Received August 10, 2005
Revised September 5, 2005
Accepted after revision October 5, 2005

¹ Case Western Reserve University

^* To whom correspondence should be addressed. E-mail: nrp{at}po.cwru.edu.

	Abstract

Carotid bodies are the sensory organs for detecting systemic hypoxia and the ensuing reflexes prevent the development of tissue/cellular hypoxia. Although every mammalian cell responds to hypoxia, O2 sensing by the carotid body is unique in that it responds instantaneously (within seconds) to even a modest drop in arterial O2. Hypoxic sensing in the carotid body requires an initial transduction step involving O2 sensor(s) and transmitter(s) for subsequent activation of the afferent nerve ending. This brief review focuses on: a) whether the transduction involves "single" or "multiple" O2 sensors? b) identity of the excitatory transmitter(s) responsible for afferent nerve activation by hypoxia and c) whether inhibitory transmitters have any functional role? The currently proposed O2 sensors include various heme containing proteins, and a variety of O2 sensitive K+ channels. It is proposed that the transduction involves an ensemble of and interactions between heme-containing proteins and O2-sensitive K+ channel proteins functioning as a "chemosome", the former for conferring sensitivity to wide range of PO2s and the later for the rapidity of the response. Hypoxia releases both excitatory and inhibitory transmitters from the carotid body. ATP is emerging as an important excitatory transmitter for afferent nerve activation by hypoxia. Whereas the inhibitory messengers act in concert with excitatory transmitters like a "push-pull" mechanism to prevent over excitation, conferring the "slowly adapting" nature of the afferent nerve activation during prolonged hypoxia. Further studies are needed to test the interactions between putative O2 sensors and excitatory and inhibitory transmitters in the carotid body.

Key Words: Chemoreceptor, Oxygen, P2 purinoceptor

This article has been cited by other articles:

				K. R. Olson Hydrogen sulfide and oxygen sensing: implications in cardiorespiratory control J. Exp. Biol., September 1, 2008; 211(17): 2727 - 2734. [Abstract] [Full Text] [PDF]

				G. Montandon, A. Bairam, and R. Kinkead Neonatal caffeine induces sex-specific developmental plasticity of the hypoxic respiratory chemoreflex in adult rats Am J Physiol Regulatory Integrative Comp Physiol, September 1, 2008; 295(3): R922 - R934. [Abstract] [Full Text] [PDF]

				M. G. Jonz and C. A. Nurse New developments on gill innervation: insights from a model vertebrate J. Exp. Biol., August 1, 2008; 211(15): 2371 - 2378. [Abstract] [Full Text] [PDF]

				K. R. Olson, M. J. Healy, Z. Qin, N. Skovgaard, B. Vulesevic, D. W. Duff, N. L. Whitfield, G. Yang, R. Wang, and S. F. Perry Hydrogen sulfide as an oxygen sensor in trout gill chemoreceptors Am J Physiol Regulatory Integrative Comp Physiol, August 1, 2008; 295(2): R669 - R680. [Abstract] [Full Text] [PDF]

				D. J. Paterson Celebrating 100 years of publishing discovery in physiology 1908 - 2008 Exp Physiol, January 1, 2008; 93(1): 1 - 15. [Full Text] [PDF]

				Z.-Y. Tan, Y. Lu, C. A. Whiteis, C. J. Benson, M. W. Chapleau, and F. M. Abboud Acid-Sensing Ion Channels Contribute to Transduction of Extracellular Acidosis in Rat Carotid Body Glomus Cells Circ. Res., November 9, 2007; 101(10): 1009 - 1019. [Abstract] [Full Text] [PDF]

				R. Varas, C. N. Wyatt, and K. J. Buckler Modulation of TASK-like background potassium channels in rat arterial chemoreceptor cells by intracellular ATP and other nucleotides J. Physiol., September 1, 2007; 583(2): 521 - 536. [Abstract] [Full Text] [PDF]

				C. E. Cooper and C. Giulivi Nitric oxide regulation of mitochondrial oxygen consumption II: molecular mechanism and tissue physiology Am J Physiol Cell Physiol, June 1, 2007; 292(6): C1993 - C2003. [Abstract] [Full Text] [PDF]

				G. Burnstock Physiology and Pathophysiology of Purinergic Neurotransmission Physiol Rev, April 1, 2007; 87(2): 659 - 797. [Abstract] [Full Text] [PDF]

				C. N. Wyatt, K. J. Mustard, S. A. Pearson, M. L Dallas, L. Atkinson, P. Kumar, C. Peers, D. G. Hardie, and A. M. Evans AMP-activated Protein Kinase Mediates Carotid Body Excitation by Hypoxia J. Biol. Chem., March 16, 2007; 282(11): 8092 - 8098. [Abstract] [Full Text] [PDF]

				T. A. Day and R. J. A. Wilson Brainstem PCO2 modulates phrenic responses to specific carotid body hypoxia in an in situ dual perfused rat preparation J. Physiol., February 1, 2007; 578(3): 843 - 857. [Abstract] [Full Text] [PDF]