid (GABA)A receptor activity and have anxiolytic effects. Post-operative use of benzodiazepines is a risk factor of delirium. Inflammatory conditions alter the anxiolytic effects of benzodiazepine. We investigated the effect of diazepam, a typical benzodiazepine anxiolytic, on changes in the emotional behavior of mice in a hole-board test after lipopolysaccharide (LPS) treatment. Diazepam dose-dependently increased the number of head-dips at doses that did not alter locomotor activity; however, diazepam dose-dependently significantly decreased the number of head-dips at doses that did not alter locomotor activity in LPS-treated mice. Flumazenil, a benzodiazepine receptor antagonist, normalized the decrease in head-dipping behavior caused by diazepam treatment in normal and LPS-treated mice. The decrease of the head-dipping effect caused by diazepam was attenuated by minocycline in LPS-treated mice. We further found that the decrease in head-dipping behavior caused by diazepam was blocked by bumetanide, a Na+-K+-2Cl- cotransporter isoform 1 (NKCC1) antagonist, in LPS-treated mice. These findings suggest that diazepam induces the anxiety-like behavior under inflammation conditions, and may cause the GABAA receptor dysfunction associated with the chloride plasticity mediated by NKCC1, which contributes to benzodiazepine-induced delirium after surgery.

Depolarizing GABAA current in the prefrontal cortex is linked with cognitive impairment in a mouse model relevant for schizophrenia

Cognitive impairment in schizophrenia (CIAS) is the most critical predictor of functional outcome. Limited understanding of the cellular mechanisms of CIAS hampers development of more effective treatments. We found that in subchronic phencyclidine (scPCP)-treated mice, an animal model that mimics CIAS, the reversal potential of GABAA currents in pyramidal neurons of the infralimbic prefrontal cortex (ILC) shifts from hyperpolarizing to depolarizing, the result of increased expression of the chloride transporter NKCC1. Further, we found that in scPCP mice, the NKCC1 antagonist bumetanide normalizes GABAA current polarity ex vivo and improves performance in multiple cognitive tasks in vivo. This behavioral effect was mimicked by selective, bilateral, NKCC1 knockdown in the ILC. Thus, we show that depolarizing GABAA currents in the ILC contributes to cognitive impairments in scPCP mice and suggest that bumetanide, an FDA-approved drug, has potential to treat or prevent CIAS and other components of the schizophrenia syndrome.

Effect of Bumetanide on Facial Nerve Regeneration in Rat Model

OBJECTIVE

We investigated the effects of bumetanide alone and in combination with dexamethasone on facial nerve regeneration in rats with facial paralysis.

STUDY DESIGN

A prospective controlled animal study.

SETTING

An animal laboratory.

SUBJECTS AND METHODS

Facial paralysis was induced in 32 Wistar rats that we then divided into 4 groups: group 1, control; group 2, bumetanide; group 3, dexamethasone; group 4, bumetanide and dexamethasone. Electroneurography was performed 1, 2, and 4 weeks later, and nerve regeneration was evaluated by electron and light microscopy and Western blotting in week 4.

RESULTS

Regarding the comparison between preoperative values and week 4, the latency difference in group 1 (1.25 milliseconds) was significantly higher than those of groups 2 to 4 (0.56, 0.34, and 0.10 milliseconds, respectively; P = .001). The latency increment in groups 2 and 3 was higher than that of group 4 (P = .002 and P = .046) in week 4, whereas groups 2 and 3 did not differ significantly (P = .291). Amplitude difference was not statistically significant from week 4 among all groups (all P > .05). The number of myelinated axons was significantly higher in all treatment groups than in the control group (P = .001). Axon number and intensity were significantly higher in group 4 as compared with groups 2 and 3 (P = .009, P = .005).

CONCLUSION

After primary neurorrhaphy, dexamethasone and bumetanide alone promoted nerve recovery based on electrophysiologic and histologic measures. Combination therapy was, however, superior.

Acute Hyperglycemia Aggravates Lung Injury via Activation of the SGK1-NKCC1 Pathway

Acute lung injury (ALI) is characterized by severe hypoxemia and has significantly high mortality rates. Acute hyperglycemia occurs in patients with conditions such as sepsis or trauma, among others, and it results in aggravated inflammation and induces damage in patients with ALI. Regulation of alveolar fluid is essential for the development and resolution of pulmonary edema in lung injury. Pulmonary sodium-potassium-chloride co-transporter 1 (NKCC1) regulates the net influx of ions and water into alveolar cells. The activation of with-no-lysine kinase 4 (WNK4), STE20/SPS1-related proline/alanine rich kinase (SPAK) and the NKCC1 pathway lead to an increase in the expression of NKCC1 and aggravation of ALI. Moreover, hyperglycemia is known to induce NKCC1 expression via the activation of the serum-glucocorticoid kinase 1 (SGK1)-NKCC1 pathway. We aim to evaluate the influence of acute hyperglycemia on the SGK1-NKCC1 pathway in ALI. ALI was induced using a high tidal volume for four hours in a rat model. Acute hyperglycemia was induced by injection with 0.5 mL of 40% glucose solution followed by continuous infusion at 2 mL/h. The animals were divided into sham, sham+ hyperglycemia, ALI, ALI + hyperglycemia, ALI + inhaled bumetanide (NKCC1 inhibitor) pretreatment, ALI + hyperglycemia + inhalational bumetanide pretreatment, and ALI + hyperglycemia + post-ALI inhalational bumetanide groups. Severe lung injury along with pulmonary edema, alveolar protein leakage, and lung inflammation was observed in ALI with hyperglycemia than in ALI without hyperglycemia. This was concurrent with the higher expression of pro-inflammatory cytokines, infiltration of neutrophils and alveolar macrophages (AM) 1, and NKCC1 expression. Inhalational NKCC1 inhibitor significantly inhibited the SGK1-NKCC1, and WNK4-SPAK-NKCC1 pathways. Additionally, it reduced pulmonary edema, inflammation, levels of pro-inflammatory cytokines, neutrophils and AM1 and increased AM2. Therefore, acute hyperglycemia aggravates lung injury via the further activation of the SGK1-NKCC1 pathway. The NKCC1 inhibitor can effectively attenuate lung injury aggravated by acute hyperglycemia.

