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Voltage-gated calcium channels in genetic epilepsies. J Neurochem 2023. [PMID: 37822150 DOI: 10.1111/jnc.15983] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2023] [Revised: 09/17/2023] [Accepted: 09/25/2023] [Indexed: 10/13/2023]
Abstract
Voltage-gated calcium channels (VGCC) are abundant in the central nervous system and serve a broad spectrum of functions, either directly in cellular excitability or indirectly to regulate Ca2+ homeostasis. Ca2+ ions act as one of the main connections in excitation-transcription coupling, muscle contraction and excitation-exocytosis coupling, including synaptic transmission. In recent years, many genes encoding VGCCs main α or additional auxiliary subunits have been associated with epilepsy. This review sums up the current state of knowledge on disease mechanisms and provides guidance on disease-specific therapies where applicable.
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Contributions of Ca V1.3 Channels to Ca 2+ Current and Ca 2+-Activated BK Current in the Suprachiasmatic Nucleus. Front Physiol 2021; 12:737291. [PMID: 34650447 PMCID: PMC8505962 DOI: 10.3389/fphys.2021.737291] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Accepted: 08/30/2021] [Indexed: 11/29/2022] Open
Abstract
Daily regulation of Ca2+– and voltage-activated BK K+ channel activity is required for action potential rhythmicity in the suprachiasmatic nucleus (SCN) of the hypothalamus, the brain's circadian clock. In SCN neurons, BK activation is dependent upon multiple types of Ca2+ channels in a circadian manner. Daytime BK current predominantly requires Ca2+ influx through L-type Ca2+ channels (LTCCs), a time when BK channels are closely coupled with their Ca2+ source. Here we show that daytime BK current is resistant to the Ca2+ chelator BAPTA. However, at night when LTCCs contribute little to BK activation, BK current decreases by a third in BAPTA compared to control EGTA conditions. In phase with this time-of-day specific effect on BK current activation, LTCC current is larger during the day. The specific Ca2+ channel subtypes underlying the LTCC current in SCN, as well as the subtypes contributing the Ca2+ influx relevant for BK current activation, have not been identified. SCN neurons express two LTCC subtypes, CaV1.2 and CaV1.3. While a role for CaV1.2 channels has been identified during the night, CaV1.3 channel modulation has also been suggested to contribute to daytime SCN action potential activity, as well as subthreshold Ca2+ oscillations. Here we characterize the role of CaV1.3 channels in LTCC and BK current activation in SCN neurons using a global deletion of CACNA1D in mouse (CaV1.3 KO). CaV1.3 KO SCN neurons had a 50% reduction in the daytime LTCC current, but not total Ca2+ current, with no difference in Ca2+ current levels at night. During the day, CaV1.3 KO neurons exhibited oscillations in membrane potential, and most neurons, although not all, also had BK currents. Changes in BK current activation were only detectable at the highest voltage tested. These data show that while CaV1.3 channels contribute to the daytime Ca2+ current, this does not translate into a major effect on the daytime BK current. These data suggest that BK current activation does not absolutely require CaV1.3 channels and may therefore also depend on other LTCC subtypes, such as CaV1.2.
