Extracellular Potassium Research Articles

Dynamics of ramping bursts in a respiratory neuron model.

Intensive computational and theoretical work has led to the development of multiple mathematical models for bursting in respiratory neurons in the pre-Bötzinger Complex (pre-BötC) of the mammalian brainstem. Nonetheless, these previous models have not captured the pre-inspiratory ramping aspects of these neurons' activity patterns, in which relatively slow tonic spiking gradually progresses to faster spiking and a full-blown burst, with a corresponding gradual development of an underlying plateau potential. In this work, we show that the incorporation of the dynamics of the extracellular potassium ion concentration into an existing model for pre-BötC neuron bursting, along with some parameter adjustments, suffices to induce this ramping behavior. Using fast-slow decomposition, we show that this activity can be considered as a form of parabolic bursting, but with burst termination at a homoclinic bifurcation rather than as a SNIC bifurcation. We also investigate the parameter-dependence of these solutions and show that the proposed model yields a greater dynamic range of burst frequencies, durations, and duty cycles than those produced by other models in the literature.

Astrocyte Ca2+-evoked ATP release regulates myelinated axon excitability and conduction speed.

Print Page SummaryIntroductionAstrocytes support neuronal function throughout the central nervous system. In the grey matter they regulate synapse number during development, remove synaptically-released neurotransmitters to terminate their action and prevent excitotoxicity, control the extracellular potassium concentration to prevent hyperexcitability, regulate blood flow to ensure an adequate energy supply, provide lactate to neurons for energy, and respond to rises of intracellular calcium concentration ([Ca2+]i) by releasing ATP and other gliotransmitters that act on neuronal receptors to modulate information processing. However, their role is unclear in the white matter, which transmits information rapidly between grey matter areas using axons wrapped with capacitance-reducing myelin, although they have been suggested to regulate myelination during development and during normal function.RationaleRecently it has been suggested that learning and memory may reflect, not only changes of synaptic function in the grey matter, but also changes of white matter function. In particular, neural circuit function might be regulated by changes in the conduction speed of myelinated axons that result in an altered arrival time of action potentials at a distant neuron. These speed changes might be brought about by alterations of the properties of the passively conducting myelinated internodes, or of the intervening excitable nodes of Ranvier where the action potential is generated. We applied immunohistochemistry to assess how astrocytes interact with myelinated axons, used neuronal stimulation and light evoked calcium uncaging in astrocytes to evoke Ca2+-dependent release of gliotransmitters, and employed electrophysiology and pharmacology to characterise how astrocyte-released substances might affect the axon initial segment (AIS) and nodes of Ranvier of myelinated neurons. Measurements of conduction velocity and computer modelling allowed us to interpret the results.ResultsAstrocytes closely approach the axons of myelinated neurons in layer V of the cerebral cortex. Uncaging Ca2+ within astrocytes, or stimulating spike trains in neurons, evoked a rise of astrocyte [Ca2+]i that triggered the release of ATP-containing vesicles from these cells. This evoked an inward current in the AIS and nodes of Ranvier of the pyramidal neurons. Pharmacology showed that this was mediated by the activation of Gs-linked adenosine A2a receptors, implying that the released ATP was converted to adenosine by extracellular enzymes. The A2a receptors raise the intracellular concentration of cyclic AMP, which activates HCN channels mediating the inward hyperpolarization-activated current Ih, and thus depolarizes the cell. In the AIS the activation of A2a receptors alters excitability and hence action potential generation, while in the nodes of Ranvier it decreases the conduction speed of the action potential along the axon.ConclusionAs in the grey matter, astrocyte [Ca2+]i regulates the release of ATP into the extracellular space in the white matter. After conversion to adenosine, this regulates the excitability and conduction speed of myelinated axons. The changes in excitability at the AIS will lead to changes in the relationship between the synaptic input and action potential output of the cell. The altered conduction speed of the myelinated axon may change neural circuit function by changing the action potential arrival time at the cell’s output synapses, thus altering the integration of signals in postsynaptic neurons. Variations in astrocyte-derived adenosine level can occur between wake and sleep states, and the extracellular adenosine concentration rises during energy deprivation conditions. These changes of adenosine level could thus control white matter information flow and neural circuit function.Astrocytes regulate myelinated axon excitability and conduction speed.For cortical neurons with myelinated axons crossing the corpus callosum (left), astrocytes regulate axon initial segment (AIS) excitability and axonal conduction speed (middle). Increases of astrocyte [Ca2+]i release ATP which, after conversion to adenosine (Ado) extracellularly, activates A2a receptors that raise the intracellular cyclic AMP concentration, and thus generate an inward current via HCN2 channels in the AIS and nodes of Ranvier (right). Created with BioRender.com.In the brain’s grey matter, astrocytes regulate synapse properties, but their role is unclear for the white matter where myelinated axons rapidly transmit information between grey matter areas. We found that, in rodents, neuronal activity raised [Ca2+]i in astrocyte processes located near action potential generating sites in the axon initial segment (AIS) and nodes of Ranvier of myelinated axons. This released ATP which was converted extracellularly to adenosine and thus, via A2a receptors, activated HCN2-containing cation channels that regulate two aspects of myelinated axon function: excitability of the AIS and speed of action potential propagation. Variations in astrocyte-derived adenosine level, between wake and sleep states or during energy deprivation, could thus control white matter information flow and neural circuit function.

