Calcium Channel CaV2.3 Subunits Regulate Hepatic Glucose Production by Modulating Leptin-Induced Excitation of Arcuate Pro-opiomelanocortin Neurons.

Leptin acts on hypothalamic pro-opiomelanocortin (POMC) neurons to regulate glucose homeostasis, but the precise mechanisms remain unclear. Here, we demonstrate that leptin-induced depolarization of POMC neurons is associated with the augmentation of a voltage-gated calcium (CaV) conductance with the properties of the "R-type" channel. Knockdown of the pore-forming subunit of the R-type (CaV2.3 or Cacna1e) conductance in hypothalamic POMC neurons prevented sustained leptin-induced depolarization. In vivo POMC-specific Cacna1e knockdown increased hepatic glucose production and insulin resistance, while body weight, feeding, or leptin-induced suppression of food intake were not changed. These findings link Cacna1e function to leptin-mediated POMC neuron excitability and glucose homeostasis and may provide a target for the treatment of diabetes.

Effect of electroacupuncture on gene expression in calcium signaling pathway in hippocampal cells in mice with cerebral ischemia reperfusion.

OBJECTIVE: To observe the regulation of electroacupuncture on gene expression at calcium signaling pathways in mice with cerebral ischemia reperfusion. METHODS: Sixty male, inbred Kunming mice were randomly assigned to three groups: repeated cerebral ischemia reperfusion group (RG, n = 24), sham-operated group (SG, n = 12), and electroacupuncture group (EG, n = 24). Mice in RG and EG groups were modeled by repeated cerebral ischemia reperfusion surgery, and EG mice were treated with electroacupuncture for 30 min after recovery from anesthesia. Changes in gene expression profile of mice hippocampi were analyzed by global expression profile microarray. Genes that were up-regulated or down-regulated greater than 1.5 folds were considered to be biologically meaningful. Real-time quantitative polymerase chain reaction (q-PCR) method was used to verify the expression of selected genes based on the algorithm [2^ (ΔΔCt)]. RESULTS: Compared with SG mice, 242 genes showed different in expressions in RG mice: 107 down-regulated and 135 up-regulated. Compared with RG mice, 609 genes showed a difference of expression in EG mice: 315 down-regulated and 375 up-regulated. Gene ontology and Kyoto Encyclopedia of Genes and Genomes analyses indicated two pathways: calcium signaling and long-term potentiation in which 11 differentially expressed genes selected. Six of the 11 genes in the calcium signaling pathway were verified after real-time q-PCR testing. CONCLUSION: Electroacupuncture treatment of cerebral ischemia reperfusion appears to regulate Atp2a2, Cacna1e, Camk2a, Gnas, Grm1, Rapgef3 genes in the calcium signaling pathway.

Lipid Regulation of Acrosome Exocytosis.

Lipids are critical regulators of mammalian sperm function, first helping prevent premature acrosome exocytosis, then enabling sperm to become competent to fertilize at the right place/time through the process of capacitation, and ultimately triggering acrosome exocytosis. Yet because they do not fit neatly into the "DNA--RNA-protein" synthetic pathway, they are understudied and poorly understood. Here, we focus on three lipids or lipid classes-cholesterol, phospholipids, and the ganglioside G(M1)--in context of the modern paradigm of acrosome exocytosis. We describe how these various- species are precisely segregated into membrane macrodomains and microdomains, simultaneously preventing premature exocytosis while acting as foci for organizing regulatory and effector molecules that will enable exocytosis. Although the mechanisms responsible for these domains are poorly defined, there is substantial evidence for their composition and functions. We present diverse ways that lipids and lipid modifications regulate capacitation and acrosome exocytosis, describing in more detail how removal of cholesterol plays a master regulatory role in enabling exocytosis through at least two complementary pathways. First, cholesterol efflux leads to proteolytic activation of phospholipase B, which cleaves both phospholipid tails. The resultant changes in membrane curvature provide a mechanism for the point fusions now known to occur far before a sperm physically interacts with the zona pellucida. Cholesterol efflux also enables G(M1) to regulate the voltage-dependent cation channel, Ca(V)2.3, triggering focal calcium transients required for acrosome exocytosis in response to subsequent whole-cell calcium rises. We close with a model integrating functions for lipids in regulating acrosome exocytosis.

A novel explanation for observed CaMKII dynamics in dendritic spines with added EGTA or BAPTA.

