GTPγS increases Nav1.8 current in small-diameter dorsal root ganglia neurons

Carl Y. Saab, Theodore Cummins, Stephen G. Waxman

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

Tetrodotoxin-resistant (TTX-R) sodium current in small-size dorsal root ganglia (DRG) neurons is upregulated by prostaglandin E2 and serotonin through a protein kinase A (PKA)/protein kinase (PKC) pathway, suggesting G protein modulation of one or more TTX-R channels in these neurons. Recently, GTPγS, a hydrolysis-resistant analogue of GTP, was shown to increase the persistent current produced by the TTX-R Na v1.9. In this study, we investigated the modulation of another TTX-R channel, Nav1.8, by GTPγS in small-diameter DRG neurons from rats using whole-cell voltage clamp recordings. Because it has been suggested that fluoride, often used in intracellular recording solutions, may bind to trace amounts of aluminum and activate G proteins, we recorded Nav1.8 currents with and without intracellular fluoride, and with the addition of deferoxamine, an aluminum chelator, to prevent fluoride-aluminum binding. Our results show that GTPγS (100 μM) caused a significant increase in Nav1.8 current (67%) with a chloride-based intracellular solution. Although the inclusion of fluoride instead of chloride in the pipette solution increased the Nav1.8 current by 177%, GTPγS further increased Nav1.8 current by 67% under these conditions. While the effect of GTP γS was prevented by pretreatment with H7 (100 μM), a non-selective PKA/PKC inhibitor, the fluoride-induced increase in Na v1.8 current was not sensitive to H7 (100 μM), or to inclusion of deferoxamine (1 mM) in the intracellular solution. We conclude that G protein activation by GTPγS increases Nav1.8 current through a PKA/PKC mechanism and that addition of fluoride to the pipette solution further enhances the current, but is not a confounding variable in the study of Nav1.8 channel modulation by G proteins independent of a PKA/PKC pathway or binding to aluminum.

Original languageEnglish (US)
Pages (from-to)415-419
Number of pages5
JournalExperimental Brain Research
Volume152
Issue number4
DOIs
StatePublished - Oct 2003
Externally publishedYes

Fingerprint

Spinal Ganglia
Fluorides
Tetrodotoxin
Cyclic AMP-Dependent Protein Kinases
GTP-Binding Proteins
Neurons
Aluminum
Deferoxamine
Guanosine Triphosphate
Chlorides
Confounding Factors (Epidemiology)
Chelating Agents
Dinoprostone
Protein Kinases
Serotonin
Hydrolysis
Sodium

Keywords

  • Fluoride
  • G proteins
  • Na1.8 current
  • Protein kinase A
  • Protein kinase C
  • Tetrodotoxin-resistant sodium channels

ASJC Scopus subject areas

  • Neuroscience(all)

Cite this

GTPγS increases Nav1.8 current in small-diameter dorsal root ganglia neurons. / Saab, Carl Y.; Cummins, Theodore; Waxman, Stephen G.

In: Experimental Brain Research, Vol. 152, No. 4, 10.2003, p. 415-419.

Research output: Contribution to journalArticle

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abstract = "Tetrodotoxin-resistant (TTX-R) sodium current in small-size dorsal root ganglia (DRG) neurons is upregulated by prostaglandin E2 and serotonin through a protein kinase A (PKA)/protein kinase (PKC) pathway, suggesting G protein modulation of one or more TTX-R channels in these neurons. Recently, GTPγS, a hydrolysis-resistant analogue of GTP, was shown to increase the persistent current produced by the TTX-R Na v1.9. In this study, we investigated the modulation of another TTX-R channel, Nav1.8, by GTPγS in small-diameter DRG neurons from rats using whole-cell voltage clamp recordings. Because it has been suggested that fluoride, often used in intracellular recording solutions, may bind to trace amounts of aluminum and activate G proteins, we recorded Nav1.8 currents with and without intracellular fluoride, and with the addition of deferoxamine, an aluminum chelator, to prevent fluoride-aluminum binding. Our results show that GTPγS (100 μM) caused a significant increase in Nav1.8 current (67{\%}) with a chloride-based intracellular solution. Although the inclusion of fluoride instead of chloride in the pipette solution increased the Nav1.8 current by 177{\%}, GTPγS further increased Nav1.8 current by 67{\%} under these conditions. While the effect of GTP γS was prevented by pretreatment with H7 (100 μM), a non-selective PKA/PKC inhibitor, the fluoride-induced increase in Na v1.8 current was not sensitive to H7 (100 μM), or to inclusion of deferoxamine (1 mM) in the intracellular solution. We conclude that G protein activation by GTPγS increases Nav1.8 current through a PKA/PKC mechanism and that addition of fluoride to the pipette solution further enhances the current, but is not a confounding variable in the study of Nav1.8 channel modulation by G proteins independent of a PKA/PKC pathway or binding to aluminum.",
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