107 research outputs found
T-type calcium channel Cav3.2 modulates dentate gyrus granule cell excitability and plasticity in a maturational stage dependent manner
No full textThroughout the brain, calcium influx via low-threshold-activated T-type calcium channels shapes neuronal excitability and plasticity contributing to numerous physiological functions such as sleep and nociception. Under pathophysiological conditions, T-type calcium channels can also impart aberrant neuronal excitability, contributing to disorders such as epilepsy. The T-type channel subtype Cav3.2 is highly expressed in the dentate gyrus (DG) of the hippocampus and mice lacking Cav3.2 (KO) exhibit impairments in hippocampal dependent learning and memory tasks, as well as attenuated development of pilocarpine induced temporal lobe epilepsy. As a result of ongoing neurogenesis, DG granule cells (GCs) are a heterogenous population with varying degrees of maturation. Throughout their maturation, GC morphology and expression of ion channels develops, altering their intrinsic excitability. While initial studies identified a role for Cav3.2 channels in the excitability of mature DG GCs, their functional relevance to the intrinsic excitability and plasticity of different GC subpopulations has not yet been examined. Using Cav3.2 knockout (KO) mice, I first examined how loss of Cav3.2 channels alters both GC intrinsic excitability and the processing of frequency-dependent inputs in subpopulations of GCs. Loss of Cav3.2 channels impacted firing patterns characteristic of GCs maturational stages, reducing low-threshold calcium spikes in immature GCs and regulating firing frequency as GCs matured. I further explored how these maturational dependent effects on intrinsic excitability impact the DG circuit by examining synaptic activity and plasticity at the medial perforant path synapse. Loss of Cav3.2 channels impaired synaptic plasticity, leading to reduced post-tetanic potentiation following theta-based stimulation. Together, these results identify Cav3.2 channels as key regulators of GC excitability and plasticity that emerge early in their maturation. Calcium influx via Cav3.2 channels is therefore predicted to have maturation-dependent contributions to DG processes including GC survival, integration and excitability, relevant for physiological functions such as learning and memory as well as pathological processes including acquired temporal lobe epilepsy.Medicine, Faculty ofGraduat
Epigallocatechin-3-gallate elicits Ca2+ spike in MCF-7 breast cancer cells: essential role of Cav3.2 channels.
No full textWe used MCF-7 human breast cancer cells that endogenously express Cav3.1 and Cav3.2 T-type Ca2+ channels toward a mechanistic study on the effect of EGCG on [Ca2+]i. Confocal Ca2+ imaging showed that EGCG induces a [Ca2+]i spike which is due to extracellular Ca2+ entry and is sensitive to catalase and to low-specificity (mibefradil) and high-specificity (Z944) T-type Ca2+channel blockers. siRNA knockdown of T-type Ca2+ channels indicated the involvement of Cav3.2 but not Cav3.1. Application of EGCG to HEK cells expressing either Cav3.2 or Cav3.1 induced enhancement of Cav3.2 and inhibition of Cav3.1 channel activity. Measurements of K+ currents in MCF-7 cells showed a reversible, catalase-sensitive inhibitory effect of EGCG, while siRNA for the Kv1.1 K+ channel induced a reduction of the EGCG [Ca2+]i spike. siRNA for Cav3.2 reduced EGCG cytotoxicity to MCF-7 cells, as measured by calcein viability assay. Together, data suggest that EGCG promotes the activation of Cav3.2 channels through K+ current inhibition leading to membrane depolarization, and in addition increases Cav3.2 currents. Cav3.2 channels are in part responsible for EGCG inhibition of MCF-7 viability, suggesting that deregulation of [Ca2+]i by EGCG may be relevant in breast cancer treatment
Amyotrophic lateral sclerosis-immunoglobulins selectively interact with neuromuscular junctions expressing P/Q-type calcium channels
No full textAmyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by a gradual loss of motoneurons. The majority of ALS cases are associated with a sporadic form whose etiology is unknown. Several pieces of evidence favor autoimmunity as a potential contributor to sporadic ALS pathology. To gain understanding concerning possible antigens interacting with IgGs from sporadic ALS patients (ALS-IgGs), we studied immunoreactivity against neuromuscular junction (NMJ), spinal cord and cerebellum of mice with and without the Ca V2.1 pore-forming subunit of the P/Q-type voltage-gated calcium (Ca 2+) channel. ALS-IgGs showed a strong reactivity against NMJs of wild-type diaphragms. ALS-IgGs also increased muscle miniature end-plate potential frequency, suggesting a functional role for ALS-IgGs on synaptic signaling. In support, in mice lacking the Ca V2.1 subunit ALS-IgGs showed significantly reduced NMJ immunoreactivity and did not alter spontaneous acetylcholine release. This difference in reactivity was absent when comparing N-type Ca 2+ channel wild-type or null mice. These results are particularly relevant because motoneurons are known to be early pathogenic targets in ALS. Our findings add further evidence supporting autoimmunity as one of the possible mechanisms contributing to ALS pathology. They also suggest that serum autoantibodies in a subset of ALS patients would interact with NMJ proteins down-regulated when P/Q-type channels are absent. © 2011 International Society for Neurochemistry.Fil: Gonzalez, Laura Elisabeth. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Biológica; ArgentinaFil: Kotler, Monica Lidia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Biológica; ArgentinaFil: Vattino, Lucas Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; ArgentinaFil: Conti, Eugenia. Hospital Británico de Buenos Aires; ArgentinaFil: Reisin, Ricardo C.. Hospital Británico de Buenos Aires; ArgentinaFil: Mulatz, Kirk J.. University of British Columbia; CanadáFil: Snutch, Terrance P.. University of British Columbia; CanadáFil: Uchitel, Osvaldo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; Argentin