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Kv3.1 and Kv3.3 subunits differentially contribute to Kv3 channels and action potential repolarization in principal neurons of the auditory brainstem. J Physiol 2020; 598:2199-2222. [DOI: 10.1113/jp279668] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2020] [Accepted: 03/25/2020] [Indexed: 12/13/2022] Open
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Topographic map refinement and synaptic strengthening of a sound localization circuit require spontaneous peripheral activity. J Physiol 2019; 597:5469-5493. [PMID: 31529505 DOI: 10.1113/jp277757] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2019] [Accepted: 09/13/2019] [Indexed: 12/21/2022] Open
Abstract
KEY POINTS Loss of the calcium sensor otoferlin disrupts neurotransmission from inner hair cells. Central auditory nuclei are functionally denervated in otoferlin knockout mice (Otof KOs) via gene ablation confined to the periphery. We employed juvenile and young adult Otof KO mice (postnatal days (P)10-12 and P27-49) as a model for lacking spontaneous activity and deafness, respectively. We studied the impact of peripheral activity on synaptic refinement in the sound localization circuit from the medial nucleus of the trapezoid body (MNTB) to the lateral superior olive (LSO). MNTB in vivo recordings demonstrated drastically reduced spontaneous spiking and deafness in Otof KOs. Juvenile KOs showed impaired synapse elimination and strengthening, manifested by broader MNTB-LSO inputs, imprecise MNTB-LSO topography and weaker MNTB-LSO fibres. The impairments persisted into young adulthood. Further functional refinement after hearing onset was undetected in young adult wild-types. Collectively, activity deprivation confined to peripheral protein loss impairs functional MNTB-LSO refinement during a critical prehearing period. ABSTRACT Circuit refinement is critical for the developing sound localization pathways in the auditory brainstem. In prehearing mice (hearing onset around postnatal day (P)12), spontaneous activity propagates from the periphery to central auditory nuclei. At the glycinergic projection from the medial nucleus of the trapezoid body (MNTB) to the lateral superior olive (LSO) of neonatal mice, super-numerous MNTB fibres innervate a given LSO neuron. Between P4 and P9, MNTB fibres are functionally eliminated, whereas the remaining fibres are strengthened. Little is known about MNTB-LSO circuit refinement after P20. Moreover, MNTB-LSO refinement upon activity deprivation confined to the periphery is largely unexplored. This leaves a considerable knowledge gap, as deprivation often occurs in patients with congenital deafness, e.g. upon mutations in the otoferlin gene (OTOF). Here, we analysed juvenile (P10-12) and young adult (P27-49) otoferlin knockout (Otof KO) mice with respect to MNTB-LSO refinement. MNTB in vivo recordings revealed drastically reduced spontaneous activity and deafness in knockouts (KOs), confirming deprivation. As RNA sequencing revealed Otof absence in the MNTB and LSO of wild-types, Otof loss in KOs is specific to the periphery. Functional denervation impaired MNTB-LSO synapse elimination and strengthening, which was assessed by glutamate uncaging and electrical stimulation. Impaired elimination led to imprecise MNTB-LSO topography. Impaired strengthening was associated with lower quantal content per MNTB fibre. In young adult KOs, the MNTB-LSO circuit remained unrefined. Further functional refinement after P12 appeared absent in wild-types. Collectively, we provide novel insights into functional MNTB-LSO circuit maturation governed by a cochlea-specific protein. The central malfunctions in Otof KOs may have implications for patients with sensorineuronal hearing loss.
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Functional implications of Ca v 2.3 R-type voltage-gated calcium channels in the murine auditory system - novel vistas from brainstem-evoked response audiometry. Eur J Neurosci 2019; 51:1583-1604. [PMID: 31603587 DOI: 10.1111/ejn.14591] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Revised: 09/11/2019] [Accepted: 10/08/2019] [Indexed: 12/25/2022]
Abstract
Voltage-gated Ca2+ channels (VGCCs) are considered to play a key role in auditory perception and information processing within the murine inner ear and brainstem. In the past, Cav 1.3 L-type VGCCs gathered most attention as their ablation causes congenital deafness. However, isolated patch-clamp investigation and localization studies repetitively suggested that Cav 2.3 R-type VGCCs are also expressed in the cochlea and further components of the ascending auditory tract, pointing to a potential functional role of Cav 2.3 in hearing physiology. Thus, we performed auditory profiling of Cav 2.3+/+ controls, heterozygous Cav 2.3+/- mice and Cav 2.3 null mutants (Cav 2.3-/- ) using brainstem-evoked response audiometry. Interestingly, click-evoked auditory brainstem responses (ABRs) revealed increased hearing thresholds in Cav 2.3+/- mice from both genders, whereas no alterations were observed in Cav 2.3-/- mice. Similar observations were made for tone burst-related ABRs in both genders. However, Cav 2.3 ablation seemed to prevent mutant mice from total hearing loss particularly in the higher frequency range (36-42 kHz). Amplitude growth function analysis revealed, i.a., significant reduction in ABR wave WI and WIII amplitude in mutant animals. In addition, alterations in WI -WIV interwave interval were observed in female Cav 2.3+/- mice whereas absolute latencies remained unchanged. In summary, our results demonstrate that Cav 2.3 VGCCs are mandatory for physiological auditory information processing in the ascending auditory tract.
