Dataset Information

Ca_v 1.3 channels play a crucial role in the formation of paroxysmal depolarization shifts in cultured hippocampal neurons.

ABSTRACT:

Objective

An increase of neuronal Ca_v 1.3 L-type calcium channels (LTCCs) has been observed in various animal models of epilepsy. However, LTCC inhibitors failed in clinical trials of epileptic treatment. There is compelling evidence that paroxysmal depolarization shifts (PDSs) involve Ca²⁺ influx through LTCCs. PDSs represent a hallmark of epileptiform activity. In recent years, a probable epileptogenic role for PDSs has been proposed. However, the implication of the two neuronal LTCC isoforms, Ca_v 1.2 and Ca_v 1.3, in PDSs remained unknown. Moreover, Ca²⁺ -dependent nonspecific cation (CAN) channels have also been suspected to contribute to PDSs. Nevertheless, direct experimental support of an important role of CAN channel activation in PDS formation is still lacking.

Methods

Primary neuronal networks derived from dissociated hippocampal neurons were generated from mice expressing a dihydropyridine-insensitive Ca_v 1.2 mutant (Ca_v 1.2DHP^-/- mice) or from Ca_v 1.3^-/- knockout mice. To investigate the role of Ca_v 1.2 and Ca_v 1.3, perforated patch-clamp recordings were made of epileptiform activity, which was elicited using either bicuculline or caffeine. LTCC activity was modulated using the dihydropyridines Bay K 8644 (agonist) and isradipine (antagonist).

Results

Distinct PDS could be elicited upon LTCC potentiation in Ca_v 1.2DHP^-/- neurons but not in Ca_v 1.3^-/- neurons. In contrast, when bicuculline led to long-lasting, seizure-like discharge events rather than PDS, these were prolonged in Ca_v 1.3^-/- neurons but not in Ca_v 1.2DHP^-/- neurons. Because only the Ca_v 1.2 isoform is functionally coupled to CAN channels in primary hippocampal networks, PDS formation does not require CAN channel activity.

Significance

Our data suggest that the LTCC requirement of PDS relates primarily to Ca_v 1.3 channels rather than to Ca_v 1.2 channels and CAN channels in hippocampal neurons. Hence, Ca_v 1.3 may represent a new therapeutic target for suppression of PDS development. The proposed epileptogenic role of PDSs may allow for a prophylactic rather than the unsuccessful seizure suppressing application of LTCC inhibitors.

SUBMITTER: Stiglbauer V

PROVIDER: S-EPMC7116787 | biostudies-literature | 2017 May

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Ca<sub>v</sub> 1.3 channels play a crucial role in the formation of paroxysmal depolarization shifts in cultured hippocampal neurons.

Stiglbauer Victoria V Hotka Matej M Ruiß Manuel M Hilber Karlheinz K Boehm Stefan S Kubista Helmut H

Epilepsia 20170311 5

<h4>Objective</h4>An increase of neuronal Ca<sub>v</sub> 1.3 L-type calcium channels (LTCCs) has been observed in various animal models of epilepsy. However, LTCC inhibitors failed in clinical trials of epileptic treatment. There is compelling evidence that paroxysmal depolarization shifts (PDSs) involve Ca<sup>2+</sup> influx through LTCCs. PDSs represent a hallmark of epileptiform activity. In recent years, a probable epileptogenic role for PDSs has been proposed. However, the implication of t ...[more]

