Chorda-evoked opening of tight junctions in rat submandibular salivary acini demonstrated by microperoxidase.

The permeability of these junctions from the interstitium to the lumen was examined by using an ultrastructural tracer, microperoxidase, in conjunction with electron microscopy. In the resting gland, the reaction product of microperoxidase was seen in the interstitial and intercellular spaces, but not within acinar lumina; thus the tight junction was impermeable to microperoxidase (junction closed). Intraductal injection of hypertonic sucrose solution (1000 mOsm; 30 microliters) caused a sustained elevation of the luminal pressure, indicating osmotic water flow into the lumen due to the presence of a hypertonic solution. In this gland no opening of the tight junctions was observed. In the chorda-stimulated gland, microperoxidase entered the lumen through the tight junctions, that is, they became permeable to microperoxidase (junction open). These findings suggest that chorda stimulation opens the acinar tight junctions and that the paracellular secretory pathway may be involved in the secretion of small molecules and water from the submandibular acini.