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D-cis-Diltiazem Can Produce Oxidative Stress in Healthy Depolarized Rods In Vivo. Invest Ophthalmol Vis Sci 2019; 59:2999-3010. [PMID: 30025125 PMCID: PMC5995482 DOI: 10.1167/iovs.18-23829] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Purpose New perspectives are needed to understand decades of contradictory reports on the neuroprotective effects of the Cav1.2 L-type calcium channel blocker d-cis-diltiazem in retinitis pigmentosa (RP) models. Here, we address, in vivo, the following two knowledge gaps regarding d-cis-diltiazem's actions in the murine outer retina: (1) do normal mouse rods contain d-cis-diltiazem-insensitive Cav1.2 L-type calcium channels? (2) Can d-cis-diltiazem modify the normal rod redox environment? Methods First, transretinal Cav1.2 L-type calcium channels were noninvasively mapped with manganese-enhanced magnetic resonance imaging (MRI) following agonist Bay K 8644 in C57BL/6 (B6) and in Cav1.2 L-type calcium channel BAY K 8644-insensitive mutant B6 mice. Second, d-cis-diltiazem-treated oxidative stress-vulnerable (B6) or -resistant [129S6 (S6)] mice were examined in vivo (QUEnch-assiSTed [QUEST] MRI) and in whole retina ex vivo (lucigenin). Retinal thickness was measured using MRI. Results The following results were observed: (1) manganese uptake patterns in BAY K 8644-treated controls and mutant mice identified in vivo Cav1.2 L-type calcium channels in inner and outer retina; and (2) d-cis-diltiazem induced rod oxidative stress in dark-adapted B6 mice but not in light-adapted B6 mice or dark-adapted S6 mice (QUEST MRI). Oxidative stress in vivo was limited to inferior outer retina in dark-adapted B6 mice approximately 1-hour post d-cis-diltiazem. By approximately 4 hours post, only superior outer retina oxidative stress was observed and whole retinal superoxide production was supernormal. All groups had unremarkable retinal thicknesses. Conclusions D-cis-diltiazem's unexpectedly complex spatiotemporal outer retinal oxidative stress pattern in vivo was dependent on genetic background and rod membrane depolarization, but not apparently dependent on Cav1.2 L-type calcium channels, providing a potential rationale for contradictory results in different RP models.
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Principal cells of the brainstem's interaural sound level detector are temporal differentiators rather than integrators. eLife 2018; 7:33854. [PMID: 29901438 PMCID: PMC6063729 DOI: 10.7554/elife.33854] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2017] [Accepted: 06/10/2018] [Indexed: 11/22/2022] Open
Abstract
The brainstem’s lateral superior olive (LSO) is thought to be crucial for localizing high-frequency sounds by coding interaural sound level differences (ILD). Its neurons weigh contralateral inhibition against ipsilateral excitation, making their firing rate a function of the azimuthal position of a sound source. Since the very first in vivo recordings, LSO principal neurons have been reported to give sustained and temporally integrating ‘chopper’ responses to sustained sounds. Neurons with transient responses were observed but largely ignored and even considered a sign of pathology. Using the Mongolian gerbil as a model system, we have obtained the first in vivo patch clamp recordings from labeled LSO neurons and find that principal LSO neurons, the most numerous projection neurons of this nucleus, only respond at sound onset and show fast membrane features suggesting an importance for timing. These results provide a new framework to interpret previously puzzling features of this circuit.
