Potassium channels: possible new therapeutic targets in Parkinson's disease

ATP-sensitive potassium channels: A double-edged sword in neurodegenerative diseases

ATP-sensitive potassium channels (K_ATP channels), a group of vital channels that link the electrical activity of the cell membrane with cell metabolism, were discovered on the ventricular myocytes of guinea pigs by Noma using the patch-clamp technique in 1983. Subsequently, K_ATP channels have been found to be expressed in pancreatic β cells, cardiomyocytes, skeletal muscle cells, and nerve cells in the substantia nigra (SN), hippocampus, cortex, and basal ganglia. K_ATP channel openers (KCOs) diazoxide, nicorandil, minoxidil, and the K_ATP channel inhibitor glibenclamide have been shown to have anti-hypertensive, anti-myocardial ischemia, and insulin-releasing regulatory effects. Increasing evidence has suggested that K_ATP channels also play roles in Alzheimer's disease (AD), Parkinson's disease (PD), vascular dementia (VD), Huntington's disease (HD) and other neurodegenerative diseases. KCOs and K_ATP channel inhibitors protect neurons from injury by regulating neuronal excitability and neurotransmitter release, inhibiting abnormal protein aggregation and Ca²⁺ overload, reducing reactive oxygen species (ROS) production and microglia activation. However, K_ATP channels have dual effects in some cases. In this review, we focus on the roles of K_ATP channels and their related openers and inhibitors in neurodegenerative diseases. This will enable us to precisely take advantage of the K_ATP channels and provide new ideas for the treatment of neurodegenerative diseases.

Physiology and Therapeutic Potential of SK, H, and M Medium AfterHyperPolarization Ion Channels

SK, HCN, and M channels are medium afterhyperpolarization (mAHP)-mediating ion channels. The three channels co-express in various brain regions, and their collective action strongly influences cellular excitability. However, significant diversity exists in the expression of channel isoforms in distinct brain regions and various subcellular compartments, which contributes to an equally diverse set of specific neuronal functions. The current review emphasizes the collective behavior of the three classes of mAHP channels and discusses how these channels function together although they play specialized roles. We discuss the biophysical properties of these channels, signaling pathways that influence the activity of the three mAHP channels, various chemical modulators that alter channel activity and their therapeutic potential in treating various neurological anomalies. Additionally, we discuss the role of mAHP channels in the pathophysiology of various neurological diseases and how their modulation can alleviate some of the symptoms.

Mitochondrial K+ channels and their implications for disease mechanisms

The field of mitochondrial ion channels underwent a rapid development during the last decade, thanks to the molecular identification of some of the nuclear-encoded organelle channels and to advances in strategies allowing specific pharmacological targeting of these proteins. Thereby, genetic tools and specific drugs aided definition of the relevance of several mitochondrial channels both in physiological as well as pathological conditions. Unfortunately, in the case of mitochondrial K⁺ channels, efforts of genetic manipulation provided only limited results, due to their dual localization to mitochondria and to plasma membrane in most cases. Although the impact of mitochondrial K⁺ channels on human diseases is still far from being genuinely understood, pre-clinical data strongly argue for their substantial role in the context of several pathologies, including cardiovascular and neurodegenerative diseases as well as cancer. Importantly, these channels are druggable targets, and their in-depth investigation could thus pave the way to the development of innovative small molecules with huge therapeutic potential. In the present review we summarize the available experimental evidence that mechanistically link mitochondrial potassium channels to the above pathologies and underline the possibility of exploiting them for therapy.

Potassium channels and their emerging role in parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder, which is associated with a selective loss of dopaminergic neurons in the substantia nigra (SN) and a reduction of dopamine in the striatum. Recently, ion channel dysfunction has been considered a reason for the pathogenesis of PD. Potassium (K⁺) channels are widespread in the central nervous system, and play key roles in modulating cellular excitability, synaptic transmission, and neurotransmitter release. Based on recent studies and data, we propose that K⁺ channels may be new therapeutic targets for PD that slow the progressive loss of dopaminergic neurons and attenuate motor and non-motor symptoms. In this review, we mainly focus on: delayed rectifier, inwardly rectifying, and double-pore K⁺ channels. We summarize the expression and function of these channels in PD-related brain regions. We also discuss the effects of pharmacological blockade or activation of K⁺ channels in the progression and treatment of PD.

