FUNCTIONAL-ANALYSIS OF A VOLTAGE-GATED SODIUM-CHANNEL AND ITS SPLICE VARIANT FROM RAT DORSAL-ROOT GANGLIA

Neurons of the dorsal root ganglia (DRG) express a diversity of voltag e-gated sodium channels. From rat DRG we have cloned and functionally expressed a tetrodotoxin-sensitive sodium channel cu subunit, NaCh6/Sc n8a/rPN4, and a splice variant, rPN4a. Primary structure analysis show s NaCh6/Scn8a/rPN4 to be highly homologous (99%) to NaCh6 and most lik ely represents the same transcript. The splice variation in rPN4a is h omologous in sequence and location to that of rat brain I. Tissue dist ribution analyzed by RT-PCR showed NaCh6/Scn8a/rPN4 to be expressed at its highest levels in rat brain, at moderate levels in spinal cord, a nd at lower levels in DRG, nodose ganglia, and superior cervical gangl ia and to be absent from sciatic nerve, heart, and skeletal muscle. In contrast, rPN4a shows no expression in brain and low-level expression in spinal cord. whereas in DRG its expression is comparable to that o f NaCh6/Scn8a/rPN4. Functional analysis of these channels expressed in Xenopus oocytes showed that NaCh6/Scn8a/rPN4 and rPN4a exhibited simi lar properties, with V-1/2 congruent to -100 mV for steady-state inact ivation and V-1/2 congruent to -40 mV for activation. rPN4a recovered from inactivation significantly faster than NaCh6/Scn8a/rPN4. NaCh6/Sc n8a/rPN4 was inhibited by tetrodotoxin with an IC50 congruent to 1 nM. Coexpression of the beta(1) subunit accelerated inactivation kinetics , but the beta(2) subunit was without effect.