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Ni2+ block of CaV3.1 (alpha1G) T-type calcium channels.

Obejero-Paz CA, Gray IP, Jones SW - J. Gen. Physiol. (2008)

Bottom Line: Na(+)).We conclude that both fast and slow block of Ca(V)3.1 by Ni(2+) are most consistent with occlusion of the pore.The exit rate of Ni(2+) for slow block is reduced at high Ni(2+) concentrations, suggesting that the site responsible for fast block can "lock in" slow block by Ni(2+), at a site located deeper within the pore.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106, USA.

ABSTRACT
Ni(2+) inhibits current through calcium channels, in part by blocking the pore, but Ni(2+) may also allosterically affect channel activity via sites outside the permeation pathway. As a test for pore blockade, we examined whether the effect of Ni(2+) on Ca(V)3.1 is affected by permeant ions. We find two components to block by Ni(2+), a rapid block with little voltage dependence, and a slow block most visible as accelerated tail currents. Rapid block is weaker for outward vs. inward currents (apparent K(d) = 3 vs. 1 mM Ni(2+), with 2 mM Ca(2+) or Ba(2+)) and is reduced at high permeant ion concentration (110 vs. 2 mM Ca(2+) or Ba(2+)). Slow block depends both on the concentration and on the identity of the permeant ion (Ca(2+) vs. Ba(2+) vs. Na(+)). Slow block is 2-3x faster in Ba(2+) than in Ca(2+) (2 or 110 mM), and is approximately 10x faster with 2 vs. 110 mM Ca(2+) or Ba(2+). Slow block is orders of magnitude slower than the diffusion limit, except in the nominal absence of divalent cations ( approximately 3 muM Ca(2+)). We conclude that both fast and slow block of Ca(V)3.1 by Ni(2+) are most consistent with occlusion of the pore. The exit rate of Ni(2+) for slow block is reduced at high Ni(2+) concentrations, suggesting that the site responsible for fast block can "lock in" slow block by Ni(2+), at a site located deeper within the pore. In contrast to the complex pore block observed for Ca(V)3.1, inhibition of Ca(V)3.2 by Ni(2+) was essentially independent of voltage, and was similar in 2 mM Ca(2+) vs. Ba(2+), consistent with inhibition by a different mechanism, at a site outside the pore.

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Bimolecular rate constants for Ni2+ block in different ionic conditions, from IIV protocols. Values include data in all concentrations of Ni2+, n = 12 (nominally Ca2+ free), n = 12 (2 mM Ca2+), n = 11 (2 mM Ba2+), n = 5 (110 mM Ca2+, all at 3 mM Ni2+), and n = 4 (110 mM Ba2+, all at 3 mM Ni2+).
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fig10: Bimolecular rate constants for Ni2+ block in different ionic conditions, from IIV protocols. Values include data in all concentrations of Ni2+, n = 12 (nominally Ca2+ free), n = 12 (2 mM Ca2+), n = 11 (2 mM Ba2+), n = 5 (110 mM Ca2+, all at 3 mM Ni2+), and n = 4 (110 mM Ba2+, all at 3 mM Ni2+).

Mentions: Fig. 10 summarizes the bimolecular rate constants for Ni2+ block in the ionic conditions examined in this study. The rate of Ni2+ entry varied by >1,000-fold, from (4.8 ± 0.3) × 107 M−1s−1 (nominally Ca2+ free, −120 mV) to (3.1 ± 0.2) × 104 M−1s−1 (110 mM Ca2+, −20 mV).


Ni2+ block of CaV3.1 (alpha1G) T-type calcium channels.

Obejero-Paz CA, Gray IP, Jones SW - J. Gen. Physiol. (2008)

Bimolecular rate constants for Ni2+ block in different ionic conditions, from IIV protocols. Values include data in all concentrations of Ni2+, n = 12 (nominally Ca2+ free), n = 12 (2 mM Ca2+), n = 11 (2 mM Ba2+), n = 5 (110 mM Ca2+, all at 3 mM Ni2+), and n = 4 (110 mM Ba2+, all at 3 mM Ni2+).
© Copyright Policy
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2483332&req=5

fig10: Bimolecular rate constants for Ni2+ block in different ionic conditions, from IIV protocols. Values include data in all concentrations of Ni2+, n = 12 (nominally Ca2+ free), n = 12 (2 mM Ca2+), n = 11 (2 mM Ba2+), n = 5 (110 mM Ca2+, all at 3 mM Ni2+), and n = 4 (110 mM Ba2+, all at 3 mM Ni2+).
Mentions: Fig. 10 summarizes the bimolecular rate constants for Ni2+ block in the ionic conditions examined in this study. The rate of Ni2+ entry varied by >1,000-fold, from (4.8 ± 0.3) × 107 M−1s−1 (nominally Ca2+ free, −120 mV) to (3.1 ± 0.2) × 104 M−1s−1 (110 mM Ca2+, −20 mV).

Bottom Line: Na(+)).We conclude that both fast and slow block of Ca(V)3.1 by Ni(2+) are most consistent with occlusion of the pore.The exit rate of Ni(2+) for slow block is reduced at high Ni(2+) concentrations, suggesting that the site responsible for fast block can "lock in" slow block by Ni(2+), at a site located deeper within the pore.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106, USA.

ABSTRACT
Ni(2+) inhibits current through calcium channels, in part by blocking the pore, but Ni(2+) may also allosterically affect channel activity via sites outside the permeation pathway. As a test for pore blockade, we examined whether the effect of Ni(2+) on Ca(V)3.1 is affected by permeant ions. We find two components to block by Ni(2+), a rapid block with little voltage dependence, and a slow block most visible as accelerated tail currents. Rapid block is weaker for outward vs. inward currents (apparent K(d) = 3 vs. 1 mM Ni(2+), with 2 mM Ca(2+) or Ba(2+)) and is reduced at high permeant ion concentration (110 vs. 2 mM Ca(2+) or Ba(2+)). Slow block depends both on the concentration and on the identity of the permeant ion (Ca(2+) vs. Ba(2+) vs. Na(+)). Slow block is 2-3x faster in Ba(2+) than in Ca(2+) (2 or 110 mM), and is approximately 10x faster with 2 vs. 110 mM Ca(2+) or Ba(2+). Slow block is orders of magnitude slower than the diffusion limit, except in the nominal absence of divalent cations ( approximately 3 muM Ca(2+)). We conclude that both fast and slow block of Ca(V)3.1 by Ni(2+) are most consistent with occlusion of the pore. The exit rate of Ni(2+) for slow block is reduced at high Ni(2+) concentrations, suggesting that the site responsible for fast block can "lock in" slow block by Ni(2+), at a site located deeper within the pore. In contrast to the complex pore block observed for Ca(V)3.1, inhibition of Ca(V)3.2 by Ni(2+) was essentially independent of voltage, and was similar in 2 mM Ca(2+) vs. Ba(2+), consistent with inhibition by a different mechanism, at a site outside the pore.

Show MeSH
Related in: MedlinePlus