Design, synthesis, and pharmacological evaluation of novel and selective COX-2 inhibitors based on bumetanide scaffold

Herein, we describe the design and synthesis of new benzenesulfonamide derivatives as selective COX-2 inhibitors based on bumetanide scaffold. Benzenesulfonamides bearing both the pyrazole 6b and the triazoles 9a, 9c were good inhibitors of COX-2 with IC50 values of 0.32, 0.28 and 0.17 µM, respectively. These benzenesulfonamides 6b, 9a and 9c exhibited a higher selectivity index than the reference drug celecoxib. Molecular modeling study showed that incorporation of bumetanide led to a unique binding mode that is most likely the reason for the observed significant COX-2 selectivity. The anti-inflammatory activity of synthesized compounds revealed that triazoles 9a and 9c demonstrated higher efficacy than celecoxib upon using in vivo carrageenan-induced rat paw edema model. Most of the prepared compounds possess low ulcerogenic potential when administered orally. Therefore, these compounds have a great potential to be developed as safe therapeutics for inflammation, pain, and other diseases where COX-2 plays important role in their pathophysiology.

CATION-CHLORIDE CO-TRANSPORTER 1 (CCC1) Mediates Plant Resistance against Pseudomonas syringae

Plasma membrane (PM) depolarization functions as an initial step in plant defense signaling pathways. However, only a few ion channels/transporters have been characterized in the context of plant immunity. Here, we show that the Arabidopsis (Arabidopsis thaliana) Na+:K+:2Cl- (NKCC) cotransporter CCC1 has a dual function in plant immunity. CCC1 functions independently of PM depolarization and negatively regulates pathogen-associated molecular pattern-triggered immunity. However, CCC1 positively regulates plant basal and effector-triggered resistance to Pseudomonas syringae pv. tomato (Pst) DC3000. In line with the compromised immunity to Pst DC3000, ccc1 mutants show reduced expression of genes encoding enzymes involved in the biosynthesis of antimicrobial peptides, camalexin, and 4-OH-ICN, as well as pathogenesis-related proteins. Moreover, genes involved in cell wall and cuticle biosynthesis are constitutively down-regulated in ccc1 mutants, and the cell walls of these mutants exhibit major changes in monosaccharide composition. The role of CCC1 ion transporter activity in the regulation of plant immunity is corroborated by experiments using the specific NKCC inhibitor bumetanide. These results reveal a function for ion transporters in immunity-related cell wall fortification and antimicrobial biosynthesis.

Functional characterization of novel bumetanide derivatives for epilepsy treatment

Temporal lobe epilepsy (TLE) is the most common type of focal epilepsies, affecting approximately 35 million people worldwide. Despite the introduction of numerous novel antiepileptic drugs during the last decades, the proportion of patients with therapy-resistant TLE is still high. As an impaired cellular chloride homeostasis appears involved in disease pathophysiology, bumetanide, an antagonist to Na-K-Cl cotransporters, gained interest as potential therapeutic option. However, bumetanide induces a strong diuretic effect and displays poor penetration across the blood-brain barrier (BBB). To reduce these unwanted effects, we modified the already described BUM690 by exchanging the allyl-into a trifluoro-ethyl group to yield BUM532. Furthermore, we exchanged the nitrogen for oxygen in the trifluoro-ethyl group to yield BUM97. In the intrahippocampal kainic acid mouse model of TLE BUM532 ± phenobarbital (PB), bumetanide ± PB and PB alone significantly reduced hippocampal paroxysmal discharges (HPDs) but not spike trains. By contrast, treatment with BUM97 suppressed HPDs as well as spike trains dose-dependently, more pronounced compared to the other tested compounds and exerted a synergistic anticonvulsant effect with PB. Moreover, at higher doses BUM97 achieved long-lasting reduction of spike trains. In pentylenetetrazole-induced acute seizures only BUM532 combined with a sub-effective dose of PB increased the seizure threshold. No diuretic effects were observed at any dose of the three derivatives. Our data demonstrate the successful optimization of the pharmacological profile of bumetanide and the potential of the improved derivative BUM97 for the treatment of therapy-resistant TLE, in particular in combinatorial drug regimens with a GABA mimetic.

Bumetanide-Derived Aquaporin 1 Inhibitors, AqB013 and AqB050 Inhibit Tube Formation of Endothelial Cells through Induction of Apoptosis and Impaired Migration In Vitro

AqB013 and AqB050 compounds inhibit aquaporin 1 (AQP1), a dual water and ion channel implicated in tumour angiogenesis. We tested AqB013 and AqB050 either as monotherapy or in combination on tube formation of murine endothelial cells (2H-11 and 3B-11) and human umbilical vascular endothelial cells (HUVECs). The mechanism underlying their anti-tubulogenic effect was explored by examining cell viability, induction of apoptosis and migration using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay, Annexin V/propidium iodide apoptosis assay and scratch wound assay. Tube formation of all the cell lines was inhibited by AqB013, AqB050 and the combination of the two compounds. The inhibition of 2H-11 and 3B-11 was frequently accompanied by impaired migration, whereas that of HUVEC treated with AqB050 and the combination was associated with reduced cell viability due to apoptosis. AqB013 and AqB050 exhibited an anti-tubulogenic effect through inhibition of AQP1-mediated cell migration and induction of apoptosis. Together with previously reported anti-tumour cell effect of AqB013 and AqB050, our findings support further evaluation of these compounds as potential cancer therapeutics.

Genetic and pharmacological inactivation of apical Na+-K+-2Cl- cotransporter 1 in choroid plexus epithelial cells reveals the physiological function of the cotransporter

Choroid plexus epithelial cells (CPECs) secrete cerebrospinal fluid (CSF). They express Na+-K+-ATPase and Na+-K+-2Cl- cotransporter 1 (NKCC1) on their apical membrane, deviating from typical basolateral membrane location in secretory epithelia. Given this peculiarity, the direction of basal net ion fluxes mediated by NKCC1 in CPECs is controversial, and cotransporter function is unclear. Determining the direction of basal NKCC1-mediated fluxes is critical to understanding the function of apical NKCC1. If NKCC1 works in the net efflux mode, it may be directly involved in CSF secretion. Conversely, if NKCC1 works in the net influx mode, it would have an absorptive function, contributing to intracellular Cl- concentration ([Cl-]i) and cell water volume (CWV) maintenance needed for CSF secretion. We resolve this long-standing debate by electron microscopy (EM), live-cell-imaging microscopy (LCIM), and intracellular Na+ and Cl- measurements in single CPECs of NKCC1+/+ and NKCC1-/- mouse. NKCC1-mediated ion and associated water fluxes are tightly linked, thus their direction is inferred by measuring CWV changes. Genetic or pharmacological NKCC1 inactivation produces CPEC shrinkage. EM of NKCC1-/- CPECs in situ shows they are shrunken, forming large dilations of their basolateral extracellular spaces, yet remaining attached by tight junctions. Normarski LCIM shows in vitro CPECs from NKCC1-/- are ~17% smaller than NKCC1+/+. CWV measurements in calcein-loaded CPECs show that bumetanide (10 μM) produces ~16% decrease in CWV in NKCC1+/+ but not in NKCC1-/- CPECs. Our findings suggest that under basal conditions apical NKCC1 is continuously active and works in the net inward flux mode maintaining [Cl-]i and CWV needed for CSF secretion.

