Immunogold EM localization of neurochemicals in human pulmonary neuroendocrine cells

Antibodies against the pulmonary neuroendocrine cell peptides gastrin-releasing peptide (bombesin), calcitonin and calcitonin gene-related peptide (CGRP) have been labeled with colloidal gold spheres for immunocytochemical localization in human fetal and newborn lung tissue. In general, the presence and amount of immunolabeling increased with increasing gestational age, with only calcitonin appearing late in fetal life. The largest percentage of neuroepithelial body (NEB) cells labeled and the largest number of labeled dense core vesicles (DCV) were in infants with chronic lung disease (bronchopulmonary dysplasia). Serial ribbons allowed identification of more than one peptide in a single NEB cell. The use of two antibodies labeled with colloidal gold spheres of different sizes allowed the identification of two peptides in the same DCV. Quantification of relative amounts of labeled peptides was not possible, as the peptide labeling with the larger size gold sphere was consistently underestimated. Colocalization to the same DCV has been shown in humans for bombesin and calcitonin, calcitonin and CGRP, bombesin and CGRP and, by others for cholecystokinin (CCK) and serotonin. Colocalization of two or more peptides or an amine to a single DCV within the same cell implies simultaneous discharge by exocytosis. The action of the two (or more) substances might be in concert, perhaps with one acting in a paracrine fashion, and the second in an autocrine fashion. In this case, the second peptide or amine might have a regulatory function in the parent cell, influencing DCV storage or rate of release.