title: Possible role of H+--alkali cation countertransport in secretory granule swelling during exocytosis.
abstract: Studies in model systems, as well as observations in intact cells, suggest that osmotic swelling of secretory granules is an essential step in exocytosis. A model is proposed whereby the low pH recorded in most secretory organelles could provide the driving force for granule swelling. The model assumes that during stimulation an exchange of H+ for alkali cations is triggered across the granule membrane. The outgoing H+ are rapidly replaced by the internal buffering capacity with a concomitant osmotic gain. The exchange is independent of anions and could be triggered by cytoplasmic Ca2+. The H+ -pump is responsible for the delta pH but independent of the exchange mechanism.
mesh_terms: D003594:Cytoplasmic Granules / Q000502:physiology*; D005089:Exocytosis; D007425:Intracellular Membranes / Q000378:metabolism; D007473:Ion Channels / Q000378:metabolism*; D008954:Models, Biological; D009997:Osmotic Pressure; D011522:Protons
chemical_list: D007473:Ion Channels; D011522:Protons