Elevation of extracellular osmolarity improves signs of myotonia congenita in vitro: a preclinical animal study

KEY POINTS

During myotonia congenita, reduced chloride (Cl- ) conductance results in impaired muscle relaxation and increased muscle stiffness after forceful voluntary contraction. Repetitive contraction of myotonic muscle decreases or even abolishes myotonic muscle stiffness, a phenomenon called 'warm up'. Pharmacological inhibition of low Cl- channels by anthracene-9-carboxylic acid in muscle from mice and ADR ('arrested development of righting response') muscle from mice showed a relaxation deficit under physiological conditions compared to wild-type muscle. At increased osmolarity up to 400 mosmol L-1 , the relaxation deficit of myotonic muscle almost reached that of control muscle. These effects were mediated by the cation and anion cotransporter, NKCC1, and anti-myotonic effects of hypertonicity were at least partly antagonized by the application of bumetanide.

ABSTRACT

Low chloride-conductance myotonia is caused by mutations in the skeletal muscle chloride (Cl- ) channel gene type 1 (CLCN1). Reduced Cl- conductance of the mutated channels results in impaired muscle relaxation and increased muscle stiffness after forceful voluntary contraction. Exercise decreases muscle stiffness, a phenomena called 'warm up'. To gain further insight into the patho-mechanism of impaired muscle stiffness and the warm-up phenomenon, we characterized the effects of increased osmolarity on myotonic function. Functional force and membrane potential measurements were performed on muscle specimens of ADR ('arrested development of righting response') mice (an animal model for low gCl- conductance myotonia) and pharmacologically-induced myotonia. Specimens were exposed to solutions of increasing osmolarity at the same time as force and membrane potentials were monitored. In the second set of experiments, ADR muscle and pharmacologically-induced myotonic muscle were exposed to an antagonist of NKCC1. Upon osmotic stress, ADR muscle was depolarized to a lesser extent than control wild-type muscle. High osmolarity diminished myotonia and facilitated the warm-up phenomenon as depicted by a faster muscle relaxation time (T90/10 ). Osmotic stress primarily resulted in the activation of the NKCC1. The inhibition of NKCC1 with bumetanide prevented the depolarization and reversed the anti-myotonic effect of high osmolarity. Increased osmolarity decreased signs of myotonia and facilitated the warm-up phenomenon in different in vitro models of myotonia. Activation of NKCC1 activity promotes warm-up and reduces the number of contractions required to achieve normal relaxation kinetics.

In Vivo Study on Mechanism Underlying Increased Pharmacological Effects of Phenobarbital in Rats with Glycerol-Induced Acute Renal Failure

The mechanism underlying the increased pharmacological effects of phenobarbital in rats with glycerol-induced acute renal failure (ARF) was examined. In the experiments, a surgical cannula was inserted in the lateral ventricle of the rats for phenobarbital infusion, and the ARF induction was performed by intramuscular administration of 50% glycerol. The onset time of anesthesia by phenobarbital was determined with the tail flick method. In addition, cerebral microsomes were prepared from excised cerebral cortices of sham and ARF rats, and the cerebral expression of the γ-aminobutyric acid (GABA)A receptor and two cation-chloride transporters, KCC2 and NKCC1, was evaluated by Western blotting, as their functions are involved in the anesthetic effects of phenobarbital. When phenobarbital was infused in the ventricle, anesthesia was induced 2.2-times faster in ARF rats than in sham rats, and there was no detectable increase in the cerebral expression of the GABAA receptor in ARF rats. It was additionally noted that the cerebral expression of KCC2 decreased, whereas that of NKCC1 was unaltered in ARF rats. These findings indicated that the anesthetic effects of phenobarbital are potentiated in ARF rats, probably due to imbalanced cerebral expression of KCC2 and NKCC1, suggesting that altered cation-chloride handling in nerve cells is associated.

Daidzein-Stimulated Increase in the Ciliary Beating Amplitude via an [Cl-]i Decrease in Ciliated Human Nasal Epithelial Cells

The effects of the isoflavone daidzein on the ciliary beat distance (CBD, which is a parameter assessing the amplitude of ciliary beating) and the ciliary beat frequency (CBF) were examined in ciliated human nasal epithelial cells (cHNECs) in primary culture. Daidzein decreased [Cl⁻]_i and enhanced CBD in cHNECs. The CBD increase that was stimulated by daidzein was mimicked by Cl⁻-free NO₃⁻ solution and bumetanide (an inhibitor of Na⁺/K⁺/2Cl⁻ cotransport), both of which decreased [Cl⁻]_i. Moreover, the CBD increase was inhibited by 5-Nitro-2-(3-phenylpropylamino)benzoic acid (NPPB, a Cl⁻ channel blocker), which increased [Cl⁻]_i. CBF was also decreased by NPPB. The rate of [Cl⁻]_i decrease evoked by Cl⁻-free NO₃⁻ solution was enhanced by daidzein. These results suggest that daidzein activates Cl⁻ channels in cHNECs. Moreover, daidzein enhanced the microbead transport driven by beating cilia in the cell sheet of cHNECs, suggesting that an increase in CBD enhances ciliary transport. An [Cl⁻]_i decrease enhanced CBD, but not CBF, in cHNECs at 37 °C, although it enhanced both at 25 °C. Intracellular Cl⁻ affects both CBD and CBF in a temperature-dependent manner. In conclusion, daidzein, which activates Cl⁻ channels to decrease [Cl⁻]_i, stimulated CBD increase in cHNECs at 37 °C. CBD is a crucial factor that can increase ciliary transport in the airways under physiological conditions.

