J Neurophysiol (December 1, 2002). 10.1152/jn.00350.2002
Submitted on 8 May 2002
Accepted on 8 August 2002

Characterization and Developmental Changes of Na⁺ Currents of Petrosal Neurons With Projections to the Carotid Body

 ¹Department of Neurology and  ²Department of Pediatrics, Yale University School of Medicine, New Haven Connecticut 06510

Cummins, Theodore R., Sulayman D. Dib-Hajj, Stephen G. Waxman, and David F. Donnelly. Characterization and Developmental Changes of Na⁺ Currents of Petrosal Neurons With Projections to the Carotid Body. J. Neurophysiol. 88: 2993-3002, 2002. Carotid body chemoreceptors transduce a decrease in arterial oxygen tension into an increase in spiking activity on the sinus nerve, and this response increases with postnatal age over the first week or two of life. Previous work from our laboratory has suggested a major role of axonal Na⁺ channels in the initiation of afferent spiking activity. Using RT-PCR of the petrosal ganglia we identified Na⁺ channel TTX-S isoforms Na_v1.1, Na_v1.6, and Na_v1.7 and the TTX-resistant (TTX-R) isoforms Na_v1.8 and Na_v1.9 at high levels. Electrophysiologic recordings (at 3 ages: 3 days, 9 days, 18-20 days) of neurons that project to the carotid body exhibited predominantly fast-inactivating sodium currents, with a bimodal recovery from inactivation at 80 mV (fast component ~ 8 ms; slow component ~90 ms). Developmental age had little effect with no change in peak current density (approximately 1.4 nA/pF) and was associated with a slight, but significant increase in the speed of recovery from inactivation at 140 and 120 mV but not at other potentials. Assuming that the same Na⁺ channel complement is present at the nerve terminal as at the soma, the association of a sensory modality (chemoreception) with a relatively uniform Na⁺ channel profile suggests that the rapid kinetics of TTX-S channels may be essential for some aspects of chemoreceptor function beyond mediating simple axonal conduction.