Selective expression of a persistent tetrodotoxin-resistant Na+ current and NaV1.9 subunit in myenteric sensory neurons.
Voltage-gated Na(+) currents play critical roles in shaping electrogenesis in neurons. Here, we have identified a TTX-resistant Na(+) current (TTX-R I(Na)) in duodenum myenteric neurons of guinea pig and rat and have sought evidence regarding the molecular identity of the channel producing this current from the expression of Na(+) channel alpha subunits and the biophysical and pharmacological properties of TTX-R I(Na). Whole-cell patch-clamp recording from in situ neurons revealed the presence of a voltage-gated Na(+) current that was highly resistant to TTX (IC(50), approximately 200 microm) and selectively distributed in myenteric sensory neurons but not in interneurons and motor neurons. TTX-R I(Na) activated slowly in response to depolarization and exhibited a threshold for activation at -50 mV. V(1/2) values of activation and steady-state inactivation were -32 and -31 mV in the absence of fluoride, respectively, which, as predicted from the window current, generated persistent currents. TTX-R I(Na) also had prominent ultraslow inactivation, which turns off 50% of the conductance at rest (-60 mV). Substituting CsF for CsCl in the intracellular solution shifted the voltage-dependent parameters of TTX-R I(Na) leftward by approximately 20 mV. Under these conditions, TTX-R I(Na) had voltage-dependent properties similar to those reported previously for NaN/Na(V)1.9 in dorsal root ganglion neurons. Consistent with this, reverse transcription-PCR, single-cell profiling, and immunostaining experiments indicated that Na(V)1.9 transcripts and subunits, but not Na(V)1.8, were expressed in the enteric nervous system and restricted to myenteric sensory neurons. TTX-R I(Na) may play an important role in regulating subthreshold electrogenesis and boosting synaptic stimuli, thereby conferring distinct integrative properties to myenteric sensory neurons.
Rugiero
François
F
Intégration des Informations Sensorielles, Unite Mixte de Recherche 6150, Centre National de la Recherche Scientifique, 13916 Marseille, France.
Mistry
Mohini
M
Sage
Dominique
D
Black
Joel A
JA
Waxman
Stephen G
SG
Crest
Marcel
M
Clerc
Nadine
N
Delmas
Patrick
P
Gola
Maurice
M
D000200:Action Potentials; D000595:Amino Acid Sequence; D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D002478:Cells, Cultured; D004553:Electric Conductivity; D006168:Guinea Pigs; D007150:Immunohistochemistry; D007700:Kinetics; D008969:Molecular Sequence Data; D009197:Myenteric Plexus / Q000166:cytology*; D062558:NAV1.9 Voltage-Gated Sodium Channel; D009475:Neurons, Afferent / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology*; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D018408:Patch-Clamp Techniques; D021122:Protein Subunits; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D015222:Sodium Channels / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology*; D014158:Transcription, Genetic
D062558:NAV1.9 Voltage-Gated Sodium Channel; D009479:Neuropeptides; D021122:Protein Subunits; D012333:RNA, Messenger; C113705:Scn11a protein, rat; D015222:Sodium Channels; D002104:Cadmium; D013779:Tetrodotoxin