Involvement of butyrate in electrogenic K+ secretion in rat rectal colon

Short-chain fatty acids (SCFAs), such as acetate, propionate, and butyrate, are synthesized from dietary carbohydrates by colonic bacterial fermentation. These SCFAs supply energy, suppress cancer, and affect ion transport. However, their roles in ion transport and regulation in the intracellular environment remain unknown. In order to elucidate the roles of SCFAs, we measured short-circuit currents (I_SC) and performed RT-PCR and immunohistochemical analyses of ion transporters in rat rectal colon. The application of 30 mM butyrate shifted I_SC in a negative direction, but did not attenuate the activity of epithelial Na⁺ channels (ENaC). The application of bumetanide, a Na⁺-K⁺-2Cl⁻ cotransporter inhibitor, to the basolateral side reduced the negative I_SC shift induced by butyrate. The application of XE991, a KCNQ-type K⁺ channel inhibitor, to the apical side decreased the I_SC shift induced by butyrate in a dose-dependent manner. The I_SC shift was independent of HCO₃⁻ and insensitive to ibuprofen, an SMCT1 inhibitor. The mucosa from rat rectal colon expressed mRNAs of H⁺-coupled monocarboxylate transporters (MCT1, MCT4, and MCT5, also referred to as SLC16A1, SLC16A3, and SLC16A4, respectively). RT-PCR and immunofluorescence analyses demonstrated that KCNQ2 and KCNQ4 localized to the apical membrane of surface cells in rat rectal colon. These results indicate that butyrate, which may be transported by H⁺-coupled monocarboxylate transporters, activates K⁺ secretion through KCNQ-type K⁺ channels on the apical membrane in rat rectal colon. KCNQ-type K⁺ channels may play a role in intestinal secretion and defense mechanisms in the gastrointestinal tract.

The immediate influence of deltamethrin on ion transport through rabbit skin. An in vitro study

Deltamethrin can be absorbed into the respiratory tract, the gastrointestinal tract and through the skin. The study was designed to assess the effect of deltamethrin on electrophysiological parameters of rabbit's skin, studied in vitro, to identify the mechanism of action and effects of short-term dermal exposure to deltamethrin. The objective of the study was to investigate changes in electrophysiological parameters after exposure to 0.01 M deltamethrin under unchanged conditions, in the presence of amiloride (sodium transport blocker) and bumetanide (chloride transport blocker). Exposure to deltamethrin reduced the electrophysiological reaction of examined tissue in unchanged conditions and during the sodium reabsorption phase but did not influence the chloride ion secretion phase. The presented data show that the pyrethroide affects transepithelial ion transport in the external layers of the skin. The inhibition of chloride and sodium ions enabled evaluation of the impact of the pesticide on dermal transport.

Bumetanide blocks the acquisition of conditioned fear in adult rats

BACKGROUND AND PURPOSE

Bumetanide has anxiolytic effects in rat models of conditioned fear. As a loop diuretic, bumetanide blocks cation-chloride co-transport and this property may allow bumetanide to act as an anxiolytic by modulating GABAergic synaptic transmission in the CNS. Its potential for the treatment of anxiety disorders deserves further investigation. In this study, we evaluated the possible involvement of the basolateral nucleus of the amygdala in the anxiolytic effect of bumetanide.

EXPERIMENTAL APPROACH

Brain slices were prepared from Wistar rats. extracellular recording, stereotaxic surgery, fear-potentiated startle response, locomotor activity monitoring and Western blotting were applied in this study.

KEY RESULTS

Systemic administration of bumetanide (15.2 mg·kg-1 , i.v.), 30 min prior to fear conditioning, significantly inhibited the acquisition of the fear-potentiated startle response. Phosphorylation of ERK in the basolateral nucleus of amygdala was reduced after bumetanide administration. In addition, suprafusion of bumetanide (5 or 10 μM) attenuated long-term potentiation in the amygdala in a dose-dependent manner. Intra-amygdala infusion of bumetanide, 15 min prior to fear conditioning, also blocked the acquisition of the fear-potentiated startle response. Finally, the possible off-target effect of bumetanide on conditioned fear was excluded by side-by-side control experiments.

CONCLUSIONS AND IMPLICATIONS

These results suggest the basolateral nucleus of amygdala plays a critical role in the anxiolytic effects of bumetanide.

Why do SGLT2 inhibitors reduce heart failure hospitalization? A differential volume regulation hypothesis

The effect of a sodium glucose cotransporter 2 inhibitor (SGLT2i) in reducing heart failure hospitalization in the EMPA-REG OUTCOMES trial has raised the possibility of using these agents to treat established heart failure. We hypothesize that osmotic diuresis induced by SGLT2 inhibition, a distinctly different diuretic mechanism than that of other diuretic classes, results in greater electrolyte-free water clearance and, ultimately, in greater fluid clearance from the interstitial fluid (IF) space than from the circulation, potentially resulting in congestion relief with minimal impact on blood volume, arterial filling and organ perfusion. We utilize a mathematical model to illustrate that electrolyte-free water clearance results in a greater reduction in IF volume compared to blood volume, and that this difference may be mediated by peripheral sequestration of osmotically inactive sodium. By coupling the model with data on plasma and urinary sodium and water in healthy subjects who received either the SGLT2i dapagliflozin or loop diuretic bumetanide, we predict that dapagliflozin produces a 2-fold greater reduction in IF volume compared to blood volume, while the reduction in IF volume with bumetanide is only 78% of the reduction in blood volume. Heart failure is characterized by excess fluid accumulation, in both the vascular compartment and interstitial space, yet many heart failure patients have arterial underfilling because of low cardiac output, which may be aggravated by conventional diuretic treatment. Thus, we hypothesize that, by reducing IF volume to a greater extent than blood volume, SGLT2 inhibitors might provide better control of congestion without reducing arterial filling and perfusion.

Bumetanide treatment during early development rescues maternal separation-induced susceptibility to stress

Stress is a major risk factor for psychiatric disorders, such as depression, posttraumatic stress disorder, and schizophrenia. Early life stress, such as maternal separation, can have long-term effects on the development of the central nervous system and pathogenesis of psychiatric disorders. In the present study, we found that maternal separation increased the susceptibility to stress in adolescent rats, increased the expression of Na+/K+/2Cl- cotransporter 1 (NKCC1) on postnatal day 14, and increased the expression of K+/2Cl- cotransporter 2 (KCC2) and γ-aminobutyric acid A (GABAA) receptor subunits on postnatal day 40 in the hippocampus. NKCC1 inhibition by the U.S. Food and Drug Administration-approved drug bumetanide during the first two postnatal weeks rescued the depressive- and anxiety-like behavior that was induced by maternal separation and decreased the expression of NKCC1, KCC2 and GABAA receptor α1 and β2,3 subunits in the hippocampus. Bumetanide treatment during early development did not adversely affect body weight or normal behaviors in naive rats, or affect serum osmolality in adult rats. These results suggest that bumetanide treatment during early development may prevent the maternal separation-induced susceptibility to stress and impairments in GABAergic transmission in the hippocampus.

