Functional regulation of T-type calcium channels by s-nitrosothiols in the rat thalamus.
Although T-type Ca(2+) channels in the reticular thalamic nucleus (nRT) have a central function in tuning neuronal excitability and are implicated in sensory processing, sleep, and epilepsy, the mechanisms involved in their regulation are poorly understood. Here we recorded T-type Ca(2+) currents from intact nRT neurons in brain slices from young rats and investigated the mechanisms of T-type channel modulation by S-nitrosothiols (SNOs). We found that extracellular application of S-nitrosoglutathione (GSNO), S-nitrosocysteine (CSNO) and S-nitroso-N-acetyl-penicillamin (SNAP) rapidly and reversibly reduced T-type currents. The effects of SNOs are strongly stereoselective at physiological concentrations: (L)-CSNO was fourfold more effective in inhibiting T-type current than was (D)-CSNO. The effects of GSNO were abolished if cells had been treated with free hemoglobin or N-ethylmaleimide, an irreversible alkylating agent but not by 8-bromoguanosine-3',5'-cyclomonophosphate sodium salt, a membrane-permeant cGMP analogue or 1H-(1,2,4) oxadiazolo (4,3-a) quinoxalin-1-one, a specific soluble guanylyl cyclase inhibitor. In addition, bath applications of GSNO inhibited T-type currents in nucleated outside-out patches and whole cell recordings to a similar extent, with minimal effect on cell-attached recordings, suggesting a direct effect of GSNO on putative extracellular thiol residues on T-type channels. Biophysical studies indicate that GSNO decreased the availability of T-type channels at physiological potentials by modifying gating and stabilizing inactive states of the channels. In current-clamp experiments, GSNO diminished the amplitude of low-threshold calcium spikes and frequency of spike firing with minimal effects on the passive membrane properties. Collectively, the results indicate that SNOs may be a class of endogenous agents that control the functional states of the thalamus.
Joksovic
Pavle M
PM
Dept. of Anesthesiology, University of Virginia Health System, Mail Box 800710, Charlottesville, VA 22908-0710, USA.
Doctor
Allan
A
Gaston
Benjamin
B
Todorovic
Slobodan M
SM
D000465:Algorithms; D000818:Animals; D020747:Calcium Channels, T-Type / Q000187:drug effects*; D020013:Calcium Signaling / Q000187:drug effects; D006152:Cyclic GMP / Q000378:metabolism; D003545:Cysteine / Q000502:physiology; D005260:Female; D006454:Hemoglobins / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D009415:Nerve Net / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051381:Rats; D026403:S-Nitrosothiols / Q000494:pharmacology*; D013779:Tetrodotoxin / Q000494:pharmacology; D013788:Thalamus / Q000187:drug effects*
D020747:Calcium Channels, T-Type; D006454:Hemoglobins; D026902:Potassium Channel Blockers; D026403:S-Nitrosothiols; D013779:Tetrodotoxin; D006152:Cyclic GMP; D003545:Cysteine