PMID: 28295232

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Project description:In the mammalian brain, presynaptic CaV 2 channels play a pivotal role in synaptic transmission by mediating fast neurotransmitter exocytosis via influx of Ca2+ into the active zone of presynaptic terminals. However, the distribution and modulation of CaV 2.2 channels at plastic hippocampal synapses remains to be elucidated. Here, we assess CaV 2.2 channels during homeostatic synaptic plasticity, a compensatory form of homeostatic control preventing excessive or insufficient neuronal activity during which extensive active zone remodelling has been described. We show that chronic silencing of neuronal activity in mature hippocampal cultures resulted in elevated presynaptic Ca2+ transients, mediated by increased levels of CaV 2.2 channels at the presynaptic site. This work focused further on the role of α2 δ-1 subunits, important regulators of synaptic transmission and CaV 2.2 channel abundance at the presynaptic membrane. We found that α2 δ-1 overexpression reduces the contribution of CaV 2.2 channels to total Ca2+ flux without altering the amplitude of the Ca2+ transients. Levels of endogenous α2 δ-1 decreased during homeostatic synaptic plasticity, whereas the overexpression of α2 δ-1 prevented homeostatic synaptic plasticity in hippocampal neurons. Together, this study reveals a key role for CaV 2.2 channels and novel roles for α2 δ-1 during synaptic plastic adaptation. KEY POINTS: The roles of CaV 2.2 channels and α2 δ-1 in homeostatic synaptic plasticity in hippocampal neurons in culture were examined. Chronic silencing of neuronal activity resulted in elevated presynaptic Ca2+ transients, mediated by increased levels of CaV 2.2 channels at presynaptic sites. The level of endogenous α2 δ-1 decreased during homeostatic synaptic plasticity, whereas overexpression of α2 δ-1 prevented homeostatic synaptic plasticity in hippocampal neurons. Together, this study reveals a key role for CaV 2.2 channels and novel roles for α2 δ-1 during synaptic plastic adaptation.

Project description:Mammalian circadian (24 h) rhythms are timed by the pattern of spontaneous action potential firing in the suprachiasmatic nucleus (SCN). This oscillation in firing is produced through circadian regulation of several membrane currents, including large-conductance Ca2+- and voltage-activated K+ (BK) and L-type Ca2+ channel (LTCC) currents. During the day steady-state BK currents depend mostly on LTCCs for activation, whereas at night they depend predominantly on ryanodine receptors (RyRs). However, the contribution of these Ca2+ channels to BK channel activation during action potential firing has not been thoroughly investigated. In this study, we used a pharmacological approach to determine that both LTCCs and RyRs contribute to the baseline membrane potential of SCN action potential waveforms, as well as action potential-evoked BK current, during the day and night, respectively. Since the baseline membrane potential is a major determinant of circadian firing rate, we focused on the LTCCs contributing to low voltage activation of BK channels during the subthreshold phase. For these experiments, two LTCC subtypes found in SCN (CaV1.2 and CaV1.3) were coexpressed with BK channels in heterologous cells, where their differential contributions could be separately measured. CaV1.3 channels produced currents that were shifted to more hyperpolarized potentials compared with CaV1.2, resulting in increased subthreshold Ca2+ and BK currents during an action potential command. These results show that although multiple Ca2+ sources in SCN can contribute to the activation of BK current during an action potential, specific BK-CaV1.3 partnerships may optimize the subthreshold BK current activation that is critical for firing rate regulation.NEW & NOTEWORTHY BK K+ channels are important regulators of firing. Although Ca2+ channels are required for their activation in excitable cells, it is not well understood how BK channels activate using these Ca2+ sources during an action potential. This study demonstrates the differences in BK current activated by CaV1.2 and CaV1.3 channels in clock neurons and heterologous cells. The results define how specific ion channel partnerships can be engaged during distinct phases of the action potential.

Dataset Information

Ca_v 1.3 channels play a crucial role in the formation of paroxysmal depolarization shifts in cultured hippocampal neurons.

Objective

Methods

Results

Significance

Publications

Ca<sub>v</sub> 1.3 channels play a crucial role in the formation of paroxysmal depolarization shifts in cultured hippocampal neurons.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

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Dataset Information

Cav 1.3 channels play a crucial role in the formation of paroxysmal depolarization shifts in cultured hippocampal neurons.

Objective

Methods

Results

Significance

Publications

Ca<sub>v</sub> 1.3 channels play a crucial role in the formation of paroxysmal depolarization shifts in cultured hippocampal neurons.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets

Ca_v 1.3 channels play a crucial role in the formation of paroxysmal depolarization shifts in cultured hippocampal neurons.