Differential impact of Kv8.2 loss on rod and cone signaling and degeneration.

Heteromeric Kv2.1/Kv8.2 channels are voltage-gated potassium channels localized to the photoreceptor inner segment. They carry IKx, which is largely responsible for setting the photoreceptor resting membrane potential. Mutations in Kv8.2 result in childhood-onset cone dystrophy with supernormal rod response (CDSRR). We generated a Kv8.2 knockout (KO) mouse and examined retinal signaling and photoreceptor degeneration to gain deeper insight into the complex phenotypes of this disease. Using electroretinograms, we show that there were delayed or reduced signaling from rods depending on the intensity of the light stimulus, consistent with reduced capacity for light-evoked changes in membrane potential. The delayed response was not seen ex vivo where extracellular potassium levels were controlled by the perfusion buffer, so we propose the in vivo alteration is influenced by genotype-associated ionic imbalance. We observed mild retinal degeneration. Signaling from cones was reduced but there was no loss of cone density. Loss of Kv8.2 altered responses to flickering light with responses attenuated at high frequencies and altered in shape at low frequencies. The Kv8.2 KO line on an all-cone retina background had reduced cone-driven ERG b wave amplitudes and underwent degeneration. Altogether, we provide insight into how a deficit in the dark current affects the health and function of photoreceptors.

Investigating the role of muscarinic acetylcholine M2 and serotonin 5-HT2B receptors, norepinephrine transporter and Kir channels in a pentylenetetrazol-kindling model of epilepsy

Epilepsy encompasses a group of neurological disorders characterized by an imbalance of electrical activity in the central nervous system (CNS) and recurrent seizures representing the principal clinical manifestation. Acetylcholine (ACh), serotonin, and norepinephrine (NE) may modulate neural activity via several mechanisms, mainly through its receptors/transporter activity and alterations in the extracellular potassium (K+) concentration via inwardly rectifying K+ (Kir) channels. Therefore, the aim of this study was to investigate the immunoreactivity pattern of these neurotransmitter, receptors/transporters and Kir channels in Pentylenetetrazol (PTZ)-kindling rat model, a well-established tool for studying chronic epilepsy.

Role of WNK1 and WNK4 in Sensing Extracellular Potassium in Principal Cells to Modulate mTORC2-Dependent Activation of Epithelial Sodium Channel

Role of WNK1 and WNK4 in Sensing Extracellular Potassium in Principal Cells to Modulate mTORC2-Dependent Activation of Epithelial Sodium Channel

Potential of Multiscale Astrocyte Imaging for Revealing Mechanisms Underlying Neurodevelopmental Disorders.

