Osmotically inactive space during hyperosmotic stress in the perfused submandibular gland of the rat

Cell volume changes were measured by an impedance method during hyperosmotic stress in the perfused rat submandibular gland. When the perfusate osmolarity was raised to 484 mosmol, the cell volume decreased and remained at a plateau level (79%). The decrease was smaller than expected from the extracellular fluid osmolarity change. Furthermore, the potassium content of the gland increased by 7% during the hyperosmotic stress. These results suggest that the cell volume changes observed during hyperosmotic stress are affected by the existence of an osmotically inactive space and by an increase in the intracellular solute content.