Intracellular Chloride Regulation in AVP+ and VIP+ Neurons of the Suprachiasmatic Nucleus

Several reports have described excitatory GABA transmission in the suprachiasmatic nucleus (SCN), the master pacemaker of circadian physiology. However, there is disagreement regarding the prevalence, timing, and neuronal location of excitatory GABA transmission in the SCN. Whether GABA is inhibitory or excitatory depends, in part, on the intracellular concentration of chloride ([Cl-]i). Here, using ratiometric Cl- imaging, we have investigated intracellular chloride regulation in AVP and VIP-expressing SCN neurons and found evidence suggesting that [Cl-]i is higher during the day than during the night in both AVP+ and VIP+ neurons. We then investigated the contribution of the cation chloride cotransporters to setting [Cl-]i in these SCN neurons and found that the chloride uptake transporter NKCC1 contributes to [Cl-]i regulation in SCN neurons, but that the KCCs are the primary regulators of [Cl-]i in SCN neurons. Interestingly, we observed that [Cl-]i is differentially regulated between AVP+ and VIP+ neurons-a low concentration of the loop diuretic bumetanide had differential effects on AVP+ and VIP+ neurons, while blocking the KCCs with VU0240551 had a larger effect on VIP+ neurons compared to AVP+ neurons.

Inflammation-dependent cerebrospinal fluid hypersecretion by the choroid plexus epithelium in posthemorrhagic hydrocephalus

The choroid plexus epithelium (CPE) secretes higher volumes of fluid (cerebrospinal fluid, CSF) than any other epithelium and simultaneously functions as the blood-CSF barrier to gate immune cell entry into the central nervous system. Posthemorrhagic hydrocephalus (PHH), an expansion of the cerebral ventricles due to CSF accumulation following intraventricular hemorrhage (IVH), is a common disease usually treated by suboptimal CSF shunting techniques. PHH is classically attributed to primary impairments in CSF reabsorption, but little experimental evidence supports this concept. In contrast, the potential contribution of CSF secretion to PHH has received little attention. In a rat model of PHH, we demonstrate that IVH causes a Toll-like receptor 4 (TLR4)- and NF-κB-dependent inflammatory response in the CPE that is associated with a ∼3-fold increase in bumetanide-sensitive CSF secretion. IVH-induced hypersecretion of CSF is mediated by TLR4-dependent activation of the Ste20-type stress kinase SPAK, which binds, phosphorylates, and stimulates the NKCC1 co-transporter at the CPE apical membrane. Genetic depletion of TLR4 or SPAK normalizes hyperactive CSF secretion rates and reduces PHH symptoms, as does treatment with drugs that antagonize TLR4-NF-κB signaling or the SPAK-NKCC1 co-transporter complex. These data uncover a previously unrecognized contribution of CSF hypersecretion to the pathogenesis of PHH, demonstrate a new role for TLRs in regulation of the internal brain milieu, and identify a kinase-regulated mechanism of CSF secretion that could be targeted by repurposed US Food and Drug Administration (FDA)-approved drugs to treat hydrocephalus.

Role of environmental stressors in determining the developmental outcome of neonatal anesthesia

BACKGROUND

The majority of studies evaluating neurocognition in humans who had procedures under anesthesia early in life found long-term deficits even though the typical anesthesia duration normalized to the human life span is much shorter than that shown to induce developmental abnormalities in rodents. Therefore, we studied whether subsequent environmental stressors contribute to deficiencies programmed by a brief neonatal etomidate exposure.

METHODS

Postnatal days (P) 4, 5, or 6, Sprague-Dawley rats, pretreated with vehicle or the Na+-K+-2Cl- (NKCC1) inhibitor, bumetanide, received two injections of etomidate resulting in anesthesia for 2h. To simulate stress after anesthesia, the animals were exposed to a single maternal separation for 3h at P10. 3-7days after exposure to etomidate the rats had increased hypothalamic NKCC1 mRNA and corticotropin releasing hormone (CRH) mRNA and decreased K+-2Cl- (KCC2) mRNA levels with greater changes in males. In rats neonatally exposed to both etomidate and maternal separation, these abnormalities persisted into adulthood. These animals also exhibited extended corticosterone responses to restraint stress with increases in total plasma corticosterone more robust in males, as well as behavioral abnormalities. Pretreatment with the NKCC1 inhibitor ameliorated most of these effects.

CONCLUSIONS

Post-anesthesia stressors may exacerbate/unmask neurodevelopmental abnormalities even after a relatively short anesthetic with etomidate, leading to dysregulated stress response systems and neurobehavioral deficiencies in adulthood. Amelioration by bumetanide suggests a mechanistic role for etomidate-enhanced gamma-aminobutyric acid type A receptor-mediated depolarization in initiating long-lasting alterations in gene expression that are further potentiated by subsequent maternal separation.

The chloride co-transporters, NKCC1 and KCC2, in experimental autoimmune encephalomyelitis (EAE)

Patients with multiple sclerosis (MS) often complain of neuropathic pain. According to the Gate Control Theory of Pain, spinal networks of GABAergic inhibitory interneurons are important in modulating nociceptive inputs from the periphery. Na+-K+-2Cl- co-transporter 1 (NKCC1) and K+-Cl- co-transporter 2 (KCC2) generally dictate the tone of GABA/glycine inhibition by regulating intracellular chloride concentrations. In this study, we investigated the role of NKCC1 and KCC2 in neuropathic pain observed in the animal model, experimental autoimmune encephalomyelitis (EAE), a commonly used model to study the pathophysiology of MS. Quantitative real-time polymerase chain reactions (qRT-PCR) analysis revealed no change in NKCC1 mRNA transcripts in dorsal root ganglia throughout EAE disease course. However, NKCC1 and KCC2 mRNA levels in the dorsal spinal cord were significantly reduced at disease onset and peak only to recover by the chronic time point. Similarly, Western blot data revealed a significant downregulation of NKCC1 and KCC2 in the dorsal spinal cord at disease onset but an upregulation of NKCC1 protein in the dorsal root ganglia at this time point. Treatment with bumetanide, an NKCC inhibitor, had no effect on mechanical hypersensitivity seen in mice with EAE even though it reversed the changes in the levels of NKCC1 and KCC2. We noted that bumetanide treatment, while effective at reversing the changes in monomeric KCC2 levels was ineffective at reversing the changes in oligomeric KCC2 which remained repressed. These results indicate that mechanical hypersensitivity in EAE is not mediated by altered levels of NKCC1.

Depolarizing γ-aminobutyric acid contributes to glutamatergic network rewiring in epilepsy

OBJECTIVE

Rewiring of excitatory glutamatergic neuronal circuits is a major abnormality in epilepsy. Besides the rewiring of excitatory circuits, an abnormal depolarizing γ-aminobutyric acidergic (GABAergic) drive has been hypothesized to participate in the epileptogenic processes. However, a remaining clinically relevant question is whether early post-status epilepticus (SE) evoked chloride dysregulation is important for the remodeling of aberrant glutamatergic neuronal circuits.

