The primary hypoxia sensor of the cardio-respiratory system is the carotid body, which is relatively insensitive at birth and matures over the first 1-2 weeks of life. Although the mechanism of chemotransduction remains obscure, glomus cells, secretory cells apposed to the afferent nerve endings, as well as the nerve endings themselves appear to form the critical chemoreceptive unit. Current models propose that hypoxia causes release of an excitatory transmitter, but identification of the purported excitatory transmitter has proven elusive and our previous results, as well those of other laboratories, demonstrate a dissociation between glomus cell secretion and afferent nerve activity. The proposed work outlines two steps in understanding the mechanism of transduction: firstly, to understand the mechanism of spike generation and secondly, to understand how the generation process is controlled by hypoxia. Towards the first aim, we demonstrate: i) that the spike generation process is highly sensitive to external Na+ perturbation or drugs which target Na+ channels, ii) chemoreceptor afferent neurons express a limited and consistent Na+ channel profile and iii) isolated, chemoreceptor afferent neurons are able to generate spontaneous action potentials which resemble the pattern as generated by the afferent nerve ending. Based on the preliminary results, our general hypothesis is that the nerve terminals are the site of action potential generation through an endogenous process, specifically, a persistent Na+ current. The proposed work: 1) uses RT-PCR and immunocytochemistry to identify Na+ channel isoforms at the soma and nerve terminals of chemoreceptor neurons; 2) examines the consequences of Na+ current perturbations on the respiratory response to hypoxia and chemoreceptor activity following drugs which target fast Na+ currents or loss (knockout) of isoforms Navl.6 and Navl.8; 3) examines the effects of disruption of Na+ channel underexpression/overexpression on the ability of the soma to generate spontaneous action potentials. The anticipated results will provide acceptance or rejection of this unique model of chemoreceptor transduction. If supported, the model should lead to a pharmacologic targeting of these processes for the improved treatment of apnea and/or dyspnea.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
1R01HL073500-01
Application #
6641064
Study Section
Special Emphasis Panel (ZRG1-ALTX-1 (02))
Program Officer
Twery, Michael
Project Start
2003-05-05
Project End
2007-04-30
Budget Start
2003-05-05
Budget End
2004-04-30
Support Year
1
Fiscal Year
2003
Total Cost
$327,000
Indirect Cost
Name
Yale University
Department
Pediatrics
Type
Schools of Medicine
DUNS #
043207562
City
New Haven
State
CT
Country
United States
Zip Code
06520
Donnelly, David F; Kim, Insook; Mulligan, Eileen M et al. (2014) Non-additive interactions between mitochondrial complex IV blockers and hypoxia in rat carotid body responses. Respir Physiol Neurobiol 190:62-9
Donnelly, David F (2013) Voltage-gated Na(+) channels in chemoreceptor afferent neurons--potential roles and changes with development. Respir Physiol Neurobiol 185:67-74
Kim, Insook; Donnelly, David F; Carroll, John L (2012) Postnatal hyperoxia impairs acute oxygen sensing of rat glomus cells by reduced membrane depolarization. Adv Exp Med Biol 758:49-54
Donnelly, David F; Bavis, Ryan W; Kim, Insook et al. (2009) Time course of alterations in pre- and post-synaptic chemoreceptor function during developmental hyperoxia. Respir Physiol Neurobiol 168:189-97
Donnelly, David F (2009) Nicotinic acetylcholine receptors do not mediate excitatory transmission in young rat carotid body. J Appl Physiol (1985) 107:1806-16
Donnelly, David F (2008) Spontaneous action potential generation due to persistent sodium channel currents in simulated carotid body afferent fibers. J Appl Physiol 104:1394-401
Donnelly, David F (2007) Orthodromic spike generation from electrical stimuli in the rat carotid body: implications for the afferent spike generation process. J Physiol 580:275-84
Faustino, Edward Vincent S; Donnelly, David F (2006) An important functional role of persistent Na+ current in carotid body hypoxia transduction. J Appl Physiol 101:1076-84
Donnelly, David F; Kim, Insook; Carle, Claire et al. (2005) Perinatal hyperoxia for 14 days increases nerve conduction time and the acute unitary response to hypoxia of rat carotid body chemoreceptors. J Appl Physiol 99:114-9