Monoamine-containing granulated cells in the frog lung.

The epithelium of the primary bronchus of the frog lung has been studied by fluorescence and electron microscopy. Clusters of five to ten, ovoid, brilliantly yellow fluorescent cells were observed in the basal portion of the epithelium. These cells contained numerous electron-dense granules of variable shape and size. The granules gave a positive argentaffin reaction at the ultrastructural level, suggesting a possible existence of monoamines in the granules. In addition, synaptic contact between the intraepithelial nerves and the cells, which was characterized by the aggregation of the granules toward the presynaptic membrane thickening of the cell, was also noted. These data are discussed in relation to similar studies in birds and mammals, and a possible function of these cells suggested.