METHODS

Osmotic minipumps were used to infuse intracerebrally a specific inhibitor of depolarizing GABAergic transmission as well as a functionally blocking antibody toward the pan-neurotrophin receptor p75 (p75NTR ). The compounds were infused between 2 and 5 days after pilocarpine-induced SE. Immunohistochemistry for NKCC1, KCC2, and ectopic recurrent mossy fiber (rMF) sprouting as well as telemetric electroencephalographic and electrophysiological recordings were performed at day 5 and 2 months post-SE.

RESULTS

Blockade of NKCC1 after SE with the specific inhibitor bumetanide restored NKCC1 and KCC2 expression, normalized chloride homeostasis, and significantly reduced the glutamatergic rMF sprouting within the dentate gyrus. This mechanism partially involves p75NTR signaling, as bumetanide application reduced SE-induced p75NTR expression and functional blockade of p75NTR decreased rMF sprouting. The early transient (3 days) post-SE infusion of bumetanide reduced rMF sprouting and recurrent seizures in the chronic epileptic phase.

INTERPRETATION

Our findings show that early post-SE abnormal depolarizing GABA and p75NTR signaling fosters a long-lasting rearrangement of glutamatergic network that contributes to the epileptogenic process. This finding defines promising and novel targets to constrain reactive glutamatergic network rewiring in adult epilepsy. Ann Neurol 2017;81:251-265.

Long-term alcohol exposure elicits hippocampal nonsynaptic epileptiform activity changes associated with expression and functional changes in NKCC1, KCC2 co-transporters and Na+/K+-ATPase

Nonsynaptic mechanism changes, particularly the enhancement of NKCC1 expression in the dentate gyrus (DG) after 4weeks of ethanol consumption, motivate the present work, in which rats were submitted to a period of chronic consumption (12weeks). Four groups of six animals (6-week-old male Wistar rats) were formed, including the control (C), ethanol 1 (E1), ethanol 2 (E2) and ethanol 3 (E3) groups. The rats in the E1, E2 and E3 groups were treated daily with a 30% v/v solution of ethanol, administered via oral gavage (1.0, 2.0 and 3.0g/kg, respectively). Nonsynaptic epileptiform activities (NEA) were induced by means of the zero-Ca2+ and high-K+ model using hippocampal slices and were recorded in the DG. The presence of NKCC1, KCC2, α1-Na+/K+-ATPase and GFAP immunoreactivity was analyzed. The results demonstrate that alcohol consumption changes NEA, and these changes are more prominent at the lower dosage. An increase in the DC shifts associated with epileptiform discharges was present with the low dose. This increase was correlated with the increment of NKCC1 expression. Confocal microscopy images indicate the NKCC1 increase was pronounced in the initial axonal segment of granule cells. The blockage of these cotransporters during NEA induction with bumetanide suppressed the DC shift increase and diminished all parameters of NEA that were quantified for all groups treated with ethanol. Therefore, the increase in NKCC1 expression and the effective activity of this cotransporter, which were observed in the treated groups, suggest that drugs that act for block NKCC1 represent promising strategies for diminishing the effects of alcohol damage on the brain.

Neonatal inhibition of Na+-K+-2Cl--cotransporter prevents ketamine induced spatial learning and memory impairments

Prolonged ketamine exposure in neonates at anesthetic doses is known to cause long-term impairments of learning and memory. A current theoretical mechanism explains this phenomenon as being neuro-excitotoxicity mediated by compensatory upregulation of N-methyl-d-aspartate receptors (NMDARs), which then initiates widespread neuroapoptosis. Additionally, the excitatory behavior of GABAergic synaptic transmission mediated by GABA_A receptors (GABA_ARs), occurring during the early neuronal development period, is proposed as contributing to the susceptibility of neonatal neurons to ketamine-induced injury. This is due to differential developmental expression patterns of Na⁺-K⁺-2Cl^- co-transporter (NKCC1) and K⁺-Cl^- co-transporter. Studies have shown that bumetanide, an NKCC1 inhibitor, allows neurons to become inhibitory rather than excitatory early in development. We thus hypothesized that bumetanide co-administration during ketamine treatment would reduce over excitation and protect the neurons from excitotoxicity. In this initial study, the Morris Water Maze test was used to assess the effects of co-administration of ketamine and bumetanide to neonatal Sprague-Dawley rats on long-term learning and memory changes seen later in life. It was revealed that bumetanide, when co-treated with ketamine neonatally, significantly impeded behavioral deficits typically seen in animals exposed to ketamine alone. Therefore, these findings suggest a new mechanism by which neonatal ketamine induced learning impairments can be prevented.

Acute spinal cord injury (SCI) transforms how GABA affects nociceptive sensitization

Noxious input can sensitize pain (nociceptive) circuits within the spinal cord, inducing a lasting increase in spinal cord neural excitability (central sensitization) that is thought to contribute to chronic pain. The development of spinally-mediated central sensitization is regulated by descending fibers and GABAergic interneurons. The current study provides evidence that spinal cord injury (SCI) transforms how GABA affects nociceptive transmission within the spinal cord, recapitulating an earlier developmental state wherein GABA has an excitatory effect. In spinally transected rats, noxious electrical stimulation and inflammation induce enhanced mechanical reactivity (EMR), a behavioral index of nociceptive sensitization. Pretreatment with the GABAA receptor antagonist bicuculline blocked these effects. Peripheral application of an irritant (capsaicin) also induced EMR. Both the induction and maintenance of this effect were blocked by bicuculline. Cellular indices of central sensitization [c-fos expression and ERK phosphorylation (pERK)] were also attenuated. In intact (sham operated) rats, bicuculline had the opposite effect. Pretreatment with a GABA agonist (muscimol) attenuated nociceptive sensitization in intact, but not spinally injured, rats. The effect of SCI on GABA function was linked to a reduction in the Cl- transporter, KCC2, leading to a reduction in intracellular Cl- that would attenuate GABA-mediated inhibition. Pharmacologically blocking the KCC2 channel (with i.t. DIOA) in intact rats mimicked the effect of SCI. Conversely, a pharmacological treatment (bumetanide) that should increase intracellular Cl- levels blocked the effect of SCI. The results suggest that GABAergic neurons drive, rather than inhibit, the development of nociceptive sensitization after spinal injury.