Behavioural effects of novel clinical candidate drugs, l-tetrahydropalmatine (l-THP) and Z944, on morphine withdrawal-induced hyperalgesia
No full textOpioid use disorder (OUD) is a major contributor to drug-related deaths worldwide. Opioid use cessation causes severe withdrawal symptoms, including prominent hyperalgesia – a contributor to the negative reinforcement of drug taking. Effective pain control is an underappreciated aspect of managing opioid withdrawal, and its absence presents a significant barrier to successful opioid detoxification. Exploring analgesic interventions for withdrawal-induced hyperalgesia may reveal novel OUD therapies. This thesis describes a model of hyperalgesia in both acute and extended withdrawal in morphine-dependent animals and the effect of two clinical candidate analgesic drugs on withdrawal-induced hyperalgesia. l-Tetrahydropalmatine (l-THP) is a tetrahydroprotoberberine compound and active ingredient of a botanical formulation used in Vietnam for OUD treatment with preclinical efficacy in neuropathic pain models. Z944 is a selective T-type calcium channel antagonist undergoing clinical trials as an anticonvulsive and analgesic. To establish drug dependence modelling intermittent access during abuse scenarios, morphine (15 mg/kg, i.p.) was given once a day, 5 days/week and Von Frey tests were conducted 2-3 times a week ~23 h after morphine injection. Animals subjected to three weeks of morphine treatment experienced a ~30% reduction in pain tolerance. To model hyperalgesia during detoxification, animals entered abstinence after 3 weeks of morphine treatment and with Von Frey testing showing that hyperalgesia was persistent for 14 days before spontaneous recovery. Both l-THP (5 or 7.5 mg/kg, p.o.) and Z944 (10 mg/kg, p.o.) were effective at attenuating hyperalgesia during acute withdrawal. Seven-day treatment with l-THP (5 mg/kg) or Z944 (10 mg/kg) in morphine-dependent animals undergoing extended withdrawal resulted in a significant increase in paw retraction thresholds compared to controls and this effect persisted after the completion of treatment. Importantly, the improvement in pain tolerance remained after treatment completion, hastening pain tolerance recovery to baseline by 61% and 80% (l-THP and Z944, respectively). Neither candidate drug influenced mechanical sensitivity in morphine-naïve animals. Overall, these findings support the hypothesis that pain management during detoxification is necessary for improved treatment outcomes. l-THP and Z944, therefore, may be a valuable addition to the currently limited arsenal of opioid detoxification treatments.Medicine, Faculty ofGraduat
A translational strategy to the identification of novel T-type calcium channel blockers targeting epilepsy
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The Sodium “Leak” Has Finally Been Plugged
No full textMost electrophysiologists generally do not speak highly of leak currents. In reality, these conductances represent a crucial functional mechanism by which neurons control resting membrane potentials. A new study in Cell by Lu et al. has surprisingly confirmed the identity of the long-sought voltage-insensitive sodium leak conductance to be encoded by the third branch of the voltage-gated sodium and calcium channel family
T-type calcium channels in burst-firing, network synchrony, and epilepsy
No full textAbstractLow voltage-activated (LVA) T-type calcium channels are well regarded as a key mechanism underlying the generation of neuronal burst-firing. Their low threshold for activation combined with a rapid and transient calcium conductance generates low-threshold calcium potentials (LTCPs), upon the crest of which high frequency action potentials fire for a brief period. Experiments using simultaneous electroencephalography (EEG) and intracellular recordings demonstrate that neuronal burst-firing is a likely causative component in the generation of normal sleep patterns as well as some pathophysiological conditions, such as epileptic seizures. However, less is known as to how these neuronal bursts impact brain behavior, in particular network synchronization. In this review we summarize recent findings concerning the role of T-type calcium channels in burst-firing and discuss how they likely contribute to the generation of network synchrony. We further outline the function of burst-firing and network synchrony in terms of epileptic seizures. This article is part of a Special Issue entitled: Calcium channels
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