Medicinal Chemistry of Potassium Channel Modulators: An Update of Recent Progress (2011-2017)

BACKGROUND

Potassium (K+) channels participate in many physiological processes, cardiac function, cell proliferation, neuronal signaling, muscle contractility, immune function, hormone secretion, osmotic pressure, changes in gene expression, and are involved in critical biological functions, and in a variety of diseases. Potassium channels represent a large family of tetrameric membrane proteins. Potassium channels activation reduces excitability, whereas channel inhibition increases excitability.

OBJECTIVE

Small molecule K+ channel activators and inhibitors interact with voltage-gated, inward rectifying, and two-pore tandem potassium channels. Due to their involvement in biological functions, and in a variety of diseases, small molecules as potassium channel modulators have received great scientific attention.

METHODS

In this review, we have compiled the literature, patents and patent applications (2011 to 2017) related to different chemical classes of potassium channel openers and blockers as therapeutic agents for the treatment of various diseases. Many different chemical classes of selective small molecule have emerged as potassium channel modulators over the past years.

CONCLUSION

This review discussed the current understanding of medicinal chemistry research in the field of potassium channel modulators to update the key advances in this field.

Blockade of fast A-type and TEA-sensitive potassium channels provide an antiparkinsonian effect in a 6-OHDA animal model

Objective:

To evaluate the effect of K⁺ channels inhibitors in treatment of parkinson’s disease (PD).

Methods:

This prospective comparative study was conducted in the Qazvin University of Medical Sciences, Iran, from April 2015 to January 2016. Male rats (n=37) received intraperitoneal doses of TEA (2 and 5 mg/kg) or 4-AP (0.5 and 1 mg/kg) twice-daily, before a stereotactic injection of 6-hydroxydopamine (6-OHDA) for the following 7 days. The 6-OHDA was injected into right medial forebrain bundle (MFB) of the rat brains. Development and severity of PD were assessed using the apomorphine-induced rotational test, the elevated body swing test and rotarod tests. Concentration of malondialdehyde (MDA), a marker of oxidative stress, was measured in rat sera.

Results:

Tetraethylammonium and 4-AP significantly reduced the number of apomorphine-induced rotations and improved motor learning in the rotarod test at both doses. Administration of 4-AP and TEA together was more effective than single administration of either agent. Malondialdehyde measurement showed that pretreatment with TEA could not prevent 6-OHDA-induced oxidative stress.

Conclusion:

Our results showed that pretreatment with TEA and 4-AP has a neuroprotective effect against 6-OHDA in dopaminergic neurons in the substantia nigra.

Mechanisms by which fibroblast growth factor 20 improves motor performance in a mouse model of Parkinson's disease

Genome-wide studies have reported that Parkinson’s disease is associated with abnormal expression of various growth factors. In this study, male C57BL/6 mice aged 10 weeks were used to establish Parkinson’s disease models using an intraperitoneal injection of 60 mg/kg 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. 28 days later, 10 or 100 ng fibroblast growth factor 20 was injected intracerebroventricularly. The electrophysiological changes in the mouse hippocampus were recorded using a full-cell patch clamp. Expression of Kv4.2 in the substantia nigra was analyzed using a western blot assay. Serum malondialdehyde levels were analyzed by enzyme-linked immunosorbent assay. The motor coordination of mice was evaluated using the rotarod test. The results showed that fibroblast growth factor 20 decreased A-type potassium current in neurons of the substantia nigra, increased long-term potentiation amplitude in the hippocampus, and downregulated Kv4.2 expression. A high dose of fibroblast growth factor 20 reduced serum malondialdehyde levels and enhanced the motor coordination of mice. These findings confirm that fibroblast growth factor 20 has a therapeutic effect on the toxicity induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and its mechanism of action is associated with the inhibition of A-type K⁺ currents and Kv4.2 expression. All animal procedures were approved by the Animal Care and Use Committee of Qilu Hospital of Shandong University, China in 2017 (approval No. KYLL-2017-0012).