We present a simplified reaction network in a single well-mixed volume that captures the general features of CaMKII dynamics observed during both synaptic input and spine depolarization. Our model can also account for the greater-than-control CaMKII activation observed with added EGTA during depolarization. Calcium input currents are modeled after experimental observations, and existing models of calmodulin and CaMKII autophosphorylation are used. After calibration against CaMKII activation data in the absence of chelators, CaMKII activation dynamics due to synaptic input via n-methyl-d-aspartate receptors are qualitatively accounted for in the presence of the chelators EGTA and BAPTA without additional adjustments to the model. To account for CaMKII activation dynamics during spine depolarization with added EGTA or BAPTA, the model invokes the modulation of CaV2.3 (R-type) voltage-dependent calcium channel (VDCC) currents observed in the presence of EGTA or BAPTA. To our knowledge, this is a novel explanation for the increased CaMKII activation seen in dendritic spines with added EGTA, and suggests that differential modulation of VDCCs by EGTA and BAPTA offers an alternative or complementary explanation for other experimental results in which addition of EGTA or BAPTA produces different effects. Our results also show that a simplified reaction network in a single, well-mixed compartment is sufficient to account for the general features of observed CaMKII dynamics.

The CaV2.3 R-type voltage-gated Ca2+ channel in mouse sleep architecture.

STUDY OBJECTIVES: Voltage-gated Ca(2+) channels (VGCCs) are key elements in mediating thalamocortical rhythmicity. Low-voltage activated (LVA) CaV 3 T-type Ca(2+) channels have been related to thalamic rebound burst firing and to generation of non-rapid eye movement (NREM) sleep. High-voltage activated (HVA) CaV 1 L-type Ca(2+) channels, on the opposite, favor the tonic mode of action associated with higher levels of vigilance. However, the role of the HVA Non-L-type CaV2.3 Ca(2+) channels, which are predominantly expressed in the reticular thalamic nucleus (RTN), still remains unclear. Recently, CaV2.3(-/-) mice were reported to exhibit altered spike-wave discharge (SWD)/absence seizure susceptibility supported by the observation that CaV2.3 mediated Ca(2+) influx into RTN neurons can trigger small-conductance Ca(2+)-activated K(+)-channel type 2 (SK2) currents capable of maintaining thalamic burst activity. Based on these studies we investigated the role of CaV2.3 R-type Ca(2+) channels in rodent sleep. METHODS: The role of CaV2.3 Ca(2+) channels was analyzed in CaV2.3(-/-) mice and controls in both spontaneous and artificial urethane-induced sleep, using implantable video-EEG radiotelemetry. Data were analyzed for alterations in sleep architecture using sleep staging software and time-frequency analysis. RESULTS: CaV2.3 deficient mice exhibited reduced wake duration and increased slow-wave sleep (SWS). Whereas mean sleep stage durations remained unchanged, the total number of SWS epochs was increased in CaV2.3(-/-) mice. Additional changes were observed for sleep stage transitions and EEG amplitudes. Furthermore, urethane-induced SWS mimicked spontaneous sleep results obtained from CaV2.3 deficient mice. Quantitative Real-time PCR did not reveal changes in thalamic CaV3 T-type Ca(2+) channel expression. The detailed mechanisms of SWS increase in CaV2.3(-/-) mice remain to be determined. CONCLUSIONS: Low-voltage activated CaV2.3 R-type Ca(2+) channels in the thalamocortical loop and extra-thalamocortical circuitries substantially regulate rodent sleep architecture thus representing a novel potential target for pharmacological treatment of sleep disorders in the future.

A fluorescence-based high-throughput screening assay for the identification of T-type calcium channel blockers.

T-type voltage-gated Ca(2+) channels have been implicated in contributing to a broad variety of human disorders, including pain, epilepsy, sleep disturbances, cardiac arrhythmias, and certain types of cancer. However, potent and selective T-type Ca(2+) channel modulators are not yet available for clinical use. This may in part be due to their unique biophysical properties that have delayed the development of high-throughput screening (HTS) assays for identifying blockers. One notable challenge is that at the normal resting membrane potential (V(m)) of cell lines commonly utilized for drug screening purposes, T-type Ca(2+) channels are largely inactivated and thus cannot be supported by typical formats of functional HTS assays to both evoke and quantify the Ca(2+) channel signal. Here we describe a simple method that can successfully support a fluorescence-based functional assay for compounds that modulate T-type Ca(2+)channels. The assay functions by exploiting the pore-forming properties of gramicidin to control the cellular V(m) in advance of T-type Ca(2+) channel activation. Using selected ionic conditions in the presence of gramicidin, T-type Ca(2+) channels are converted from the unavailable, inactivated state to the available, resting state, where they can be subsequently activated by application of extracellular K(+). The fidelity of the assay has been pharmacologically characterized with sample T-type Ca(2+) channel blockers whose potency has been determined by conventional manual patch-clamp techniques. This method has the potential for applications in high-throughput fluorometric imaging plate reader (FLIPR(R), Molecular Devices, Sunnyvale, CA) formats with cell lines expressing either recombinant or endogenous T-type Ca(2+) channels.

Altered thalamocortical rhythmicity in Ca(v)2.3-deficient mice.

