[Arterial chemoreceptors: cellular and molecular mechanisms in the adaptative and homeostatic function of the carotid body].
The carotid body is a sensory chemoreceptor organ located in the vicinity of the carotid bifurcation. Structurally it is composed of cell clusters formed by chemoreceptor and supporting cells. The sensory nerve endings of the carotid sinus nerve penetrate the clusters to synapse with chemoreceptor cells. The carotid body plays an important role in the control of ventilation during hypoxia, hypercapnia and acidosis. Hypoxia and other natural stimuli are detected by chemoreceptor cells which upon stimulation increase their rate of release of neurotransmitters. Neurotransmitters in turn increase the action potential frequency in the carotid sinus nerve which via its central projections to the brainstem activates ventilation. This review is devoted to the cellular aspects of the function of this chemoreceptor organ. From a brief description of the complex structure of the carotid body, we go to present a summary of the main prevailing theories concerning the transduction mechanisms for hypoxic and acidic/hypercapnic stimuli, with special emphasis on the electrical properties of cultured chemoreceptors cells. A special attention is provided to the possible significance of reactive oxygen species as mediators of the hypoxic transduction cascade. The neurotransmission between chemoreceptor cells and the sensory nerve endings is also covered in certain detail. After a brief historical presentation of the theories of communication between these two structures, we examine, following the classical criteria of neurotransmission, the functional significance of acetylcholine, dopamine, substance P and other neurotransmitters known to be present in chemoreceptor cells.