Physiological Roles and Therapeutic Potential of Ca2+ Activated Potassium Channels in the Nervous System

Within the potassium ion channel family, calcium activated potassium (K_Ca) channels are unique in their ability to couple intracellular Ca²⁺ signals to membrane potential variations. K_Ca channels are diversely distributed throughout the central nervous system and play fundamental roles ranging from regulating neuronal excitability to controlling neurotransmitter release. The physiological versatility of K_Ca channels is enhanced by alternative splicing and co-assembly with auxiliary subunits, leading to fundamental differences in distribution, subunit composition and pharmacological profiles. Thus, understanding specific K_Ca channels’ mechanisms in neuronal function is challenging. Based on their single channel conductance, K_Ca channels are divided into three subtypes: small (SK, 4–14 pS), intermediate (IK, 32–39 pS) and big potassium (BK, 200–300 pS) channels. This review describes the biophysical characteristics of these K_Ca channels, as well as their physiological roles and pathological implications. In addition, we also discuss the current pharmacological strategies and challenges to target K_Ca channels for the treatment of various neurological and psychiatric disorders.

Potassium Channels: A Potential Therapeutic Target for Parkinson's Disease

The pathogenesis of the second major neurodegenerative disorder, Parkinson's disease (PD), is closely associated with the dysfunction of potassium (K⁺) channels. Therefore, PD is also considered to be an ion channel disease or neuronal channelopathy. Mounting evidence has shown that K⁺ channels play crucial roles in the regulations of neurotransmitter release, neuronal excitability, and cell volume. Inhibition of K⁺ channels enhances the spontaneous firing frequency of nigral dopamine (DA) neurons, induces a transition from tonic firing to burst discharge, and promotes the release of DA in the striatum. Recently, three K⁺ channels have been identified to protect DA neurons and to improve the motor and non-motor symptoms in PD animal models: small conductance (SK) channels, A-type K⁺ channels, and K_V7/KCNQ channels. In this review, we summarize the physiological and pharmacological effects of the three K⁺ channels. We also describe in detail the laboratory investigations regarding K⁺ channels as a potential therapeutic target for PD.

Diversity of astroglial responses across human neurodegenerative disorders and brain aging

Astrogliopathy refers to alterations of astrocytes occurring in diseases of the nervous system, and it implies the involvement of astrocytes as key elements in the pathogenesis and pathology of diseases and injuries of the central nervous system. Reactive astrocytosis refers to the response of astrocytes to different insults to the nervous system, whereas astrocytopathy indicates hypertrophy, atrophy/degeneration and loss of function and pathological remodeling occurring as a primary cause of a disease or as a factor contributing to the development and progression of a particular disease. Reactive astrocytosis secondary to neuron loss and astrocytopathy due to intrinsic alterations of astrocytes occur in neurodegenerative diseases, overlap each other, and, together with astrocyte senescence, contribute to disease-specific astrogliopathy in aging and neurodegenerative diseases with abnormal protein aggregates in old age. In addition to the well-known increase in glial fibrillary acidic protein and other proteins in reactive astrocytes, astrocytopathy is evidenced by deposition of abnormal proteins such as β-amyloid, hyper-phosphorylated tau, abnormal α-synuclein, mutated huntingtin, phosphorylated TDP-43 and mutated SOD1, and PrPres , in Alzheimer's disease, tauopathies, Lewy body diseases, Huntington's disease, amyotrophic lateral sclerosis and Creutzfeldt-Jakob disease, respectively. Astrocytopathy in these diseases can also be manifested by impaired glutamate transport; abnormal metabolism and release of neurotransmitters; altered potassium, calcium and water channels resulting in abnormal ion and water homeostasis; abnormal glucose metabolism; abnormal lipid and, particularly, cholesterol metabolism; increased oxidative damage and altered oxidative stress responses; increased production of cytokines and mediators of the inflammatory response; altered expression of connexins with deterioration of cell-to-cell networks and transfer of gliotransmitters; and worsening function of the blood brain barrier, among others. Increased knowledge of these aspects will permit a better understanding of brain aging and neurodegenerative diseases in old age as complex disorders in which neurons are not the only players.