Bumetanide, an Inhibitor of NKCC1 (Na-K-2Cl Cotransporter Isoform 1), Enhances Propofol-Induced Loss of Righting Reflex but Not Its Immobilizing Actions in Neonatal Rats

Gamma-aminobutyric acid (GABA) has been shown to induce excitation on immature neurons due to increased expression of Na+-K+-2Cl- co-transporter isoform 1 (NKCC1), and the transition of GABAergic signaling from excitatory to inhibitory occurs before birth in the rat spinal cord and spreads rostrally according to the developmental changes in cation-chloride co-transporter expression. We previously showed that midazolam activates the hippocampal CA3 area and induces less sedation in neonatal rats compared with adolescent rats in an NKCC1-dependent manner. In the present study, we tested the hypothesis that propofol-induced loss of righting reflex (LORR) but not immobilizing actions are modulated by NKCC1-dependent mechanisms and reduced in neonatal rats compared with adolescent rats. We estimated neuronal activity in the cortex, hippocampus and thalamus after propofol administration with or without bumetanide, an NKCC1 inhibitor, by immunostaining of phosphorylated cyclic adenosine monophosphate-response element binding protein (pCREB). We studied effects of bumetanide on propofol-induced LORR and immobilizing actions in postnatal day 7 and 28 (P7 and P28) rats. The pCREB expression in the cortex (P = 0.001) and hippocampus (P = 0.01) was significantly greater in the rats receiving propofol only than in the rats receiving propofol plus bumetanide at P 7. Propofol-induced LORR or immobilizing effects did not differ significantly between P7 and P28. Bumetanide significantly enhanced propofol-induced LORR (P = 0.031) but not immobilization in P7 rats. These results are partially consistent with our hypothesis. They suggest that propofol may activate the rostral but not caudal central nervous system dependently on NKCC1, and these differential actions may underlie the different properties of sedative and immobilizing actions observed in neonatal rats.

Compromised GABAergic inhibition contributes to tumor-associated epilepsy

Glioblastoma Multiforme (GBM) is the most common form of primary brain tumor with 30-50% of patients presenting with epilepsy. These tumor-associated seizures are often resistant to traditional antiepileptic drug treatment and persist after tumor resection. This suggests that changes in the peritumoral tissue underpin epileptogenesis. It is known that glioma cells extrude pathological concentrations of glutamate which is thought to play a role in tumor progression and the development of epilepsy. Given that pathological concentrations of glutamate have been shown to dephosphorylate and downregulate the potassium chloride cotransporter KCC2, we hypothesized that glioma-induced alterations in KCC2 in the peritumoral region may play a role in tumor-associated epilepsy. Consistent with this hypothesis, we observe a decrease in total KCC2 expression and a dephosphorylation of KCC2 at residue Ser940 in a glioma model which exhibits hyperexcitability and the development of spontaneous seizures. To determine whether the reduction of KCC2 could potentially contribute to tumor-associated epilepsy, we generated mice with a focal knockdown of KCC2 by injecting AAV2-Cre-GFP into the cortex of floxed KCC2 mice. The AAV2-Cre-mediated knockdown of KCC2 was sufficient to induce the development of spontaneous seizures. Further, blocking NKCC1 with bumetanide to offset the loss of KCC2 reduced the seizure susceptibility in glioma-implanted mice. These findings support a mechanism of tumor-associated epilepsy involving downregulation of KCC2 in the peritumoral region leading to compromised GABAergic inhibition and suggest that modulating chloride homeostasis may be useful for seizure control.

The Effects of Bumetanide on Human Umbilical Artery Contractions

The authors investigate the effect of bumetan ide, an inhibitor of NKCC1 and a loop diuretic, on the tone of human umbilical artery (HUA). Rings of HUA (n = 35) from vaginal deliveries were suspended for isometric tension recordings in organ baths. Cumulative concentration-response curves to serotonin, histamine, and KCl were performed in the absence (control) or in the presence of bumetanide. The relaxant effect of bumetanide was also evaluated in serotonin- and histamine-induced contractions. Bumetanide inhibited HUA tone in serotonin- and histamine-induced contractions with significant changes in the potency (pD(2)) and maximum contractile response (E(max)) values. However, only pD( 2) values for KCl-induced contraction significantly changed in the presence of bumetanide. Bumetanide caused concentration-dependent and sustained relaxations in serotonin-induced contraction; however, there was refractoriness in histamine-induced contraction. These findings raise the possibility that NKCC1 may play a role in the regulation of the umbilical artery tone.

The search for NKCC1-selective drugs for the treatment of epilepsy: Structure-function relationship of bumetanide and various bumetanide derivatives in inhibiting the human cation-chloride cotransporter NKCC1A

The Na(+)-K(+)-Cl(-) cotransporter NKCC1 plays a major role in the regulation of intraneuronal Cl(-) concentration. Abnormal functionality of NKCC1 has been implicated in several brain disorders, including epilepsy. Bumetanide is the only available selective NKCC1 inhibitor, but also inhibits NKCC2, which can cause severe adverse effects during treatment of brain disorders. A NKCC1-selective bumetanide derivative would therefore be a desirable option. In the present study, we used the Xenopus oocyte heterologous expression system to compare the effects of bumetanide and several derivatives on the two major human splice variants of NKCCs, hNKCC1A and hNKCC2A. The derivatives were selected from a series of ~5000 3-amino-5-sulfamoylbenzoic acid derivatives, covering a wide range of structural modifications and diuretic potencies. To our knowledge, such structure-function relationships have not been performed before for NKCC1. Half maximal inhibitory concentrations (IC50s) of bumetanide were 0.68 (hNKCC1A) and 4.0μM (hNKCC2A), respectively, indicating that this drug is 6-times more potent to inhibit hNKCC1A than hNKCC2A. Side chain substitutions in the bumetanide molecule variably affected the potency to inhibit hNKCC1A. This allowed defining the minimal structural requirements necessary for ligand interaction. Unexpectedly, only a few of the bumetanide derivatives examined were more potent than bumetanide to inhibit hNKCC1A, and most of them also inhibited hNKCC2A, with a highly significant correlation between IC50s for the two NKCC isoforms. These data indicate that the structural requirements for inhibition of NKCC1 and NKCC2 are similar, which complicates development of bumetanide-related compounds with high selectivity for NKCC1.

Role of Steroids in Hyperexcitatory Adverse and Anesthetic Effects of Sevoflurane in Neonatal Rats

Recent studies have demonstrated that long-term developmental effects of neonatal anesthesia were more prominent in males. We tested whether steroids, in general, and sex steroids, in particular, are involved in the mediation of sevoflurane-caused paradoxical cortical seizures during the early postnatal period.