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Expression of functional inhibitory neurotransmitter transporters GlyT1, GAT-1, and GAT-3 by astrocytes of inferior colliculus and hippocampus. Mol Brain 2018; 11:4. [PMID: 29370841 PMCID: PMC5785846 DOI: 10.1186/s13041-018-0346-y] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2017] [Accepted: 01/03/2018] [Indexed: 12/18/2022] Open
Abstract
Neuronal inhibition is mediated by glycine and/or GABA. Inferior colliculus (IC) neurons receive glycinergic and GABAergic inputs, whereas inhibition in hippocampus (HC) predominantly relies on GABA. Astrocytes heterogeneously express neurotransmitter transporters and are expected to adapt to the local requirements regarding neurotransmitter homeostasis. Here we analyzed the expression of inhibitory neurotransmitter transporters in IC and HC astrocytes using whole-cell patch-clamp and single-cell reverse transcription-PCR. We show that most astrocytes in both regions expressed functional glycine transporters (GlyTs). Activation of these transporters resulted in an inward current (IGly) that was sensitive to the competitive GlyT1 agonist sarcosine. Astrocytes exhibited transcripts for GlyT1 but not for GlyT2. Glycine did not alter the membrane resistance (RM) arguing for the absence of functional glycine receptors (GlyRs). Thus, IGly was mainly mediated by GlyT1. Similarly, we found expression of functional GABA transporters (GATs) in all IC astrocytes and about half of the HC astrocytes. These transporters mediated an inward current (IGABA) that was sensitive to the competitive GAT-1 and GAT-3 antagonists NO711 and SNAP5114, respectively. Accordingly, transcripts for GAT-1 and GAT-3 were found but not for GAT-2 and BGT-1. Only in hippocampal astrocytes, GABA transiently reduced RM demonstrating the presence of GABAA receptors (GABAARs). However, IGABA was mainly not contaminated by GABAAR-mediated currents as RM changes vanished shortly after GABA application. In both regions, IGABA was stronger than IGly. Furthermore, in HC the IGABA/IGly ratio was larger compared to IC. Taken together, our results demonstrate that astrocytes are heterogeneous across and within distinct brain areas. Furthermore, we could show that the capacity for glycine and GABA uptake varies between both brain regions.
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Temporal processing capacity in auditory-deprived superior paraolivary neurons is rescued by sequential plasticity during early development. Neuroscience 2016; 337:315-330. [DOI: 10.1016/j.neuroscience.2016.09.014] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2016] [Revised: 09/01/2016] [Accepted: 09/09/2016] [Indexed: 01/04/2023]
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GDF-15 enhances intracellular Ca2+ by increasing Cav1.3 expression in rat cerebellar granule neurons. Biochem J 2016; 473:1895-904. [PMID: 27114559 PMCID: PMC4925162 DOI: 10.1042/bcj20160362] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2015] [Accepted: 04/25/2016] [Indexed: 12/17/2022]
Abstract
GDF-15 (growth/differentiation factor 15) is a novel member of the TGF (transforming growth factor)-β superfamily that has critical roles in the central and peripheral nervous systems. We reported previously that GDF-15 increased delayed rectifier outward K+ currents and Kv2.1 α subunit expression through TβRII (TGF-β receptor II) to activate Src kinase and Akt/mTOR (mammalian target of rapamycin) signalling in rat CGNs (cerebellar granule neurons). In the present study, we found that treatment of CGNs with GDF-15 for 24 h increased the intracellular Ca2+ concentration ([Ca2+]i) in response to membrane depolarization, as determined by Ca2+ imaging. Whole-cell current recordings indicated that GDF-15 increased the inward Ca2+ current (ICa) without altering steady-state activation of Ca2+ channels. Treatment with nifedipine, an inhibitor of L-type Ca2+ channels, abrogated GDF-15-induced increases in [Ca2+]i and ICa. The GDF-15-induced increase in ICa was mediated via up-regulation of the Cav1.3 α subunit, which was attenuated by inhibiting Akt/mTOR and ERK (extracellular-signal-regulated kinase) pathways and by pharmacological inhibition of Src-mediated TβRII phosphorylation. Given that Cav1.3 is not only a channel for Ca2+ influx, but also a transcriptional regulator, our data confirm that GDF-15 induces protein expression via TβRII and activation of a non-Smad pathway, and provide novel insight into the mechanism of GDF-15 function in neurons.
