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Background T-type calcium channels (T-channels) are widely distributed in the central and peripheral nervous system, where they mediate calcium entry and regulate the intrinsic excitability of neurons. T-channels are dysregulated in response to alcohol administration and withdrawal. We therefore investigated acute ethanol ( Et OH) effects and the underlying mechanism of action in human embryonic kidney ( HEK) 293 cell lines, as well as effects on native currents recorded from dorsal root ganglion ( DRG) neurons cultured from Long-Evans rats. Methods Whole-cell voltage-clamp recordings were performed at 32 to 34°C in both HEK cell lines and DRG neurons. The recordings were taken after a 10-minute application of Et OH or protein kinase C ( PKC) activator (phorbol 12-myristate 13-acetate [ PMA]). Results We recorded T-type Ca2+ currents (T-currents) from 3 channel isoforms ( Ca V3.1, Ca V3.2, and Ca V3.3) before and during administration of Et OH. We found that only 1 isoform, Ca V3.2, was significantly affected by EtOH. Et OH reduced current density as well as producing a hyperpolarizing shift in steady-state inactivation of both Ca V3.2 currents from HEK 293 cell lines and in native T-currents from DRG neurons that are known to be enriched in Ca V3.2. A myristoylated PKC peptide inhibitor ( MPI) blocked the major Et OH effects, in both the cell lines and the DRG neurons. However, PMA effects were more complex. Lower concentration PMA (100 nM) replicated the major effects of Et OH, while higher concentration PMA (1 μM) did not, suggesting that the Et OH effects operate through activation of PKC and were mimicked by lower concentration of PMA. Conclusions Et OH primarily affects the CaV3.2 isoform of T-type Ca2+ channels acting through PKC, highlighting a novel target and mechanism for Et OH effects on excitable membranes. [ABSTRACT FROM AUTHOR]

Some epilepsies are linked to inherited traits, but many appear to arise through acquired alterations in neuronal excitability. Status epilepticus (SE) is associated with numerous changes that promote spontaneous recurrent seizures (SRS), and studies have suggested that hippocampal T-type Ca2+ channels underlie increased bursts of activity integral to the generation of these seizures. The thalamus also contributes to epileptogenesis, but no studies have directly assessed channel alterations in the thalamus during SE or subsequent periods of SRS. We therefore investigated longitudinal changes in thalamic T-type channels in a mouse pilocarpine model of epilepsy. T-type channel gene expression was not affected during SE; however CaV3.2 mRNA was significantly upregulated at both 10 d post-SE (seizure-free period) and 31 d post-SE (SRS-period). Overall T-type current density increased during the SRS period, and the steady-state inactivation shifted from a more hyperpolarized membrane potential during the latent stage, to a more depolarized membrane potential during the SRS period. CaV3.2 functional involvement was verified with CaV3.2 inhibitors that reduced the native T-type current in mice 31 d post-SE, but not in controls. Burst discharges of thalamic neurons reflected the changes in whole-cell currents, and we used a computational model to relate changes observed during epileptogenesis to a decreased tendency to burst in the seizure-free period, or an increased tendency to burst during the period of SRS. We conclude that SE produces an acquired channelopathy by inducing long-term alterations in thalamic T-type channels that contribute to characteristic changes in excitability observed during epileptogenesis and SRS. [ABSTRACT FROM AUTHOR]

Some epilepsies are linked to inherited traits, but many appear to arise through acquired alterations in neuronal excitability. Status epilepticus (SE) is associated with numerous changes that promote spontaneous recurrent seizures (SRS), and studies have suggested that hippocampal T-type Ca(2+) channels underlie increased bursts of activity integral to the generation of these seizures. The thalamus also contributes to epileptogenesis, but no studies have directly assessed channel alterations in the thalamus during SE or subsequent periods of SRS. We therefore investigated longitudinal changes in thalamic T-type channels in a mouse pilocarpine model of epilepsy. T-type channel gene expression was not affected during SE; however Ca(V)3.2 mRNA was significantly upregulated at both 10 d post-SE (seizure-free period) and 31 d post-SE (SRS-period). Overall T-type current density increased during the SRS period, and the steady-state inactivation shifted from a more hyperpolarized membrane potential during the latent stage, to a more depolarized membrane potential during the SRS period. Ca(V)3.2 functional involvement was verified with Ca(V)3.2 inhibitors that reduced the native T-type current in mice 31 d post-SE, but not in controls. Burst discharges of thalamic neurons reflected the changes in whole-cell currents, and we used a computational model to relate changes observed during epileptogenesis to a decreased tendency to burst in the seizure-free period, or an increased tendency to burst during the period of SRS. We conclude that SE produces an acquired channelopathy by inducing long-term alterations in thalamic T-type channels that contribute to characteristic changes in excitability observed during epileptogenesis and SRS.