METHODS

Cortical electroencephalograms, hippocampal synaptic activity, serum levels of steroids and the loss of the righting reflex (LORR), a marker of anesthetic effect, were measured on postnatal days 4-6 in Sprague Dawley rats of both genders exposed to 2.1% sevoflurane.

RESULTS

Episodes of seizures, persistent spikes in electroencephalograms and increases in serum corticosterone were similar in both genders. In the order of increasing potency, the corticosteroid receptor antagonist RU 28318, the estradiol receptor antagonist ICI 182780 and the estradiol synthesis inhibitor formestane decreased sevoflurane-induced seizures. Exogenous estradiol increased sevoflurane-caused seizures, spikes and serum levels of corticosterone. These estradiol-enhanced seizures and spikes were depressed by ICI 182780 and the NKCC1 inhibitor, bumetanide, while RU 28318 decreased seizures only. In hippocampal CA1 neurons, estradiol increased the amplitude, rise time and area under the curve of gamma-aminobutyric acid type A receptor (GABAAR)-mediated miniature postsynaptic currents. Exogenous estradiol shortened, while ICI 182780 and formestane lengthened the time needed for sevoflurane to induce LORR.

CONCLUSION

These findings provide evidence for gender-independent acute electroencephalographic effects of sevoflurane at this age. Corticosterone and estradiol are involved in the mediation of sevoflurane-induced seizures. Estradiol, but not corticosterone, also contributes to sevoflurane-caused spikes, by enhancing GABAAR-mediated excitation in the cortex. By increasing GABAAR-mediated inhibition in more mature caudal regions of the brain, estradiol contributes to sevoflurane-induced LORR.

Increased Slc12a1 expression in β-cells and improved glucose disposal in Slc12a2 heterozygous mice

The products of the Slc12a1 and Slc12a2 genes, commonly known as Na(+)-dependent K(+)2Cl(-) co-transporters NKCC2 and NKCC1, respectively, are the targets for the diuretic bumetanide. NKCCs are implicated in the regulation of intracellular chloride concentration ([Cl(-)]i) in pancreatic β-cells, and as such, they may play a role in glucose-stimulated plasma membrane depolarization and insulin secretion. Unexpectedly, permanent elimination of NKCC1 does not preclude insulin secretion, an event potentially linked to the homeostatic regulation of additional Cl(-) transporters expressed in β-cells. In this report we provide evidence for such a mechanism. Mice lacking a single allele of Slc12a2 exhibit lower fasting glycemia, increased acute insulin response (AIR) and lower blood glucose levels 15-30 min after a glucose load when compared to mice harboring both alleles of the gene. Furthermore, heterozygous expression or complete absence of Slc12a2 associates with increased NKCC2 protein expression in rodent pancreatic β-cells. This has been confirmed by using chronic pharmacological down-regulation of NKCC1 with bumetanide in the mouse MIN6 β-cell line or permanent molecular silencing of NKCC1 in COS7 cells, which results in increased NKCC2 expression. Furthermore, MIN6 cells chronically pretreated with bumetanide exhibit increased initial rates of Cl(-) uptake while preserving glucose-stimulated insulin secretion. Together, our results suggest that NKCCs are involved in insulin secretion and that a single Slc12a2 allele may protect β-cells from failure due to increased homeostatic expression of Slc12a1.

Secretion of Na(+), K(+) and fluid by the Malpighian (renal) tubule of the larval cabbage looper Trichoplusia ni (Lepidoptera: Noctuidae)

The Malpighian (renal) tubules play important roles in ionic and osmotic homeostasis in insects. In Lepidoptera, the Malpighian tubules are structurally regionalized and the concentration of Na(+) and K(+) in the secreted fluid varies depending on the segment of tubule analyzed. In this work, we have characterized fluid and ion (Na(+), K(+), H(+)) transport by tubules of the larval stage of the cabbage looper Trichoplusia ni; we have also evaluated the effects of fluid secretion inhibitors and stimulants on fluid and ion transport. Ramsay assays showed that fluid was secreted by the iliac plexus but not by the yellow and white regions of the tubule. K(+) and Na(+) were secreted by the distal iliac plexus (DIP) and K(+) was reabsorbed in downstream regions. The fluid secretion rate decreased>50% after 25μM bafilomycin A1, 500μM amiloride or 50μM bumetanide was added to the bath. The concentration of K(+) in the secreted fluid did not change, whereas the concentration of Na(+) in the secreted fluid decreased significantly when tubules were exposed to bafilomycin A1 or amiloride. Addition of 500μM cAMP or 1μM 5-HT to the bath stimulated fluid secretion and resulted in a decrease in K(+) concentration in the secreted fluid. An increase in Na(+) concentration in the secreted fluid was observed only in cAMP-stimulated tubules. Secreted fluid pH and the transepithelial electrical potential (TEP) did not change when tubules were stimulated. Taken together, our results show that the secretion of fluid is carried out by the upper regions (DIP) in T. ni Malpighian tubules. Upper regions of the tubules secrete K(+), whereas lower regions reabsorb it. Stimulation of fluid secretion is correlated with a decrease in the K(+)/Na(+) ratio.

KCC2 function modulates in vitro ictogenesis

GABAA receptor-mediated inhibition is active and may contribute to epileptiform synchronization. The efficacy of inhibition relies on low levels of intracellular Cl(-), which are controlled by KCC2 activity. This evidence has led us to analyze with field potential recordings the effects induced by the KCC2 blockers VU0240551 (10 μM) or bumetanide (50 μM) and by the KCC2 enhancer CLP257 (100 μM) on the epileptiform discharges generated by piriform and entorhinal cortices (PC and EC, respectively) in an in vitro brain slice preparation. Ictal- and interictal-like discharges along with high-frequency oscillations (HFOs, ripples: 80-200 Hz, fast ripples: 250-500 Hz) were recorded from these two regions during application of 4-aminopyridine (4AP, 50 μM). Blocking KCC2 activity with either VU024055 or high doses of bumetanide abolished ictal discharge in both PC and EC; in addition, these experimental procedures decreased the interval of occurrence and duration of interictal discharges. In contrast, enhancing KCC2 activity with CLP257 increased ictal discharge duration in both regions. Finally, blocking KCC2 activity decreased the duration and amplitude of pharmacologically isolated synchronous GABAergic events whereas enhancing KCC2 activity led to an increase in their duration. Our data demonstrate that in vitro ictogenesis is abolished or facilitated by inhibiting or enhancing KCC2 activity, respectively. We propose that these effects may result from the reduction of GABAA receptor-dependent increases in extracellular K(+) that are known to rest on KCC2 function.