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Regulation of the calcium channel alpha(1G) subunit by divalent cations and organic blockers
L Lacinová1, N Klugbauer, F Hofmann
1Institut für Pharmakologie und Toxikologie der Technischen Universität München, Biedersteiner Str. 29, 80802, München, Germany. lacinova@ipt.med.tu-muenchen.de
Abstract:
The pharmacological properties of the expressed murine T-type alpha(1G) channel were characterized using the whole cell patch clamp configuration. Ba(2+) or Ca(2+) were used as charge carriers. Both I(Ba) and I(Ca) were blocked by Ni(2+) and Cd(2+) with IC(50) values of 0.47+/-0.04 and 1.13+/-0.06 mM (Ni(2+)) and 162+/-13 and 658+/-23 microM (Cd(2+)), respectively. Ni(2+), but not Cd(2+), modified the gating of channel activation. Ni(2+) consistently accelerated channel deactivation while Cd(2+) had a similar effect only on I(Ca). The alpha(1G) channel was potently blocked by mibefradil in a dose- and voltage-dependent manner. I(Ba) was moderately blocked by phenytoin (IC(50) 73.9+/-1.9 microM) and was resistant to the block by valproate. Also 3 mM ethosuximide blocked 20 and 35% of the I(Ba) at a HP of -100 and -60 mV, respectively, while 5 mM amiloride inhibited I(Ba) by 38% and significantly slowed current activation. The alpha(1G) channel was not affected by 10 microM tetrodotoxin. Both 1 microM (+)isradipine and 10 microM nifedipine inhibited 18 and 14% of I(Ba) amplitude at a HP of -100 mV, and 23% and 29% of I(Ba) amplitude at a HP of -60 mV, respectively. The alpha(1G) current was minimally activated by 1 microM Bay K 8644.
Insights
This study characterizes the murine T-type alpha(1G) channel, revealing its sensitivity to blockers like Ni(2+), Cd(2+), and mibefradil. Findings illuminate potential therapeutic targets for channelopathies.
Area of Science:
- Pharmacology
- Neuroscience
- Ion Channel Physiology
Background:
- T-type calcium channels, specifically the alpha(1G) subunit, play crucial roles in neuronal excitability and neurotransmitter release.
- Understanding the pharmacological profile of alpha(1G) channels is essential for developing targeted therapies for neurological disorders.
Purpose of the Study:
- To electrophysiologically characterize the pharmacological properties of the expressed murine T-type alpha(1G) channel.
- To investigate the effects of various ions and drugs on alpha(1G) channel function.
Main Methods:
- Whole-cell patch clamp electrophysiology was employed to record barium (Ba(2+)) and calcium (Ca(2+)) currents through the alpha(1G) channel.
- The effects of different ion concentrations (Ni(2+), Cd(2+)) and pharmacological agents (mibefradil, phenytoin, valproate, ethosuximide, amiloride, tetrodotoxin, isradipine, nifedipine, Bay K 8644) were assessed.
Main Results:
- Ni(2+) and Cd(2+) blocked alpha(1G) currents with distinct IC(50) values, and Ni(2+) altered channel gating.
- Mibefradil demonstrated potent, dose- and voltage-dependent block, while phenytoin showed moderate block.
- Ethosuximide and amiloride partially inhibited currents, with amiloride also affecting activation kinetics; tetrodotoxin had no effect.
Conclusions:
- The murine alpha(1G) T-type channel exhibits specific sensitivities to a range of ions and drugs, including potent block by mibefradil.
- Differential effects of Ni(2+) and Cd(2+) on channel gating suggest distinct binding sites or mechanisms.
- These findings provide a pharmacological basis for targeting alpha(1G) channels in conditions involving T-type channel dysfunction.