Astrocytes provide trophic and metabolic support to neurons and modulate circuit formation during development. In addition, astrocytes help maintain neuronal homeostasis through neurovascular coupling, blood–brain barrier maintenance, clearance of metabolites and nonfunctional proteins via the glymphatic system, extracellular potassium buffering, and regulation of synaptic activity. Thus, astrocyte dysfunction may contribute to a myriad of neurological disorders. Indeed, astrocyte dysfunction during development has been implicated in Rett disease, Alexander’s disease, epilepsy, and autism, among other disorders. Numerous disease model mice have been established to investigate these diseases, but important preclinical findings on etiology and pathophysiology have not translated into clinical interventions. A multidisciplinary approach is required to elucidate the mechanism of these diseases because astrocyte dysfunction can result in altered neuronal connectivity, morphology, and activity. Recent progress in neuroimaging techniques has enabled noninvasive investigations of brain structure and function at multiple spatiotemporal scales, and these technologies are expected to facilitate the translation of preclinical findings to clinical studies and ultimately to clinical trials. Here, we review recent progress on astrocyte contributions to neurodevelopmental and neuropsychiatric disorders revealed using novel imaging techniques, from microscopy scale to mesoscopic scale.

Methyl-Beta-Cyclodextrin Restores KIR Channel Function in Brain Endothelium of Female Alzheimer's Disease Mice.

Background:As the sixth-leading cause of death in the United States, Alzheimer’s disease (AD) entails deteriorating endothelial control of blood flow throughout the brain. In particular, reduced inward-rectifying K+ (KIR) channel function in animal models of aging and AD compromises endothelial function and optimal perfusion of brain parenchyma. Deficient endothelial KIR channels may result from aberrant interaction with plasma membrane cholesterol as a primary regulator of membrane fluidity and ion channels.Objective:We tested the hypothesis that mild methyl-β-cyclodextrin (MβCD) treatment to reduce membrane cholesterol may restore endothelial KIR channel function in brain endothelium of old AD mice.Methods:Membrane potential was continuously measured in isolated endothelial tubes from posterior cerebral arteries of young (1 to 3 months) and old (16 to 19 months) female 3xTg-AD mice before and after mild treatment with the cholesterol-removing agent MβCD (1 mmol/L). Elevated extracellular potassium ([K+]E; 15 mmol/L) and NS309 (1μmol/L) activated KIR and Ca2+-activated K+ (SKCa/IKCa) channels respectively before and after MβCD treatment.Results:SKCa/IKCa channel function for producing hyperpolarization remained stable regardless of age group and MβCD treatment (ΔVm: ∼–33 mV). However, as deficient during AD, KIR channel function was restored (ΔVm: –9±1 mV) versus pre-MβCD conditions (–5±1 mV); a progressive effect that reached –14±1 mV hyperpolarization at 60 min following MβCD washout.Conclusion:In female animals, MβCD treatment of brain endothelium selectively restores KIR versus SKCa/IKCa channel function during AD. Thus, the endothelial cholesterol-KIR channel interface is a novel target for ameliorating perfusion of the AD brain.

In Vivo Neocortical [K]o Modulation by Targeted Stimulation of Astrocytes.

A normally functioning nervous system requires normal extracellular potassium ion concentration ([K]o). Throughout the nervous system, several processes, including those of an astrocytic nature, are involved in [K]o regulation. In this study we investigated the effect of astrocytic photostimulation on [K]o. We hypothesized that in vivo photostimulation of eNpHR-expressing astrocytes leads to a decreased [K]o. Using optogenetic and electrophysiological techniques we showed that stimulation of eNpHR-expressing astrocytes resulted in a significantly decreased resting [K]o and evoked K responses. The amplitude of the concomitant spreading depolarization-like events also decreased. Our results imply that astrocytic membrane potential modification could be a potential tool for adjusting the [K]o.

