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

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. The communication between cells and nerves are through reciprocal chemical synapses and electrical coupling forming a "tripartite synapse" which allows to process of sensory stimuli within carotid body that involves neurotransmission, autocrine and paracrine pathways. In this network there are a variety of neurotransmitters and neuromodulators including adenosine 5'-triphosphate (ATP). Cells and nerves express ATP receptors, i.e., purinergic receptors. Here we used double immunofluorescence associated with laser confocal microscopy to detect in the human carotid body, as well as the petrosal and cervical sympathetic ganglia, the ATP receptor P2X7 and pannexin 1, an ATP permeable channel. Immunofluorescence for P2X7r and pannexin 1 within the glomeruli of the carotid body forms a broad cellular network whose pattern corresponds to that of type II cells. Moreover, both 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 occurrence and distribution of P2X7r and pannexin 1 is reported here for the first time in the human carotid body which are restricted to type II cells and nerves. The role of this purinergic receptor in the carotid body, if any, remains to be elucidated, but it probably provides new evidence for gliotransmission.