Ca_V3.2 is the major molecular substrate for redox regulation of T‐type Ca²⁺ channels in the rat and mouse thalamus

Abstract

Although T-type Ca2+ channels in the thalamus play a crucial role in determining neuronal excitability and are involved in sensory processing and pathophysiology of epilepsy, little is known about the molecular mechanisms involved in their regulation. Here, we report that reducing agents, including endogenous sulfur-containing amino acid L-cysteine, selectively enhance native T-type currents in reticular thalamic (nRT) neurons and recombinant Ca V 3.2 (α1H) currents, but not native and recombinant Ca V 3.1 (α1G)-and Ca V 3.3 (α1I)-based currents. Consistent with this data, T-type currents of nRT neurons from transgenic mice lacking Ca V 3.2 channel expression were not modulated by reducing agents. In contrast, oxidizing agents inhibited all native and recombinant T-type currents non-selectively. Thus, our findings directly demonstrate that Ca V 3.2 channels are the main molecular substrate for redox regulation of neuronal T-type channels. In addition, because thalamic T-type channels generate low-threshold Ca 2+ spikes that directly correlate with burst firing in these neurons, differential redox regulation of these channels may have an important function in controlling cellular excitability in physiological and pathological conditions and fine-tuning of the flow of sensory information into the central nervous system.

Cell-Specific Alterations of T-Type Calcium Current in Painful Diabetic Neuropathy Enhance Excitability of Sensory Neurons

“…However, we feel that this is unlikely because diabetic DRG T-type currents potently blocked with Ni 2ϩ (IC 50 of 10 M) and increased with L-cysteine (maximal effect achieved with 100 M). In contrast, ␣1I and ␣1G type currents are blocked only by higher concentrations of Ni 2ϩ (IC 50 of 250 M) and are not altered even by 10-fold higher concentrations of L-cysteine (Joksovic et al, 2006). Finally, our qRT-PCR analysis of DRGs from diabetic rats confirms the notion that the relative ratio of T-type channel isoforms is not altered.…”

“…Next, we examined the pharmacological properties of these cells, because some variants of T-type currents with different kinetic properties also exhibit different sensitivity to specific pharmacological tools, such as nickel, a T-type channel blocker , and L-cysteine, an endogenous T-type channel agonist (Joksovic et al, 2006). Figure 4 A shows representative traces, and Figure 4 B shows representative time courses from experiments in which nickel reversibly blocked T-type current in a concentration-dependent manner (3, 10, 30, and 100 M; left panels) and L-cysteine (100 M; right panels) reversibly enhanced these currents.…”

Reducing Agents Sensitize C-Type Nociceptors by Relieving High-Affinity Zinc Inhibition of T-Type Calcium Channels

“…H191 is required for the reducing agent sensitivity of Ca v 3.2 T-channels We reported previously that reducing agents enhance Ca v 3.2 T-currents but not Ca v 3.1 or Ca v 3.3 T-currents, whereas oxidizing agents such as DTNB inhibit all three T-currents to a similar degree (Joksovic et al, 2006). Furthermore, knock-out studies have demonstrated that Ca v 3.2 is overwhelmingly the predominant T-channel isoform in small DRG neurons (Chen et al, 2003).…”

“…2C,D). Because the effects of oxidizing agents are conserved across T-channels (Joksovic et al, 2006), we were unable to track their molecular determinant using this chimeric strategy.…”

Targeting Calcium Channels to Block Tumor Vascularization

“…Once again, these effects arose when NaHS was administrated at 1.5-13.5 mM. Interestingly, earlier reports demonstrated that L-cysteine selectively potentiates recombinant CaV3.2-dependent, but not CaV3.1-and CaV3.3-, currents [50]. A mechanistic link between H2S and the onset of the Cai waves might be provided by the protein-kinase A (PKA)\cAMP pathway.…”