Type II Cells in the Human Carotid Body Display P2X7 Receptor and Pannexin-1 Immunoreactivity

TL;DR

This study identifies P2X7 receptors and pannexin-1 in type II cells of the human carotid body, suggesting a role in gliotransmission.

Contribution

The study is the first to show P2X7r and pannexin-1 in human carotid body type II cells, linking them to potential gliotransmission mechanisms.

Findings

P2X7 receptors and pannexin-1 are present in type II cells of the human carotid body.

P2X7r and pannexin-1 are also found in nerve profiles of the carotid body and ganglia.

P2X7r distribution varies between petrosal and cervical sympathetic ganglia.

Abstract

The carotid body is a peripheral chemoreceptor that consists of clusters of chemoreceptive type I cells, glia-like type II cells, afferent and efferent nerves, and sinusoidal capillaries and arterioles. Cells and nerves communicate through reciprocal chemical synapses and electrical coupling that form a “tripartite synapse,” which allows for the process of sensory stimuli within the carotid body involving neurotransmission, autocrine, and paracrine pathways. In this network there are a variety of neurotransmitters and neuromodulators including adenosine 5′-triphosphate (ATP). Carotid body cells and nerve fibre terminals express ATP receptors, i.e., purinergic receptors. Here we used double immunofluorescence associated with laser confocal microscopy to detect the ATP receptor P2X7 and pannexin 1 (an ATP permeable channel) in the human carotid body, as well as the petrosal and cervical sympathetic ganglia. Immunofluorescence for P2X7r and pannexin 1 forms a broad cellular network within the glomeruli of the carotid body, whose pattern corresponds to that of type II cells. Moreover, both P2X7r and pannexin 1 were also detected in nerve profiles. In the petrosal ganglion, the distribution of P2X7r was restricted to satellite glial cells, whereas in the cervical sympathetic ganglion, P2X7r was found in neurons and glial satellite cells. The role of this purinergic receptor in the carotid body, if any, remains to be elucidated, but it probably provides new evidence for gliotransmission.

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