We examined the distribution of binding sites for alpha-atrial natriuretic peptide (125I-ANP1–28) and the recently discovered porcine brain natriuretic peptide (125I-pBNP) on immunocytochemically identified cells in dissociated culture preparations of the rat trachea. Specific binding sites for both125I-ANP1–28and125I-pBNP were evenly distributed over distinet subpopulations of smooth muscle myosin-like immunoreactive muscle cells, fibronectin-like immunoreactive fibroblasts and S-100-like immunoreactive glial cells. Neither keratin-like immunoreactive epithelial cells nor protein gene product 9.5-like immunoreactive paratracheal neurones expressed natriuretic peptide binding sites, although autoradiographically labelled glial cells were seen in close association with both neuronal cell bodies and neurites. The binding of each radiolabelled peptide was abolished by the inclusion of either excess (1 μM) unlabelled rat ANP or excess unlabelled porcine BNP, suggesting that ANP and BNP share binding sites in the trachea. Furthermore, the ring-deleted analogue, Des-Gln18, Ser19, Gly20, Leu21, Gly22-ANF4–23-NH2, strongly competed for specific125I-ANP1–28and125I-pBNP binding sites in the tracheal cultures; this suggests that virtually all binding sites were of the “clearance” (ANP-C or ANF-R2) rece
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