Electrophysiological characterization of the tetrodotoxin-resistant Na + channel, Na v1.9, in mouse dorsal root ganglion neurons

Maruyama Hiroshi

Yamamoto Mitsuko

Ohishi Yoshiaki

Matsutomi Tomoya

Zheng Taixing

Nakata Yoshihiro

Wood John N.

Ogata Nobukuni

Pflügers Archiv : European Journal of Physiology

The Na+ channel isoform, Navl.9 (NaN/SNS2), is preferentially expressed in small neurones of the dorsal root ganglia and thought to mediate a novel tetrodotoxin-resistant (TTX-R) Na+ current. We investigated properties of the Na+ current mediated by Nav1.9 (INaN) using whole-cell patch-clamp recording. To isolate INaN from a heterogeneous TTX-R Na+ current that also contained another type of TTX-R Na+ current mediated by Nay1.8 (SNS/PN3), we used Nay1.8-null mutant mice. Since F- that had been used as an internal anion in earlier studies was shown to produce negative shifts of the activation and inactivation kinetics of INaN, INaN was recorded with Cl- as an internal anion. The activation threshold for INaN was about 20 mV more negative than that for other Na+ currents, activation and inactivation were extremely slow giving rise to a persistent Na+ current, and the peak amplitude was too small (less than 0.5 nA) to carry an action potential generation. Thus, Nav1.9 is a 'background' Na+ channel that probably regulates excitability at a subthreshold voltage range and influences spike discharges that are predominantly mediated by other Na+ channels. Since functional expression of INaN declined with time after dissociation and recovered in step with concurrent glial outgrowth, Nav1.9 is an 'inducible' Na+ channel. Moreover, Nav1.9 is a 'kindling' Na+ channel, since the peak amplitude of INaN under whole cell patch clamp recording started to increase explosively after a variable period of delay, as if 'inactive' or 'silent' Nav1.9 channels were unmasked. Such an unusual increase of the current was not observed under nystatin-perforated recording and was prevented by ATP supplemented in the patch internal solution, indicating that the rupture of the patch membrane affected the normal behavior of Nav1.9. The inducible and kindling properties of INaN may provide an additional insight into the plasticity of Na+ channels that are related to pathological functions of Na+ channels accompanying abnormal pain states.

Na channel

Dorsal root ganglion neuron

Tetrodotoxin

Patch-clamp

Gating

Medical sciences [ 490 ]

eng

Springer

Copyright (c) 2004 Springer-Verlag. "The original publication is available at www.springerlink.com"

[ISSN] 0031-6768

[DOI] 10.1007/s00424-004-1315-0

[NCID] AA00771833

[DOI] http://dx.doi.org/10.1007/s00424-004-1315-0