Voltage-gated calcium channels (VGCCs) are key regulators of neuronal excitability and important factors in epileptogenesis and neurodegeneration. Recent findings suggest a novel, important proictogenic and proneuroapoptotic role of the Ca(v)2.3 E/R-type VGCCs in convulsive generalized tonic-clonic and hippocampal seizures. Though Ca(v)2.3 is also expressed in key structures of the thalamocortical circuitry, their functional relevance in non-convulsive absence seizure activity remains unknown. To this end, we investigated absence specific spike-wave discharge (SWD) susceptibility in control and Ca(v)2.3-deficient mice by systemic administration of gamma-hydroxybutyrolactone (GBL, 70 mg/kg i.p.), followed by electrocorticographic radiotelemetric recordings, behavioral analysis and histomorphological characterization. Based on motoric studies, SWD and power-spectrum density (PSD) analysis, our results demonstrate that Ca(v)2.3(-/-) mice exhibit increased absence seizure susceptibility and altered absence seizure architecture compared to control animals. This study provides evidence for the first time that Ca(v)2.3 E/R-type Ca2+ channels are important in modulating thalamocortical hyperoscillation exerting anti-epileptogenic effects in non-convulsive absence seizures.

Subunits of voltage-gated calcium channels in murine spiral ganglion cells.

CONCLUSION: The results show that alpha1D, alpha1E, alpha2/delta, beta1, and beta3 subunits are expressed in spiral ganglion cells (SGCs), and the coexpression of alpha1D and alpha1E suggests the presence of L-type and R-type calcium channels in mammalian SGCs. OBJECTIVE: To investigate the types of subunits of voltage-gated calcium channels in SGCs of the mouse. MATERIALS AND METHODS: SGCs were isolated from cochleae of neonatal mice and cultured for 24 h. Total RNA was extracted from cultured cells. After reverse transcription, the resulting cDNA was amplified by PCR with primers targeted to nucleotide sequences corresponding to seven different calcium channel subunits. The types of calcium channel subunits were identified by PCR analysis and nucleotide sequencing. RESULTS: RT-PCR showed the strong and consistent amplification of alpha1D, alpha1E, alpha2/delta, beta1, and beta3 subunits from the mRNA of SGCs, and nucleotide sequencing confirmed the identity of mouse cochlear subunit cDNAs.

Preassociation of calmodulin with voltage-gated Ca(2+) channels revealed by FRET in single living cells.

Among the most intriguing forms of Ca(2+) channel modulation is the regulation of L-type and P/Q-type channels by intracellular Ca(2+), acting via unconventional channel-calmodulin (CaM) interactions. In particular, overexpressing Ca(2+)-insensitive mutant CaM abolishes Ca(2+)-dependent modulation, hinting that Ca(2+)-free CaM may "preassociate" with these channels to enhance detection of local Ca(2+). Despite the far-reaching consequences of this proposal, in vitro experiments testing for preassociation provide conflicting results. Here, we develop a three filter-cube fluorescence resonance energy transfer method (three-cube FRET) to directly probe for constitutive associations between channel subunits and CaM in single living cells. This FRET assay detects Ca(2+)-independent associations between CaM and the pore-forming alpha(1) subunit of L-type, P/Q-type, and, surprisingly, R-type channels. These results now definitively demonstrate channel-CaM preassociation in resting cells and underscore the potential of three-cube FRET for probing protein-protein interactions.

Sarco-endoplasmic ATPase blocker 2,5-Di(tert-butyl)-1, 4-benzohydroquinone inhibits N-, P-, and Q- but not T-, L-, or R-type calcium currents in central and peripheral neurons.

The effects of 2,5-di(tert-butyl)-1,4-benzohydroquinone (tBHQ), a synthetic phenolic antioxidant and a blocker of the sarco-endoplasmic ATPase, were evaluated on low and high voltage-activated Ca(2+) currents (ICas) with rodent dorsal root ganglion, hippocampal, and motor neurons. In all cell types tested, tBHQ (IC(50) = 35 microM) blocked ICa at concentrations used to inhibit sarco-endoplasmic ATPase. This effect was specific to tBHQ because the other sarco-endoplasmic reticulum calcium ATPase pump inhibitors (thapsigargin and cyclopiazonic acid) had no effect. Selective blockade of the N-type current with omega-conotoxin GVIA and of P- (motoneuron) or Q-type currents (hippocampal neuron) with omega-agatoxin IVA indicated that tBHQ inhibited N, P, and Q types of ICa. tBHQ had no effect on nitrendipine-sensitive (L-type) and residual drug-resistant (R-type) ICa, nor on the low voltage-activated T-type ICa. Contrary to neuronal cells, the L-type ICa was inhibited by tBHQ in a differentiated mouse neuroblastoma and rat glioma hybrid cell line. Injection of cDNAs encoding the alpha1A, alpha1B, alpha1C, and alpha1E subunits into oocytes showed that tBHQ blocked ICas at the level of the pore-forming protein. This effect of tBHQ on ICa should be considered when interpreting results obtained with tBHQ used on neuronal preparations. It also may be useful for developing new strategies for the generation of more potent intracellular calcium transient inhibitors.