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Genetic dissection of horizontal cell inhibitory signaling in mice in complete darkness in vivo. Invest Ophthalmol Vis Sci 2015; 56:3132-9. [PMID: 26024096 DOI: 10.1167/iovs.15-16581] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
PURPOSE To test the hypothesis that horizontal cell (HC) inhibitory signaling controls the degree to which rod cell membranes are depolarized as measured by the extent to which L-type calcium channels (LTCCs) are open in complete darkness in the mouse retina in vivo. METHODS Dark-adapted wild-type (wt), CACNA1F (Ca(v)1.4(-/-)), arrestin-1 (Arr1(-/-)), and CACNA1D (Ca(v)1.3(-/-)) C57Bl/6 mice were studied. Manganese-enhanced MRI (MEMRI) evaluated the extent that rod LTCCs are open as an index of loss of HC inhibitory signaling. Subgroups were pretreated with D-cis-diltiazem (DIL) at a dose that specifically antagonizes Ca(v)1.2 channels in vivo. RESULTS Knockout mice predicted to have impaired HC inhibitory signaling (Ca(v)1.4(-/-) or Arr1(-/-)) exhibited greater than normal rod manganese uptake; inner retinal uptake was also supernormal. Genetically knocking out a closely associated gene not expected to impact HC inhibitory signaling (CACNA1D) did not generate this phenotype. The Arr1(-/-) mice exhibited the largest rod uptake of manganese. Manganese-enhanced MRI of DIL-treated Arr1(-/-) mice suggested a greater number of operant LTCC subtypes (i.e., Ca(v)1.2, 1.3, and 1.4) in rods and inner retina than that in DIL-treated Ca(v)1.4(-/-) mice (i.e., Ca(v)1.3). The Ca(v)1.3(-/-) + DIL-treated mice exhibited evidence for a compensatory contribution from Ca(v)1.2 LTCCs. CONCLUSIONS The data suggest that loss of HC inhibitory signaling is the proximate cause leading to maximally open LTCCs in rods, and possibly inner retinal cells, in mice in total darkness in vivo, regardless of compensatory changes in LTCC subtype manifested in the mutant mice.
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MRI of rod cell compartment-specific function in disease and treatment in vivo. Prog Retin Eye Res 2015; 51:90-106. [PMID: 26344734 DOI: 10.1016/j.preteyeres.2015.09.001] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Revised: 08/26/2015] [Accepted: 09/01/2015] [Indexed: 10/23/2022]
Abstract
Rod cell oxidative stress is a major pathogenic factor in retinal disease, such as diabetic retinopathy (DR) and retinitis pigmentosa (RP). Personalized, non-destructive, and targeted treatment for these diseases remains elusive since current imaging methods cannot analytically measure treatment efficacy against rod cell compartment-specific oxidative stress in vivo. Over the last decade, novel MRI-based approaches that address this technology gap have been developed. This review summarizes progress in the development of MRI since 2006 that enables earlier evaluation of the impact of disease on rod cell compartment-specific function and the efficacy of anti-oxidant treatment than is currently possible with other methods. Most of the new assays of rod cell compartment-specific function are based on endogenous contrast mechanisms, and this is expected to facilitate their translation into patients with DR and RP, and other oxidative stress-based retinal diseases.