Modeling NaV1.1/SCN1A sodium channel mutations in a microcircuit with realistic ion concentration dynamics suggests differential GABAergic mechanisms leading to hyperexcitability in epilepsy and hemiplegic migraine.

Loss of function mutations of SCN1A, the gene coding for the voltage-gated sodium channel NaV1.1, cause different types of epilepsy, whereas gain of function mutations cause sporadic and familial hemiplegic migraine type 3 (FHM-3). However, it is not clear yet how these opposite effects can induce paroxysmal pathological activities involving neuronal networks’ hyperexcitability that are specific of epilepsy (seizures) or migraine (cortical spreading depolarization, CSD). To better understand differential mechanisms leading to the initiation of these pathological activities, we used a two-neuron conductance-based model of interconnected GABAergic and pyramidal glutamatergic neurons, in which we incorporated ionic concentration dynamics in both neurons. We modeled FHM-3 mutations by increasing the persistent sodium current in the interneuron and epileptogenic mutations by decreasing the sodium conductance in the interneuron. Therefore, we studied both FHM-3 and epileptogenic mutations within the same framework, modifying only two parameters. In our model, the key effect of gain of function FHM-3 mutations is ion fluxes modification at each action potential (in particular the larger activation of voltage-gated potassium channels induced by the NaV1.1 gain of function), and the resulting CSD-triggering extracellular potassium accumulation, which is not caused only by modifications of firing frequency. Loss of function epileptogenic mutations, on the other hand, increase GABAergic neurons’ susceptibility to depolarization block, without major modifications of firing frequency before it. Our modeling results connect qualitatively to experimental data: potassium accumulation in the case of FHM-3 mutations and facilitated depolarization block of the GABAergic neuron in the case of epileptogenic mutations. Both these effects can lead to pyramidal neuron hyperexcitability, inducing in the migraine condition depolarization block of both the GABAergic and the pyramidal neuron. Overall, our findings suggest different mechanisms of network hyperexcitability for migraine and epileptogenic NaV1.1 mutations, implying that the modifications of firing frequency may not be the only relevant pathological mechanism.

DEHT is a suitable plasticizer option for phthalate-free storage of irradiated red blood cells.

Due to increasing concerns about possible endocrine-disrupting properties, the use of the plasticizer di(2-ethylhexyl) phthalate (DEHP) will be banned in future blood storage. Di(2-ethylhexyl) terephthalate (DEHT) provides sufficient red blood cell (RBC) quality during conventional blood bank storage. It is important that a new plasticizer also maintains acceptable quality during exposure to high cell stress, such as irradiation, which is commonly used to prevent graft-versus-host disease. A total of 59 RBC units were collected and processed in polyvinyl chloride (PVC)-DEHT or PVC-DEHP blood bags combined with either saline-adenine-glucose-mannitol (SAGM) or phosphate-adenine-glucose-guanosine-saline-mannitol (PAGGSM) additive solution. All units were X-ray irradiated on day 2 post-collection. Sampling for assessment of parameters of storage lesion was performed on day 2 pre-irradiation and day 14 and 28 post-irradiation. Though irradiation increased cell stress, DEHT/PAGGSM and current common European preference DEHP/SAGM were equally affected up to 14 days post-irradiation for all measured parameters. At day 28, haemolysis and microvesicle count were slightly increased in DEHT, whereas extracellular potassium ions, glucose, lactate, pH, mean corpuscular volume and microvesicle phosphatidylserine remained unaffected by plasticizer choice throughout storage. No individual unit exceeded 0.8% haemolysis, not even in DEHT/SAGM, the combination overall most affected by irradiation. Of the four combinations, membrane stability was least impacted in DEHP/PAGGSM. We demonstrate that DEHT is a suitable plasticizer for storage of RBCs after X-ray irradiation cell stress. This strengthens the option of DEHT as a viable non-phthalate substitute for DEHP.

Intracranial pressure spikes trigger spreading depolarizations.

