Complex modulation of Cav3.1 T-type calcium channel by nickel

• Published in: Cellular and molecular life sciences : CMLS 2013-05, Vol.70 (9), p.1653-1661
• Main Authors: Nosal, Olena V., Lyubanova, Olga P., Naidenov, Valeri G., Shuba, Yaroslav M.
• Format: Article
• Language: English
• Subjects: Biochemistry; Biomedical and Life Sciences; Biomedicine; Cell Biology; Life Sciences; Research Article
• ISSN: 1420-682X; 1420-9071
• DOI: 10.1007/s00018-012-1225-9

Nickel is considered to be a selective blocker of low-voltage-activated T-type calcium channel. Recently, the Ni 2+ -binding site with critical histidine-191 (H191) within the extracellular IS3–IS4 domain of the most Ni 2+ -sensitive Ca v 3.2 T-channel isoform has been identified. All calcium channels are postulated to also have intrapore-binding site limiting maximal current carried by permeating divalent cations (PDC) and determining the blockade by non-permeating ones. However, the contribution of the two sites to the overall Ni 2+ effect and its dependence on PDC remain uncertain. Here we compared Ni 2+ action on the wild-type “Ni 2+ -insensitive” Ca v 3.1 w/t channel and Ca v 3.1 Q172H mutant having glutamine (Q) equivalent to H191 of Ca v 3.2 replaced by histidine. Each channel was expressed in Xenopus oocytes, and Ni 2+ blockade of Ca 2+ , Sr 2+ , or Ba 2+ currents was assessed by electrophysiology. Inhibition of Ca v 3.1 w/t by Ni 2+ conformed to two sites binding. Ni 2+ binding with high-affinity site (IC 50  = 0.03–3 μM depending on PDC) produced maximal inhibition of 20–30 % and was voltage-dependent, consistent with its location within the channel’s pore. Most of the inhibition (70–80 %) was produced by Ni 2+ binding with low-affinity site (IC 50  = 240–700 μM). Q172H-mutation mainly affected low-affinity binding (IC 50  = 120–160 μM). The IC 50 of Ni 2+ binding with both sites in the Ca v 3.1 w/t and Ca v 3.1 Q172H was differentially modulated by PDC, suggesting a varying degree of competition of Ca 2+ , Sr 2+ , or Ba 2+ with Ni 2+ . We conclude that differential Ni 2+ -sensitivity of T-channel subtypes is determined only by H-containing external binding sites, which, in the absence of Ni 2+ , may be occupied by PDC, influencing in turn the channel’s permeation.