Mechanisms of inhibition of T-type calcium current in the reticular thalamic neurons by 1-octanol: implication of the protein kinase C pathway.
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 IC(50) of approximately 4 muM. In contrast, 1-octanol was up to 30-fold less potent in inhibiting recombinant Ca(V)3.3 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 4alpha-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.
Joksovic
Pavle M
PM
Department of Anesthesiology, University of Virginia Health System, Charlottesville, VA 22908-0710, USA.
Choe
Won Joo
WJ
Nelson
Michael T
MT
Orestes
Peihan
P
Brimelow
Barbara C
BC
Todorovic
Slobodan M
SM
D020003:1-Octanol / Q000494:pharmacology*; D000777:Anesthetics; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020747:Calcium Channels, T-Type / Q000187:drug effects* / Q000378:metabolism; D002460:Cell Line; D006801:Humans; D020128:Inhibitory Concentration 50; D009474:Neurons / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D013788:Thalamus / Q000166:cytology*
D000777:Anesthetics; D020747:Calcium Channels, T-Type; D011493:Protein Kinase C; D020003:1-Octanol; D002118:Calcium