The Mode of Secretion of the Clara Cell in Rat Bronchiole: A Freeze-Fracture Study

Abstract

Freeze-fracture was used to study the nonciliated epithelial (Clara) cell of rat bronchiole. En face views of the P face of the luminal cell membrane reveal particle-free bulging and circular depressions at the presumptive sites of the membrane fusion between the cell membrane and secretory granule membrane. Cross fracture views of the cytoplasm reveal the membranous continuity from the secretory granule to the luminal cell membrane with the decrease of the intramembrane particles. These findings indicate that the mode of secretion of the Clara cell is a merocrine secretion by exocytosis.