The involvement of Eag1 potassium channels and miR-34a in rotenone-induced death of dopaminergic SH-SY5Y cells

The loss of dopaminergic neurons and the resultant motor impairment are hallmarks of Parkinson's disease. The SH‑SY5Y cell line is a model of dopaminergic neurons, and allows for the study of dopaminergic neuronal injury. Previous studies have revealed changes in Ether à go‑go 1 (Eag1) potassium channel expression during p53-induced SH‑SY5Y apoptosis, and the regulatory involvement of microRNA‑34a (miR‑34a) was demonstrated. In the present study, the involvement of Eag1 and miR‑34a in rotenone‑induced SH‑SY5Y cell injury was investigated. Rotenone is a neurotoxin, which is often used to generate models of Parkinson's disease, since it causes the death of nigrostriatal neurons by inducing intracellular aggregation of alpha synuclein and ubiquitin. In the present study, rotenone resulted in a dose‑dependent decrease in cell viability, as revealed by 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide (MTT) and trypan blue cell counting assays. In addition, Eag1 was demonstrated to be constitutively expressed by SH‑SY5Y cells, and involved in cell viability. Suppression of Eag1 with astemizole resulted in a dose‑dependent decrease in cell viability, as revealed by MTT assay. Astemizole also enhanced the severity of rotenone‑induced injury in SH‑SY5Y cells. RNA interference against Eag1, using synthetic small interfering RNAs (siRNAs), corroborated this finding, as siRNAs potentiated rotenone‑induced injury. Eag1‑targeted siRNAs (kv10.1‑3 or EAG1hum_287) resulted in a statistically significant 16.4‑23.5% increase in vulnerability to rotenone. An increased number of apoptotic nuclei were observed in cells transfected with EAG1hum_287. Notably, this siRNA intensified rotenone‑induced apoptosis, as revealed by an increase in caspase 3/7 activity. Conversely, a miR‑34a inhibitor was demonstrated to exert neuroprotective effects. The viability of cells exposed to rotenone for 24 or 48 h and treated with miR‑34a inhibitor was restored by 8.4‑8.8%. In conclusion, Eag1 potassium channels and miR‑34a are involved in the response to rotenone-induced injury in SH‑SY5Y cells. The neuroprotective effect of mir‑34a inhibitors merits further investigations in animal models of Parkinson's disease.

Changes in SK channel expression in the basal ganglia after partial nigrostriatal dopamine lesions in rats: Functional consequences

Parkinson's disease (PD) is a progressive neurodegenerative disease originating from the loss of dopamine (DA) neurons in the substantia nigra pars compacta (SNC). The small-conductance calcium-activated potassium (SK) channels play an essential role in the regulation of midbrain DA neuron activity patterns, as well as excitability of other types of neurons of the basal ganglia. We therefore questioned whether the SK channel expression in the basal ganglia is modified in parkinsonian rats and how this could impact behavioral performance in a reaction time task. We used a rat model of early PD in which the progressive nigrostriatal DA degeneration was produced by bilateral infusions of 6-hydroxydopamine (6-OHDA) into the striatum. In situ hybridization of SK2 and SK3 mRNA and binding of iodinated apamin (SK2/SK3 blocker) were performed at 1, 8 or 21 days postsurgery in sham and 6-OHDA lesion groups. A significant decrease of SK3 channel expression was found in the SNC of lesioned animals at the three time points, with no change of SK2 channel expression. Interestingly, an upregulation of SK2 mRNA and apamin binding was found in the subthalamic nucleus (STN) at 21 days postlesion. These results were confirmed using quantitative real time polymerase chain reaction (qRT-PCR) approach. Functionally, the local infusion of apamin into the STN of parkinsonian rats enhanced the akinetic deficits produced by nigrostriatal DA lesions in a reaction time task while apamin infusion into the SNC had an opposite effect. These effects disappear when the positive modulator of SK channels (CyPPA) is co-administered with apamin. These findings suggest that an upregulation of SK2 channels in the STN may underlie the physiological adjustment to increased subthalamic excitability following partial DA denervation.

