Pharmacological properties of neuronal TTX-resistant sodium channels and the role of a critical serine pore residue.
Voltage-gated sodium channels can be characterized by their sensitivity to inhibitors. Na(v)1.5 is sensitive to block by cadmium and extracellular QX-314, but relatively insensitive to tetrodotoxin and saxitoxin. Na(v)1.4 is tetrodotoxin- and saxitoxin-sensitive but resistant to cadmium and extracellular QX-314. Na(v)1.8 and Na(v)1.9 generate slowly inactivating (I(TTXr-Slow)) and persistent (I(TTXr-Per)) currents in sensory neurons that are tetrodotoxin-resistant. Tetrodotoxin sensitivity is largely determined by the identity of a single residue; tyrosine 401 in Na(v)1.4, cysteine 374 in Na(v)1.5 and serine 356 and 355 in Na(v)1.8 and Na(v)1.9. We asked whether Na(v)1.8 and Na(v)1.9 share other pharmacological properties as a result of this serine residue. I(TTXr-Slow) and I(TTXr-Per) were saxitoxin-resistant and resistant to internal QX-314. I(TTXr-Slow) was also resistant to external QX-314 and displayed a approximately fourfold higher sensitivity than I(TTXr-Per) to cadmium. The impact of the serine residue was investigated by replacing tyrosine 401 in Na(v)1.4 with serine (Y401S) or cysteine (Y401C). Both mutants were resistant to tetrodotoxin and saxitoxin. Whereas Na(v)1.4-Y401C displayed an increased sensitivity to cadmium and extracellular QX-314, the serine substitution did not alter the sensitivity of Na(v)1.4 to cadmium or QX-314. Our data indicates that while the serine residue determines the sensitivity of I(TTXr-Slow) and I(TTXr-Per) to tetrodotoxin and saxitoxin, it does not determine their insensitivity to QX-314 or their differential sensitivities to cadmium.
Klinik für Anästhesiologie, Friedrich-Alexander-Universität Erlangen-Nuremberg, Krankenhausstr. 12, 91054 Erlangen, Germany.
Andreas
A
Leffler
Raimund I
RI
Herzog
Sulayman D
SD
Dib-Hajj
Stephen G
SG
Waxman
Theodore R
TR
Cummins
D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D002460:Cell Line; D045604:Extracellular Fluid; D005727:Ganglia, Spinal / Q000502:physiology; D006801:Humans; D007424:Intracellular Fluid; D008012:Lidocaine / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D009475:Neurons, Afferent / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D012530:Saxitoxin / Q000494:pharmacology; D012694:Serine / Q000502:physiology*; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000737:chemistry* / Q000187:drug effects; D013779:Tetrodotoxin / Q000494:pharmacology*
D015222:Sodium Channels; D002104:Cadmium; C012647:QX-314; D012530:Saxitoxin; D013779:Tetrodotoxin; D012694:Serine; D008012:Lidocaine; D012964:Sodium