Spreading depolarizations are highly prevalent and spatiotemporally punctuated events worsening the outcome of brain injury. Trigger factors are poorly understood but may be linked to sudden worsening in supply-demand mismatch in compromised tissue. Sustained or transient elevations in intracranial pressure are also prevalent in the injured brain. Here, using a mouse model of large hemispheric ischaemic stroke, we show that mild and brief intracranial pressure elevations (20 or 30 mmHg for just 3 min) potently trigger spreading depolarizations in ischaemic penumbra (4-fold increase in spreading depolarization occurrence). We also show that 30 mmHg intracranial pressure spikes as brief as 30 s are equally effective. In contrast, sustained intracranial pressure elevations to the same level for 30 min do not significantly increase the spreading depolarization rate, suggesting that an abrupt disturbance in the steady state equilibrium is required to trigger a spreading depolarization. Laser speckle flowmetry consistently showed a reduction in tissue perfusion, and two-photon pO2 microscopy revealed a drop in venous pO2 during the intracranial pressure spikes suggesting increased oxygen extraction fraction, and therefore, worsening supply-demand mismatch. These haemodynamic changes during intracranial pressure spikes were associated with highly reproducible increases in extracellular potassium levels in penumbra. Consistent with the experimental data, a higher rate of intracranial pressure spikes was associated with spreading depolarization clusters in a retrospective series of patients with aneurysmal subarachnoid haemorrhage with strong temporal correspondence. Altogether, our data show that intracranial pressure spikes, even when mild and brief, are capable of triggering spreading depolarizations. Aggressive prevention of intracranial pressure spikes may help reduce spreading depolarization occurrence and improve outcomes after brain injury.

A model of metabolic supply-demand mismatch leading to secondary brain injury

Secondary brain injury (SBI) is defined as new or worsening injury to the brain after an initial neurologic insult, such as hemorrhage, trauma, ischemic stroke, or infection. It is a common and potentially preventable complication following many types of primary brain injury (PBI). However, mechanistic details about how PBI leads to additional brain injury and evolves into SBI are poorly characterized. In this work, we propose a mechanistic model for the metabolic supply demand mismatch hypothesis (MSDMH) of SBI. Our model, based on the Hodgkin-Huxley model, supplemented with additional dynamics for extracellular potassium, oxygen concentration, and excitotoxity, provides a high-level unified explanation for why patients with acute brain injury frequently develop SBI. We investigate how decreased oxygen, increased extracellular potassium, excitotoxicity, and seizures can induce SBI and suggest three underlying paths for how events following PBI may lead to SBI. The proposed model also helps explain several important empirical observations, including the common association of acute brain injury with seizures, the association of seizures with tissue hypoxia and so on. In contrast to current practices which assume that ischemia plays the predominant role in SBI, our model suggests that metabolic crisis involved in SBI can also be nonischemic. Our findings offer a more comprehensive understanding of the complex interrelationship among potassium, oxygen, excitotoxicity, seizures, and SBI.NEW & NOTEWORTHY We present a novel mechanistic model for the metabolic supply demand mismatch hypothesis (MSDMH), which attempts to explain why patients with acute brain injury frequently develop seizure activity and secondary brain injury (SBI). Specifically, we investigate how decreased oxygen, increased extracellular potassium, excitotoxicity, seizures, all common sequalae of primary brain injury (PBI), can induce SBI and suggest three underlying paths for how events following PBI may lead to SBI.

Distinct signatures of calcium activity in brain mural cells.

Pericytes have been implicated in various neuropathologies, yet little is known about their function and signaling pathways in health. Here, we characterized calcium dynamics of cortical mural cells in anesthetized or awake Pdgfrb-CreERT2;Rosa26< LSL-GCaMP6s > mice and in acute brain slices. Smooth muscle cells (SMCs) and ensheathing pericytes (EPs), also named as terminal vascular SMCs, revealed similar calcium dynamics in vivo. In contrast, calcium signals in capillary pericytes (CPs) were irregular, higher in frequency, and occurred in cellular microdomains. In the absence of the vessel constricting agent U46619 in acute slices, SMCs and EPs revealed only sparse calcium signals, whereas CPs retained their spontaneous calcium activity. Interestingly, chemogenetic activation of neurons in vivo and acute elevations of extracellular potassium in brain slices strongly decreased calcium activity in CPs. We propose that neuronal activation and an extracellular increase in potassium suppress calcium activity in CPs, likely mediated by Kir2.2 and KATP channels.

