Carbon-dioxide-induced exocytotic insertion of H+ pumps in turtle-bladder luminal membrane: role of cell pH and calcium

Nature. 1985 Apr 4-10;314(6010):443-6. doi: 10.1038/314443a0.


The contents of endocytic vesicles and other intracellular organelles (such as Golgi and microsomes) are acidified by an electrogenic proton-translocating ATPase that is remarkably similar to that found in urinary epithelia. We recently found that the number of H+ ATPases in the apical plasma membrane of these epithelia is regulated by exocytotic insertion of endocytic vesicles whose membranes contain this H+ pump. Carbon dioxide, a major stimulus for urinary acidification, causes rapid fusion of these vesicles with the luminal membrane, thereby inserting these pumps there and increasing the rate of net transepithelial H+ secretion; CO2 also inhibits endocytic retrieval of the pumps from the luminal membrane. Such reciprocal regulation of endocytosis and exocytosis by a physiological modulator makes this system particularly attractive for studying the cellular events regulating membrane fusion. Here we present evidence that CO2 induces exocytosis by a cascade of events, the first step of which is cytoplasmic acidification. Cell acidification then increases calcium activity, which causes the fusion event.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Biological Transport, Active
  • Calcium / physiology*
  • Carbon Dioxide / physiology*
  • Colchicine / pharmacology
  • Exocytosis*
  • Hydrogen-Ion Concentration*
  • Intracellular Membranes / metabolism
  • Membrane Fusion
  • Proton-Translocating ATPases / metabolism*
  • Turtles
  • Urinary Bladder / metabolism


  • Carbon Dioxide
  • Proton-Translocating ATPases
  • Colchicine
  • Calcium