Nitric oxide increases persistent sodium current in rat hippocampal neurons.
1. The effects of nitric oxide (NO) donors on whole-cell, TTX-sensitive sodium currents and single sodium channels in excised patches were examined in rat hippocampal neurons. The whole-cell sodium current consisted of a large transient component (INa,t) and a smaller, inactivation-resistant, persistent component (INa,p). 2. In acutely dissociated neurons, the amplitude of the whole-cell INa, p increased by 60-80 % within a few minutes of exposure to either of two NO donors, sodium nitroprusside (SNP, 100 microM) or S-nitroso-N-acetyl-DL-penicillamine (SNAP, 100 microM). 3. The amplitude of INa,t was not changed significantly by the same concentrations of SNP and SNAP, indicating that NO had a selective effect on INa,p. 4. Both NO donors significantly increased the mean persistent current in excised inside-out patches from cultured hippocampal neurons. SNP at 10-100 microM increased average mean persistent current at a pipette potential (Vp) of +30 mV from -0.010 +/- 0.014 pA (control) to -2.91 +/- 1.41 pA (n = 10). SNAP at 3-100 microM increased the average mean inward current in six inside-out patches from -0.07 +/- 0.02 to -0.30 +/- 0.08 pA (Vp = +30 mV). 5. The increase in persistent Na+ channel activity recorded in inside-out patches in the presence of SNP or SNAP could be reversed by the reducing agent dithiothreitol (DTT, 2-5 mM) or by lidocaine (1-10 microM). 6. The average mean current recorded in the presence of SNP was 10-fold higher than that elicited by SNAP. The time delay before an increase was observed was shorter with SNP (4.0 +/- 0.8 min, n = 8) than with SNAP (8.4 +/- 1.6 min, n = 7). 7. A component of the SNP molecule added on its own, 5 mM sodium cyanide (NaCN), increased mean current in excised inside-out patches (Vp = +30 mV) from -0.06 +/- 0.04 to -0.58 +/- 0.21 pA (n = 19). This increase in channel activity could be blocked by 10 microM lidocaine and 2-5 mM DTT. 8. These results suggest that NO may directly increase the activity of neuronal persistent Na+ channels, but not transient Na+ channels, through an oxidizing action directly on the channel protein or on a closely associated regulatory protein in the plasma membrane.
Hammarström
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AK
Membrane Biology Program, John Curtin School of Medical Research, Australian National University, PO Box 334, Canberra, ACT, 2601 Australia. anna.hammarstrom@anu.edu.au
Gage
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PW
D000818:Animals; D002478:Cells, Cultured; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D004229:Dithiothreitol / Q000494:pharmacology; D006624:Hippocampus / Q000187:drug effects* / Q000378:metabolism; D008012:Lidocaine / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects; D009569:Nitric Oxide / Q000494:pharmacology*; D009599:Nitroprusside / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010396:Penicillamine / Q000031:analogs & derivatives / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D015222:Sodium Channels / Q000378:metabolism*; D012966:Sodium Cyanide / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
C110881:S-nitro-N-acetylpenicillamine; D015222:Sodium Channels; D009599:Nitroprusside; D009569:Nitric Oxide; D013779:Tetrodotoxin; D008012:Lidocaine; D004228:Dithionitrobenzoic Acid; D010396:Penicillamine; D012966:Sodium Cyanide; D004229:Dithiothreitol