Intracellular potassium depletion enhances apoptosis induced by staurosporine in cultured trigeminal satellite glial cells

Purpose Satellite glial cells (SGC) surrounding neurons in sensory ganglia can buffer extracellular potassium, regulating the excitability of injured neurons and possibly influencing a shift from acute to neuropathic pain. SGC apoptosis may be a key component in this process. This work evaluated induction or enhancement of apoptosis in cultured trigeminal SGC following changes in intracellular potassium [K]ic. Materials and methods We developed SGC primary cultures from rat trigeminal ganglia (TG). Purity of our cultures was confirmed using immunofluorescence and western blot analysis for the presence of the specific marker of SGC, glutamine synthetase (GS). SGC [K]ic was depleted using hypo-osmotic shock and 4 mM bumetanide plus 10 mM ouabain. [K]ic was measured using the K+ fluorescent indicator potassium benzofuran isophthalate (PBFI-AM). Results SGC tested positive for GS and hypo-osmotic shock induced a significant decrease in [K]ic at every evaluated time. Cells were then incubated for 5 h with either 2 mM staurosporine (STS) or 20 ng/ml of TNF-α and evaluated for early apoptosis and late apoptosis/necrosis by flow cytometry using annexin V and propidium iodide. A significant increase in early apoptosis, from 16 to 38%, was detected in SGC with depleted [K]ic after incubation with STS. In contrast, TNF-α did not increase early apoptosis in normal or [K]ic depleted SGC. Conclusion Hypo-osmotic shock induced a decrease in intracellular potassium in cultured trigeminal SGC and this enhanced apoptosis induced by STS that is associated with the mitochondrial pathway. These results suggest that K+ dysregulation may underlie apoptosis in trigeminal SGC.

Activity-mediated accumulation of potassium induces a switch in firing pattern and neuronal excitability type.

During normal neuronal activity, ionic concentration gradients across a neuron's membrane are often assumed to be stable. Prolonged spiking activity, however, can reduce transmembrane gradients and affect voltage dynamics. Based on mathematical modeling, we investigated the impact of neuronal activity on ionic concentrations and, consequently, the dynamics of action potential generation. We find that intense spiking activity on the order of a second suffices to induce changes in ionic reversal potentials and to consistently induce a switch from a regular to an intermittent firing mode. This transition is caused by a qualitative alteration in the system's voltage dynamics, mathematically corresponding to a co-dimension-two bifurcation from a saddle-node on invariant cycle (SNIC) to a homoclinic orbit bifurcation (HOM). Our electrophysiological recordings in mouse cortical pyramidal neurons confirm the changes in action potential dynamics predicted by the models: (i) activity-dependent increases in intracellular sodium concentration directly reduce action potential amplitudes, an effect typically attributed solely to sodium channel inactivation; (ii) extracellular potassium accumulation switches action potential generation from tonic firing to intermittently interrupted output. Thus, individual neurons may respond very differently to the same input stimuli, depending on their recent patterns of activity and/or the current brain-state.

Familial pseudohyperkalemia induces significantly higher levels of extracellular potassium in early storage of red cell concentrates without affecting other standard measures of quality: A case control and allele frequency study