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L-type Calcium Channel Cav1.2 Is Required for Maintenance of Auditory Brainstem Nuclei. J Biol Chem 2015; 290:23692-710. [PMID: 26242732 DOI: 10.1074/jbc.m115.672675] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Indexed: 12/13/2022] Open
Abstract
Cav1.2 and Cav1.3 are the major L-type voltage-gated Ca(2+) channels in the CNS. Yet, their individual in vivo functions are largely unknown. Both channel subunits are expressed in the auditory brainstem, where Cav1.3 is essential for proper maturation. Here, we investigated the role of Cav1.2 by targeted deletion in the mouse embryonic auditory brainstem. Similar to Cav1.3, loss of Cav1.2 resulted in a significant decrease in the volume and cell number of auditory nuclei. Contrary to the deletion of Cav1.3, the action potentials of lateral superior olive (LSO) neurons were narrower compared with controls, whereas the firing behavior and neurotransmission appeared unchanged. Furthermore, auditory brainstem responses were nearly normal in mice lacking Cav1.2. Perineuronal nets were also unaffected. The medial nucleus of the trapezoid body underwent a rapid cell loss between postnatal days P0 and P4, shortly after circuit formation. Phosphorylated cAMP response element-binding protein (CREB), nuclear NFATc4, and the expression levels of p75NTR, Fas, and FasL did not correlate with cell death. These data demonstrate for the first time that both Cav1.2 and Cav1.3 are necessary for neuronal survival but are differentially required for the biophysical properties of neurons. Thus, they perform common as well as distinct functions in the same tissue.
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The role of L-type voltage-gated calcium channels Cav1.2 and Cav1.3 in normal and pathological brain function. Cell Tissue Res 2014; 357:463-76. [DOI: 10.1007/s00441-014-1936-3] [Citation(s) in RCA: 83] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Accepted: 05/27/2014] [Indexed: 10/25/2022]
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Central auditory function of deafness genes. Hear Res 2014; 312:9-20. [DOI: 10.1016/j.heares.2014.02.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/23/2013] [Revised: 01/31/2014] [Accepted: 02/10/2014] [Indexed: 01/11/2023]
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Cav1.2 and Cav1.3 L-type calcium channels operate in a similar voltage range but show different coupling to Ca(2+)-dependent conductances in hippocampal neurons. Am J Physiol Cell Physiol 2014; 306:C1200-13. [PMID: 24760982 DOI: 10.1152/ajpcell.00329.2013] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
In the central nervous system, L-type voltage-gated calcium channels (LTCCs) come in two isoforms, namely Cav1.2 and Cav1.3 channels. It has been shown previously that these channels differ in biophysical properties, in subcellular localization, and in the coupling to the gene transcription machinery. In previous work on rat hippocampal neurons we have identified an excitatory cation conductance and an inhibitory potassium conductance as important LTCC coupling partners. Notably, a stimulus-dependent interplay of LTCC-mediated Ca(2+) influx and activation of these Ca(2+)-dependent conductances was found to give rise to characteristic voltage responses. However, the contribution of Cav1.2 and Cav1.3 to these voltage responses remained unknown. Hence, the relative contribution of the LTCC isoforms therein was the focus of the current study on hippocampal neurons derived from genetically modified mice, which either lack a LTCC isoform (Cav1.3 knockout mice) or express a dihydropyridine-insensitive LTCC isoform (Cav1.2DHP(-)-knockin mice). We identified common and alternate ion channel couplings of Cav1.2 and Cav1.3 channels. Whereas hyperpolarizing Ca(2+)-dependent conductances were coupled to both Cav1.2 and Cav1.3 channels, an afterdepolarizing potential was only induced by the activity of Cav1.2 channels. Unexpectedly, the activity of Cav1.2 channels was found at relatively hyperpolarized membrane voltages. Our data add important information about the differences between Cav1.2 and Cav1.3 channels that furthers our understanding of the physiological and pathophysiological neuronal roles of these calcium channels. Moreover, our findings suggest that Cav1.3 knockout mice together with Cav1.2DHP(-)-knockin mice provide valuable models for future investigation of hippocampal LTCC-dependent afterdepolarizations.
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