Abstract
Recent studies indicate that T-type calcium channels (T-channels) in the thalamus are cellular targets for general anesthetics. Here, we recorded T-currents and underlying low-threshold calcium spikes from neurons of nucleus reticularis thalami (nRT) in brain slices from young rats and investigated the mechanisms of their modulation by an anesthetic alcohol, 1-octanol. We found that 1-octanol inhibited native T-currents at subanesthetic concentrations with an IC50 of approximately 4 μM. In contrast, 1-octanol was up to 30-fold less potent in inhibiting recombinant CaV3.3 T-channels heterologously expressed in human embryonic kidney cells. Inhibition of both native and recombinant T-currents was accompanied by a hyperpolarizing shift in steady-state inactivation, indicating that 1-octanol stabilized inactive states of the channel. To explore the mechanisms underlying higher 1-octanol potency in inhibiting native nRT T-currents, we tested the effect of the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) and PKC inhibitors. We found that PMA caused a modest increase of T-current, whereas the inactive PMA analog 4α-PMA failed to affect T-current in nRT neurons. In contrast, 12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo(2,3-a)pyrrolo(3,4-c)-carbazole (Go 6976), an inhibitor of calcium-dependent PKC, decreased baseline T-current amplitude in nRT cells and abolished the effects of subsequently applied 1-octanol. The effects of 1-octanol were also abolished by chelation of intracellular calcium ions with 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid. Taken together, these results suggest that inhibition of calcium-dependent PKC signaling is a possible molecular substrate for modulation of T-channels in nRT neurons by 1-octanol.
Footnotes
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↵1 Department of Psychiatry, Yale University, New Haven, Connecticut.
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↵2 Department of Anesthesiology, InJe University, Ilsan Paik Hospital & College of Medicine, Goyang-city, South Korea.
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This work was supported by the grants from the National Institutes of Health National Institute of General Medical Sciences [Grant GM070726] and the National Institutes of Health National Institute of Neurological Disorders and Stroke [Grant F31-NS059190].
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Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.109.059931.
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ABBREVIATIONS:
- T-channel
- transient (T-type) Ca2+ channel
- LTS
- low-threshold Ca2+ spikes
- nRT
- reticular thalamic nucleus
- HEK
- human embryonic kidney
- I-V
- current-voltage
- TTX
- tetrodotoxin
- PMA
- phorbol 12-myristate 13-acetate
- Go 6976
- 12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo(2,3-a)pyrrolo(3,4-c)-carbazole
- BAPTA
- 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid
- PKC
- protein kinase C.
- Received July 29, 2009.
- Accepted October 21, 2009.
- © 2010 The American Society for Pharmacology and Experimental Therapeutics
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