Physiology of salivary secretion.

Abstract

The aim of the present work was to explain the mechanism of the acinar secretion of the salivary gland during stimulation. The following items were discussed and concluded. (1) The acinus is the majority of cells being the powerful transport system of the fluid from interstitial side to lumen. (2) Osmotic flow was clarified being a cause of water transport, in which the osmolality gradient across the acinus epithelium was initiated by a preceded salt transport. (3) The grades of osmotic gradient, of hydraulic conductivity, and of semipermeable property of gland epithelia were described. (4) On salt transport during stimulation, Na+ inflow across the basal plasma membrane and Na+ extrusion across the luminal membrane of the acinus cell were discussed with respect to the electrochemical gradient and ionic flow. From the electrophysiological work and the ionic distribution of the salivary gland, it is concluded that massive Na+ inflow and K+ outflow across the basal plasma membrane was a passive process due to an increase of permeability to those ion during stimulation, but the process of Na+ extrusion across the plasma membranes of the luminal side of the cell as well as of the secretory granules was active. (5) The electrochemical gradient for Na+ and K+ at the basal plasma membrane which had an important role for passive Na+ and K+ transport may be maintained by ouabain-sensitive Na+-K+ pump as most other cells. (6) A model for salt transport across the acinar cell was proposed. Intracellular Na+ due to passive Na+ inflow may activate cooperatively the Na(Cl) transport system at luminal plasma membrane and membrane of secretory granules in high levels of (Na+)in. Though it also activated the Na+ -K+ transport at the basal plasma membrane in any level of (Na+)in. (7) Energetics for the ion transport of gland was discussed with a transport-work rate equation as well as oxygen consumption in secretory state. It is assumed that the energy in active transport at the luminal plasma membrane requires more than the dissipated energy in passive process at the basal plasma membrane. The energy for active transport across the luminal plasma membrane may be corresponded to a main part of oxygen consumption for ion transport across the overall epithelium. (8) The phenomena of osmotic flow coupling with salt flow and of passive ionic flow coupling with electrochemical gradient which is maintained by Na+ -K+ pump may be an expression of production and utilization of negative entropy which is a characteristic of biological membrane.