Astrocytes as new targets to improve cognitive functions

Astrocytes are now viewed as key elements of brain wiring as well as neuronal communication. Indeed, they not only bridge the gap between metabolic supplies by blood vessels and neurons, but also allow fine control of neurotransmission by providing appropriate signaling molecules and insulation through a tight enwrapping of synapses. Recognition that astroglia is essential to neuronal communication is nevertheless fairly recent and the large body of evidence dissecting such role has focused on the synaptic level by identifying neuro- and gliotransmitters uptaken and released at synaptic or extrasynaptic sites. Yet, more integrated research deciphering the impact of astroglial functions on neuronal network activity have led to the reasonable assumption that the role of astrocytes in supervising synaptic activity translates in influencing neuronal processing and cognitive functions. Several investigations using recent genetic tools now support this notion by showing that inactivating or boosting astroglial function directly affects cognitive abilities. Accordingly, brain diseases resulting in impaired cognitive functions have seen their physiopathological mechanisms revisited in light of this primary protagonist of brain processing. We here provide a review of the current knowledge on the role of astrocytes in cognition and in several brain diseases including neurodegenerative disorders, psychiatric illnesses, as well as other conditions such as epilepsy. Potential astroglial therapeutic targets are also discussed.

Sodium and Potassium Relating to Parkinson's Disease and Traumatic Brain Injury

Alkali metals, especially sodium and potassium, are plentiful and vital in biological systems. They take on important roles in health and disease. Such roles include the regulation of homeostasis, osmosis, blood pressure, electrolytic equilibria, and electric current. However, there is a limit to our present understanding; the ions have a great ability and capacity for action in health and disease, much greater than our current understanding. For the regulation of physiological homeostasis, there is a crucial regulator (renin-angiotensin system, RAS), found at both peripheral and central levels. Misregulation of the Na(+)-K(+) pump, and sodium channels in RAS are important for the understanding of disease progression, hypertension, diabetes, and neurodegenerative diseases, etc. In particular, RAS displays direct or indirect interaction important to Parkinson's disease (PD). In this chapter, the relationship between the regulation of sodium/potassium concentration and PD was sought. In addition, some recent biochemical and clinical findings are also discussed that help describe sodium and potassium in the context of traumatic brain injury (TBI). TBI is caused from the heavy striking of the head; this strongly affects ion flux in the affected tissue (brain) and damages cellular regulation systems. Thus, inappropriate concentrations of ions (hyper- and hyponatremia, and hyper- and hypokalemia) will perturb homeostasis giving rise to important and far reaching effects. These changes also impact osmotic pressure and the concentration of other metal ions, such as the calcium(II) ion.

SK channel blockade reverses cognitive and motor deficits induced by nigrostriatal dopamine lesions in rats

Parkinson's disease has traditionally been viewed as a motor disorder caused by the loss of dopamine (DA) neurons. However, emotional and cognitive syndromes can precede the onset of the motor deficits and provide an opportunity for therapeutic intervention. Potassium channels have recently emerged as potential new targets in the treatment of Parkinson's disease. The selective blockade of small conductance calcium-activated K+ channels (SK channels) by apamin is known to increase burst firing in midbrain DA neurons and therefore DA release. We thus investigated the effects of systemic administration of apamin on the motor, cognitive deficits and anxiety present after bilateral nigrostriatal 6-hydroxydopamine (6-OHDA) lesions in rats. Apamin administration (0.1 or 0.3 mg/kg i.p.) counteracted the depression, anxiety-like behaviors evaluated on sucrose consumption and in the elevated plus maze, social recognition and spatial memory deficits produced by partial 6-OHDA lesions. Apamin also reduced asymmetric motor deficits on circling behavior and postural adjustments in the unilateral extensive 6-OHDA model. The partial 6-OHDA lesions (56% striatal DA depletion) produced 20% decrease of iodinated apamin binding sites in the substantia nigra pars compacta in correlation with the loss of tyrosine hydroxylase positive cells, without modifying apamin binding in brain regions receiving DAergic innervation. Striatal extracellular levels of DA, not detectable after 6-OHDA lesions, were enhanced by apamin treatment as measured by in vivo microdialysis. These results indicate that blocking SK channels may reinstate minimal DA activity in the striatum to alleviate the non-motor symptoms induced by partial striatal DA lesions.

