Functional expression of the multimodal extracellular calcium-sensing receptor in pulmonary neuroendocrine cells.

The Ca2+-sensing receptor (CaSR) is the master regulator of whole body, extracellular free ionized [Ca2+]o. In addition to sensing [Ca2+]o, CaSR integrates inputs from a variety of different physiological stimuli. The CaSR is also expressed in many regions outside of the [Ca2+]o homeostatic system, including the fetal lung where it plays a crucial role in lung development. Here we show that neuroepithelial bodies (NEBs) of the postnatal mouse lung express a functional CaSR. NEBs are densely innervated groups of neuroendocrine epithelial cells in the lung representing complex sensory receptors in the airways and exhibiting stem cell characteristics. qRT-PCR performed on laser microdissected samples from GAD67-GFP mouse lung cryosections revealed exclusive expression of the CaSR in the NEB microenvironment. CaSR immunoreactivity was present at NEB cells from postnatal day 14 onwards. Confocal imaging of lung slices revealed that NEB cells responded to an increase of [Ca2+]o with a rise in intracellular Ca2+ ([Ca2+]i); an effect mimicked by several membrane-impermeant CaSR agonists (e.g. the calcimimetic R-568) and that was blocked by the calcilytic, Calhex-231. Blocking TRPC channels attenuated the CaSR-dependent increases in [Ca2+]i, suggesting that Ca2+ influx through TRPC channels contributes to the total [Ca2+]i signal evoked by the CaSR in NEBs. CaSR also regulated baseline [Ca2+]i in NEBs and, via paracrine signaling from Clara-like cells, co-ordinated intercellular communication in the NEB microenvironment. These data suggest that the NEB CaSR integrates multiple signals converging on this complex chemosensory unit, and is a key regulator of this intrapulmonary airway stem cell niche.