Familial pseudohyperkalemia (FP) is characterized by an increased rate of potassium leakage in refrigerated red cells and is associated with the minor allele of the single nucleotide polymorphism rs148211042 (R723Q) in the ABCB6 gene. The study aims were to obtain the minor allele frequencies of ABCB6 variants and to measure supernatant potassium accumulation, and other red cell storage parameters, in red cell concentrates (RCC) from carriers of variant rs148211042 under standard blood bank conditions. Whole blood units were collected from 6 FP individuals and 11 controls and processed into RCC in additive solution. RCC were sampled and tested over cold storage for full blood count, extracellular potassium, glucose, lactate, microvesicle release, deformability, hemolysis, pH, adenosine triphosphate, and 2,3-diphosphoglycerate. Screening of genotyped cohorts identified that variant rs148211042 is present in 1 in 394 British citizens of European ancestry. FP RCC had significantly higher supernatant potassium at all time points from day 3 onwards (p < .001) and higher mean cell volume (p=.032) than controls. The initial rate of potassium release was higher in FP RCC; supernatant potassium reached 46.0 (23.8-57.6) mmol/L (mean [range]) by day 5, increasing to 68.9 (58.8-73.7) mmol/L by day 35. Other quality parameters were not significantly different between FP RCC and controls. These data suggest that if a blood donor has FP, reducing the RCC shelf-life to 5 days may be insufficient to reduce the risk of hyperkalemia in clinical scenarios such as neonatal large volume transfusion.

Fast–Slow Variable Dissection with Two Slow Variables: A Case Study on Bifurcations Underlying Bursting for Seizure and Spreading Depression

The identification of nonlinear dynamics of bursting patterns related to multiple time scales and pathology of brain tissues is still an open problem. In the present paper, representative cases of bursting related to seizure (SZ) and spreading depression (SD) simulated in a theoretical model are analyzed. When the fast–slow variable dissection method with only one slow variable (extracellular potassium concentration, [Formula: see text]) taken as the bifurcation parameter of the fast subsystem is used, the mismatch between bifurcation points of the fast subsystem and the beginning and ending phases of burst appears. To overcome this problem, both slow variables [Formula: see text] and [Formula: see text] (intracellular sodium concentration) are regarded as bifurcation parameters of the fast subsystem, which exhibits three codimension-2 bifurcation points and multiple codimension-1 bifurcation curves containing the saddle-node bifurcation on an invariant cycle (SNIC), the supercritical Hopf bifurcation (the border between spiking and the depolarization block), and the saddle homoclinic (HC) bifurcation. The bursting patterns for SD are related to the Hopf bifurcation and the depolarization block while for SZ to SNIC. Furthermore, at the intersection points between the bursting trajectory and the bifurcation curves in plane ([Formula: see text], [Formula: see text]), the initial or termination phases of burst match the SNIC or HC point well or the Hopf point to a certain extent due to the slow passage effect, showing that the fast–slow variable dissection method with suitable process is still effective to analyze bursting activities. The results present the complex bifurcations underlying the bursting patterns and a proper performing process for the fast–slow variable dissection with two slow variables, which are helpful for modulation to bursting patterns related to brain disfunction.

Acute Kidney Injury in a Patient with Trisomy 21.

1. Hannah S. Kim, MD* 2. Francesca Costigliolo, MD† 3. Serena Bagnasco, MD† 4. Jeffrey Fadrowski, MD, MHS* 5. Rebecca L. Ruebner, MD, MSCE* 1. *Division of Pediatric Nephrology and 2. †Division of Pathology, Johns Hopkins University, Baltimore, MD A 5-year-old former 34-week girl with trisomy 21, hypothyroidism, and obstructive sleep apnea presents to the emergency department with a chief complaint of fever. She initially presented to her pediatrician 3 weeks earlier with sore throat and was diagnosed as having group A streptococcal pharyngitis. She completed 10 days of amoxicillin with resolution of sore throat. Now for the past 3 days she has had fever, chest pain, decreased enteral intake, and emesis. Review of systems is negative for diarrhea, gross hematuria, dysuria, polyuria, polydipsia, edema, weight loss, rash, arthralgia, arthritis, oral ulcers, epistaxis, and hemoptysis. She has had normal growth. She takes levothyroxine and took several doses of ibuprofen for fever over the past several weeks. There is no family history of kidney disease. She had no recent travel or sick contacts. On physical examination her weight is 45.2 lb (20.5 kg) (65th percentile); height, 46.1 in (117 cm) (62% percentile); temperature, 100.8°F (38.2°C); heart rate, 110 beats/min; respiratory rate, 24 breaths/min; oxygen saturation, 100% on room air; and blood pressure, 92/42 mm Hg (systolic 31st and diastolic 9th percentiles for age and sex). There is no pharyngeal injection or exudate. She appears well-hydrated, including moist mucous membranes. Lungs are clear to auscultation. Her abdomen is soft, nontender, and nondistended. There is no edema, and she has brisk capillary refill. She has no rash or joint swelling, erythema, or warmth. Laboratory evaluation includes a white blood cell count of 15,310/µL (15.31×109/L) with 83.6% neutrophils and 0.8% bands; hemoglobin …