Subcellular expression and neuroprotective effects of SK channels in human dopaminergic neurons

Small-conductance Ca(2+)-activated K(+) channel activation is an emerging therapeutic approach for treatment of neurological diseases, including stroke, amyotrophic lateral sclerosis and schizophrenia. Our previous studies showed that activation of SK channels exerted neuroprotective effects through inhibition of NMDAR-mediated excitotoxicity. In this study, we tested the therapeutic potential of SK channel activation of NS309 (25 μM) in cultured human postmitotic dopaminergic neurons in vitro conditionally immortalized and differentiated from human fetal mesencephalic cells. Quantitative RT-PCR and western blotting analysis showed that differentiated dopaminergic neurons expressed low levels of SK2 channels and high levels of SK1 and SK3 channels. Further, protein analysis of subcellular fractions revealed expression of SK2 channel subtype in mitochondrial-enriched fraction. Mitochondrial complex I inhibitor rotenone (0.5 μM) disrupted the dendritic network of human dopaminergic neurons and induced neuronal death. SK channel activation reduced mitochondrial membrane potential, while it preserved the dendritic network, cell viability and ATP levels after rotenone challenge. Mitochondrial dysfunction and delayed dopaminergic cell death were prevented by increasing and/or stabilizing SK channel activity. Overall, our findings show that activation of SK channels provides protective effects in human dopaminergic neurons, likely via activation of both membrane and mitochondrial SK channels. Thus, SK channels are promising therapeutic targets for neurodegenerative disorders such as Parkinson's disease, where dopaminergic cell loss is associated with progression of the disease.

Mitochondrial small conductance SK2 channels prevent glutamate-induced oxytosis and mitochondrial dysfunction

Small conductance calcium-activated potassium (SK2/K(Ca)2.2) channels are known to be located in the neuronal plasma membrane where they provide feedback control of NMDA receptor activity. Here, we provide evidence that SK2 channels are also located in the inner mitochondrial membrane of neuronal mitochondria. Patch clamp recordings in isolated mitoplasts suggest insertion into the inner mitochondrial membrane with the C and N termini facing the intermembrane space. Activation of SK channels increased mitochondrial K(+) currents, whereas channel inhibition attenuated these currents. In a model of glutamate toxicity, activation of SK2 channels attenuated the loss of the mitochondrial transmembrane potential, blocked mitochondrial fission, prevented the release of proapoptotic mitochondrial proteins, and reduced cell death. Neuroprotection was blocked by specific SK2 inhibitory peptides and siRNA targeting SK2 channels. Activation of mitochondrial SK2 channels may therefore represent promising targets for neuroprotective strategies in conditions of mitochondrial dysfunction.

Potassium channels: a review of broadening therapeutic possibilities for neurological diseases

Potassium (K(+)) channels are encoded by approximately 80 genes in mammals. They are expressed in many tissues and have diverse physiological roles. Human K(+) channels are divided mainly into calcium (Ca(2+))-activated (K(Ca)), inward-rectifying (K(IR)), two-pore (K(2P)), and voltage-gated (K(v)) channels. The K(v) channels form the largest family, with approximately 40 genes. Owing to their involvement in many diseases and their specific expression patterns and physiological roles, K(+) channels present an attractive target for the development of new therapies. This review summarizes the physiological and pathophysiological roles of various potassium channels with respect to their therapeutic potential for disorders with a disturbed neuronal excitability such as epilepsy, migraine, neuropathic pain, or stroke.

Chronic dopamine depletion augments the functional expression of K-ATP channels in the rat subthalamic nucleus

Symptoms of Parkinson's disease caused by dopamine depletion are associated with burst firing in the subthalamic nucleus (STN). Moreover, regularization or suppression of STN neuronal activity is thought to improve symptoms of Parkinson's disease. We reported recently that N-methyl-D-aspartate (NMDA) receptor stimulation of rat STN neurons evokes ATP-sensitive K(+) (K-ATP) current via a Ca(2+)- and nitric oxide-dependent mechanism. The present studies were done to determine whether or not K-ATP channel function in STN neurons is altered in a model of chronic dopamine depletion. Brain slices were prepared from rats with unilateral dopamine depletion caused by intracerebral 6-hydroxydopamine (6-OHDA) injections. Whole-cell patch-clamp recordings showed that NMDA evoked more outward current at -70 mV and greater positive slope conductance in STN neurons located ipsilateral to 6-OHDA treatment compared to neurons located contralateral. Moreover, extracellular, loose-patch recordings showed that NMDA increased spontaneous firing rate in STN neurons in slices from normal rats, whereas NMDA produced a tolbutamide-sensitive inhibition of firing rate in STN neurons located ipsilateral to 6-OHDA treatment. These results show that K-ATP channel function in STN neurons is up-regulated by chronic dopamine deficiency. We suggest that K-ATP channel activation in the STN might benefit symptoms of Parkinson's disease.

