Significance of extensive `leaky' cell junctions in the avian salt gland
Abstract
CURRENT models for hypertonic sodium secretion by salt glands assume there are physiologically tight junctions between the principal cells of the secretory tubules and that these cells actively secrete sodium across the cell membrane at the lumen in a one-stage process1. Our recent data require consideration of a new two-stage hypothesis concerning the secretory mechanism. Our freeze-fracture studies demonstrate that these cell junctions (zonulae occludentes) in the nasal salt gland of the herring gull (Fig. 1) should be classified as `very leaky'2. Also, the extraordinary conformation of the apices of the principal cells within the epithelium makes these cell junctions most extensive (Fig. 2). Therefore, we propose that the salt glands of vertebrates produce their hypertonic effluent from the primary isotonic secretion of the peripheral cells at the ends of the secretory tubules, followed by the secondary reabsorption of water through the leaky junctions of the principal cells and not simply by the extrusion of Na+ across the luminal membranes of the principal cells. This new hypothesis is consistent with the accepted theories of sweat gland and salivary gland function, except that in the salt gland the second stage after isotonic secretion is water absorption, rather than salt reabsorption.
- Publication:
-
Nature
- Pub Date:
- August 1977
- DOI:
- 10.1038/268555a0
- Bibcode:
- 1977Natur.268..555E