Removal of membrane cholesterol selectively restores K IR channel function in brain endothelium during Alzheimer's disease

The number of Alzheimer's disease (AD) patients (~44 million worldwide; ~5.8 million Americans) continues to rise, while there is no effective treatment available and etiology remains obscure. Incidence of AD increases with aging due, in large part, to deteriorating endothelial control of blood flow throughout the brain. Further, K+ channels, particularly inward-rectifying K+ (KIR2.x) channels, are integral to endothelial function and optimal perfusion of brain parenchyma. Our group has identified reduced KIR2.x channel function as a new manifestation of endothelial “dysfunction” during aging and AD, whereas function of small- and intermediate-Ca2+-activated K+ (SKCa/IKCa) channels is stable throughout. Moreover, we reasoned that apparently deficient KIR2.x channels could be due to their aberrant interaction with plasma membrane cholesterol, a major regulator of membrane fluidity and ion channels. Hence, we tested the hypothesis that reduction of membrane cholesterol may restore KIR channel function in brain endothelium of old AD mice. Membrane potential (Vm) was measured in posterior cerebral endothelial “tubes” of female 3xTg-AD mice (16 to 19 mo; n=12) before and after mild treatment with the cholesterol-removing agent methyl-β-cyclodextrin (MβCD; 1 mM). We used elevated extracellular potassium([K+]E;15 mM) and NS309 (1 µM) to activate KIR2.x and SKCa/IKCa channels respectively. SKCa/IKCa channel function for producing hyperpolarization (more negative Vm) remains stable after MβCD treatment (ΔVm, mV; -31±1 vs. control, -33±2), revealing that SKCa/IKCa channels are not significantly impacted by membrane cholesterol. However, KIR2.x channel function is progressively restored and enhanced in a time-dependent manner following washout of MβCD (ΔVm, mV; control, -5±1; 30 min washout, -9±1; 60 min, -14±1). Altogether, our findings demonstrate that cholesterol intervention of brain endothelium selectively restores KIR2.x vs. SKCa/IKCa channel function during AD. Thus, endothelial cholesterol-KIR channel interaction is a novel therapeutic target for ameliorating cerebrovascular function to optimize perfusion of the AD brain.

Temperature Dependence on the Passive Effects of K+ on Membrane Potential of Skeletal Muscle as an Educational Module

The presentation reports on the implementation of a CURE (Course-based Undergraduate Research Experience) by modifying a standardized physiological laboratory protocol that measures changes in resting membrane potential concerning the concentration of extracellular potassium ions [K+]o. The CURE investigation determines how temperature influences resting membrane potential. Crayfish were used as models to empirically address the effects of temperature and [K+]o change. Experimentally, the skeletal muscle of a crayfish served as a model to obtain data due to the robust nature of the preparation for student laboratories. Graphing membrane potential in relation to both [K+]o and temperature, along with theoretical curves for the Nernst and Goldman-Hodgkin-Katz (G-H-K) equations, provided a visual representation of the significance of temperature on membrane potential and in these equations. Freely available online software was used in addressing the theoretical values one would expect for changing the variables in the G-H-K equation, which gave students a deeper understanding of its use in measuring membrane potential values. A pre- and post-survey over content comprehension and student views on the activities were also obtained.