Verification of expressions of Kir2 as potential peripheral biomarkers in lymphocytes from patients with Parkinson's disease

Prior studies have reported gene expression alterations in peripheral blood lymphocytes (PBLs) obtained from patients with Parkinson's disease (PD) as compared to healthy controls. These alterations can not only be regarded as potential biomarkers, but also enhance understanding of the pathogenic mechanism of PD. In the present study, the gene expression levels of dopamine receptor (D2, D3), inward rectified potassium channels subunits Kir2 (Kir2.1, Kir2.2, Kir2.3, Kir2.4) and ATP-sensitive potassium channel subunit Kir6.2 in PBLs were analyzed using quantitative real-time PCR among 20 PD patients with medication, 10 PD patients without medication and 16 healthy controls, respectively. The results showed that there was a significantly decrease of the D2, D3 mRNA expression in PBLs of PD patients compared with that in healthy controls. The four inward rectified potassium channels Kir2.1, Kir2.2, Kir2.3, and Kir2.4 mRNA expression in PBLs from PD patients were also significantly down-regulated than that from age-matched healthy controls. However, there was no apparent difference in expression of another potassium channel Kir6.2 mRNA between PD patients and healthy controls. We proposed that the Kir2 potassium channels mRNA on blood lymphocytes may be regarded as a potential biomarker for PD screening.

Progesterone blocks multiple routes of ion flux

The administration of progesterone as a neuroprotective agent following traumatic brain injury has recently entered phase III clinical trials. Previous work has demonstrated that therapeutic concentrations of progesterone decrease excitotoxicity through direct inhibition of voltage-gated calcium channels, an action independent of the nuclear progesterone receptor. Here we report using cultured rat striatal neurons that these same concentrations of progesterone also block voltage-gated potassium channels, sodium channels and GABA(A) currents. The actions of progesterone act at the surface membrane of neurons in a steroid specific, voltage-independent, concentration-dependent manner. Notably, these broad actions of progesterone on ion channel and neurotransmitter receptor function mirror those of dihydropyridines, and indicate potential shared mechanisms of action, the prospective of additional therapeutic applications, and possibly, untoward effects.

Modulation of the activity of dopaminergic neurons by SK channels: a potential target for the treatment of Parkinson's disease?

SK channels are small conductance calcium-activated potassium channels that are widely expressed in different neurons with distinct subtypes. They play an important role in modulating synaptic plasticity, dopaminergic neurotransmission, and learning and memory. The present review was mainly focused on the recent findings on the contradictory roles of SK channels in modulating dopaminergic neurons in substantia nigra and in the pathogenesis of Parkinson's disease (PD). Besides, whether modulation of SK channels could be a potential target for PD treatment was also discussed.

Evidence for gender-specific transcriptional profiles of nigral dopamine neurons in Parkinson disease

Background

Epidemiological data suggest that the male gender is one of the risks factors for the development of Parkinson Disease (PD). Also, differences in the clinical manifestation and the course of PD have been observed between males and females. However, little is known about the molecular aspects underlying gender-specificity in PD. To address this issue, we determined the gene expression profiles of male and female dopamine (DA) neurons in sporadic PD.

Methodology/Principal Findings

We analyzed Affymetrix-based microarrays on laser microdissected DA neurons from postmortem brains of sporadic PD patients and age-matched controls across genders. Pathway enrichment demonstrated that major cellular pathways involved in PD pathogenesis showed different patterns of deregulation between males and females with more prominent downregulation of genes related to oxidative phosporylation, apoptosis, synaptic transmission and transmission of nerve impulse in the male population. In addition, we found upregulation of gene products for metabolic processes and mitochondrial energy consumption in the age-matched male control neurons. On the single cell level, selected data validation using quantitative Real-Time (qRT)-PCR was consistent with microarray raw data and supported some of the observations from data analysis.

Conclusions/Significance

On the molecular level, our results provide evidence that the expression profiles of aged normal and PD midbrain DA neurons are gender-specific. The observed differences in the expression profiles suggest a disease bias of the male gender, which could be in concordance with clinical observations that the male gender represents a risk factor for sporadic PD. Validation of gene expression by qRT-PCR supported the microarray results, but also pointed to several caveats involved in data interpretation.